cold dark matter: Topics by Science.gov

Sample records for cold dark matter

Cold dark matter plus not-so-clumpy dark relics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Diamanti, Roberta; Ando, Shin'ichiro; Weniger, Christoph

Various particle physics models suggest that, besides the (nearly) cold dark matter that accounts for current observations, additional but sub-dominant dark relics might exist. These could be warm, hot, or even contribute as dark radiation. We present here a comprehensive study of two-component dark matter scenarios, where the first component is assumed to be cold, and the second is a non-cold thermal relic. Considering the cases where the non-cold dark matter species could be either a fermion or a boson, we derive consistent upper limits on the non-cold dark relic energy density for a very large range of velocity dispersions,more » covering the entire range from dark radiation to cold dark matter. To this end, we employ the latest Planck Cosmic Microwave Background data, the recent BOSS DR11 and other Baryon Acoustic Oscillation measurements, and also constraints on the number of Milky Way satellites, the latter of which provides a measure of the suppression of the matter power spectrum at the smallest scales due to the free-streaming of the non-cold dark matter component. We present the results on the fraction f {sub ncdm} of non-cold dark matter with respect to the total dark matter for different ranges of the non-cold dark matter masses. We find that the 2σ limits for non-cold dark matter particles with masses in the range 1–10 keV are f {sub ncdm}≤0.29 (0.23) for fermions (bosons), and for masses in the 10–100 keV range they are f {sub ncdm}≤0.43 (0.45), respectively.« less
Condensation of galactic cold dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Visinelli, Luca

2016-07-07

We consider the steady-state regime describing the density profile of a dark matter halo, if dark matter is treated as a Bose-Einstein condensate. We first solve the fluid equation for “canonical” cold dark matter, obtaining a class of density profiles which includes the Navarro-Frenk-White profile, and which diverge at the halo core. We then solve numerically the equation obtained when an additional “quantum pressure” term is included in the computation of the density profile. The solution to this latter case is finite at the halo core, possibly avoiding the “cuspy halo problem” present in some cold dark matter theories. Withinmore » the model proposed, we predict the mass of the cold dark matter particle to be of the order of M{sub χ}c{sup 2}≈10{sup −24} eV, which is of the same order of magnitude as that predicted in ultra-light scalar cold dark matter models. Finally, we derive the differential equation describing perturbations in the density and the pressure of the dark matter fluid.« less
Gravitational waves in cold dark matter

NASA Astrophysics Data System (ADS)

Flauger, Raphael; Weinberg, Steven

2018-06-01

We study the effects of cold dark matter on the propagation of gravitational waves of astrophysical and primordial origin. We show that the dominant effect of cold dark matter on gravitational waves from astrophysical sources is a small frequency dependent modification of the propagation speed of gravitational waves. However, the magnitude of the effect is too small to be detected in the near future. We furthermore show that the spectrum of primordial gravitational waves in principle contains detailed information about the properties of dark matter. However, depending on the wavelength, the effects are either suppressed because the dark matter is highly nonrelativistic or because it contributes a small fraction of the energy density of the universe. As a consequence, the effects of cold dark matter on primordial gravitational waves in practice also appear too small to be detectable.
Singlet particles as cold dark matter in a noncommutative space-time

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ettefaghi, M. M.

2009-03-15

We extend the noncommutative (NC) standard model to incorporate singlet particles as cold dark matter. In the NC space-time, the singlet particles can be coupled to the U(1) gauge field in the adjoint representation. We study the relic density of the singlet particles due to the NC induced interaction. Demanding either the singlet fermion or the singlet scalar to serve as cold dark matter and the NC induced interactions to be relevant to the dark matter production, we obtain the corresponding relations between the NC scale and the dark matter masses, which are consistent with some existing bounds.
Astronomical Constraints on Quantum Cold Dark Matter

NASA Astrophysics Data System (ADS)

Spivey, Shane; Musielak, Z.; Fry, J.

2012-01-01

A model of quantum (`fuzzy') cold dark matter that accounts for both the halo core problem and the missing dwarf galaxies problem, which plague the usual cold dark matter paradigm, is developed. The model requires that a cold dark matter particle has a mass so small that its only allowed physical description is a quantum wave function. Each such particle in a galactic halo is bound to a gravitational potential that is created by luminous matter and by the halo itself, and the resulting wave function is described by a Schrödinger equation. To solve this equation on a galactic scale, we impose astronomical constraints that involve several density profiles used to fit data from simulations of dark matter galactic halos. The solutions to the Schrödinger equation are quantum waves which resemble the density profiles acquired from simulations, and they are used to determine the mass of the cold dark matter particle. The effects of adding certain types of baryonic matter to the halo, such as a dwarf elliptical galaxy or a supermassive black hole, are also discussed.
One dark matter mystery: halos in the cosmic web

NASA Astrophysics Data System (ADS)

Gaite, Jose

2015-01-01

The current cold dark matter cosmological model explains the large scale cosmic web structure but is challenged by the observation of a relatively smooth distribution of matter in galactic clusters. We consider various aspects of modeling the dark matter around galaxies as distributed in smooth halos and, especially, the smoothness of the dark matter halos seen in N-body cosmological simulations. We conclude that the problems of the cold dark matter cosmology on small scales are more serious than normally admitted.
Dark matter and cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schramm, D.N.

1992-03-01

The cosmological dark matter problem is reviewed. The Big Bang Nucleosynthesis constraints on the baryon density are compared with the densities implied by visible matter, dark halos, dynamics of clusters, gravitational lenses, large-scale velocity flows, and the {Omega} = 1 flatness/inflation argument. It is shown that (1) the majority of baryons are dark; and (2) non-baryonic dark matter is probably required on large scales. It is also noted that halo dark matter could be either baryonic or non-baryonic. Descrimination between ``cold`` and ``hot`` non-baryonic candidates is shown to depend on the assumed ``seeds`` that stimulate structure formation. Gaussian density fluctuations,more » such as those induced by quantum fluctuations, favor cold dark matter, whereas topological defects such as strings, textures or domain walls may work equally or better with hot dark matter. A possible connection between cold dark matter, globular cluster ages and the Hubble constant is mentioned. Recent large-scale structure measurements, coupled with microwave anisotropy limits, are shown to raise some questions for the previously favored density fluctuation picture. Accelerator and underground limits on dark matter candidates are also reviewed.« less
Dark matter and cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schramm, D.N.

1992-03-01

The cosmological dark matter problem is reviewed. The Big Bang Nucleosynthesis constraints on the baryon density are compared with the densities implied by visible matter, dark halos, dynamics of clusters, gravitational lenses, large-scale velocity flows, and the {Omega} = 1 flatness/inflation argument. It is shown that (1) the majority of baryons are dark; and (2) non-baryonic dark matter is probably required on large scales. It is also noted that halo dark matter could be either baryonic or non-baryonic. Descrimination between cold'' and hot'' non-baryonic candidates is shown to depend on the assumed seeds'' that stimulate structure formation. Gaussian density fluctuations,more » such as those induced by quantum fluctuations, favor cold dark matter, whereas topological defects such as strings, textures or domain walls may work equally or better with hot dark matter. A possible connection between cold dark matter, globular cluster ages and the Hubble constant is mentioned. Recent large-scale structure measurements, coupled with microwave anisotropy limits, are shown to raise some questions for the previously favored density fluctuation picture. Accelerator and underground limits on dark matter candidates are also reviewed.« less
Dark matter and cosmology

NASA Astrophysics Data System (ADS)

Schramm, David N.

1992-07-01

The cosmological dark matter problem is reviewed. The Big Bang Nucleosynthesis constraints on the baryon density are compared with the densities implied by visible matter, dark halos, dynamics of clusters, gravitational lenses, large-scale velocity flows, and the Ω = 1 flatness/inflation argument. It is shown that (1) the majority of baryons are dark; and (2) non-baryonic dark matter is probably required on large scales. It is also noted that halo dark matter could be either baryonic or non-baryonic. Descrimination between ``cold'' and ``hot'' non-baryonic candidates is shown to depend on the assumed ``seeds'' that stimulate structure formation. Gaussian density fluctuations, such as those induced by quantum fluctuations, favor cold dark matter, whereas topological defects such as strings, textures or domain walls may work equally or better with hot dark matter. A possible connection between cold dark matter, globular cluster ages and the Hubble constant is mentioned. Recent large-scale structure measurements, coupled with microwave anisotropy limits, are shown to raise some questions for the previously favored density fluctuation picture. Accelerator and underground limits on dark matter candidates are also reviewed.
Dark matter and cosmology

NASA Astrophysics Data System (ADS)

Schramm, D. N.

1992-03-01

The cosmological dark matter problem is reviewed. The Big Bang nucleosynthesis constraints on the baryon density are compared with the densities implied by visible matter, dark halos, dynamics of clusters, gravitational lenses, large-scale velocity flows, and the omega = 1 flatness/inflation argument. It is shown that (1) the majority of baryons are dark; and (2) non-baryonic dark matter is probably required on large scales. It is also noted that halo dark matter could be either baryonic or non-baryonic. Descrimination between 'cold' and 'hot' non-baryonic candidates is shown to depend on the assumed 'seeds' that stimulate structure formation. Gaussian density fluctuations, such as those induced by quantum fluctuations, favor cold dark matter, whereas topological defects such as strings, textures or domain walls may work equally or better with hot dark matter. A possible connection between cold dark matter, globular cluster ages, and the Hubble constant is mentioned. Recent large-scale structure measurements, coupled with microwave anisotropy limits, are shown to raise some questions for the previously favored density fluctuation picture. Accelerator and underground limits on dark matter candidates are also reviewed.
Large- and small-scale constraints on power spectra in Omega = 1 universes

NASA Technical Reports Server (NTRS)

Gelb, James M.; Gradwohl, Ben-Ami; Frieman, Joshua A.

1993-01-01

The CDM model of structure formation, normalized on large scales, leads to excessive pairwise velocity dispersions on small scales. In an attempt to circumvent this problem, we study three scenarios (all with Omega = 1) with more large-scale and less small-scale power than the standard CDM model: (1) cold dark matter with significantly reduced small-scale power (inspired by models with an admixture of cold and hot dark matter); (2) cold dark matter with a non-scale-invariant power spectrum; and (3) cold dark matter with coupling of dark matter to a long-range vector field. When normalized to COBE on large scales, such models do lead to reduced velocities on small scales and they produce fewer halos compared with CDM. However, models with sufficiently low small-scale velocities apparently fail to produce an adequate number of halos.
Clumpy cold dark matter

NASA Technical Reports Server (NTRS)

Silk, Joseph; Stebbins, Albert

1993-01-01

A study is conducted of cold dark matter (CDM) models in which clumpiness will inhere, using cosmic strings and textures suited to galaxy formation. CDM clumps of 10 million solar mass/cu pc density are generated at about z(eq) redshift, with a sizable fraction surviving. Observable implications encompass dark matter cores in globular clusters and in galactic nuclei. Results from terrestrial dark matter detection experiments may be affected by clumpiness in the Galactic halo.
Cold light dark matter in extended seesaw models

NASA Astrophysics Data System (ADS)

Boulebnane, Sami; Heeck, Julian; Nguyen, Anne; Teresi, Daniele

2018-04-01

We present a thorough discussion of light dark matter produced via freeze-in in two-body decays A→ B DM . If A and B are quasi-degenerate, the dark matter particle has a cold spectrum even for keV masses. We show this explicitly by calculating the transfer function that encodes the impact on structure formation. As examples for this setup we study extended seesaw mechanisms with a spontaneously broken global U(1) symmetry, such as the inverse seesaw. The keV-scale pseudo-Goldstone dark matter particle is then naturally produced cold by the decays of the quasi-degenerate right-handed neutrinos.
Tying dark matter to baryons with self-interactions.

PubMed

Kaplinghat, Manoj; Keeley, Ryan E; Linden, Tim; Yu, Hai-Bo

2014-07-11

Self-interacting dark matter (SIDM) models have been proposed to solve the small-scale issues with the collisionless cold dark matter paradigm. We derive equilibrium solutions in these SIDM models for the dark matter halo density profile including the gravitational potential of both baryons and dark matter. Self-interactions drive dark matter to be isothermal and this ties the core sizes and shapes of dark matter halos to the spatial distribution of the stars, a radical departure from previous expectations and from cold dark matter predictions. Compared to predictions of SIDM-only simulations, the core sizes are smaller and the core densities are higher, with the largest effects in baryon-dominated galaxies. As an example, we find a core size around 0.3 kpc for dark matter in the Milky Way, more than an order of magnitude smaller than the core size from SIDM-only simulations, which has important implications for indirect searches of SIDM candidates.
Cosmological explosions from cold dark matter perturbations

NASA Technical Reports Server (NTRS)

Scherrer, Robert J.

1992-01-01

The cosmological-explosion model is examined for a universe dominated by cold dark matter in which explosion seeds are produced from the growth of initial density perturbations of a given form. Fragmentation of the exploding shells is dominated by the dark-matter potential wells rather than the self-gravity of the shells, and particular conditions are required for the explosions to bootstrap up to very large scales. The final distribution of dark matter is strongly correlated with the baryons on small scales, but uncorrelated on large scales.
Bose-Einstein condensation of dark matter axions.

PubMed

Sikivie, P; Yang, Q

2009-09-11

We show that cold dark matter axions thermalize and form a Bose-Einstein condensate (BEC). We obtain the axion state in a homogeneous and isotropic universe, and derive the equations governing small axion perturbations. Because they form a BEC, axions differ from ordinary cold dark matter in the nonlinear regime of structure formation and upon entering the horizon. Axion BEC provides a mechanism for the production of net overall rotation in dark matter halos, and for the alignment of cosmic microwave anisotropy multipoles.
Partially acoustic dark matter, interacting dark radiation, and large scale structure

NASA Astrophysics Data System (ADS)

Chacko, Zackaria; Cui, Yanou; Hong, Sungwoo; Okui, Takemichi; Tsai, Yuhsinz

2016-12-01

The standard paradigm of collisionless cold dark matter is in tension with measurements on large scales. In particular, the best fit values of the Hubble rate H 0 and the matter density perturbation σ 8 inferred from the cosmic microwave background seem inconsistent with the results from direct measurements. We show that both problems can be solved in a framework in which dark matter consists of two distinct components, a dominant component and a subdominant component. The primary component is cold and collisionless. The secondary component is also cold, but interacts strongly with dark radiation, which itself forms a tightly coupled fluid. The growth of density perturbations in the subdominant component is inhibited by dark acoustic oscillations due to its coupling to the dark radiation, solving the σ 8 problem, while the presence of tightly coupled dark radiation ameliorates the H 0 problem. The subdominant component of dark matter and dark radiation continue to remain in thermal equilibrium until late times, inhibiting the formation of a dark disk. We present an example of a simple model that naturally realizes this scenario in which both constituents of dark matter are thermal WIMPs. Our scenario can be tested by future stage-IV experiments designed to probe the CMB and large scale structure.
Partially acoustic dark matter, interacting dark radiation, and large scale structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chacko, Zackaria; Cui, Yanou; Hong, Sungwoo

The standard paradigm of collisionless cold dark matter is in tension with measurements on large scales. In particular, the best fit values of the Hubble rate H 0 and the matter density perturbation σ 8 inferred from the cosmic microwave background seem inconsistent with the results from direct measurements. We show that both problems can be solved in a framework in which dark matter consists of two distinct components, a dominant component and a subdominant component. The primary component is cold and collisionless. The secondary component is also cold, but interacts strongly with dark radiation, which itself forms a tightlymore » coupled fluid. The growth of density perturbations in the subdominant component is inhibited by dark acoustic oscillations due to its coupling to the dark radiation, solving the σ 8 problem, while the presence of tightly coupled dark radiation ameliorates the H 0 problem. The subdominant component of dark matter and dark radiation continue to remain in thermal equilibrium until late times, inhibiting the formation of a dark disk. We present an example of a simple model that naturally realizes this scenario in which both constituents of dark matter are thermal WIMPs. Our scenario can be tested by future stage-IV experiments designed to probe the CMB and large scale structure.« less
Partially acoustic dark matter, interacting dark radiation, and large scale structure

DOE PAGES

Chacko, Zackaria; Cui, Yanou; Hong, Sungwoo; ...

2016-12-21

The standard paradigm of collisionless cold dark matter is in tension with measurements on large scales. In particular, the best fit values of the Hubble rate H 0 and the matter density perturbation σ 8 inferred from the cosmic microwave background seem inconsistent with the results from direct measurements. We show that both problems can be solved in a framework in which dark matter consists of two distinct components, a dominant component and a subdominant component. The primary component is cold and collisionless. The secondary component is also cold, but interacts strongly with dark radiation, which itself forms a tightlymore » coupled fluid. The growth of density perturbations in the subdominant component is inhibited by dark acoustic oscillations due to its coupling to the dark radiation, solving the σ 8 problem, while the presence of tightly coupled dark radiation ameliorates the H 0 problem. The subdominant component of dark matter and dark radiation continue to remain in thermal equilibrium until late times, inhibiting the formation of a dark disk. We present an example of a simple model that naturally realizes this scenario in which both constituents of dark matter are thermal WIMPs. Our scenario can be tested by future stage-IV experiments designed to probe the CMB and large scale structure.« less
Warm and cold fermionic dark matter via freeze-in

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klasen, Michael; Yaguna, Carlos E., E-mail: michael.klasen@uni-muenster.de, E-mail: carlos.yaguna@uni-muenster.de

2013-11-01

The freeze-in mechanism of dark matter production provides a simple and intriguing alternative to the WIMP paradigm. In this paper, we analyze whether freeze-in can be used to account for the dark matter in the so-called singlet fermionic model. In it, the SM is extended with only two additional fields, a singlet scalar that mixes with the Higgs boson, and the dark matter particle, a fermion assumed to be odd under a Z{sub 2} symmetry. After numerically studying the generation of dark matter, we analyze the dependence of the relic density with respect to all the free parameters of themore » model. These results are then used to obtain the regions of the parameter space that are compatible with the dark matter constraint. We demonstrate that the observed dark matter abundance can be explained via freeze-in over a wide range of masses extending down to the keV range. As a result, warm and cold dark matter can be obtained in this model. It is also possible to have dark matter masses well above the unitarity bound for WIMPs.« less

Is dark matter with long-range interactions a solution to all small-scale problems of Λ cold dark matter cosmology?

PubMed

van den Aarssen, Laura G; Bringmann, Torsten; Pfrommer, Christoph

2012-12-07

The cold dark matter paradigm describes the large-scale structure of the Universe remarkably well. However, there exists some tension with the observed abundances and internal density structures of both field dwarf galaxies and galactic satellites. Here, we demonstrate that a simple class of dark matter models may offer a viable solution to all of these problems simultaneously. Their key phenomenological properties are velocity-dependent self-interactions mediated by a light vector messenger and thermal production with much later kinetic decoupling than in the standard case.
Dark matter universe.

PubMed

Bahcall, Neta A

2015-10-06

Most of the mass in the universe is in the form of dark matter--a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations--from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is "cold" (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology--a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)--fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle.
Influence of ∼7 keV sterile neutrino dark matter on the process of reionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudakovskyi, Anton; Iakubovskyi, Dmytro, E-mail: rudakovskyi@gmail.com, E-mail: iakubovskyi@nbi.ku.dk

2016-06-01

Recent reports of a weak unidentified emission line at ∼3.5 keV found in spectra of several matter-dominated objects may give a clue to resolve the long-standing problem of dark matter. One of the best physically motivated particle candidate able to produce such an extra line is sterile neutrino with the mass of ∼7 keV . Previous works show that sterile neutrino dark matter with parameters consistent with the new line measurement modestly affects structure formation compared to conventional cold dark matter scenario. In this work, we concentrate for the first time on contribution of the sterile neutrino dark matter ablemore » to produce the observed line at ∼3.5 keV, to the process of reionization. By incorporating dark matter power spectra for ∼7 keV sterile neutrinos into extended semi-analytical 'bubble' model of reionization we obtain that such sterile neutrino dark matter would produce significantly sharper reionization compared to widely used cold dark matter models, impossible to 'imitate' within the cold dark matter scenario under any reasonable choice of our model parameters, and would have a clear tendency of lowering both the redshift of reionization and the electron scattering optical depth (although the difference is still below the existing model uncertainties). Further dedicated studies of reionization (such as 21 cm measurements or studies of kinetic Sunyaev-Zeldovich effect) will thus be essential for reconstruction of particle candidate responsible the ∼3.5 keV line.« less
Warm dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horiuchi, Shunsaku, E-mail: horiuchi@vt.edu

2016-06-21

The cold dark matter paradigm has been extremely successful in explaining the large-scale structure of the Universe. However, it continues to face issues when confronted by observations on sub-Galactic scales. A major caveat, now being addressed, has been the incomplete treatment of baryon physics. We first summarize the small-scale issues surrounding cold dark matter and discuss the solutions explored by modern state-of-the-art numerical simulations including treatment of baryonic physics. We identify the too big to fail in field galaxies as among the best targets to study modifications to dark matter, and discuss the particular connection with sterile neutrino warm darkmore » matter. We also discuss how the recently detected anomalous 3.55 keV X-ray lines, when interpreted as sterile neutrino dark matter decay, provide a very good description of small-scale observations of the Local Group.« less
Cold dark matter confronts the cosmic microwave background - Large-angular-scale anisotropies in Omega sub 0 + lambda 1 models

NASA Technical Reports Server (NTRS)

Gorski, Krzysztof M.; Silk, Joseph; Vittorio, Nicola

1992-01-01

A new technique is used to compute the correlation function for large-angle cosmic microwave background anisotropies resulting from both the space and time variations in the gravitational potential in flat, vacuum-dominated, cold dark matter cosmological models. Such models with Omega sub 0 of about 0.2, fit the excess power, relative to the standard cold dark matter model, observed in the large-scale galaxy distribution and allow a high value for the Hubble constant. The low order multipoles and quadrupole anisotropy that are potentially observable by COBE and other ongoing experiments should definitively test these models.
Statistics of the cosmic Mach number from numerical simulations of a cold dark matter universe

NASA Technical Reports Server (NTRS)

Suto, Yasushi; Cen, Renyue; Ostriker, Jeremiah P.

1992-01-01

Results are presented of an analysis of the cosmic Mach number, M, the ratio of the streaming velocity, v, to the random velocity dispersion, sigma, of galaxies in a given patch of the universe, which was performed on the basis of hydrodynamical simulations of the cold dark matter scenario. Galaxy formation is modeled by application of detailed physical processes rather than by the ad hoc assumption of 'bias' between dark matter and galaxy fluctuations. The correlation between M and sigma is found to be very weak for both components. No evidence is found for a physical 'velocity bias' in the quantities which appear in the definition of M. Standard cold-dark-matter-dominated universes are in conflict, at a statistically significant level, with the available observation, in that they predict a Mach number considerably lower than is observed.
Dark matter dynamics in Abell 3827: new data consistent with standard cold dark matter

NASA Astrophysics Data System (ADS)

Massey, Richard; Harvey, David; Liesenborgs, Jori; Richard, Johan; Stach, Stuart; Swinbank, Mark; Taylor, Peter; Williams, Liliya; Clowe, Douglas; Courbin, Frédéric; Edge, Alastair; Israel, Holger; Jauzac, Mathilde; Joseph, Rémy; Jullo, Eric; Kitching, Thomas D.; Leonard, Adrienne; Merten, Julian; Nagai, Daisuke; Nightingale, James; Robertson, Andrew; Romualdez, Luis Javier; Saha, Prasenjit; Smit, Renske; Tam, Sut-Ieng; Tittley, Eric

2018-06-01

We present integral field spectroscopy of galaxy cluster Abell 3827, using Atacama Large Millimetre Array (ALMA) and Very Large Telescope/Multi-Unit Spectroscopic Explorer. It reveals an unusual configuration of strong gravitational lensing in the cluster core, with at least seven lensed images of a single background spiral galaxy. Lens modelling based on Hubble Space Telescope imaging had suggested that the dark matter associated with one of the cluster's central galaxies may be offset. The new spectroscopic data enable better subtraction of foreground light, and better identification of multiple background images. The inferred distribution of dark matter is consistent with being centred on the galaxies, as expected by Λ cold dark matter. Each galaxy's dark matter also appears to be symmetric. Whilst, we do not find an offset between mass and light (suggestive of self-interacting dark matter) as previously reported, the numerical simulations that have been performed to calibrate Abell 3827 indicate that offsets and asymmetry are still worth looking for in collisions with particular geometries. Meanwhile, ALMA proves exceptionally useful for strong lens image identifications.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Aurich, R.; Lustig, S., E-mail: ralf.aurich@uni-ulm.de, E-mail: sven.lustig@uni-ulm.de

Early-matter-like dark energy is defined as a dark energy component whose equation of state approaches that of cold dark matter (CDM) at early times. Such a component is an ingredient of unified dark matter (UDM) models, which unify the cold dark matter and the cosmological constant of the ΛCDM concordance model into a single dark fluid. Power series expansions in conformal time of the perturbations of the various components for a model with early-matter-like dark energy are provided. They allow the calculation of the cosmic microwave background (CMB) anisotropy from the primordial initial values of the perturbations. For a phenomenologicalmore » UDM model, which agrees with the observations of the local Universe, the CMB anisotropy is computed and compared with the CMB data. It is found that a match to the CMB observations is possible if the so-called effective velocity of sound c{sub eff} of the early-matter-like dark energy component is very close to zero. The modifications on the CMB temperature and polarization power spectra caused by varying the effective velocity of sound are studied.« less
Properties of Local Group galaxies in hydrodynamical simulations of sterile neutrino dark matter cosmologies

NASA Astrophysics Data System (ADS)

Lovell, Mark R.; Bose, Sownak; Boyarsky, Alexey; Crain, Robert A.; Frenk, Carlos S.; Hellwing, Wojciech A.; Ludlow, Aaron D.; Navarro, Julio F.; Ruchayskiy, Oleg; Sawala, Till; Schaller, Matthieu; Schaye, Joop; Theuns, Tom

2017-07-01

We study galaxy formation in sterile neutrino dark matter models that differ significantly from both cold and from 'warm thermal relic' models. We use the eagle code to carry out hydrodynamic simulations of the evolution of pairs of galaxies chosen to resemble the Local Group, as part of the APOSTLE simulations project. We compare cold dark matter (CDM) with two sterile neutrino models with 7 keV mass: one, the warmest among all models of this mass (LA120) and the other, a relatively cold case (LA10). We show that the lower concentration of sterile neutrino subhaloes compared to their CDM counterparts makes the inferred inner dark matter content of galaxies like Fornax (or Magellanic Clouds) less of an outlier in the sterile neutrino cosmologies. In terms of the galaxy number counts, the LA10 simulations are indistinguishable from CDM when one takes into account halo-to-halo (or 'simulation-to-simulation') scatter. In order for the LA120 model to match the number of Local Group dwarf galaxies, a higher fraction of low-mass haloes is required to form galaxies than is predicted by the eagle simulations. As the census of the Local Group galaxies nears completion, this population may provide a strong discriminant between cold and warm dark matter models.
A hydrodynamic approach to cosmology - Texture-seeded cold dark matter and hot dark matter cosmogonies

NASA Technical Reports Server (NTRS)

Cen, R. Y.; Ostriker, J. P.; Spergel, D. N.; Turok, N.

1991-01-01

Hydrodynamical simulations of galaxy formation in a texture-seeded cosmology are presented, with attention given to Omega = 1 galaxies dominated by both hot dark matter (HDM) and cold dark matter (CDM). The simulations include both gravitational and hydrodynamical physics with a detailed treatment of collisional and radiative thermal processes, and use a cooling criterion to estimate galaxy formation. Background radiation fields and Zel'dovich-Sunyaev fluctuations are explicitly computed. The derived galaxy mass function is well fitted by the observed Schechter luminosity function for a baryonic M/L of 3 and total M/L of 60 in galaxies. In both HDM and CDM texture scenarios, the 'galaxies' and 'clusters' are significantly more strongly correlated than the dark matter due to physical bias processes. The slope of the correlation function in both cases is consistent with observations. In contrast to Gaussian models, peaks in the dark matter density distributrion are less correlated than average.
QCD Axion Dark Matter with a Small Decay Constant

NASA Astrophysics Data System (ADS)

Co, Raymond T.; Hall, Lawrence J.; Harigaya, Keisuke

2018-05-01

The QCD axion is a good dark matter candidate. The observed dark matter abundance can arise from misalignment or defect mechanisms, which generically require an axion decay constant fa˜O (1011) GeV (or higher). We introduce a new cosmological origin for axion dark matter, parametric resonance from oscillations of the Peccei-Quinn symmetry breaking field, that requires fa˜(108- 1011) GeV . The axions may be warm enough to give deviations from cold dark matter in large scale structure.
A fresh look into the interacting dark matter scenario

NASA Astrophysics Data System (ADS)

Escudero, Miguel; Lopez-Honorez, Laura; Mena, Olga; Palomares-Ruiz, Sergio; Villanueva-Domingo, Pablo

2018-06-01

The elastic scattering between dark matter particles and radiation represents an attractive possibility to solve a number of discrepancies between observations and standard cold dark matter predictions, as the induced collisional damping would imply a suppression of small-scale structures. We consider this scenario and confront it with measurements of the ionization history of the Universe at several redshifts and with recent estimates of the counts of Milky Way satellite galaxies. We derive a conservative upper bound on the dark matter-photon elastic scattering cross section of σγ DM < 8 × 10‑10 σT (mDM/GeV) at 95% CL, about one order of magnitude tighter than previous constraints from satellite number counts. Due to the strong degeneracies with astrophysical parameters, the bound on the dark matter-photon scattering cross section derived here is driven by the estimate of the number of Milky Way satellite galaxies. Finally, we also argue that future 21 cm probes could help in disentangling among possible non-cold dark matter candidates, such as interacting and warm dark matter scenarios. Let us emphasize that bounds of similar magnitude to the ones obtained here could be also derived for models with dark matter-neutrino interactions and would be as constraining as the tightest limits on such scenarios.
Distinguishing cold dark matter dwarfs from self-interacting dark matter dwarfs in baryonic simulations

NASA Astrophysics Data System (ADS)

Strickland, Emily; Fitts, Alex; Boylan-Kolchin, Michael

2018-01-01

Our collaboration has simulated several high-resolution (mbaryon = 500Mo, mdm = 2500Mo) cosmological zoom-in simulations of isolated dwarf galaxies. We simulate each galaxy in standard cold dark matter (ΛCDM) as well as a self-interacting dark matter (SIDM) (with a cross section of σ/m ~ 1 cm2/g), both with and without baryons, to identify distinguishing characteristics between the two. The simulations are run using GIZMO, a meshless-finite-mass (MFM) hydrodynamical code, and are part of the Feedback in Realistic Environments (FIRE) project. By analyzing both the global properties and inner structure of the dwarfs in varying dark matter prescriptions, we provide a side-by-side comparison of isolated, dark matter dominated galaxies at the mass scale where differences in the two models of dark matter are thought to be the most obvious. We find that the edge of classical dwarfs and ultra-faint dwarfs (UFDs) (at ~105 Mo) provides the clearest window for distinguishing between the two theories. Here our SIDM galaxies continue to display a cored inner profile unlike their CDM counterparts. The SIDM versions of each galaxy also have measurably lower stellar velocity dispersions than their CDM counterparts.
Isocurvature cold dark matter fluctuations

NASA Technical Reports Server (NTRS)

Efstathiou, G.; Bond, J. R.

1986-01-01

According to Preskill et al. (1983), the axion field represents a particularly attractive candidate for the dark matter in the universe. In many respects it behaves like other forms of cold dark matter, such as massive gravitinos, photinos, and monopoles. It is, however, a pseudo-Goldstone boson of very low mass, and it is only because of rapid coherent oscillations of the field that it can dominate the mass density of the universe. In the present paper it is assumed that the isocurvature mode is dominant. The linear evolution calculations conducted do not depend upon specific details of particle physics. For this reason, the conducted discussion is applicable to any cold dark matter model with isocurvature perturbations. The results of the study lead to the conclusion that scale-invariant isocurvature perturbations do not seem an attractive possibility for the origin of large-scale structure. The findings strengthen the review that primordial adiabatic perturbations were the dominant fluctuations in the early stages of the Big Bang.
The distribution of dark matter, galaxies, and the intergalactic medium in a cold dark matter dominated universe

NASA Technical Reports Server (NTRS)

Ryu, Dongsu; Vishniac, Ethan T.; Chiang, Wei-Hwan

1988-01-01

The evolution and distribution of galaxies and the intergalactic medium (IGM) have been studied, along with collisionless dark matter in a Universe dominated by cold dark matter. The Einstein-deSitter universe with omega sub 0 = 1 and h = 0.5 was considered (here h = H sub 0 bar 100/kms/Mpc and H sub 0 is the present value of the Hubble constant). It is assumed that initially dark matter composes 90 pct and baryonic matter composes 10 pct of total mass, and that the primordial baryonic matter is comprised of H and He, with the abundance of He equal to 10 pct of H by number. Galaxies are allowed to form out of the IGM, if the total density and baryonic density satisfy an overdensity criterion. Subsequently, the newly formed galaxies release 10 to the 60th ergs of energy into the IGM over a period of 10 to the 8th years. Calculations have been performed with 32 to the 3rd dark matter particles and 32 to the 3rd cells in a cube with comoving side length L = 9.6/h Mpc. Dark matter particles and galaxies have been followed with an N-body code, while the IGM has been followed with a fluid code.
The distribution of dark matter, galaxies, and the intergalactic medium in a cold dark matter dominated universe

NASA Astrophysics Data System (ADS)

Ryu, Dongsu; Vishniac, Ethan T.; Chiang, Wei-Hwan

1988-11-01

The evolution and distribution of galaxies and the intergalactic medium (IGM) have been studied, along with collisionless dark matter in a Universe dominated by cold dark matter. The Einstein-deSitter universe with omega0 = 1 and h = 0.5 was considered (here h = H0 bar 100/kms/Mpc and H0 is the present value of the Hubble constant). It is assumed that initially dark matter composes 90 pct and baryonic matter composes 10 pct of total mass, and that the primordial baryonic matter is comprised of H and He, with the abundance of He equal to 10 pct of H by number. Galaxies are allowed to form out of the IGM, if the total density and baryonic density satisfy an overdensity criterion. Subsequently, the newly formed galaxies release 10 to the 60th ergs of energy into the IGM over a period of 10 to the 8th years. Calculations have been performed with 32 to the 3rd dark matter particles and 32 to the 3rd cells in a cube with comoving side length L = 9.6/h Mpc. Dark matter particles and galaxies have been followed with an N-body code, while the IGM has been followed with a fluid code.
Simulating the cold dark matter-neutrino dipole with TianNu

DOE PAGES

Inman, Derek; Yu, Hao-Ran; Zhu, Hong-Ming; ...

2017-04-20

Measurements of neutrino mass in cosmological observations rely on two-point statistics that are hindered by significant degeneracies with the optical depth and galaxy bias. The relative velocity effect between cold dark matter and neutrinos induces a large scale dipole in the matter density field and may be able to provide orthogonal constraints to standard techniques. In this paper, we numerically investigate this dipole in the TianNu simulation, which contains cold dark matter and 50 meV neutrinos. We first compute the dipole using a new linear response technique where we treat the displacement caused by the relative velocity as a phasemore » in Fourier space and then integrate the matter power spectrum over redshift. Then, we compute the dipole numerically in real space using the simulation density and velocity fields. We find excellent agreement between the linear response and N-body methods. Finally, utilizing the dipole as an observational tool requires two tracers of the matter distribution that are differently biased with respect to the neutrino density.« less
QCD Axion Dark Matter with a Small Decay Constant.

PubMed

Co, Raymond T; Hall, Lawrence J; Harigaya, Keisuke

2018-05-25

The QCD axion is a good dark matter candidate. The observed dark matter abundance can arise from misalignment or defect mechanisms, which generically require an axion decay constant f_{a}∼O(10^{11}) GeV (or higher). We introduce a new cosmological origin for axion dark matter, parametric resonance from oscillations of the Peccei-Quinn symmetry breaking field, that requires f_{a}∼(10^{8}-10^{11}) GeV. The axions may be warm enough to give deviations from cold dark matter in large scale structure.
Cosmic background radiation anisotropy in an open inflation, cold dark matter cosmogony

NASA Technical Reports Server (NTRS)

Kamionkowski, Marc; Ratra, Bharat; Spergel, David N.; Sugiyama, Naoshi

1994-01-01

We compute the cosmic background radiation anisotropy, produced by energy-density fluctuations generated during an early epoch of inflation, in an open cosmological model based on the cold dark matter scenario. At Omega(sub 0) is approximately 0.3-0.4, the Cosmic Background Explorer (COBE) normalized open model appears to be consistent with most observations.
Self-interacting dark matter constraints in a thick dark disk scenario

NASA Astrophysics Data System (ADS)

Vattis, Kyriakos; Koushiappas, Savvas M.

2018-05-01

A thick dark matter disk is predicted in cold dark matter simulations as the outcome of the interaction between accreted satellites and the stellar disk in Milky Way-sized halos. We study the effects of a self-interacting thick dark disk on the energetic neutrino flux from the Sun. We find that for particle masses between 100 GeV and 1 TeV and dark matter annihilation to τ+τ-, either the self-interaction may not be strong enough to solve the small-scale structure motivation or a dark disk cannot be present in the Milky Way.

Axions and dark matter

NASA Astrophysics Data System (ADS)

Yang, Qiaoli

2017-05-01

Dark matter constitutes about 23% of the total energy density of the universe, but its properties are still little known besides that it should be composed by cold and weakly interacting particles. Many beyond Standard Model theories can provide proper candidates to serve as dark matter and the axion introduced to solve the strong CP problem turns out to be an attractive one. In this paper, we briefly review several important features of the axion and the axion dark matter.
Constraints on the Dark Matter Particle Mass from the Number of Milky Way Satellites

DTIC Science & Technology

2010-04-12

but our lower mass limits do not necessarily apply to mixed dark matter cosmologies . Higgs decay produced sterile neutrinos can, however, constitute...simulations of the growth of Milky Way-sized halos in cold and warm dark matter cosmologies . The number of dark matter satellites in our simulated Milky...tions of WDM cosmologies due to numerical artifacts produced by discrete sampling of the gravitational poten- tial with a finite number of particles
Point sources from dissipative dark matter

NASA Astrophysics Data System (ADS)

Agrawal, Prateek; Randall, Lisa

2017-12-01

If a component of dark matter has dissipative interactions, it can cool to form compact astrophysical objects with higher density than that of conventional cold dark matter (sub)haloes. Dark matter annihilations might then appear as point sources, leading to novel morphology for indirect detection. We explore dissipative models where interaction with the Standard Model might provide visible signals, and show how such objects might give rise to the observed excess in gamma rays arising from the galactic center.
Galaxies and gas in a cold dark matter universe

NASA Technical Reports Server (NTRS)

Katz, Neal; Hernquist, Lars; Weinberg, David H.

1992-01-01

We use a combined gravity/hydrodynamics code to simulate the formation of structure in a random 22 Mpc cube of a cold dark matter universe. Adiabatic compression and shocks heat much of the gas to temperatures of 10 exp 6 - 10 exp 7 K, but a fraction of the gas cools radiatively to about 10 exp 4 K and condenses into discrete, highly overdense lumps. We identify these lumps with galaxies. The high-mass end of their baryonic mass function fits the form of the observed galaxy luminosity function. They retain independent identities after their dark halos merge, so gravitational clustering produces groups of galaxies embedded in relatively smooth envelopes of hot gas and dark matter. The galaxy correlation function is approximately an r exp -2.1 power law from separations of 35 kpc to 7 Mpc. Galaxy fluctuations are biased relative to dark matter fluctuations by a factor b about 1.5. We find no significant 'velocity bias' between galaxies and dark matter particles. However, virial analysis of the simulation's richest group leads to an estimated Omega of about 0.3, even though the simulation adopts Omega = 1.
Perturbations from cosmic strings in cold dark matter

NASA Technical Reports Server (NTRS)

Albrecht, Andreas; Stebbins, Albert

1992-01-01

A systematic linear analysis of the perturbations induced by cosmic strings in cold dark matter is presented. The power spectrum is calculated and it is found that the strings produce a great deal of power on small scales. It is shown that the perturbations on interesting scales are the result of many uncorrelated string motions, which indicates a much more Gaussian distribution than was previously supposed.
Perturbations from cosmic strings in cold dark matter

NASA Technical Reports Server (NTRS)

Albrecht, Andreas; Stebbins, Albert

1991-01-01

A systematic linear analysis of the perturbations induced by cosmic strings in cold dark matter is presented. The power spectrum is calculated and it is found that the strings produce a great deal of power on small scales. It is shown that the perturbations on interesting scales are the result of many uncorrelated string motions, which indicates a much more Gaussian distribution than was previously supposed.
Radio telescope search for the resonant conversion of cold dark matter axions from the magnetized astrophysical sources

NASA Astrophysics Data System (ADS)

Huang, Fa Peng; Kadota, Kenji; Sekiguchi, Toyokazu; Tashiro, Hiroyuki

2018-06-01

We study the conditions for the adiabatic resonant conversion of the cold dark matter (CDM) axions into photons in the astrophysically sourced strong magnetic fields such as those in the neutron star magnetosphere. We demonstrate the possibility that the forthcoming radio telescopes such as the SKA (Square Kilometre Array) can probe those photon signals from the CDM axions.
Sterile neutrino dark matter with supersymmetry

NASA Astrophysics Data System (ADS)

Shakya, Bibhushan; Wells, James D.

2017-08-01

Sterile neutrino dark matter, a popular alternative to the WIMP paradigm, has generally been studied in non-supersymmetric setups. If the underlying theory is supersymmetric, we find that several interesting and novel dark matter features can arise. In particular, in scenarios of freeze-in production of sterile neutrino dark matter, its superpartner, the sterile sneutrino, can play a crucial role in early Universe cosmology as the dominant source of cold, warm, or hot dark matter, or of a subdominant relativistic population of sterile neutrinos that can contribute to the effective number of relativistic degrees of freedom Neff during big bang nucleosynthesis.
The Formation of Shell Galaxies Similar to NGC 7600 in the Cold Dark Matter Cosmogony

NASA Astrophysics Data System (ADS)

Cooper, Andrew P.; Martínez-Delgado, David; Helly, John; Frenk, Carlos; Cole, Shaun; Crawford, Ken; Zibetti, Stefano; Carballo-Bello, Julio A.; GaBany, R. Jay

2011-12-01

We present new deep observations of "shell" structures in the halo of the nearby elliptical galaxy NGC 7600, alongside a movie of galaxy formation in a cold dark matter (CDM) universe. The movie, based on an ab initio cosmological simulation, shows how continuous accretion of clumps of dark matter and stars creates a swath of diffuse circumgalactic structures. The disruption of a massive clump on a near-radial orbit creates a complex system of transient concentric shells which bare a striking resemblance to those of NGC 7600. With the aid of the simulation we interpret NGC 7600 in the context of the CDM model.
Dark matter universe

PubMed Central

Bahcall, Neta A.

2015-01-01

Most of the mass in the universe is in the form of dark matter—a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations—from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is “cold” (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology—a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)—fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle. PMID:26417091
Cosmological simulations of multicomponent cold dark matter.

PubMed

Medvedev, Mikhail V

2014-08-15

The nature of dark matter is unknown. A number of dark matter candidates are quantum flavor-mixed particles but this property has never been accounted for in cosmology. Here we explore this possibility from the first principles via extensive N-body cosmological simulations and demonstrate that the two-component dark matter model agrees with observational data at all scales. Substantial reduction of substructure and flattening of density profiles in the centers of dark matter halos found in simulations can simultaneously resolve several outstanding puzzles of modern cosmology. The model shares the "why now?" fine-tuning caveat pertinent to all self-interacting models. Predictions for direct and indirect detection dark matter experiments are made.
A gravitationally lensed quasar with quadruple images separated by 14.62 arcseconds.

PubMed

Inada, Naohisa; Oguri, Masamune; Pindor, Bartosz; Hennawi, Joseph F; Chiu, Kuenley; Zheng, Wei; Ichikawa, Shin-Ichi; Gregg, Michael D; Becker, Robert H; Suto, Yasushi; Strauss, Michael A; Turner, Edwin L; Keeton, Charles R; Annis, James; Castander, Francisco J; Eisenstein, Daniel J; Frieman, Joshua A; Fukugita, Masataka; Gunn, James E; Johnston, David E; Kent, Stephen M; Nichol, Robert C; Richards, Gordon T; Rix, Hans-Walter; Sheldon, Erin Scott; Bahcall, Neta A; Brinkmann, J; Ivezić, Zeljko; Lamb, Don Q; McKay, Timothy A; Schneider, Donald P; York, Donald G

2003-12-18

Gravitational lensing is a powerful tool for the study of the distribution of dark matter in the Universe. The cold-dark-matter model of the formation of large-scale structures (that is, clusters of galaxies and even larger assemblies) predicts the existence of quasars gravitationally lensed by concentrations of dark matter so massive that the quasar images would be split by over 7 arcsec. Numerous searches for large-separation lensed quasars have, however, been unsuccessful. All of the roughly 70 lensed quasars known, including the first lensed quasar discovered, have smaller separations that can be explained in terms of galaxy-scale concentrations of baryonic matter. Although gravitationally lensed galaxies with large separations are known, quasars are more useful cosmological probes because of the simplicity of the resulting lens systems. Here we report the discovery of a lensed quasar, SDSS J1004 + 4112, which has a maximum separation between the components of 14.62 arcsec. Such a large separation means that the lensing object must be dominated by dark matter. Our results are fully consistent with theoretical expectations based on the cold-dark-matter model.
Hints on the nature of dark matter from the properties of Milky Way satellites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderhalden, Donnino; Diemand, Juerg; Schneider, Aurel

2013-03-01

The nature of dark matter is still unknown and one of the most fundamental scientific mysteries. Although successfully describing large scales, the standard cold dark matter model (CDM) exhibits possible shortcomings on galactic and sub-galactic scales. It is exactly at these highly non-linear scales where strong astrophysical constraints can be set on the nature of the dark matter particle. While observations of the Lyman-α forest probe the matter power spectrum in the mildly non-linear regime, satellite galaxies of the Milky Way provide an excellent laboratory as a test of the underlying cosmology on much smaller scales. Here we present resultsmore » from a set of high resolution simulations of a Milky Way sized dark matter halo in eight distinct cosmologies: CDM, warm dark matter (WDM) with a particle mass of 2 keV and six different cold plus warm dark matter (C+WDM) models, varying the fraction, f{sub wdm}, and the mass, m{sub wdm}, of the warm component. We used three different observational tests based on Milky Way satellite observations: the total satellite abundance, their radial distribution and their mass profile. We show that the requirement of simultaneously satisfying all three constraints sets very strong limits on the nature of dark matter. This shows the power of a multi-dimensional small scale approach in ruling out models which would be still allowed by large scale observations.« less
A model for the distribution of dark matter, galaxies, and the intergalactic medium in a cold dark matter-dominated universe

NASA Technical Reports Server (NTRS)

Ryu, Dongsu; Vishniac, Ethan T.; Chiang, Wei-Hwan

1989-01-01

The spatial distribution of the cold-dark-matter (CDM) and baryonic components of CDM-dominated cosmological models are characterized, summarizing the results of recent theoretical investigations. The evolution and distribution of matter in an Einstein-de Sitter universe on length scales small enough so that the Newtonian approximation is valid is followed chronologically, assuming (1) that the galaxies, CDM, and the intergalactic medium (IGM) are coupled by gravity, (2) that galaxies form by taking mass and momentum from the IGM, and (3) that the IGM responds to the energy input from the galaxies. The results of the numerical computations are presented in extensive graphs and discussed in detail.
Observational constraints on variable equation of state parameters of dark matter and dark energy after Planck

NASA Astrophysics Data System (ADS)

Kumar, Suresh; Xu, Lixin

2014-10-01

In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann-Robertson-Walker space-time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier-Polarski-Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck + WMAP9 + WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch.
Chiral gravitational waves and baryon superfluid dark matter

NASA Astrophysics Data System (ADS)

Alexander, Stephon; McDonough, Evan; Spergel, David N.

2018-05-01

We develop a unified model of darkgenesis and baryogenesis involving strongly interacting dark quarks, utilizing the gravitational anomaly of chiral gauge theories. In these models, both the visible and dark baryon asymmetries are generated by the gravitational anomaly induced by the presence of chiral primordial gravitational waves. We provide a concrete model of an SU(2) gauge theory with two massless quarks. In this model, the dark quarks condense and form a dark baryon charge superfluid (DBS), in which the Higgs-mode acts as cold dark matter. We elucidate the essential features of this dark matter scenario and discuss its phenomenological prospects.
Lepton flavor violation induced by dark matter

NASA Astrophysics Data System (ADS)

Arcadi, Giorgio; Ferreira, C. P.; Goertz, Florian; Guzzo, M. M.; Queiroz, Farinaldo S.; Santos, A. C. O.

2018-04-01

Guided by gauge principles we discuss a predictive and falsifiable UV complete model where the Dirac fermion that accounts for the cold dark matter abundance in our Universe induces the lepton flavor violation (LFV) decays μ →e γ and μ →e e e as well as μ -e conversion. We explore the interplay between direct dark matter detection, relic density, collider probes and lepton flavor violation to conclusively show that one may have a viable dark matter candidate yielding flavor violation signatures that can be probed in the upcoming experiments. In fact, keeping the dark matter mass at the TeV scale, a sizable LFV signal is possible, while reproducing the correct dark matter relic density and meeting limits from direct-detection experiments.
Search for Boosted Dark Matter Interacting with Electrons in Super-Kamiokande.

PubMed

Kachulis, C; Abe, K; Bronner, C; Hayato, Y; Ikeda, M; Iyogi, K; Kameda, J; Kato, Y; Kishimoto, Y; Marti, Ll; Miura, M; Moriyama, S; Nakahata, M; Nakano, Y; Nakayama, S; Okajima, Y; Orii, A; Pronost, G; Sekiya, H; Shiozawa, M; Sonoda, Y; Takeda, A; Takenaka, A; Tanaka, H; Tasaka, S; Tomura, T; Akutsu, R; Kajita, T; Kaneyuki, K; Nishimura, Y; Okumura, K; Tsui, K M; Labarga, L; Fernandez, P; Blaszczyk, F D M; Gustafson, J; Kearns, E; Raaf, J L; Stone, J L; Sulak, L R; Berkman, S; Tobayama, S; Goldhaber, M; Elnimr, M; Kropp, W R; Mine, S; Locke, S; Weatherly, P; Smy, M B; Sobel, H W; Takhistov, V; Ganezer, K S; Hill, J; Kim, J Y; Lim, I T; Park, R G; Himmel, A; Li, Z; O'Sullivan, E; Scholberg, K; Walter, C W; Ishizuka, T; Nakamura, T; Jang, J S; Choi, K; Learned, J G; Matsuno, S; Smith, S N; Amey, J; Litchfield, R P; Ma, W Y; Uchida, Y; Wascko, M O; Cao, S; Friend, M; Hasegawa, T; Ishida, T; Ishii, T; Kobayashi, T; Nakadaira, T; Nakamura, K; Oyama, Y; Sakashita, K; Sekiguchi, T; Tsukamoto, T; Abe, K E; Hasegawa, M; Suzuki, A T; Takeuchi, Y; Yano, T; Hayashino, T; Hiraki, T; Hirota, S; Huang, K; Jiang, M; Nakamura, K E; Nakaya, T; Quilain, B; Patel, N D; Wendell, R A; Anthony, L H V; McCauley, N; Pritchard, A; Fukuda, Y; Itow, Y; Murase, M; Muto, F; Mijakowski, P; Frankiewicz, K; Jung, C K; Li, X; Palomino, J L; Santucci, G; Vilela, C; Wilking, M J; Yanagisawa, C; Ito, S; Fukuda, D; Ishino, H; Kibayashi, A; Koshio, Y; Nagata, H; Sakuda, M; Xu, C; Kuno, Y; Wark, D; Di Lodovico, F; Richards, B; Tacik, R; Kim, S B; Cole, A; Thompson, L; Okazawa, H; Choi, Y; Ito, K; Nishijima, K; Koshiba, M; Totsuka, Y; Suda, Y; Yokoyama, M; Calland, R G; Hartz, M; Martens, K; Simpson, C; Suzuki, Y; Vagins, M R; Hamabe, D; Kuze, M; Yoshida, T; Ishitsuka, M; Martin, J F; Nantais, C M; Tanaka, H A; Konaka, A; Chen, S; Wan, L; Zhang, Y; Wilkes, R J; Minamino, A

2018-06-01

A search for boosted dark matter using 161.9 kt yr of Super-Kamiokande IV data is presented. We search for an excess of elastically scattered electrons above the atmospheric neutrino background, with a visible energy between 100 MeV and 1 TeV, pointing back to the Galactic center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic center and Sun are calculated. Limits are also calculated for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay. This is the first experimental search for boosted dark matter from the Galactic center or the Sun interacting in a terrestrial detector.
Search for Boosted Dark Matter Interacting with Electrons in Super-Kamiokande

NASA Astrophysics Data System (ADS)

Kachulis, C.; Abe, K.; Bronner, C.; Hayato, Y.; Ikeda, M.; Iyogi, K.; Kameda, J.; Kato, Y.; Kishimoto, Y.; Marti, Ll.; Miura, M.; Moriyama, S.; Nakahata, M.; Nakano, Y.; Nakayama, S.; Okajima, Y.; Orii, A.; Pronost, G.; Sekiya, H.; Shiozawa, M.; Sonoda, Y.; Takeda, A.; Takenaka, A.; Tanaka, H.; Tasaka, S.; Tomura, T.; Akutsu, R.; Kajita, T.; Kaneyuki, K.; Nishimura, Y.; Okumura, K.; Tsui, K. M.; Labarga, L.; Fernandez, P.; Blaszczyk, F. d. M.; Gustafson, J.; Kearns, E.; Raaf, J. L.; Stone, J. L.; Sulak, L. R.; Berkman, S.; Tobayama, S.; Goldhaber, M.; Elnimr, M.; Kropp, W. R.; Mine, S.; Locke, S.; Weatherly, P.; Smy, M. B.; Sobel, H. W.; Takhistov, V.; Ganezer, K. S.; Hill, J.; Kim, J. Y.; Lim, I. T.; Park, R. G.; Himmel, A.; Li, Z.; O'Sullivan, E.; Scholberg, K.; Walter, C. W.; Ishizuka, T.; Nakamura, T.; Jang, J. S.; Choi, K.; Learned, J. G.; Matsuno, S.; Smith, S. N.; Amey, J.; Litchfield, R. P.; Ma, W. Y.; Uchida, Y.; Wascko, M. O.; Cao, S.; Friend, M.; Hasegawa, T.; Ishida, T.; Ishii, T.; Kobayashi, T.; Nakadaira, T.; Nakamura, K.; Oyama, Y.; Sakashita, K.; Sekiguchi, T.; Tsukamoto, T.; Abe, KE.; Hasegawa, M.; Suzuki, A. T.; Takeuchi, Y.; Yano, T.; Hayashino, T.; Hiraki, T.; Hirota, S.; Huang, K.; Jiang, M.; Nakamura, KE.; Nakaya, T.; Quilain, B.; Patel, N. D.; Wendell, R. A.; Anthony, L. H. V.; McCauley, N.; Pritchard, A.; Fukuda, Y.; Itow, Y.; Murase, M.; Muto, F.; Mijakowski, P.; Frankiewicz, K.; Jung, C. K.; Li, X.; Palomino, J. L.; Santucci, G.; Vilela, C.; Wilking, M. J.; Yanagisawa, C.; Ito, S.; Fukuda, D.; Ishino, H.; Kibayashi, A.; Koshio, Y.; Nagata, H.; Sakuda, M.; Xu, C.; Kuno, Y.; Wark, D.; Di Lodovico, F.; Richards, B.; Tacik, R.; Kim, S. B.; Cole, A.; Thompson, L.; Okazawa, H.; Choi, Y.; Ito, K.; Nishijima, K.; Koshiba, M.; Totsuka, Y.; Suda, Y.; Yokoyama, M.; Calland, R. G.; Hartz, M.; Martens, K.; Simpson, C.; Suzuki, Y.; Vagins, M. R.; Hamabe, D.; Kuze, M.; Yoshida, T.; Ishitsuka, M.; Martin, J. F.; Nantais, C. M.; Tanaka, H. A.; Konaka, A.; Chen, S.; Wan, L.; Zhang, Y.; Wilkes, R. J.; Minamino, A.; Super-Kamiokande Collaboration

2018-06-01

A search for boosted dark matter using 161.9 kt yr of Super-Kamiokande IV data is presented. We search for an excess of elastically scattered electrons above the atmospheric neutrino background, with a visible energy between 100 MeV and 1 TeV, pointing back to the Galactic center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic center and Sun are calculated. Limits are also calculated for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay. This is the first experimental search for boosted dark matter from the Galactic center or the Sun interacting in a terrestrial detector.
Adding Spice to Vanilla LCDM simulations: From Alternative Cosmologies to Lighting up Galaxies

NASA Astrophysics Data System (ADS)

Jahan Elahi, Pascal

2015-08-01

Cold Dark Matter simulations have formed the backbone of our theoretical understanding of cosmological structure formation. Predictions from the Lambda Cold Dark Matter (LCDM) cosmology, in which the Universe contains two major dark components, namely Dark Matter and Dark Energy, are in excellent agreement with the Large-Scale Structures observed, i.e., the distribution of galaxies across cosmic time. However, this paradigm is in tension with observations at small-scales, from the number and properties of satellite galaxies around galaxies such as the Milky Way and Andromeda, to the lensing statistics of massive galaxy clusters. I will present several alternative models of cosmology (from Warm Dark Matter to coupled Dark Matter-Dark Energy models) and how they compare to vanilla LCDM by studying formation of groups and clusters dark matter only and adiabatic hydrodynamical zoom simulations. I will show how modifications to the dark sector can lead to some surprising results. For example, Warm Dark Matter, so often examined on small satellite galaxies scales, can be probed observationally using weak lensing at cluster scales. Coupled dark sectors, where dark matter decays into dark energy and experiences an effective gravitational potential that differs from that experienced by normal matter, is effectively hidden away from direct observations of galaxies. Studies like these are vital if we are to pinpoint observations which can look for unique signatures of the physics that governs the hidden Universe. Of course, all of these predictions are unfortunately affected by uncertain galaxy formation physics. I will end by presenting results from a comparison study of numerous hydrodynamical codes, the nIFTY cluster comparison project, and how even how purely adiabatic simulations run with different codes give in quite different galaxy populations. The galaxies that form in these simulations, which all attempt to reproduce the observed galaxy population via not unreasonable subgrid physics, can and do vary in stellar mass, morphology and gas fraction.

THE NUMBER OF TIDAL DWARF SATELLITE GALAXIES IN DEPENDENCE OF BULGE INDEX

DOE Office of Scientific and Technical Information (OSTI.GOV)

López-Corredoira, Martín; Kroupa, Pavel, E-mail: martinlc@iac.es, E-mail: pavel@astro.uni-bonn.de

We show that a significant correlation (up to 5σ) emerges between the bulge index, defined to be larger for a larger bulge/disk ratio, in spiral galaxies with similar luminosities in the Galaxy Zoo 2 of the Sloan Digital Sky Survey and the number of tidal-dwarf galaxies in the catalog by Kaviraj et al. In the standard cold or warm dark matter cosmological models, the number of satellite galaxies correlates with the circular velocity of the dark matter host halo. In generalized gravity models without cold or warm dark matter, such a correlation does not exist, because host galaxies cannot capture infalling dwarfmore » galaxies due to the absence of dark-matter-induced dynamical friction. However, in such models, a correlation is expected to exist between the bulge mass and the number of satellite galaxies because bulges and tidal-dwarf satellite galaxies form in encounters between host galaxies. This is not predicted by dark matter models in which bulge mass and the number of satellites are a priori uncorrelated because higher bulge/disk ratios do not imply higher dark/luminous ratios. Hence, our correlation reproduces the prediction of scenarios without dark matter, whereas an explanation is not found readily from the a priori predictions of the standard scenario with dark matter. Further research is needed to explore whether some application of the standard theory may explain this correlation.« less
The dark matter distribution of M87 and NGC 1399

NASA Technical Reports Server (NTRS)

Tsai, John C.

1993-01-01

Recent X-ray observations of clusters of galaxies indicate that, outside the innermost about 100 kpc region, the ratio of dark matter density to baryonic matter density declines with radius. We show that this result is consistent with a cold dark matter simulation, suggesting the presence of dissipationless dark matter in the observed clusters. This is contrary to previous suggestions that dissipational baryonic dark matter is required to explain the decline in the density ratio. The simulation further shows that, in the inner 100 kpc region, the density ratio should rise with radius. We confirm this property in M87 and NGC 1399, which are close enough to allow the determination of the density ratio in the required inner region. X-ray mappings of the dark matter distribution in clusters of galaxies are therefore consistent with the presence of dissipationless dark matter.
Dynamics of a spherically symmetric inhomogeneous coupled dark energy model with coupling term proportional to non relatvistic matter

NASA Astrophysics Data System (ADS)

Izquierdo, Germán; Blanquet-Jaramillo, Roberto C.; Sussman, Roberto A.

2018-01-01

The quasi-local scalar variables approach is applied to a spherically symmetric inhomogeneous Lemaître-Tolman-Bondi metric containing a mixture of non-relativistic cold dark matter and coupled dark energy with constant equation of state. The quasi-local coupling term considered is proportional to the quasi-local cold dark matter energy density and a quasi-local Hubble factor-like scalar via a coupling constant α . The autonomous numerical system obtained from the evolution equations is classified for different choices of the free parameters: the adiabatic constant of the dark energy w and α . The presence of a past attractor in a non-physical region of the energy densities phase-space of the system makes the coupling term non physical when the energy flows from the matter to the dark energy in order to avoid negative values of the dark energy density in the past. On the other hand, if the energy flux goes from dark energy to dark matter, the past attractor lies in a physical region. The system is also numerically solved for some interesting initial profiles leading to different configurations: an ever expanding mixture, a scenario where the dark energy is completely consumed by the non-relativistic matter by means of the coupling term, a scenario where the dark energy disappears in the inner layers while the outer layers expand as a mixture of both sources, and, finally, a structure formation toy model scenario, where the inner shells containing the mixture collapse while the outer shells expand.
Elastically Decoupling Dark Matter.

PubMed

Kuflik, Eric; Perelstein, Maxim; Lorier, Nicolas Rey-Le; Tsai, Yu-Dai

2016-06-03

We present a novel dark matter candidate, an elastically decoupling relic, which is a cold thermal relic whose present abundance is determined by the cross section of its elastic scattering on standard model particles. The dark matter candidate is predicted to have a mass ranging from a few to a few hundred MeV, and an elastic scattering cross section with electrons, photons and/or neutrinos in the 10^{-3}-1 fb range.
νΛMDM: A model for sterile neutrino and dark matter reconciles cosmological and neutrino oscillation data after BICEP2

NASA Astrophysics Data System (ADS)

Ko, P.; Tang, Yong

2014-12-01

We propose an ultraviolet complete theory for cold dark matter (CDM) and sterile neutrinos that can accommodate both cosmological data and neutrino oscillation experiments within 1σ level. We assume a new U(1)X dark gauge symmetry which is broken at ∼ O (MeV) scale resulting light dark photon. Such a light mediator for DM's self-scattering and scattering-off sterile neutrinos can resolve three controversies for cold DM on small cosmological scales: cusp vs. core, too-big-to-fail and missing satellites. We can also accommodate ∼ O (1) eV scale sterile neutrinos as the hot dark matter (HDM) and can fit some neutrino anomalies from neutrino oscillation experiments within 1σ. Finally, the right amount of HDM can make a sizable contribution to dark radiation, and also helps to reconcile the tension between the data on the tensor-to-scalar ratio reported by Planck and BICEP2 Collaborations.
The Structure of Dark Matter Halos in Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Burkert, A.

1995-07-01

Recent observations indicate that dark matter halos have flat central density profiles. Cosmological simulations with nonbaryonic dark matter, however, predict self-similar halos with central density cusps. This contradiction has lead to the conclusion that dark matter must be baryonic. Here it is shown that the dark matter halos of dwarf spiral galaxies represent a one-parameter family with self-similar density profiles. The observed global halo parameters are coupled with each other through simple scaling relations which can be explained by the standard cold dark matter model if one assumes that all the halos formed from density fluctuations with the same primordial amplitude. We find that the finite central halo densities correlate with the other global parameters. This result rules out scenarios where the flat halo cores formed subsequently through violent dynamical processes in the baryonic component. These cores instead provide important information on the origin and nature of dark matter in dwarf galaxies.
Adding Spice to Vanilla LCDM simulations: Alternative Cosmologies & Lighting up Simulations

NASA Astrophysics Data System (ADS)

Jahan Elahi, Pascal

2015-08-01

Cold Dark Matter simulations have formed the backbone of our theoretical understanding of cosmological structure formation. Predictions from the Lambda Cold Dark Matter (LCDM) cosmology, where the Universe contains two dark components, namely Dark Matter & Dark Energy, are in excellent agreement with the Large-Scale Structures observed, i.e., the distribution of galaxies across cosmic time. However, this paradigm is in tension with observations at small-scales, from the number and properties of satellite galaxies around galaxies such as the Milky Way and Andromeda, to the lensing statistics of massive galaxy clusters. I will present several alternative models of cosmology (from Warm Dark Matter to coupled Dark Matter-Dark Energy models) and how they compare to vanilla LCDM by studying formation of groups and clusters dark matter only and adiabatic hydrodynamical zoom simulations. I will show how modifications to the dark sector can lead to some surprising results. For example, Warm Dark Matter, so often examined on small satellite galaxies scales, can be probed observationally using weak lensing at cluster scales. Coupled dark sectors, where dark matter decays into dark energy and experiences an effective gravitational potential that differs from that experienced by normal matter, is effectively hidden away from direct observations of galaxies. Studies like these are vital if we are to pinpoint observations which can look for unique signatures of the physics that governs the hidden Universe. Finally, I will discuss how all of these predictions are affected by uncertain galaxy formation physics. I will present results from a major comparison study of numerous hydrodynamical codes, the nIFTY cluster comparison project. This comparison aims to understand the code-to-code scatter in the properties of dark matter haloes and the galaxies that reside in them. We find that even in purely adiabatic simulations, different codes form clusters with very different X-ray profiles. The galaxies that form in these simulations, which all use codes that attempt to reproduce the observed galaxy population via not unreasonable subgrid physics, vary in stellar mass, morphology and gas fraction, sometimes by an order of magnitude. I will end with a discussion of precision cosmology in light of these results.
Recent heavy particle decay in a matter dominated universe

NASA Astrophysics Data System (ADS)

Olive, K. A.; Seckel, D.; Vishniac, E.

1984-09-01

The cold matter scenario for galaxy formation solves the dark matter problem very nicely on small scales corresponding to galaxies and clusters of galaxies. It is, however, difficult to reconcile with a Universe with an Einstein-deSitter value of (UC OMEGA) = 1. Cold matter and (UC OMEGA) = 1 can be made compatible while retaining the feature that the Universe is matter dominated today. This is done by means of heavy (cold) particles whose decay subsequently leads to the unbinding of a large fraction of lighter clustered matter.
Recent heavy-particle decay in a matter-dominated universe

NASA Astrophysics Data System (ADS)

Olive, K. A.; Seckel, D.; Vishniac, E.

1985-05-01

The cold-matter scenario for galaxy formation solves the dark-matter problem very nicely on small scales corresponding to galaxies and clusters of galaxies. It is, however, difficult to reconcile with a universe with an Einstein-deSitter value of Ω = 1. It is shown here that cold matter and Ω = 1 can be made compatible while retaining the feature that the universe is matter-dominated today. This is done by means of heavy (cold) particles whose decay subsequently leads to the unbinding of a large fraction of lighter clustered matter.
On the Generation of the Hubble Sequence Through an Internal Secular Dynamical Process

DTIC Science & Technology

2004-01-01

is apparently brought about by the fact that spiral galaxies still have varying reserves of baryonic dark matter to form stars, therefore as the...central baryonic dark matter supply, thus the ellipticals in more advanced stage of evolution (which also generally have larger L) will experi- ence...This view is particularly favored by the currently popular hierarchical clustering/cold dark matter (CDM) paradigm of structure formation and evolution
Cosmological tachyon condensation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bilic, Neven; Tupper, Gary B.; Viollier, Raoul D.

2009-07-15

We consider the prospects for dark matter/energy unification in k-essence type cosmologies. General mappings are established between the k-essence scalar field, the hydrodynamic and braneworld descriptions. We develop an extension of the general relativistic dust model that incorporates the effects of both pressure and the associated acoustic horizon. Applying this to a tachyon model, we show that this inhomogeneous 'variable Chaplygin gas' does evolve into a mixed system containing cold dark matter like gravitational condensate in significant quantities. Our methods can be applied to any dark energy model, as well as to mixtures of dark energy and traditional dark matter.
Annihilation of singlet fermionic dark matter into two photons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ettefaghi, M.M.; Moazzemi, R., E-mail: mettefaghi@qom.ac.ir, E-mail: r.moazzemi@qom.ac.ir

2013-02-01

We consider an extension of the standard model in which a singlet fermionic particle, to serve as cold dark matter, and a singlet Higgs are added. We perform a reanalysis on the free parameters. In particular, demanding a correct relic abundance of dark matter, we derive and plot the coupling of the singlet fermion with the singlet Higgs, g{sub s}, versus the dark matter mass. We analytically compute the pair annihilation cross section of singlet fermionic dark matter into two photons. The thermally averaged of this cross section is calculated for wide range of energies and plotted versus dark mattermore » mass using g{sub s} consistent with the relic abundance condition. We also compare our results with the Fermi-Lat observations.« less
Sourcing dark matter and dark energy from α-attractors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mishra, Swagat S.; Sahni, Varun; Shtanov, Yuri, E-mail: swagat@iucaa.in, E-mail: varun@iucaa.in, E-mail: shtanov@bitp.kiev.ua

In [1], Kallosh and Linde drew attention to a new family of superconformal inflationary potentials, subsequently called α-attractors [2]. The α-attractor family can interpolate between a large class of inflationary models. It also has an important theoretical underpinning within the framework of supergravity. We demonstrate that the α-attractors have an even wider appeal since they may describe dark matter and perhaps even dark energy. The dark matter associated with the α-attractors, which we call α-dark matter (αDM), shares many of the attractive features of fuzzy dark matter, with V (φ) = ½ m {sup 2}φ{sup 2}, while having none ofmore » its drawbacks. Like fuzzy dark matter, αDM can have a large Jeans length which could resolve the cusp-core and substructure problems faced by standard cold dark matter. αDM also has an appealing tracker property which enables it to converge to the late-time dark matter asymptote, ( w ) ≅ 0, from a wide range of initial conditions. It thus avoids the enormous fine-tuning problems faced by the m {sup 2}φ{sup 2} potential in describing dark matter.« less
Probing Self-interacting Dark Matter with Disk Galaxies in Cluster Environments

NASA Astrophysics Data System (ADS)

Secco, Lucas F.; Farah, Amanda; Jain, Bhuvnesh; Adhikari, Susmita; Banerjee, Arka; Dalal, Neal

2018-06-01

Self-interacting dark matter (SIDM) has long been proposed as a solution to small-scale problems posed by standard cold dark matter. We use numerical simulations to study the effect of dark matter interactions on the morphology of disk galaxies falling into galaxy clusters. The effective drag force on dark matter leads to offsets of the stellar disk with respect to the surrounding halo, causing distortions in the disk. For anisotropic scattering cross sections of 0.5 and 1.0 {cm}}2 {{{g}}}-1, we show that potentially observable warps, asymmetries, and thickening of the disk occur in simulations. We discuss observational tests of SIDM with galaxy surveys and more realistic simulations needed to obtain detailed predictions.
Prospects for detecting supersymmetric dark matter in the Galactic halo.

PubMed

Springel, V; White, S D M; Frenk, C S; Navarro, J F; Jenkins, A; Vogelsberger, M; Wang, J; Ludlow, A; Helmi, A

2008-11-06

Dark matter is the dominant form of matter in the Universe, but its nature is unknown. It is plausibly an elementary particle, perhaps the lightest supersymmetric partner of known particle species. In this case, annihilation of dark matter in the halo of the Milky Way should produce gamma-rays at a level that may soon be observable. Previous work has argued that the annihilation signal will be dominated by emission from very small clumps (perhaps smaller even than the Earth), which would be most easily detected where they cluster together in the dark matter haloes of dwarf satellite galaxies. Here we report that such small-scale structure will, in fact, have a negligible impact on dark matter detectability. Rather, the dominant and probably most easily detectable signal will be produced by diffuse dark matter in the main halo of the Milky Way. If the main halo is strongly detected, then small dark matter clumps should also be visible, but may well contain no stars, thereby confirming a key prediction of the cold dark matter model.
Cold dark energy constraints from the abundance of galaxy clusters

DOE PAGES

Heneka, Caroline; Rapetti, David; Cataneo, Matteo; ...

2017-10-05

We constrain cold dark energy of negligible sound speed using galaxy cluster abundance observations. In contrast to standard quasi-homogeneous dark energy, negligible sound speed implies clustering of the dark energy fluid at all scales, allowing us to measure the effects of dark energy perturbations at cluster scales. We compare those models and set the stage for using non-linear information from semi-analytical modelling in cluster growth data analyses. For this, we recalibrate the halo mass function with non-linear characteristic quantities, the spherical collapse threshold and virial overdensity, that account for model and redshift-dependent behaviours, as well as an additional mass contributionmore » for cold dark energy. Here in this paper, we present the first constraints from this cold dark matter plus cold dark energy mass function using our cluster abundance likelihood, which self-consistently accounts for selection effects, covariances and systematic uncertainties. We combine cluster growth data with cosmic microwave background, supernovae Ia and baryon acoustic oscillation data, and find a shift between cold versus quasi-homogeneous dark energy of up to 1σ. We make a Fisher matrix forecast of constraints attainable with cluster growth data from the ongoing Dark Energy Survey (DES). For DES, we predict ~ 50 percent tighter constraints on (Ωm, w) for cold dark energy versus wCDM models, with the same free parameters. Overall, we show that cluster abundance analyses are sensitive to cold dark energy, an alternative, viable model that should be routinely investigated alongside the standard dark energy scenario.« less
Cold dark energy constraints from the abundance of galaxy clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heneka, Caroline; Rapetti, David; Cataneo, Matteo

We constrain cold dark energy of negligible sound speed using galaxy cluster abundance observations. In contrast to standard quasi-homogeneous dark energy, negligible sound speed implies clustering of the dark energy fluid at all scales, allowing us to measure the effects of dark energy perturbations at cluster scales. We compare those models and set the stage for using non-linear information from semi-analytical modelling in cluster growth data analyses. For this, we recalibrate the halo mass function with non-linear characteristic quantities, the spherical collapse threshold and virial overdensity, that account for model and redshift-dependent behaviours, as well as an additional mass contributionmore » for cold dark energy. Here in this paper, we present the first constraints from this cold dark matter plus cold dark energy mass function using our cluster abundance likelihood, which self-consistently accounts for selection effects, covariances and systematic uncertainties. We combine cluster growth data with cosmic microwave background, supernovae Ia and baryon acoustic oscillation data, and find a shift between cold versus quasi-homogeneous dark energy of up to 1σ. We make a Fisher matrix forecast of constraints attainable with cluster growth data from the ongoing Dark Energy Survey (DES). For DES, we predict ~ 50 percent tighter constraints on (Ωm, w) for cold dark energy versus wCDM models, with the same free parameters. Overall, we show that cluster abundance analyses are sensitive to cold dark energy, an alternative, viable model that should be routinely investigated alongside the standard dark energy scenario.« less
Dark Matter or Modified Dynamics? Hints from Galaxy Kinematics

NASA Astrophysics Data System (ADS)

Gentile, G.

2010-12-01

I show two observational projects I am involved in, which are aimed at understanding better the existence and nature of dark matter, and also aimed at testing alternatives to galactic dark matter such as MOND (Modified Newtonian Dynamics). I present new HI observations of the nearby dwarf galaxy NGC 3741. This galaxy has an extremely extended HI disc (42 B-band exponential scalelengths). The distribution and kinematics are accurately derived by building model data cubes, which closely reproduce the observations. Mass modelling of the rotation curve shows that a cored dark matter halo or MOND provide very good fits, whereas Cold Dark Matter density profiles fail to fit the data. I also show new results about tidal dwarf galaxies, which within the CDM framework are expected to be dark matter-free but whose kinematics instead show a mass discrepancy, exactly of the magnitude that is expected in MOND (Modified Newtonian Dynamics).
Relieving the tension between weak lensing and cosmic microwave background with interacting dark matter and dark energy models

NASA Astrophysics Data System (ADS)

An, Rui; Feng, Chang; Wang, Bin

2018-02-01

We constrain interacting dark matter and dark energy (IDMDE) models using a 450-degree-square cosmic shear data from the Kilo Degree Survey (KiDS) and the angular power spectra from Planck's latest cosmic microwave background measurements. We revisit the discordance problem in the standard Lambda cold dark matter (ΛCDM) model between weak lensing and Planck datasets and extend the discussion by introducing interacting dark sectors. The IDMDE models are found to be able to alleviate the discordance between KiDS and Planck as previously inferred from the ΛCDM model, and moderately favored by a combination of the two datasets.
Significant gamma lines from inert Higgs dark matter.

PubMed

Gustafsson, Michael; Lundström, Erik; Bergström, Lars; Edsjö, Joakim

2007-07-27

One way to unambiguously confirm the existence of particle dark matter and determine its mass would be to detect its annihilation into monochromatic gamma-rays in upcoming telescopes. One of the most minimal models for dark matter is the inert doublet model, obtained by adding another Higgs doublet with no direct coupling to fermions. For a mass between 40 and 80 GeV, the lightest of the new inert Higgs particles can give the correct cosmic abundance of cold dark matter in agreement with current observations. We show that for this scalar dark matter candidate, the annihilation signal of monochromatic gammagamma and Zgamma final states would be exceptionally strong. The energy range and rates for these gamma-ray line signals make them ideal to search for with the soon upcoming GLAST satellite.

The Cold Dark Matter Search test stand warm electronics card

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hines, Bruce; /Colorado U., Denver; Hansen, Sten

A card which does the signal processing for four SQUID amplifiers and two charge sensitive channels is described. The card performs the same functions as is presently done with two custom 9U x 280mm Eurocard modules, a commercial multi-channel VME digitizer, a PCI to GPIB interface, a PCI to VME interface and a custom built linear power supply. By integrating these functions onto a single card and using the power over Ethernet standard, the infrastructure requirements for instrumenting a Cold Dark Matter Search (CDMS) detector test stand are significantly reduced.
Theoretical Comparison Between Candidates for Dark Matter

NASA Astrophysics Data System (ADS)

McKeough, James; Hira, Ajit; Valdez, Alexandra

2017-01-01

Since the generally-accepted view among astrophysicists is that the matter component of the universe is mostly dark matter, the search for dark matter particles continues unabated. The Large Underground Xenon (LUX) improvements, aided by advanced computer simulations at the U.S. Department of Energy's Lawrence Berkeley National Laboratory's (Berkeley Lab) National Energy Research Scientific Computing Center (NERSC) and Brown University's Center for Computation and Visualization (CCV), can potentially eliminate some particle models of dark matter. Generally, the proposed candidates can be put in three categories: baryonic dark matter, hot dark matter, and cold dark matter. The Lightest Supersymmetric Particle(LSP) of supersymmetric models is a dark matter candidate, and is classified as a Weakly Interacting Massive Particle (WIMP). Similar to the cosmic microwave background radiation left over from the Big Bang, there is a background of low-energy neutrinos in our Universe. According to some researchers, these may be the explanation for the dark matter. One advantage of the Neutrino Model is that they are known to exist. Dark matter made from neutrinos is termed ``hot dark matter''. We formulate a novel empirical function for the average density profile of cosmic voids, identified via the watershed technique in ΛCDM N-body simulations. This function adequately treats both void size and redshift, and describes the scale radius and the central density of voids. We started with a five-parameter model. Our research is mainly on LSP and Neutrino models.
Toward electroweak scale cold dark matter with local dark gauge symmetry and beyond the DM EFT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ko, Pyungwon, E-mail: pko@kias.re.kr

2016-06-21

In this talk, I describe a class of electroweak (EW) scale dark matter (DM) models where its stability or longevity are the results of underlying dark gauge symmetries: stable due to unbroken local dark gauge symmetry or topology, or long-lived due to the accidental global symmetry of dark gauge theories. Compared with the usual phenomenological dark matter models (including DM EFT or simplified DM models), DM models with local dark gauge symmetries include dark gauge bosons, dark Higgs bosons and sometimes excited dark matter. And dynamics among these fields are completely fixed by local gauge principle. The idea of singletmore » portals including the Higgs portal can thermalize these hidden sector dark matter very efficiently, so that these DM could be easily thermal DM. I also discuss the limitation of the usual DM effective field theory or simplified DM models without the full SM gauge symmetry, and emphasize the importance of the full SM gauge symmetry and renormalizability especially for collider searches for DM.« less
Research Progress on Dark Matter Model Based on Weakly Interacting Massive Particles

NASA Astrophysics Data System (ADS)

He, Yu; Lin, Wen-bin

2017-04-01

The cosmological model of cold dark matter (CDM) with the dark energy and a scale-invariant adiabatic primordial power spectrum has been considered as the standard cosmological model, i.e. the ΛCDM model. Weakly interacting massive particles (WIMPs) become a prominent candidate for the CDM. Many models extended from the standard model can provide the WIMPs naturally. The standard calculations of relic abundance of dark matter show that the WIMPs are well in agreement with the astronomical observation of ΩDM h2 ≈0.11. The WIMPs have a relatively large mass, and a relatively slow velocity, so they are easy to aggregate into clusters, and the results of numerical simulations based on the WIMPs agree well with the observational results of cosmic large-scale structures. In the aspect of experiments, the present accelerator or non-accelerator direct/indirect detections are mostly designed for the WIMPs. Thus, a wide attention has been paid to the CDM model based on the WIMPs. However, the ΛCDM model has a serious problem for explaining the small-scale structures under one Mpc. Different dark matter models have been proposed to alleviate the small-scale problem. However, so far there is no strong evidence enough to exclude the CDM model. We plan to introduce the research progress of the dark matter model based on the WIMPs, such as the WIMPs miracle, numerical simulation, small-scale problem, and the direct/indirect detection, to analyze the criterion for discriminating the ;cold;, ;hot;, and ;warm; dark matter, and present the future prospects for the study in this field.
Dark matter, long-range forces, and large-scale structure

NASA Technical Reports Server (NTRS)

Gradwohl, Ben-Ami; Frieman, Joshua A.

1992-01-01

If the dark matter in galaxies and clusters is nonbaryonic, it can interact with additional long-range fields that are invisible to experimental tests of the equivalence principle. We discuss the astrophysical and cosmological implications of a long-range force coupled only to the dark matter and find rather tight constraints on its strength. If the force is repulsive (attractive), the masses of galaxy groups and clusters (and the mean density of the universe inferred from them) have been systematically underestimated (overestimated). We explore the consequent effects on the two-point correlation function, large-scale velocity flows, and microwave background anisotropies, for models with initial scale-invariant adiabatic perturbations and cold dark matter.
A quantitative approach to the topology of large-scale structure. [for galactic clustering computation

NASA Technical Reports Server (NTRS)

Gott, J. Richard, III; Weinberg, David H.; Melott, Adrian L.

1987-01-01

A quantitative measure of the topology of large-scale structure: the genus of density contours in a smoothed density distribution, is described and applied. For random phase (Gaussian) density fields, the mean genus per unit volume exhibits a universal dependence on threshold density, with a normalizing factor that can be calculated from the power spectrum. If large-scale structure formed from the gravitational instability of small-amplitude density fluctuations, the topology observed today on suitable scales should follow the topology in the initial conditions. The technique is illustrated by applying it to simulations of galaxy clustering in a flat universe dominated by cold dark matter. The technique is also applied to a volume-limited sample of the CfA redshift survey and to a model in which galaxies reside on the surfaces of polyhedral 'bubbles'. The topology of the evolved mass distribution and 'biased' galaxy distribution in the cold dark matter models closely matches the topology of the density fluctuations in the initial conditions. The topology of the observational sample is consistent with the random phase, cold dark matter model.
SQUID-based microwave cavity search for dark-matter axions.

PubMed

Asztalos, S J; Carosi, G; Hagmann, C; Kinion, D; van Bibber, K; Hotz, M; Rosenberg, L J; Rybka, G; Hoskins, J; Hwang, J; Sikivie, P; Tanner, D B; Bradley, R; Clarke, J

2010-01-29

Axions in the microeV mass range are a plausible cold dark-matter candidate and may be detected by their conversion into microwave photons in a resonant cavity immersed in a static magnetic field. We report the first result from such an axion search using a superconducting first-stage amplifier (SQUID) replacing a conventional GaAs field-effect transistor amplifier. This experiment excludes KSVZ dark-matter axions with masses between 3.3 microeV and 3.53 microeV and sets the stage for a definitive axion search utilizing near quantum-limited SQUID amplifiers.
Fast Parallel Tree Codes for Gravitational and Fluid Dynamical N-Body Problems

DTIC Science & Technology

1993-01-01

The particles represent the so-called " Dark Matter " eral times the the full message latency for every remote which is believed to dominate the mass...Katz, L. Herquist, and D. H. Weinberg. Galax- R. Acad. Sci. Paris, 306(I):739-742, 1988. ies and gas in a cold dark matter universe. Ap. J., [111 A...57(3):566-569, 1983. dark matter halos. Ap. J., 378:496, 1991. [30] G. Pedrizzetti. Insight into singular vortex flows. [17] C. C. Dyer and P. S. S
Gravitational detection of a low-mass dark satellite galaxy at cosmological distance.

PubMed

Vegetti, S; Lagattuta, D J; McKean, J P; Auger, M W; Fassnacht, C D; Koopmans, L V E

2012-01-18

The mass function of dwarf satellite galaxies that are observed around Local Group galaxies differs substantially from simulations based on cold dark matter: the simulations predict many more dwarf galaxies than are seen. The Local Group, however, may be anomalous in this regard. A massive dark satellite in an early-type lens galaxy at a redshift of 0.222 was recently found using a method based on gravitational lensing, suggesting that the mass fraction contained in substructure could be higher than is predicted from simulations. The lack of very low-mass detections, however, prohibited any constraint on their mass function. Here we report the presence of a (1.9 ± 0.1) × 10(8) M dark satellite galaxy in the Einstein ring system JVAS B1938+666 (ref. 11) at a redshift of 0.881, where M denotes the solar mass. This satellite galaxy has a mass similar to that of the Sagittarius galaxy, which is a satellite of the Milky Way. We determine the logarithmic slope of the mass function for substructure beyond the local Universe to be 1.1(+0.6)(-0.4), with an average mass fraction of 3.3(+3.6)(-1.8) per cent, by combining data on both of these recently discovered galaxies. Our results are consistent with the predictions from cold dark matter simulations at the 95 per cent confidence level, and therefore agree with the view that galaxies formed hierarchically in a Universe composed of cold dark matter.
Dragging force on galaxies due to streaming dark matter

NASA Technical Reports Server (NTRS)

Hara, Tetsuya; Miyoshi, Shigeru

1990-01-01

It has been reported that galaxies in large regions (approx. 10(exp 2) Mpc), including some clusters of galaxies, may be streaming coherently with velocities up to 600 km/sec or more with respect to the rest frame determined by the microwave background radiation. On the other hand, it is suggested that the dominant mass component of the universe is dark matter. Because we can only speculate the motion of dark matter from the galaxy motions, much attention should be paid to the correlation of velocities between the observed galaxies and cold dark matter. So the authors investigated whether such coherent large-scale streaming velocities are due to dark matter or only to baryonic objects which may be formed by piling up of gases due to some explosive events. It seems that, although each galaxy will not follow the motion of dark matter, clusters of galaxies may represent the velocity field of dark matter. The origin of the velocity field of dark matter would be due to the initial adiabatic perturbations and, in fact, the observed peculiar velocities of clusters are within the allowed region constrained from the isotropy of the microwave background radiation.
Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows.

PubMed

Governato, F; Brook, C; Mayer, L; Brooks, A; Rhee, G; Wadsley, J; Jonsson, P; Willman, B; Stinson, G; Quinn, T; Madau, P

2010-01-14

For almost two decades the properties of 'dwarf' galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies-bulgeless and with shallow central dark-matter profiles-arise naturally in these simulations.
Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago

NASA Astrophysics Data System (ADS)

Genzel, R.; Schreiber, N. M. Förster; Übler, H.; Lang, P.; Naab, T.; Bender, R.; Tacconi, L. J.; Wisnioski, E.; Wuyts, S.; Alexander, T.; Beifiori, A.; Belli, S.; Brammer, G.; Burkert, A.; Carollo, C. M.; Chan, J.; Davies, R.; Fossati, M.; Galametz, A.; Genel, S.; Gerhard, O.; Lutz, D.; Mendel, J. T.; Momcheva, I.; Nelson, E. J.; Renzini, A.; Saglia, R.; Sternberg, A.; Tacchella, S.; Tadaki, K.; Wilman, D.

2017-03-01

In the cold dark matter cosmology, the baryonic components of galaxies—stars and gas—are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius—a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.
Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago.

PubMed

Genzel, R; Schreiber, N M Förster; Übler, H; Lang, P; Naab, T; Bender, R; Tacconi, L J; Wisnioski, E; Wuyts, S; Alexander, T; Beifiori, A; Belli, S; Brammer, G; Burkert, A; Carollo, C M; Chan, J; Davies, R; Fossati, M; Galametz, A; Genel, S; Gerhard, O; Lutz, D; Mendel, J T; Momcheva, I; Nelson, E J; Renzini, A; Saglia, R; Sternberg, A; Tacchella, S; Tadaki, K; Wilman, D

2017-03-15

In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.
Off-shell dark matter: A cosmological relic of quantum gravity

NASA Astrophysics Data System (ADS)

Saravani, Mehdi; Afshordi, Niayesh

2017-02-01

We study a novel proposal for the origin of cosmological cold dark matter (CDM) which is rooted in the quantum nature of spacetime. In this model, off-shell modes of quantum fields can exist in asymptotic states as a result of spacetime nonlocality (expected in generic theories of quantum gravity) and play the role of CDM, which we dub off-shell dark matter (O f DM ). However, their rate of production is suppressed by the scale of nonlocality (e.g. Planck length). As a result, we show that O f DM is only produced in the first moments of big bang, and then effectively decouples (except through its gravitational interactions). We examine the observational predictions of this model: In the context of cosmic inflation, we show that this proposal relates the reheating temperature to the inflaton mass, which narrows down the uncertainty in the number of e -foldings of specific inflationary scenarios. We also demonstrate that O f DM is indeed cold, and discuss potentially observable signatures on small scale matter power spectrum.
Ultra Light Axionic Dark Matter: Galactic Halos and Implications for Observations with Pulsar Timing Arrays

NASA Astrophysics Data System (ADS)

de Martino, Ivan; Broadhurst, Tom; Tye, S.-H. Henry; Chiueh, Tzihong; Shive, Hsi-Yu; Lazkoz, Ruth

2018-01-01

The cold dark matter (CDM) paradigm successfully explains the cosmic structure over an enormous span of redshifts. However, it fails when probing the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. Moreover, the lack of experimental detection of Weakly Interacting Massive Particle (WIMP) favors alternative candidates such as light axionic dark matter that naturally arise in string theory. Cosmological N-body simulations have shown that axionic dark matter forms a solitonic core of size of ≃ 150 pc in the innermost region of the galactic halos. The oscillating scalar field associated to the axionic dark matter halo produces an oscillating gravitational potential that induces a time dilation of the pulse arrival time of ≃ 400 ns/(m_B/10^{-22} eV) for pulsar within such a solitonic core. Over the whole galaxy, the averaged predicted signal may be detectable with current and forthcoming pulsar timing array telescopes.
Dipolar dark matter with massive bigravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanchet, Luc; Heisenberg, Lavinia; Department of Physics & The Oskar Klein Centre, AlbaNova University Centre,Roslagstullsbacken 21, 10691 Stockholm

2015-12-14

Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the twomore » metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.« less
Dipolar dark matter with massive bigravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanchet, Luc; Heisenberg, Lavinia, E-mail: blanchet@iap.fr, E-mail: laviniah@kth.se

2015-12-01

Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the twomore » metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.« less
Evolution of velocity dispersion along cold collisionless flows

DOE PAGES

Banik, Nilanjan; Sikivie, Pierre

2016-05-01

We found that the infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We also discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behaviour of the velocity dispersion near caustics. The results aremore » used to derive an upper limit on the energy dispersion of the Big Flow from the sharpness of its nearby caustic, and a prediction for the dispersions in its velocity components.« less
COBE DMR-normalized open inflation cold dark matter cosmogony

NASA Technical Reports Server (NTRS)

Gorski, Krzysztof M.; Ratra, Bharat; Sugiyama, Naoshi; Banday, Anthony J.

1995-01-01

A cut-sky orthogonal mode analysis of the 2 year COBE DMR 53 and 90 GHz sky maps (in Galactic coordinates) is used to determine the normalization of an open inflation model based on the cold dark matter (CDM) scenario. The normalized model is compared to measures of large-scale structure in the universe. Although the DMR data alone does not provide sufficient discriminative power to prefer a particular value of the mass density parameter, the open model appears to be reasonably consistent with observations when Omega(sub 0) is approximately 0.3-0.4 and merits further study.
Origin of ΔN{sub eff} as a result of an interaction between dark radiation and dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bjaelde, Ole Eggers; Das, Subinoy; Moss, Adam, E-mail: oeb@phys.au.dk, E-mail: subinoy@physik.rwth-aachen.de, E-mail: Adam.Moss@nottingham.ac.uk

2012-10-01

Results from the Wilkinson Microwave Anisotropy Probe (WMAP), Atacama Cosmology Telescope (ACT) and recently from the South Pole Telescope (SPT) have indicated the possible existence of an extra radiation component in addition to the well known three neutrino species predicted by the Standard Model of particle physics. In this paper, we explore the possibility of the apparent extra dark radiation being linked directly to the physics of cold dark matter (CDM). In particular, we consider a generic scenario where dark radiation, as a result of an interaction, is produced directly by a fraction of the dark matter density effectively decayingmore » into dark radiation. At an early epoch when the dark matter density is negligible, as an obvious consequence, the density of dark radiation is also very small. As the Universe approaches matter radiation equality, the dark matter density starts to dominate thereby increasing the content of dark radiation and changing the expansion rate of the Universe. As this increase in dark radiation content happens naturally after Big Bang Nucleosynthesis (BBN), it can relax the possible tension with lower values of radiation degrees of freedom measured from light element abundances compared to that of the CMB. We numerically confront this scenario with WMAP+ACT and WMAP+SPT data and derive an upper limit on the allowed fraction of dark matter decaying into dark radiation.« less

Cold dark matter: Controversies on small scales.

PubMed

Weinberg, David H; Bullock, James S; Governato, Fabio; Kuzio de Naray, Rachel; Peter, Annika H G

2015-10-06

The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. We review the current observational and theoretical status of these "small-scale controversies." Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years.
Dark Matter Detection Using Helium Evaporation and Field Ionization

NASA Astrophysics Data System (ADS)

Maris, Humphrey J.; Seidel, George M.; Stein, Derek

2017-11-01

We describe a method for dark matter detection based on the evaporation of helium atoms from a cold surface and their subsequent detection using field ionization. When a dark matter particle scatters off a nucleus of the target material, elementary excitations (phonons or rotons) are produced. Excitations which have an energy greater than the binding energy of helium to the surface can result in the evaporation of helium atoms. We propose to detect these atoms by ionizing them in a strong electric field. Because the binding energy of helium to surfaces can be below 1 meV, this detection scheme opens up new possibilities for the detection of dark matter particles in a mass range down to 1 MeV /c2 .
Dark Matter Detection Using Helium Evaporation and Field Ionization.

PubMed

Maris, Humphrey J; Seidel, George M; Stein, Derek

2017-11-03

We describe a method for dark matter detection based on the evaporation of helium atoms from a cold surface and their subsequent detection using field ionization. When a dark matter particle scatters off a nucleus of the target material, elementary excitations (phonons or rotons) are produced. Excitations which have an energy greater than the binding energy of helium to the surface can result in the evaporation of helium atoms. We propose to detect these atoms by ionizing them in a strong electric field. Because the binding energy of helium to surfaces can be below 1 meV, this detection scheme opens up new possibilities for the detection of dark matter particles in a mass range down to 1 MeV/c^{2}.
Variable sound speed in interacting dark energy models

NASA Astrophysics Data System (ADS)

Linton, Mark S.; Pourtsidou, Alkistis; Crittenden, Robert; Maartens, Roy

2018-04-01

We consider a self-consistent and physical approach to interacting dark energy models described by a Lagrangian, and identify a new class of models with variable dark energy sound speed. We show that if the interaction between dark energy in the form of quintessence and cold dark matter is purely momentum exchange this generally leads to a dark energy sound speed that deviates from unity. Choosing a specific sub-case, we study its phenomenology by investigating the effects of the interaction on the cosmic microwave background and linear matter power spectrum. We also perform a global fitting of cosmological parameters using CMB data, and compare our findings to ΛCDM.
Gravitational waves from dark first order phase transitions and dark photons

NASA Astrophysics Data System (ADS)

Addazi, Andrea; Marcianò, Antonino

2018-01-01

Cold Dark Matter particles may interact with ordinary particles through a dark photon, which acquires a mass thanks to a spontaneous symmetry breaking mechanism. We discuss a dark photon model in which the scalar singlet associated to the spontaneous symmetry breaking has an effective potential that induces a first order phase transition in the early Universe. Such a scenario provides a rich phenomenology for electron-positron colliders and gravitational waves interferometers, and may be tested in several different channels. The hidden first order phase transition implies the emission of gravitational waves signals, which may constrain the dark photon’s space of parameters. Compared limits from electron-positron colliders, astrophysics, cosmology and future gravitational waves interferometers such as eLISA, U-DECIGO and BBO are discussed. This highly motivates a cross-checking strategy of data arising from experiments dedicated to gravitational waves, meson factories, the International Linear Collider (ILC), the Circular Electron Positron Collider (CEPC) and other underground direct detection experiments of cold dark matter candidates. Supported by the Shanghai Municipality (KBH1512299) and Fudan University (JJH1512105)
Static structure of chameleon dark matter as an explanation of dwarf spheroidal galaxy cores

NASA Astrophysics Data System (ADS)

Chanda, Prolay Krishna; Das, Subinoy

2017-04-01

We propose a novel mechanism that explains the cored dark matter density profile in recently observed dark matter rich dwarf spheroidal galaxies. In our scenario, dark matter particle mass decreases gradually as a function of distance towards the center of a dwarf galaxy due to its interaction with a chameleon scalar. At closer distance towards the Galactic center the strength of attractive scalar fifth force becomes much stronger than gravity and is balanced by the Fermi pressure of the dark matter cloud; thus, an equilibrium static configuration of the dark matter halo is obtained. Like the case of soliton star or fermion Q-star, the stability of the dark matter halo is obtained as the scalar achieves a static profile and reaches an asymptotic value away from the Galactic center. For simple scalar-dark matter interaction and quadratic scalar self-interaction potential, we show that dark matter behaves exactly like cold dark matter (CDM) beyond a few kpc away from the Galactic center but at closer distance it becomes lighter and Fermi pressure cannot be ignored anymore. Using Thomas-Fermi approximation, we numerically solve the radial static profile of the scalar field, fermion mass and dark matter energy density as a function of distance. We find that for fifth force mediated by an ultralight scalar, it is possible to obtain a flattened dark matter density profile towards the Galactic center. In our scenario, the fifth force can be neglected at distance r ≥1 kpc from the Galactic center and dark matter can be simply treated as heavy nonrelativistic particles beyond this distance, thus reproducing the success of CDM at large scales.
"Non-cold" dark matter at small scales: a general approach

NASA Astrophysics Data System (ADS)

Murgia, R.; Merle, A.; Viel, M.; Totzauer, M.; Schneider, A.

2017-11-01

Structure formation at small cosmological scales provides an important frontier for dark matter (DM) research. Scenarios with small DM particle masses, large momenta or hidden interactions tend to suppress the gravitational clustering at small scales. The details of this suppression depend on the DM particle nature, allowing for a direct link between DM models and astrophysical observations. However, most of the astrophysical constraints obtained so far refer to a very specific shape of the power suppression, corresponding to thermal warm dark matter (WDM), i.e., candidates with a Fermi-Dirac or Bose-Einstein momentum distribution. In this work we introduce a new analytical fitting formula for the power spectrum, which is simple yet flexible enough to reproduce the clustering signal of large classes of non-thermal DM models, which are not at all adequately described by the oversimplified notion of WDM . We show that the formula is able to fully cover the parameter space of sterile neutrinos (whether resonantly produced or from particle decay), mixed cold and warm models, fuzzy dark matter, as well as other models suggested by effective theory of structure formation (ETHOS). Based on this fitting formula, we perform a large suite of N-body simulations and we extract important nonlinear statistics, such as the matter power spectrum and the halo mass function. Finally, we present first preliminary astrophysical constraints, based on linear theory, from both the number of Milky Way satellites and the Lyman-α forest. This paper is a first step towards a general and comprehensive modeling of small-scale departures from the standard cold DM model.
Primeval galaxies and cold dark matter

NASA Technical Reports Server (NTRS)

Silk, Joseph; Szalay, Alexander S.

1987-01-01

In the context of the cold dark matter theory for the large-scale matter distribution, the onset of galaxy formation is a gradual process, with star formation being initiated at z = about 10 and reaching a peak for luminous galaxies at z = about 1. The mass function of galaxy cores matches the observed quasar luminosity function at z = 2-3. Primeval galaxies are envisaged as a collection of many interacting and merging clumps, attaining a peak luminosity that is an order of magnitude below that achieved in models in which galaxy formation is initiated abruptly. Hence, ongoing searches for primeval galaxies would not necessarily have been successful unless they are designed to find moderately low-luminosity, low-surface-brigtness extended objects at low redshift.
Cosmic microwave background anisotropies in cold dark matter models with cosmological constant: The intermediate versus large angular scales

NASA Technical Reports Server (NTRS)

Stompor, Radoslaw; Gorski, Krzysztof M.

1994-01-01

We obtain predictions for cosmic microwave background anisotropies at angular scales near 1 deg in the context of cold dark matter models with a nonzero cosmological constant, normalized to the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) detection. The results are compared to those computed in the matter-dominated models. We show that the coherence length of the Cosmic Microwave Background (CMB) anisotropy is almost insensitive to cosmological parameters, and the rms amplitude of the anisotropy increases moderately with decreasing total matter density, while being most sensitive to the baryon abundance. We apply these results in the statistical analysis of the published data from the UCSB South Pole (SP) experiment (Gaier et al. 1992; Schuster et al. 1993). We reject most of the Cold Dark Matter (CDM)-Lambda models at the 95% confidence level when both SP scans are simulated together (although the combined data set renders less stringent limits than the Gaier et al. data alone). However, the Schuster et al. data considered alone as well as the results of some other recent experiments (MAX, MSAM, Saskatoon), suggest that typical temperature fluctuations on degree scales may be larger than is indicated by the Gaier et al. scan. If so, CDM-Lambda models may indeed provide, from a point of view of CMB anisotropies, an acceptable alternative to flat CDM models.
Probing gravity at cosmological scales by measurements which test the relationship between gravitational lensing and matter overdensity.

PubMed

Zhang, Pengjie; Liguori, Michele; Bean, Rachel; Dodelson, Scott

2007-10-05

The standard cosmology is based on general relativity (GR) and includes dark matter and dark energy and predicts a fixed relationship between the gravitational potentials responsible for gravitational lensing and the matter overdensity. Alternative theories of gravity often make different predictions. We propose a set of measurements which can test this relationship, thereby distinguishing between dark energy or matter models and models in which gravity differs from GR. Planned surveys will be able to measure E(G), an observational quantity whose expectation value is equal to the ratio of the Laplacian of the Newtonian potentials to the peculiar velocity divergence, to percent accuracy. This will easily separate alternatives such as the cold dark matter model with a cosmological constant, Dvali-Gabadadze-Porrati, TeVeS, and f(R) gravity.
Modeling The Distribution Of Dark Matter And Its Connection To Galaxies

NASA Astrophysics Data System (ADS)

Mao, Yao-Yuan

2016-06-01

Despite the mysterious nature of dark matter and dark energy, the Lambda-Cold Dark Matter (LCDM) model provides a reasonably accurate description of the evolution of the cosmos and the distribution of galaxies. Today, we are set to tackle more specific and quantitative questions about the galaxy formation physics, the nature of dark matter, and the connection between the dark and the visible components. The answers to these questions are however elusive, because dark matter is not directly observable, and various unknowns lie between what we can observe and what we can calculate. Hence, mathematical models that bridge the observable and the calculable are essential for the study of modern cosmology. The aim of my thesis work is to improve existing models and also to construct new models for various aspects of the dark matter distribution, as dark matter structures the cosmic web and forms the nests of visible galaxies. Utilizing a series of cosmological dark matter simulations which span a wide dynamical range and a statistical sample of zoom-in simulations which focus on individual dark matter halos, we develop models for the spatial and velocity distribution of dark matter particles, the abundance of dark substructures, and the empirical connection between dark matter and galaxies. As more precise observational results become available, more accurate models are then required to test the consistency between these results and the LCDM predictions. For all the models we investigate, we find that the formation history of dark matter halos always plays a crucial role. Neglecting the halo formation history would result in systematic biases when we interpret various observational results, including dark matter direct detection experiments, the detection of dark substructures with strong-lensed systems, the large-scale spatial clustering of galaxies, and the abundance of dwarf galaxies. Rectifying this, our work will enable us to fully utilize the complementary power of diverse observational datasets to test the LCDM model and to seek new physics.
Cosmological simulations of decaying dark matter: implications for small-scale structure of dark matter haloes

NASA Astrophysics Data System (ADS)

Wang, Mei-Yu; Peter, Annika H. G.; Strigari, Louis E.; Zentner, Andrew R.; Arant, Bryan; Garrison-Kimmel, Shea; Rocha, Miguel

2014-11-01

We present a set of N-body simulations of a class of models in which an unstable dark matter particle decays into a stable dark matter particle and a non-interacting light particle with decay lifetime comparable to the Hubble time. We study the effects of the recoil kick velocity (Vk) received by the stable dark matter on the structures of dark matter haloes ranging from galaxy-cluster to Milky Way-mass scales. For Milky Way-mass haloes, we use high-resolution, zoom-in simulations to explore the effects of decays on Galactic substructure. In general, haloes with circular velocities comparable to the magnitude of kick velocity are most strongly affected by decays. We show that models with lifetimes Γ-1 ˜ H_0^{-1} and recoil speeds Vk ˜ 20-40 km s-1 can significantly reduce both the abundance of Galactic subhaloes and their internal densities. We find that decaying dark matter models that do not violate current astrophysical constraints can significantly mitigate both the `missing satellites problem' and the more recent `too big to fail problem'. These decaying models predict significant time evolution of haloes, and this implies that at high redshifts decaying models exhibit the similar sequence of structure formation as cold dark matter. Thus, decaying dark matter models are significantly less constrained by high-redshift phenomena than warm dark matter models. We conclude that models of decaying dark matter make predictions that are relevant for the interpretation of small galaxies observations in the Local Group and can be tested as well as by forthcoming large-scale surveys.
Modified gravity and the CMB

NASA Astrophysics Data System (ADS)

Brax, Philippe; Davis, Anne-Christine

2012-01-01

We consider the effect of modified gravity on the peak structure of the cosmic microwave background (CMB) spectrum. We focus on simple models of modified gravity mediated by a massive scalar field coupled to both baryons and cold dark matter. This captures the features of chameleon, symmetron, dilaton, and f(R) models. We find that the CMB peaks can be affected in three independent ways provided the Compton radius of the massive scalar is not far-off the sound horizon at last scattering. When the coupling of the massive scalar to cold dark matter is large, the anomalous growth of the cold dark matter perturbation inside the Compton radius induces a change in the peak amplitudes. When the coupling to baryons is moderately large, the speed of sound is modified and the peaks shifted to higher momenta. Finally when both couplings are nonvanishing, a new contribution proportional to the Newton potential appears in the Sachs-Wolfe temperature and increases the peak amplitudes. We also show how, given any temporal evolution of the scalar field mass, one can engineer a corresponding modified gravity model of the chameleon type. This opens up the possibility of having independent constraints on modified gravity from the CMB peaks and large scale structures at low redshifts.
Cold dark matter: Controversies on small scales

PubMed Central

Weinberg, David H.; Bullock, James S.; Governato, Fabio; Kuzio de Naray, Rachel; Peter, Annika H. G.

2015-01-01

The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way’s dwarf galaxy satellites. We review the current observational and theoretical status of these “small-scale controversies.” Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years. PMID:25646464
Is Self-Interacting Dark Matter Undergoing Dark Fusion?

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDermott, Samuel D.

2017-11-02

We suggest that two-to-two dark matter fusion may be the relaxation process that resolves the small-scale structure problems of the cold collisionless dark matter paradigm. In order for the fusion cross section to scale correctly across many decades of astrophysical masses from dwarf galaxies to galaxy clusters, we require the fractional binding energy released to be greater than v^n ~ [10^{-(2-3)}]^n, where n=1,2 depends on local dark sector chemistry. The size of the dark-sector interaction cross sections must be sigma ~ 0.1-1 barn, moderately larger than for Standard Model deuteron fusion, indicating a dark nuclear scale Lambda ~ O(100 MeV).more » Dark fusion firmly predicts constant sigma v below the characteristic velocities of galaxy clusters. Observations of the inner structure of galaxy groups with velocity dispersion of several hundred kilometer per second, of which a handful have been identified, could differentiate dark fusion from a dark photon model.« less
Is Self-Interacting Dark Matter Undergoing Dark Fusion?

NASA Astrophysics Data System (ADS)

McDermott, Samuel D.

2018-06-01

We suggest that two-to-two dark matter fusion may be the relaxation process that resolves the small-scale structure problems of the cold collisionless dark matter paradigm. In order for the fusion cross section to scale correctly across many decades of astrophysical masses from dwarf galaxies to galaxy clusters, we require the fractional binding energy released to be greater than vn˜(10-(2 -3 ))n , where n =1 , 2 depends on local dark sector chemistry. The size of the dark-sector interaction cross sections must be σ˜0.1 - 1 barn, moderately larger than for standard model deuteron fusion, indicating a dark nuclear scale Λ ˜O (100 MeV ) . Dark fusion firmly predicts constant σ v below the characteristic velocities of galaxy clusters. Observations of the inner structure of galaxy groups with velocity dispersion of several hundred kilometers per second, of which a handful have been identified, could differentiate dark fusion from a dark photon model.
A hydrodynamic treatment of the tilted cold dark matter cosmological scenario

NASA Technical Reports Server (NTRS)

Cen, Renyue; Ostriker, Jeremiah P.

1993-01-01

A standard hydrodynamic code coupled with a particle-mesh code is used to compute the evolution of a tilted cold dark matter (TCDM) model containing both baryonic matter and dark matter. Six baryonic species are followed, with allowance for both collisional and radiative ionization in every cell. The mean final Zel'dovich-Sunyaev y parameter is estimated to be (5.4 +/- 2.7) x 10 exp -7, below currently attainable observations, with an rms fluctuation of about (6.0 +/- 3.0) x 10 exp -7 on arcmin scales. The rate of galaxy formation peaks at a relatively late epoch (z is about 0.5). In the case of mass function, the smallest objects are stabilized against collapse by thermal energy: the mass-weighted mass spectrum peaks in the vicinity of 10 exp 9.1 solar masses, with a reasonable fit to the Schechter luminosity function if the baryon mass to blue light ratio is about 4. It is shown that a bias factor of 2 required for the model to be consistent with COBE DMR signals is probably a natural outcome in the present multiple component simulations.
Constraints and consequences of reducing small scale structure via large dark matter-neutrino interactions

DOE PAGES

Bertoni, Bridget; Ipek, Seyda; McKeen, David; ...

2015-04-30

Here, cold dark matter explains a wide range of data on cosmological scales. However, there has been a steady accumulation of evidence for discrepancies between simulations and observations at scales smaller than galaxy clusters. One promising way to affect structure formation on small scales is a relatively strong coupling of dark matter to neutrinos. We construct an experimentally viable, simple, renormalizable model with new interactions between neutrinos and dark matter and provide the first discussion of how these new dark matter-neutrino interactions affect neutrino phenomenology. We show that addressing the small scale structure problems requires asymmetric dark matter with amore » mass that is tens of MeV. Generating a sufficiently large dark matter-neutrino coupling requires a new heavy neutrino with a mass around 100 MeV. The heavy neutrino is mostly sterile but has a substantial τ neutrino component, while the three nearly massless neutrinos are partly sterile. This model can be tested by future astrophysical, particle physics, and neutrino oscillation data. Promising signatures of this model include alterations to the neutrino energy spectrum and flavor content observed from a future nearby supernova, anomalous matter effects in neutrino oscillations, and a component of the τ neutrino with mass around 100 MeV.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Jesus, J.F.; Pereira, S.H., E-mail: jfjesus@itapeva.unesp.br, E-mail: shpereira@gmail.com

In this work the results from the quantum process of matter creation have been used in order to constrain the mass of the dark matter particles in an accelerated Cold Dark Matter model (Creation Cold Dark Matter, CCDM). In order to take into account a back reaction effect due to the particle creation phenomenon, it has been assumed a small deviation ε for the scale factor in the matter dominated era of the form t{sup 2/3+ε}. Based on recent H(z) data, the best fit values for the mass of dark matter created particles and the ε parameter have been foundmore » as m = 1.6× 10{sup 3} GeV, restricted to a 68.3% c.l. interval of 1.5 < m < 6.3× 10{sup 7}) GeV and ε = -0.250{sup +0.15}{sub -0.096} at 68.3% c.l. For these best fit values the model correctly recovers a transition from decelerated to accelerated expansion and admits a positive creation rate near the present era. Contrary to recent works in CCDM models where the creation rate was phenomenologically derived, here we have used a quantum mechanical result for the creation rate of real massive scalar particles, given a self consistent justification for the physical process. This method also indicates a possible solution to the so called ''dark degeneracy'', where one can not distinguish if it is the quantum vacuum contribution or quantum particle creation which accelerates the Universe expansion.« less
Large-scale structure in a texture-seeded cold dark matter cosmogony

NASA Technical Reports Server (NTRS)

Park, Changbom; Spergel, David N.; Turok, Nail

1991-01-01

This paper studies the formation of large-scale structure by global texture in a flat universe dominated by cold dark matter. A code for evolution of the texture fields was combined with an N-body code for evolving the dark matter. The results indicate some promising aspects: with only one free parameter, the observed galaxy-galaxy correlation function is reproduced, clusters of galaxies are found to be significantly clustered on a scale of 20-50/h Mpc, and coherent structures of over 50/h Mpc in the galaxy distribution were found. The large-scale streaming motions observed are in good agreement with the observations: the average magnitude of the velocity field smoothed over 30/h Mpc is 430 km/sec. Global texture produces a cosmic Mach number that is compatible with observation. Also, significant evolution of clusters at low redshift was seen. Possible problems for the theory include too high velocity dispersions in clusters, and voids which are not as empty as those observed.

Detection of weak gravitational lensing distortions of distant galaxies by cosmic dark matter at large scales

PubMed

Wittman; Tyson; Kirkman; Dell'Antonio; Bernstein

2000-05-11

Most of the matter in the Universe is not luminous, and can be observed only through its gravitational influence on the appearance of luminous matter. Weak gravitational lensing is a technique that uses the distortions of the images of distant galaxies as a tracer of dark matter: such distortions are induced as the light passes through large-scale distributions of dark matter in the foreground. The patterns of the induced distortions reflect the density of mass along the line of sight and its distribution, and the resulting 'cosmic shear' can be used to distinguish between alternative cosmologies. But previous attempts to measure this effect have been inconclusive. Here we report the detection of cosmic shear on angular scales of up to half a degree using 145,000 galaxies and along three separate lines of sight. We find that the dark matter is distributed in a manner consistent with either an open universe, or a flat universe that is dominated by a cosmological constant. Our results are inconsistent with the standard cold-dark-matter model.
Is Self-Interacting Dark Matter Undergoing Dark Fusion?

DOE PAGES

McDermott, Samuel D.

2018-06-01

Here, we suggest that two-to-two dark matter fusion may be the relaxation process that resolves the small-scale structure problems of the cold collisionless dark matter paradigm. In order for the fusion cross section to scale correctly across many decades of astrophysical masses from dwarf galaxies to galaxy clusters, we require the fractional binding energy released to be greater than v n~(10 –(2–3)) n, where n=1, 2 depends on local dark sector chemistry. The size of the dark-sector interaction cross sections must be σ~0.1–1 barn, moderately larger than for standard model deuteron fusion, indicating a dark nuclear scale Λ~O(100 MeV). Darkmore » fusion firmly predicts constant σv below the characteristic velocities of galaxy clusters. Observations of the inner structure of galaxy groups with velocity dispersion of several hundred kilometers per second, of which a handful have been identified, could differentiate dark fusion from a dark photon model.« less
Is Self-Interacting Dark Matter Undergoing Dark Fusion?

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDermott, Samuel D.

Here, we suggest that two-to-two dark matter fusion may be the relaxation process that resolves the small-scale structure problems of the cold collisionless dark matter paradigm. In order for the fusion cross section to scale correctly across many decades of astrophysical masses from dwarf galaxies to galaxy clusters, we require the fractional binding energy released to be greater than v n~(10 –(2–3)) n, where n=1, 2 depends on local dark sector chemistry. The size of the dark-sector interaction cross sections must be σ~0.1–1 barn, moderately larger than for standard model deuteron fusion, indicating a dark nuclear scale Λ~O(100 MeV). Darkmore » fusion firmly predicts constant σv below the characteristic velocities of galaxy clusters. Observations of the inner structure of galaxy groups with velocity dispersion of several hundred kilometers per second, of which a handful have been identified, could differentiate dark fusion from a dark photon model.« less
Diffuse neutrino supernova background as a cosmological test

NASA Astrophysics Data System (ADS)

Barranco, J.; Bernal, A.; Delepine, D.

2018-05-01

The future detection and measurement of the diffuse neutrino supernova background will provide us with information about supernova neutrino emission and the cosmic core-collapse supernova rate. Little has been said about the information that this measurement could give us about the expansion history of the Universe. The purpose of this article is to study the change of the predicted diffuse supernova neutrino background as a function of the cosmological model. In particular, we study three different models: the Λ–Cold Dark Matter model, the Logotropic universe and a bulk viscous matter-dominated universe. By fitting the free parameters of each model with the supernova Ia probe, we calculate the predicted number of events in these three models. We found that the spectra and number of events for the Λ–Cold dark matter model and the Logotropic model are almost indistinguishable, while a bulk viscous matter-dominated cosmological model predicts more events.
Self-Interacting Dark Matter Can Explain Diverse Galactic Rotation Curves

NASA Astrophysics Data System (ADS)

Kamada, Ayuki; Kaplinghat, Manoj; Pace, Andrew B.; Yu, Hai-Bo

2017-09-01

The rotation curves of spiral galaxies exhibit a diversity that has been difficult to understand in the cold dark matter (CDM) paradigm. We show that the self-interacting dark matter (SIDM) model provides excellent fits to the rotation curves of a sample of galaxies with asymptotic velocities in the 25 - 300 km /s range that exemplify the full range of diversity. We assume only the halo concentration-mass relation predicted by the CDM model and a fixed value of the self-interaction cross section. In dark-matter-dominated galaxies, thermalization due to self-interactions creates large cores and reduces dark matter densities. In contrast, thermalization leads to denser and smaller cores in more luminous galaxies and naturally explains the flatness of rotation curves of the highly luminous galaxies at small radii. Our results demonstrate that the impact of the baryons on the SIDM halo profile and the scatter from the assembly history of halos as encoded in the concentration-mass relation can explain the diverse rotation curves of spiral galaxies.
Self-Interacting Dark Matter Can Explain Diverse Galactic Rotation Curves.

PubMed

Kamada, Ayuki; Kaplinghat, Manoj; Pace, Andrew B; Yu, Hai-Bo

2017-09-15

The rotation curves of spiral galaxies exhibit a diversity that has been difficult to understand in the cold dark matter (CDM) paradigm. We show that the self-interacting dark matter (SIDM) model provides excellent fits to the rotation curves of a sample of galaxies with asymptotic velocities in the 25-300 km/s range that exemplify the full range of diversity. We assume only the halo concentration-mass relation predicted by the CDM model and a fixed value of the self-interaction cross section. In dark-matter-dominated galaxies, thermalization due to self-interactions creates large cores and reduces dark matter densities. In contrast, thermalization leads to denser and smaller cores in more luminous galaxies and naturally explains the flatness of rotation curves of the highly luminous galaxies at small radii. Our results demonstrate that the impact of the baryons on the SIDM halo profile and the scatter from the assembly history of halos as encoded in the concentration-mass relation can explain the diverse rotation curves of spiral galaxies.
Galaxy motions cause trouble for cosmology

NASA Astrophysics Data System (ADS)

Boylan-Kolchin, Michael

2018-02-01

According to the widely accepted dark energy plus cold dark matter (ΛCDM) model, dark matter is responsible for both the growth of cosmological structures and the motions of galaxies relative to the expansion of the universe. The dynamics of small galaxies orbiting larger ones provides a crucial window into this mysterious dark matter, which leaves its gravitational mark throughout the universe but has not yet been detected directly. On page 534 of this issue, Müller et al. (1) describe observations of satellite galaxies around Centaurus A, the largest galaxy system in the vicinity of the Milky Way. The results may lead to either a better understanding of galaxy formation within the ΛCDM model or a push to overthrow its underlying assumptions.
Inflation and dark matter in the inert doublet model

NASA Astrophysics Data System (ADS)

Choubey, Sandhya; Kumar, Abhass

2017-11-01

We discuss inflation and dark matter in the inert doublet model coupled non-minimally to gravity where the inert doublet is the inflaton and the neutral scalar part of the doublet is the dark matter candidate. We calculate the various inflationary parameters like n s , r and P s and then proceed to the reheating phase where the inflaton decays into the Higgs and other gauge bosons which are non-relativistic owing to high effective masses. These bosons further decay or annihilate to give relativistic fermions which are finally responsible for reheating the universe. At the end of the reheating phase, the inert doublet which was the inflaton enters into thermal equilibrium with the rest of the plasma and its neutral component later freezes out as cold dark matter with a mass of about 2 TeV.
Seeded hot dark matter models with inflation

NASA Technical Reports Server (NTRS)

Gratsias, John; Scherrer, Robert J.; Steigman, Gary; Villumsen, Jens V.

1993-01-01

We examine massive neutrino (hot dark matter) models for large-scale structure in which the density perturbations are produced by randomly distributed relic seeds and by inflation. Power spectra, streaming velocities, and the Sachs-Wolfe quadrupole fluctuation are derived for this model. We find that the pure seeded hot dark matter model without inflation produces Sachs-Wolfe fluctuations far smaller than those seen by COBE. With the addition of inflationary perturbations, fluctuations consistent with COBE can be produced. The COBE results set the normalization of the inflationary component, which determines the large-scale (about 50/h Mpc) streaming velocities. The normalization of the seed power spectrum is a free parameter, which can be adjusted to obtain the desired fluctuations on small scales. The power spectra produced are very similar to those seen in mixed hot and cold dark matter models.
Axion dark matter searches

DOE PAGES

Stern, Ian P.

2014-01-01

We report nearly all astrophysical and cosmological data point convincingly to a large component of cold dark matter in the Universe. The axion particle, first theorized as a solution to the strong charge-parity problem of quantum chromodynamics, has been established as a prominent CDM candidate. Cosmic observation and particle physics experiments have bracketed the unknown mass of the axion between approximately a μeV and a meV. The Axion Dark Matter eXperiement (ADMX) has successfully completed searches between 1.9 and 3.7 μeV down to the KSVZ photon-coupling limit. ADMX and the Axion Dark Matter eXperiement High-Frequency (ADMX-HF) will search for axionsmore » at weaker coupling and/or higher frequencies within the next few years. Status of the experiments, current research and development, and projected mass-coupling exclusion limits are presented.« less
Universal clustering of dark matter in phase space

NASA Astrophysics Data System (ADS)

Zavala, Jesús; Afshordi, Niayesh

2016-03-01

We have recently introduced a novel statistical measure of dark matter clustering in phase space, the particle phase-space average density (P2SAD). In a two-paper series, we studied the structure of P2SAD in the Milky Way-size Aquarius haloes, constructed a physically motivated model to describe it, and illustrated its potential as a powerful tool to predict signals sensitive to the nanostructure of dark matter haloes. In this work, we report a remarkable universality of the clustering of dark matter in phase space as measured by P2SAD within the subhaloes of host haloes across different environments covering a range from dwarf-size to cluster-size haloes (1010-1015 M⊙). Simulations show that the universality of P2SAD holds for more than seven orders of magnitude, over a 2D phase space, covering over three orders of magnitude in distance/velocity, with a simple functional form that can be described by our model. Invoking the universality of P2SAD, we can accurately predict the non-linear power spectrum of dark matter at small scales all the way down to the decoupling mass limit of cold dark matter particles. As an application, we compute the subhalo boost to the annihilation of dark matter in a wide range of host halo masses.
Criticality and big brake singularities in the tachyonic evolutions of closed Friedmann universes with cold dark matter

NASA Astrophysics Data System (ADS)

Horváth, Zsolt; Keresztes, Zoltán; Kamenshchik, Alexander Yu.; Gergely, László Á.

2015-05-01

The evolution of a closed Friedmann universe filled by a tachyon scalar field with a trigonometric potential and cold dark matter (CDM) is investigated. A subset of the evolutions consistent to 1 σ confidence level with the Union 2.1 supernova data set is identified. The evolutions of the tachyon field are classified. Some of them evolve into a de Sitter attractor, while others proceed through a pseudotachyonic regime into a sudden future singularity. Critical evolutions leading to big brake singularities in the presence of CDM are found and a new type of cosmological evolution characterized by singularity avoidance in the pseudotachyon regime is presented.
Anisotropies of the cosmic microwave background in nonstandard cold dark matter models

NASA Technical Reports Server (NTRS)

Vittorio, Nicola; Silk, Joseph

1992-01-01

Small angular scale cosmic microwave anisotropies in flat, vacuum-dominated, cold dark matter cosmological models which fit large-scale structure observations and are consistent with a high value for the Hubble constant are reexamined. New predictions for CDM models in which the large-scale power is boosted via a high baryon content and low H(0) are presented. Both classes of models are consistent with current limits: an improvement in sensitivity by a factor of about 3 for experiments which probe angular scales between 7 arcmin and 1 deg is required, in the absence of very early reionization, to test boosted CDM models for large-scale structure formation.
Cold dark matter and degree-scale cosmic microwave background anisotropy statistics after COBE

NASA Technical Reports Server (NTRS)

Gorski, Krzysztof M.; Stompor, Radoslaw; Juszkiewicz, Roman

1993-01-01

We conduct a Monte Carlo simulation of the cosmic microwave background (CMB) anisotropy in the UCSB South Pole 1991 degree-scale experiment. We examine cold dark matter cosmology with large-scale structure seeded by the Harrison-Zel'dovich hierarchy of Gaussian-distributed primordial inhomogeneities normalized to the COBE-DMR measurement of large-angle CMB anisotropy. We find it statistically implausible (in the sense of low cumulative probability F lower than 5 percent, of not measuring a cosmological delta-T/T signal) that the degree-scale cosmological CMB anisotropy predicted in such models could have escaped a detection at the level of sensitivity achieved in the South Pole 1991 experiment.
Radial dependence of the dark matter distribution in M33

NASA Astrophysics Data System (ADS)

López Fune, E.; Salucci, P.; Corbelli, E.

2017-06-01

The stellar and gaseous mass distributions, as well as the extended rotation curve, in the nearby galaxy M33 are used to derive the radial distribution of dark matter density in the halo and to test cosmological models of galaxy formation and evolution. Two methods are examined to constrain the dark mass density profiles. The first method deals directly with fitting the rotation curve data in the range of galactocentric distances 0.24 ≤ r ≤ 22.72 kpc. Using the results of collisionless Λ cold dark matter numerical simulations, we confirm that the Navarro-Frenkel-White (NFW) dark matter profile provides a better fit to the rotation curve data than the cored Burkert profile (BRK) profile. The second method relies on the local equation of centrifugal equilibrium and on the rotation curve slope. In the aforementioned range of distances, we fit the observed velocity profile, using a function that has a rational dependence on the radius, and we derive the slope of the rotation curve. Then, we infer the effective matter densities. In the radial range 9.53 ≤ r ≤ 22.72 kpc, the uncertainties induced by the luminous matter (stars and gas) become negligible, because the dark matter density dominates, and we can determine locally the radial distribution of dark matter. With this second method, we tested the NFW and BRK dark matter profiles and we can confirm that both profiles are compatible with the data, even though in this case the cored BRK density profile provides a more reasonable value for the baryonic-to-dark matter ratio.
A White Paper on keV sterile neutrino Dark Matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adhikari, R.; Agostini, M.; Ky, N. Anh

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved—cosmology, astrophysics, nuclear, and particle physics—in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arisingmore » from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.« less
A White Paper on keV sterile neutrino Dark Matter

DOE PAGES

Adhikari, R.

2017-01-13

Here, we present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. First, we review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterilemore » neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. Our paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.« less
A White Paper on keV sterile neutrino Dark Matter

NASA Astrophysics Data System (ADS)

Adhikari, R.; Agostini, M.; Ky, N. Anh; Araki, T.; Archidiacono, M.; Bahr, M.; Baur, J.; Behrens, J.; Bezrukov, F.; Bhupal Dev, P. S.; Borah, D.; Boyarsky, A.; de Gouvea, A.; Pires, C. A. de S.; de Vega, H. J.; Dias, A. G.; Di Bari, P.; Djurcic, Z.; Dolde, K.; Dorrer, H.; Durero, M.; Dragoun, O.; Drewes, M.; Drexlin, G.; Düllmann, Ch. E.; Eberhardt, K.; Eliseev, S.; Enss, C.; Evans, N. W.; Faessler, A.; Filianin, P.; Fischer, V.; Fleischmann, A.; Formaggio, J. A.; Franse, J.; Fraenkle, F. M.; Frenk, C. S.; Fuller, G.; Gastaldo, L.; Garzilli, A.; Giunti, C.; Glück, F.; Goodman, M. C.; Gonzalez-Garcia, M. C.; Gorbunov, D.; Hamann, J.; Hannen, V.; Hannestad, S.; Hansen, S. H.; Hassel, C.; Heeck, J.; Hofmann, F.; Houdy, T.; Huber, A.; Iakubovskyi, D.; Ianni, A.; Ibarra, A.; Jacobsson, R.; Jeltema, T.; Jochum, J.; Kempf, S.; Kieck, T.; Korzeczek, M.; Kornoukhov, V.; Lachenmaier, T.; Laine, M.; Langacker, P.; Lasserre, T.; Lesgourgues, J.; Lhuillier, D.; Li, Y. F.; Liao, W.; Long, A. W.; Maltoni, M.; Mangano, G.; Mavromatos, N. E.; Menci, N.; Merle, A.; Mertens, S.; Mirizzi, A.; Monreal, B.; Nozik, A.; Neronov, A.; Niro, V.; Novikov, Y.; Oberauer, L.; Otten, E.; Palanque-Delabrouille, N.; Pallavicini, M.; Pantuev, V. S.; Papastergis, E.; Parke, S.; Pascoli, S.; Pastor, S.; Patwardhan, A.; Pilaftsis, A.; Radford, D. C.; Ranitzsch, P. C.-O.; Rest, O.; Robinson, D. J.; Rodrigues da Silva, P. S.; Ruchayskiy, O.; Sanchez, N. G.; Sasaki, M.; Saviano, N.; Schneider, A.; Schneider, F.; Schwetz, T.; Schönert, S.; Scholl, S.; Shankar, F.; Shrock, R.; Steinbrink, N.; Strigari, L.; Suekane, F.; Suerfu, B.; Takahashi, R.; Van, N. Thi Hong; Tkachev, I.; Totzauer, M.; Tsai, Y.; Tully, C. G.; Valerius, K.; Valle, J. W. F.; Venos, D.; Viel, M.; Vivier, M.; Wang, M. Y.; Weinheimer, C.; Wendt, K.; Winslow, L.; Wolf, J.; Wurm, M.; Xing, Z.; Zhou, S.; Zuber, K.

2017-01-01

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved—cosmology, astrophysics, nuclear, and particle physics—in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.
A White Paper on keV sterile neutrino Dark Matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adhikari, R.

Here, we present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. First, we review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterilemore » neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. Our paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.« less
Dark Matter Reality Check: Chandra Casts Cloud On Alternative Theory

NASA Astrophysics Data System (ADS)

2002-10-01

New evidence from NASA's Chandra X-ray Observatory challenges an alternative theory of gravity that eliminates the need for dark matter. The observation also narrows the field for competing forms of dark matter, the elusive material thought to be the dominant form of matter in the universe. An observation of the galaxy NGC 720 shows it is enveloped in a slightly flattened, or ellipsoidal cloud of hot gas that has an orientation different from that of the optical image of the galaxy. The flattening is too large to be explained by theories in which stars and gas are assumed to contain most of the mass in the galaxy. "The shape and orientation of the hot gas cloud require it to be confined by an egg-shaped dark matter halo," said David Buote of the University of California, Irvine, and lead author of a report on this research in the 2002 September 20 issue of The Astrophysical Journal. "This means that dark matter is not just an illusion due to a shortcoming of the standard theory of gravity - it is real." According to the generally accepted standard theory of gravity, the hot X-ray cloud would need an additional source of gravity - a halo of dark matter - to keep the hot gas from expanding away. The mass of dark matter required would be about five to ten times the mass of the stars in the galaxy. If the dark matter tracked the optical light from the stars in the galaxy, the hot X-ray cloud would be more round than it is. The flattened shape of the hot gas cloud requires a flattened dark matter halo. An alternative theory of gravity called MOND, for Modified Newtonian Dynamics, was proposed in 1983 by Mordecai Milgrom of the Weizmann Institute in Israel, and has remained viable over the years. MOND does away with the need for dark matter by modifying the theory where the acceleration produced by gravity is very small, such as the outskirts of galaxies. However, MOND cannot explain the Chandra observation of NGC 720. This is apparently the first dynamical evidence that has successfully distinguished dark matter from MOND. The researchers also found that the Chandra data fit predictions of the cold dark matter theories, according to which dark matter consists of slowly moving particles, which interact with each other and "normal" matter only through gravity. Other forms of dark matter, such as self-interacting dark matter, and cold molecular dark matter, are not consistent with the observation in that they require a dark matter halo that is too round or too flat, respectively. "Chandra's ability to precisely identify and locate the point-like sources contaminating the diffuse emission in the X-ray image was absolutely essential," said Buote. "Only then could we make accurate measurements of the shape and orientation of the X-ray image contours." The conclusion from the Chandra data that NGC 720 possesses a dark matter halo assumes that the hot gas cloud has not been unduly disturbed by collisions or mergers with other galaxies in the last 100 million years. The lack of evidence of such activity indicates that this assumption is valid. Chandra observed NGC 720, which is about 80 million light years from Earth, for 11 hours with the Advanced CCD Imaging Spectrometer (ACIS). Other members of the team include Tesla Jeltema and Claude Canizares of Massachusetts Institute of Technology (MIT) in Cambridge, and Gordon Garmire of Pennsylvania State University in University Park. Penn State and MIT developed the instrument for NASA. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.

Thin Planes of Satellites in ΛCDM are not kinematically coherent

NASA Astrophysics Data System (ADS)

Buck, Tobias; Dutton, Aaron A.; Macciò, Andrea V.

2017-03-01

Recently it has been shown by Ibata et al. (2013) that a large fraction of the dwarf satellite galaxies found in the PAndAS survey (McConnachie et al. 2009) and orbiting the Andromeda galaxy are surprisingly aligned in a thin, extended, and kinematically coherent planar structure. The presence of such a structure seems to challenge the current Cold Dark Matter paradigm of structure formation (Ibata et al. 2014, Pawlowski et al. 2014), which predicts a more uniform distribution of satellites around central objects. We show that it is possible to obtain a thin, extended, rotating plane of satellites resembling the one in Andromeda in cosmological collisionless simulations based on this model. Our new 21 high-resolution simulations (see Buck et al. 2015) show a correlation between the formation time of the dark matter halo and the thickness of the plane of satellites. Our simulations have a high incidence of satellite planes as thin, extended, and as rich as the one in Andromeda and with a very coherent kinematic structure when we select early forming haloes. By tracking the formation of the satellites in the plane we show that they have mainly been accreted onto the main object along thin dark matter filaments at high redshift (Dekel et al. 2009, Libeskind et al. 2009, 2011). Our results show that the presence of a thin, extended, rotating plane of satellites is not a challenge for the Cold Dark Matter paradigm, but actually supports one of the predictions of this paradigm related to the presence of filaments of dark matter around galaxies at high redshift.
First Constraints on Fuzzy Dark Matter from Lyman-α Forest Data and Hydrodynamical Simulations

NASA Astrophysics Data System (ADS)

Iršič, Vid; Viel, Matteo; Haehnelt, Martin G.; Bolton, James S.; Becker, George D.

2017-07-01

We present constraints on the masses of extremely light bosons dubbed fuzzy dark matter (FDM) from Lyman-α forest data. Extremely light bosons with a de Broglie wavelength of ˜1 kpc have been suggested as dark matter candidates that may resolve some of the current small scale problems of the cold dark matter model. For the first time, we use hydrodynamical simulations to model the Lyman-α flux power spectrum in these models and compare it to the observed flux power spectrum from two different data sets: the XQ-100 and HIRES/MIKE quasar spectra samples. After marginalization over nuisance and physical parameters and with conservative assumptions for the thermal history of the intergalactic medium (IGM) that allow for jumps in the temperature of up to 5000 K, XQ-100 provides a lower limit of 7.1 ×10-22 eV , HIRES/MIKE returns a stronger limit of 14.3 ×10-22 eV , while the combination of both data sets results in a limit of 20 ×10-22 eV (2 σ C.L.). The limits for the analysis of the combined data sets increases to 37.5 ×10-22 eV (2 σ C.L.) when a smoother thermal history is assumed where the temperature of the IGM evolves as a power law in redshift. Light boson masses in the range 1 - 10 ×10-22 eV are ruled out at high significance by our analysis, casting strong doubts that FDM helps solve the "small scale crisis" of the cold dark matter models.
A tilted cold dark matter cosmological scenario

NASA Technical Reports Server (NTRS)

Cen, Renyue; Gnedin, Nickolay Y.; Kofman, Lev A.; Ostriker, Jeremiah P.

1992-01-01

A new cosmological scenario based on CDM but with a power spectrum index of about 0.7-0.8 is suggested. This model is predicted by various inflationary models with no fine tuning. This tilted CDM model, if normalized to COBE, alleviates many problems of the standard CDM model related to both small-scale and large-scale power. A physical bias of galaxies over dark matter of about two is required to fit spatial observations.
Cosmic string with a light massive neutrino

NASA Technical Reports Server (NTRS)

Albrecht, Andreas; Stebbins, Albert

1992-01-01

We have estimated the power spectra of density fluctuations produced by cosmic strings with neutrino hot dark matter (HDM). Normalizing at 8/h Mpc, we find that the spectrum has more power on small scales than HDM + inflation, less than cold dark matter (CDM) + inflation, and significantly less the CDM + strings. With HDM, large wakes give significant contribution to the power on the galaxy scale and may give rise to large sheets of galaxies.
Wandering in the Lyman-alpha forest: a study of dark matter-dark radiation interactions

NASA Astrophysics Data System (ADS)

Krall, Rebecca; Cyr-Racine, Francis-Yan; Dvorkin, Cora

2017-09-01

The amplitude of large-scale matter fluctuations inferred from the observed Sunyaev-Zeldovich (SZ) cluster mass function and from weak gravitational lensing studies, when taken at face value, is in tension with measurements of the cosmic microwave background (CMB) and baryon acoustic oscillation (BAO). In this work, we revisit whether this possible discrepancy can be attributed to new interactions in the dark matter sector. Focusing on a cosmological model where dark matter interacts with a dark radiation species until the epoch of matter-radiation equality, we find that measurements of the Lyman-alpha flux power spectrum from the Sloan Digital Sky Survey provide no support to the hypothesis that new dark matter interactions can resolve the possible tension between CMB and large-scale structure (LSS). Indeed, while the addition of dark matter-dark radiation interactions leads to an improvement of 2Δ ln L=12 with respect to the standard Λ cold dark matter (ΛCDM) model when only CMB, BAO, and LSS data are considered, the inclusion of Lyman-alpha data reduces the improvement of the fit to 2Δ ln L=6 relative to ΛCDM . We thus conclude that the statistical evidence for new dark matter interactions (largely driven by the Planck SZ dataset) is marginal at best, and likely caused by systematics in the data. We also perform a Fisher forecast analysis for the reach of a future dataset composed of a CMB-S4 experiment combined with the Large Synoptic Survey Telescope galaxy survey. We find that the constraint on the effective number of fluid-like dark radiation species, Δ Nfluid, will be improved by an order of magnitude compared to current bounds.
Wandering in the Lyman-alpha forest: a study of dark matter-dark radiation interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krall, Rebecca; Cyr-Racine, Francis-Yan; Dvorkin, Cora, E-mail: rkrall@physics.harvard.edu, E-mail: fcyrraci@physics.harvard.edu, E-mail: dvorkin@physics.harvard.edu

The amplitude of large-scale matter fluctuations inferred from the observed Sunyaev-Zeldovich (SZ) cluster mass function and from weak gravitational lensing studies, when taken at face value, is in tension with measurements of the cosmic microwave background (CMB) and baryon acoustic oscillation (BAO). In this work, we revisit whether this possible discrepancy can be attributed to new interactions in the dark matter sector. Focusing on a cosmological model where dark matter interacts with a dark radiation species until the epoch of matter-radiation equality, we find that measurements of the Lyman-alpha flux power spectrum from the Sloan Digital Sky Survey provide nomore » support to the hypothesis that new dark matter interactions can resolve the possible tension between CMB and large-scale structure (LSS). Indeed, while the addition of dark matter-dark radiation interactions leads to an improvement of 2ΔlnL=12 with respect to the standard Λ cold dark matter (ΛCDM) model when only CMB, BAO, and LSS data are considered, the inclusion of Lyman-alpha data reduces the improvement of the fit to 2ΔlnL=6 relative to ΛCDM . We thus conclude that the statistical evidence for new dark matter interactions (largely driven by the Planck SZ dataset) is marginal at best, and likely caused by systematics in the data. We also perform a Fisher forecast analysis for the reach of a future dataset composed of a CMB-S4 experiment combined with the Large Synoptic Survey Telescope galaxy survey. We find that the constraint on the effective number of fluid-like dark radiation species, Δ N {sub fluid}, will be improved by an order of magnitude compared to current bounds.« less
A small amount of mini-charged dark matter could cool the baryons in the early Universe.

PubMed

Muñoz, Julian B; Loeb, Abraham

2018-05-01

The dynamics of our Universe is strongly influenced by pervasive-albeit elusive-dark matter, with a total mass about five times the mass of all the baryons 1,2 . Despite this, its origin and composition remain a mystery. All evidence for dark matter relies on its gravitational pull on baryons, and thus such evidence does not require any non-gravitational coupling between baryons and dark matter. Nonetheless, some small coupling would explain the comparable cosmic abundances of dark matter and baryons 3 , as well as solving structure-formation puzzles in the pure cold-dark-matter models 4 . A vast array of observations has been unable to find conclusive evidence for any non-gravitational interactions of baryons with dark matter 5-9 . Recent observations by the EDGES collaboration, however, suggest that during the cosmic dawn, roughly 200 million years after the Big Bang, the baryonic temperature was half of its expected value 10 . This observation is difficult to reconcile with the standard cosmological model but could be explained if baryons are cooled down by interactions with dark matter, as expected if their interaction rate grows steeply at low velocities 11 . Here we report that if a small fraction-less than one per cent-of the dark matter has a mini-charge, a million times smaller than the charge on the electron, and a mass in the range of 1-100 times the electron mass, then the data 10 from the EDGES experiment can be explained while remaining consistent with all other observations. We also show that the entirety of the dark matter cannot have a mini-charge.
Cosmology solved? Maybe

NASA Astrophysics Data System (ADS)

Turner, Michael S.

1999-03-01

For two decades the hot big-bang model as been referred to as the standard cosmology - and for good reason. For just as long cosmologists have known that there are fundamental questions that are not answered by the standard cosmology and point to a grander theory. The best candidate for that grander theory is inflation + cold dark matter. It holds that the Universe is flat, that slowly moving elementary particles left over from the earliest moments provide the cosmic infrastructure, and that the primeval density inhomogeneities that seed all the structure arose from quantum fluctuations. There is now prima facie evidence that supports two basic tenets of this paradigm. An avalanche of high-quality cosmological observations will soon make this case stronger or will break it. Key questions remain to be answered; foremost among them are: identification and detection of the cold dark matter particles and elucidation of the dark-energy component. These are exciting times in cosmology!
Neutrino spectroscopy can probe the dark matter content in the Sun.

PubMed

Lopes, Ilídio; Silk, Joseph

2010-10-22

After being gravitationally captured, low-mass cold dark-matter particles (mass range from 5 to ~50 × 10(9) electron volts) are thought to drift to the center of the Sun and affect its internal structure. Solar neutrinos provide a way to probe the physical processes occurring in the Sun's core. Solar neutrino spectroscopy, in particular, is expected to measure the neutrino fluxes produced in nuclear reactions in the Sun. Here, we show how the presence of dark-matter particles inside the Sun will produce unique neutrino flux distributions in (7)Be-ν and (8)B-ν, as well as (13)N-ν, (15)O-ν, and (17)F-ν.
WIMP dark matter and unitarity-conserving inflation via a gauge singlet scalar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kahlhoefer, Felix; McDonald, John, E-mail: felix.kahlhoefer@desy.de, E-mail: j.mcdonald@lancaster.ac.uk

2015-11-01

A gauge singlet scalar with non-minimal coupling to gravity can drive inflation and later freeze out to become cold dark matter. We explore this idea by revisiting inflation in the singlet direction (S-inflation) and Higgs Portal Dark Matter in light of the Higgs discovery, limits from LUX and observations by Planck. We show that large regions of parameter space remain viable, so that successful inflation is possible and the dark matter relic abundance can be reproduced. Moreover, the scalar singlet can stabilise the electroweak vacuum and at the same time overcome the problem of unitarity-violation during inflation encountered by Higgsmore » Inflation, provided the singlet is a real scalar. The 2-σ Planck upper bound on n{sub s} imposes that the singlet mass is below 2 TeV, so that almost the entire allowed parameter range can be probed by XENON1T.« less
Cosmic background radiation anisotropies in universes dominated by nonbaryonic dark matter

NASA Technical Reports Server (NTRS)

Bond, J. R.; Efstathiou, G.

1984-01-01

Detailed calculations of the temperature fluctuations in the cosmic background radiation for universes dominated by massive collisionless relics of the big bang are presented. An initially adiabatic constant curvature perturbation spectrum is assumed. In models with cold dark matter, the simplest hypothesis - that galaxies follow the mass distribution leads to small-scale anisotropies which exceed current observational limits if omega is less than 0.2 h to the -4/3. Since low values of omega are indicated by dynamical studies of galaxy clustering, cold particle models in which light traces mass are probably incorrect. Reheating of the pregalactic medium is unlikely to modify this conclusion. In cold particle or neutrino-dominated universes with omega = 1, presented predictions for small-scale and quadrupole anisotropies are below current limits. In all cases, the small-scale fluctuations are predicted to be about 10 percent linearly polarized.
Warm dark matter via ultra-violet freeze-in: reheating temperature and non-thermal distribution for fermionic Higgs portal dark matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, John

2016-08-17

Warm dark matter (WDM) of order keV mass may be able to resolve the disagreement between structure formation in cold dark matter simulations and observations. The detailed properties of WDM will depend upon its energy distribution, in particular how it deviates from the thermal distribution usually assumed in WDM simulations. Here we focus on WDM production via the Ultra-Violet (UV) freeze-in mechanism, for the case of fermionic Higgs portal dark matter ψ produced via the portal interaction ψ-barψH{sup †}H/Λ. We introduce a new method to simplify the computation of the non-thermal energy distribution of dark matter from freeze-in. We showmore » that the non-thermal energy distribution from UV freeze-in is hotter than the corresponding thermal distribution and has the form of a Bose-Einstein distribution with a non-thermal normalization. The resulting range of dark matter fermion mass consistent with observations is 5–7 keV. The reheating temperature must satisfy T{sub R}≳120 GeV in order to account for the observed dark matter density when m{sub ψ}≈5 keV, where the lower bound on T{sub R} corresponds to the limit where the fermion mass is entirely due to electroweak symmetry breaking via the portal interaction. The corresponding bound on the interaction scale is Λ≳6.0×10{sup 9} GeV.« less
Effect of supersonic relative motion between baryons and dark matter on collapsed objects

NASA Astrophysics Data System (ADS)

Asaba, Shinsuke; Ichiki, Kiyotomo; Tashiro, Hiroyuki

2016-01-01

Great attention is given to the first star formation and the epoch of reionization as main targets of planned large radio interferometries (e.g. Square Kilometre Array). Recently, it is claimed that the supersonic relative velocity between baryons and cold dark matter can suppress the abundance of first stars and impact the cosmological reionization process. Therefore, in order to compare observed results with theoretical predictions it is important to examine the effect of the supersonic relative motion on the small-scale structure formation. In this paper, we investigate this effect on the nonlinear structure formation in the context of the spherical collapse model in order to understand the fundamental physics in a simple configuration. We show the evolution of the dark matter sphere with the relative velocity by both using N-body simulations and numerically calculating the equation of motion for the dark matter mass shell. The effects of the relative motion in the spherical collapse model appear as the delay of the collapse time of dark matter halos and the decrease of the baryon mass fraction within the dark matter sphere. Based on these results, we provide the fitting formula of the critical density contrast for collapses with the relative motion effect and calculate the mass function of dark matter halos in the Press-Schechter formalism. As a result, the relative velocity decreases the abundance of dark matter halos whose mass is smaller than 108M⊙/h .
Distinguishing CDM dwarfs from SIDM dwarfs in baryonic simulations

NASA Astrophysics Data System (ADS)

Strickland, Emily; Fitts, Alex B.; Boylan-Kolchin, Michael

2017-06-01

Dwarf galaxies in the nearby Universe are the most dark-matter-dominated systems known. They are therefore natural probes of the nature of dark matter, which remains unknown. Our collaboration has performed several high-resolution cosmological zoom-in simulations of isolated dwarf galaxies. We simulate each galaxy in standard cold dark matter (ΛCDM) as well as self-interacting dark matter (SIDM, with a cross section of σ/m ~ 1 cm2/g), both with and without baryons, in order to identify distinguishing characteristics between the two. The simulations are run using GIZMO, a meshless-finite-mass hydrodynamical code, and are part of the Feedback in Realistic Environments (FIRE) project. By analyzing both the global properties and inner structure of the dwarfs in varying dark matter prescriptions, we provide a side-by-side comparison of isolated, dark-matter-dominated galaxies at the mass scale where differences in the two models of dark matter are thought to be the most obvious. We find that the edge of classical dwarfs and ultra-faint dwarfs (at stellar masses of ~105 solar masses) provides the clearest window for distinguishing between the two theories. At these low masses, our SIDM galaxies have a cored inner density profile, while their CDM counterparts have “cuspy” centers. The SIDM versions of each galaxy also have measurably lower stellar velocity dispersions than their CDM counterparts. Future observations of ultra faint dwarfs with JWST and 30-m telescopes will be able to discern whether such alternate theories of dark matter are viable.
A cosmic book. [of physics of early universe

NASA Technical Reports Server (NTRS)

Peebles, P. J. E.; Silk, Joseph

1988-01-01

A system of assigning odds to the basic elements of cosmological theories is proposed in order to evaluate the strengths and weaknesses of the theories. A figure of merit for the theories is obtained by counting and weighing the plausibility of each of the basic elements that is not substantially supported by observation or mature fundamental theory. The magnetized strong model is found to be the most probable. In order of decreasing probability, the ranking for the rest of the models is: (1) the magnetized string model with no exotic matter and the baryon adiabatic model; (2) the hot dark matter model and the model of cosmic string loops; (3) the canonical cold dark matter model, the cosmic string loops model with hot dark matter, and the baryonic isocurvature model; and (4) the cosmic string loops model with no exotic matter.
Rigging dark haloes: why is hierarchical galaxy formation consistent with the inside-out build-up of thin discs?

NASA Astrophysics Data System (ADS)

Pichon, C.; Pogosyan, D.; Kimm, T.; Slyz, A.; Devriendt, J.; Dubois, Y.

2011-12-01

State-of-the-art hydrodynamical simulations show that gas inflow through the virial sphere of dark matter haloes is focused (i.e. has a preferred inflow direction), consistent (i.e. its orientation is steady in time) and amplified (i.e. the amplitude of its advected specific angular momentum increases with time). We explain this to be a consequence of the dynamics of the cosmic web within the neighbourhood of the halo, which produces steady, angular momentum rich, filamentary inflow of cold gas. On large scales, the dynamics within neighbouring patches drives matter out of the surrounding voids, into walls and filaments before it finally gets accreted on to virialized dark matter haloes. As these walls/filaments constitute the boundaries of asymmetric voids, they acquire a net transverse motion, which explains the angular momentum rich nature of the later infall which comes from further away. We conjecture that this large-scale driven consistency explains why cold flows are so efficient at building up high-redshift thin discs inside out.
Probing dark matter with star clusters: a dark matter core in the ultra-faint dwarf Eridanus II

NASA Astrophysics Data System (ADS)

Contenta, Filippo; Balbinot, Eduardo; Petts, James A.; Read, Justin I.; Gieles, Mark; Collins, Michelle L. M.; Peñarrubia, Jorge; Delorme, Maxime; Gualandris, Alessia

2018-05-01

We present a new technique to probe the central dark matter (DM) density profile of galaxies that harnesses both the survival and observed properties of star clusters. As a first application, we apply our method to the `ultra-faint' dwarf Eridanus II (Eri II) that has a lone star cluster ˜45 pc from its centre. Using a grid of collisional N-body simulations, incorporating the effects of stellar evolution, external tides and dynamical friction, we show that a DM core for Eri II naturally reproduces the size and the projected position of its star cluster. By contrast, a dense cusped galaxy requires the cluster to lie implausibly far from the centre of Eri II (>1 kpc), with a high inclination orbit that must be observed at a particular orbital phase. Our results, therefore, favour a DM core. This implies that either a cold DM cusp was `heated up' at the centre of Eri II by bursty star formation or we are seeing an evidence for physics beyond cold DM.
Using voids to unscreen modified gravity

NASA Astrophysics Data System (ADS)

Falck, Bridget; Koyama, Kazuya; Zhao, Gong-Bo; Cautun, Marius

2018-04-01

The Vainshtein mechanism, present in many models of gravity, is very effective at screening dark matter haloes such that the fifth force is negligible and general relativity is recovered within their Vainshtein radii. Vainshtein screening is independent of halo mass and environment, in contrast to e.g. chameleon screening, making it difficult to test. However, our previous studies have found that the dark matter particles in filaments, walls, and voids are not screened by the Vainshtein mechanism. We therefore investigate whether cosmic voids, identified as local density minima using a watershed technique, can be used to test models of gravity that exhibit Vainshtein screening. We measure density, velocity, and screening profiles of stacked voids in cosmological N-body simulations using both dark matter particles and dark matter haloes as tracers of the density field. We find that the voids are completely unscreened, and the tangential velocity and velocity dispersion profiles of stacked voids show a clear deviation from Λ cold dark matter at all radii. Voids have the potential to provide a powerful test of gravity on cosmological scales.
MEASURING DARK MATTER PROFILES NON-PARAMETRICALLY IN DWARF SPHEROIDALS: AN APPLICATION TO DRACO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jardel, John R.; Gebhardt, Karl; Fabricius, Maximilian H.

2013-02-15

We introduce a novel implementation of orbit-based (or Schwarzschild) modeling that allows dark matter density profiles to be calculated non-parametrically in nearby galaxies. Our models require no assumptions to be made about velocity anisotropy or the dark matter profile. The technique can be applied to any dispersion-supported stellar system, and we demonstrate its use by studying the Local Group dwarf spheroidal galaxy (dSph) Draco. We use existing kinematic data at larger radii and also present 12 new radial velocities within the central 13 pc obtained with the VIRUS-W integral field spectrograph on the 2.7 m telescope at McDonald Observatory. Ourmore » non-parametric Schwarzschild models find strong evidence that the dark matter profile in Draco is cuspy for 20 {<=} r {<=} 700 pc. The profile for r {>=} 20 pc is well fit by a power law with slope {alpha} = -1.0 {+-} 0.2, consistent with predictions from cold dark matter simulations. Our models confirm that, despite its low baryon content relative to other dSphs, Draco lives in a massive halo.« less
A BARYONIC SOLUTION TO THE MISSING SATELLITES PROBLEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brooks, Alyson M.; Kuhlen, Michael; Zolotov, Adi

2013-03-01

It has been demonstrated that the inclusion of baryonic physics can alter the dark matter densities in the centers of low-mass galaxies, making the central dark matter slope more shallow than predicted in pure cold dark matter simulations. This flattening of the dark matter profile can occur in the most luminous subhalos around Milky Way mass galaxies. Zolotov et al. have suggested a correction to be applied to the central masses of dark matter-only satellites in order to mimic the affect of (1) the flattening of the dark matter cusp due to supernova feedback in luminous satellites and (2) enhancedmore » tidal stripping due to the presence of a baryonic disk. In this paper, we apply this correction to the z = 0 subhalo masses from the high resolution, dark matter-only Via Lactea II (VL2) simulation, and find that the number of massive subhalos is dramatically reduced. After adopting a stellar mass to halo mass relationship for the VL2 halos, and identifying subhalos that are (1) likely to be destroyed by stripping and (2) likely to have star formation suppressed by photo-heating, we find that the number of massive, luminous satellites around a Milky Way mass galaxy is in agreement with the number of observed satellites around the Milky Way or M31. We conclude that baryonic processes have the potential to solve the missing satellites problem.« less

A Baryonic Solution to the Missing Satellites Problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brooks, Alyson M.; Kuhlen, Michael; Zolotov, Adi

2013-03-01

It has been demonstrated that the inclusion of baryonic physics can alter the dark matter densities in the centers of low-mass galaxies, making the central dark matter slope more shallow than predicted in pure cold dark matter simulations. This flattening of the dark matter profile can occur in the most luminous subhalos around Milky Way mass galaxies. Zolotov et al. have suggested a correction to be applied to the central masses of dark matter-only satellites in order to mimic the affect of (1) the flattening of the dark matter cusp due to supernova feedback in luminous satellites and (2) enhancedmore » tidal stripping due to the presence of a baryonic disk. In this paper, we apply this correction to the z = 0 subhalo masses from the high resolution, dark matter-only Via Lactea II (VL2) simulation, and find that the number of massive subhalos is dramatically reduced. After adopting a stellar mass to halo mass relationship for the VL2 halos, and identifying subhalos that are (1) likely to be destroyed by stripping and (2) likely to have star formation suppressed by photo-heating, we find that the number of massive, luminous satellites around a Milky Way mass galaxy is in agreement with the number of observed satellites around the Milky Way or M31. We conclude that baryonic processes have the potential to solve the missing satellites problem« less
Is a massive tau neutrino just what cold dark matter needs?

NASA Technical Reports Server (NTRS)

Dodelson, Scott; Gyuk, Geza; Turner, Michael S.

1994-01-01

The cold dark matter (CDM) scenario for structure formation in the Universe is very attractive and has many successes; however, when its spectrum of density perturbations is normalized to the COBE anisotropy measurement the level of inhomogeneity predicted on small scales is too large. This can be remedied by a tau neutrino of mass 1 MeV - 10MeV and lifetime 0.1 sec - 100 sec whose decay products include electron neutrinos because it allows the total energy density in relativistic particles to be doubled without interfering with nucleosynthesis. The anisotropies predicted on the degree scale for 'tau CDM' are larger than standard CDM. Experiments at e(sup +/-) collides may be able to probe such a mass range.
Gravitational lensing in a cold dark matter universe

NASA Technical Reports Server (NTRS)

Narayan, Ramesh; White, Simon D. M.

1988-01-01

Gravitational lensing due to mass condensations in a biased cold dark matter (CDM) universe is investigated using the Press-Schechter (1974) theory with density fluctuation amplitudes taken from previous N-body work. Under the critical assumption that CDM haloes have small core radii, a distribution of image angular separations for high-z lensed quasars with a peak at about 1 arcsec and a half-width of a factor of about 10. Allowing for selection effects at small angular separations, this is in good agreement with the observed separations. The estimated frequency of lensing is somewhat lower than that observed, but the discrepancy can be removed by invoking amplification bias and by making a small upward adjustment to the density fluctuation amplitudes assumed in the CDM model.
Galaxy formation

PubMed Central

Peebles, P. J. E.

1998-01-01

It is argued that within the standard Big Bang cosmological model the bulk of the mass of the luminous parts of the large galaxies likely had been assembled by redshift z ∼ 10. Galaxy assembly this early would be difficult to fit in the widely discussed adiabatic cold dark matter model for structure formation, but it could agree with an isocurvature version in which the cold dark matter is the remnant of a massive scalar field frozen (or squeezed) from quantum fluctuations during inflation. The squeezed field fluctuations would be Gaussian with zero mean, and the distribution of the field mass therefore would be the square of a random Gaussian process. This offers a possibly interesting new direction for the numerical exploration of models for cosmic structure formation. PMID:9419326
First Constraints on Fuzzy Dark Matter from Lyman-α Forest Data and Hydrodynamical Simulations.

PubMed

Iršič, Vid; Viel, Matteo; Haehnelt, Martin G; Bolton, James S; Becker, George D

2017-07-21

We present constraints on the masses of extremely light bosons dubbed fuzzy dark matter (FDM) from Lyman-α forest data. Extremely light bosons with a de Broglie wavelength of ∼1 kpc have been suggested as dark matter candidates that may resolve some of the current small scale problems of the cold dark matter model. For the first time, we use hydrodynamical simulations to model the Lyman-α flux power spectrum in these models and compare it to the observed flux power spectrum from two different data sets: the XQ-100 and HIRES/MIKE quasar spectra samples. After marginalization over nuisance and physical parameters and with conservative assumptions for the thermal history of the intergalactic medium (IGM) that allow for jumps in the temperature of up to 5000 K, XQ-100 provides a lower limit of 7.1×10^{-22} eV, HIRES/MIKE returns a stronger limit of 14.3×10^{-22} eV, while the combination of both data sets results in a limit of 20×10^{-22} eV (2σ C.L.). The limits for the analysis of the combined data sets increases to 37.5×10^{-22} eV (2σ C.L.) when a smoother thermal history is assumed where the temperature of the IGM evolves as a power law in redshift. Light boson masses in the range 1-10×10^{-22} eV are ruled out at high significance by our analysis, casting strong doubts that FDM helps solve the "small scale crisis" of the cold dark matter models.
The Prolate Dark Matter Halo of the Andromeda Galaxy

NASA Astrophysics Data System (ADS)

Hayashi, Kohei; Chiba, Masashi

2014-07-01

We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi & Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for its dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.
The prolate dark matter halo of the Andromeda galaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayashi, Kohei; Chiba, Masashi, E-mail: k.hayasi@astr.tohoku.ac.jp, E-mail: chiba@astr.tohoku.ac.jp

We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi and Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for itsmore » dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.« less
Effective Dark Matter Halo Catalog in f(R) Gravity.

PubMed

He, Jian-Hua; Hawken, Adam J; Li, Baojiu; Guzzo, Luigi

2015-08-14

We introduce the idea of an effective dark matter halo catalog in f(R) gravity, which is built using the effective density field. Using a suite of high resolution N-body simulations, we find that the dynamical properties of halos, such as the distribution of density, velocity dispersion, specific angular momentum and spin, in the effective catalog of f(R) gravity closely mimic those in the cold dark matter model with a cosmological constant (ΛCDM). Thus, when using effective halos, an f(R) model can be viewed as a ΛCDM model. This effective catalog therefore provides a convenient way for studying the baryonic physics, the galaxy halo occupation distribution and even semianalytical galaxy formation in f(R) cosmologies.
Majorana dark matter with B+L gauge symmetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chao, Wei; Guo, Huai-Ke; Zhang, Yongchao

Here, we present a new model that extends the Standard Model (SM) with the local B + L symmetry, and point out that the lightest new fermion, introduced to cancel anomalies and stabilized automatically by the B + L symmetry, can serve as the cold dark matter candidate. We also study constraints on the model from Higgs measurements, electroweak precision measurements as well as the relic density and direct detections of the dark matter. Our numerical results reveal that the pseudo-vector coupling of with Z and the Yukawa coupling with the SM Higgs are highly constrained by the latest resultsmore » of LUX, while there are viable parameter space that could satisfy all the constraints and give testable predictions.« less
Majorana dark matter with B+L gauge symmetry

DOE PAGES

Chao, Wei; Guo, Huai-Ke; Zhang, Yongchao

2017-04-07

Here, we present a new model that extends the Standard Model (SM) with the local B + L symmetry, and point out that the lightest new fermion, introduced to cancel anomalies and stabilized automatically by the B + L symmetry, can serve as the cold dark matter candidate. We also study constraints on the model from Higgs measurements, electroweak precision measurements as well as the relic density and direct detections of the dark matter. Our numerical results reveal that the pseudo-vector coupling of with Z and the Yukawa coupling with the SM Higgs are highly constrained by the latest resultsmore » of LUX, while there are viable parameter space that could satisfy all the constraints and give testable predictions.« less
Photons in dense nuclear matter: Random-phase approximation

NASA Astrophysics Data System (ADS)

Stetina, Stephan; Rrapaj, Ermal; Reddy, Sanjay

2018-04-01

We present a comprehensive and pedagogic discussion of the properties of photons in cold and dense nuclear matter based on the resummed one-loop photon self-energy. Correlations among electrons, muons, protons, and neutrons in β equilibrium that arise as a result of electromagnetic and strong interactions are consistently taken into account within the random phase approximation. Screening effects, damping, and collective excitations are systematically studied in a fully relativistic setup. Our study is relevant to the linear response theory of dense nuclear matter, calculations of transport properties of cold dense matter, and investigations of the production and propagation of hypothetical vector bosons such as the dark photons.
Ultracompact Minihalos as Probes of Inflationary Cosmology.

PubMed

Aslanyan, Grigor; Price, Layne C; Adams, Jenni; Bringmann, Torsten; Clark, Hamish A; Easther, Richard; Lewis, Geraint F; Scott, Pat

2016-09-30

Cosmological inflation generates primordial density perturbations on all scales, including those far too small to contribute to the cosmic microwave background. At these scales, isolated ultracompact minihalos of dark matter can form well before standard structure formation, if the perturbations have sufficient amplitude. Minihalos affect pulsar timing data and are potentially bright sources of gamma rays. The resulting constraints significantly extend the observable window of inflation in the presence of cold dark matter, coupling two of the key problems in modern cosmology.
Too hot to handle? Analytic solutions for massive neutrino or warm dark matter cosmologies

NASA Astrophysics Data System (ADS)

Slepian, Zachary; Portillo, Stephen K. N.

2018-05-01

We obtain novel closed-form solutions to the Friedmann equation for cosmological models containing a component whose equation of state is that of radiation (w = 1/3) at early times and that of cold pressureless matter (w = 0) at late times. The equation of state smoothly transitions from the early to late-time behavior and exactly describes the evolution of a species with a Dirac Delta function distribution in momentum magnitudes |p_0| (i.e. all particles have the same |p_0|). Such a component, here termed "hot matter", is an approximate model for both neutrinos and warm dark matter. We consider it alone and in combination with cold matter and with radiation, also obtaining closed-form solutions for the growth of super-horizon perturbations in each case. The idealized model recovers t(a) to better than 1.5% accuracy for all a relative to a Fermi-Dirac distribution (as describes neutrinos). We conclude by adding the second moment of the distribution to our exact solution and then generalizing to include all moments of an arbitrary momentum distribution in a closed-form solution.
Too hot to handle? Analytic solutions for massive neutrino or warm dark matter cosmologies

NASA Astrophysics Data System (ADS)

Slepian, Zachary; Portillo, Stephen K. N.

2018-07-01

We obtain novel closed-form solutions to the Friedmann equation for cosmological models containing a component whose equation of state is that of radiation (w = 1/3) at early times and that of cold pressureless matter (w= 0) at late times. The equation of state smoothly transitions from the early- to late-time behaviour and exactly describes the evolution of a species with a Dirac delta function distribution in momentum magnitudes |{p}_0| (i.e. all particles have the same |{p}_0|). Such a component, here termed `hot matter', is an approximate model for both neutrinos and warm dark matter. We consider it alone and in combination with cold matter and with radiation, also obtaining closed-form solutions for the growth of superhorizon perturbations in each case. The idealized model recovers t(a) to better than 1.5 per cent accuracy for all a relative to a Fermi-Dirac distribution (as describes neutrinos). We conclude by adding the second moment of the distribution to our exact solution and then generalizing to include all moments of an arbitrary momentum distribution in a closed-form solution.
Dark-matter QCD-axion searches.

PubMed

Rosenberg, Leslie J

2015-10-06

In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There's no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10(-(6-3)) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and experiments are discussed, but I hope to give a sense of the current experimental landscape of the search for dark-matter axions.
Dark-matter QCD-axion searches

PubMed Central

Rosenberg, Leslie J

2015-01-01

In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There’s no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10−(6–3) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and experiments are discussed, but I hope to give a sense of the current experimental landscape of the search for dark-matter axions. PMID:25583487
Can particle-creation phenomena replace dark energy?

NASA Astrophysics Data System (ADS)

Debnath, Subhra; Sanyal, Abhik Kumar

2011-07-01

Particle creation at the expense of the gravitational field might be sufficient to explain the cosmic evolution history, without the need of dark energy at all. This phenomena has been investigated in a recent work by Lima et al (Class. Quantum Grav. 2008 25 205006) assuming particle creation at the cost of gravitational energy in the late Universe. However, the model does not satisfy the WMAP constraint on the matter-radiation equality (Steigman et al 2009 J. Cosmol. Astropart. Phys. JCAP06(2009)033). Here, we have suggested a model, in the same framework, which fits perfectly with SNIa data at low redshift as well as an early integrated Sachs-Wolfe effect on the matter-radiation equality determined by WMAP at high redshift. Such a model requires the presence of nearly 26% primeval matter in the form of baryons and cold dark matter.
Limits on cold dark matter cosmologies from new anisotropy bounds on the cosmic microwave background

NASA Technical Reports Server (NTRS)

Vittorio, Nicola; Meinhold, Peter; Lubin, Philip; Muciaccia, Pio Francesco; Silk, Joseph

1991-01-01

A self-consistent method is presented for comparing theoretical predictions of and observational upper limits on CMB anisotropy. New bounds on CDM cosmologies set by the UCSB South Pole experiment on the 1 deg angular scale are presented. An upper limit of 4.0 x 10 to the -5th is placed on the rms differential temperature anisotropy to a 95 percent confidence level and a power of the test beta = 55 percent. A lower limit of about 0.6/b is placed on the density parameter of cold dark matter universes with greater than about 3 percent baryon abundance and a Hubble constant of 50 km/s/Mpc, where b is the bias factor, equal to unity only if light traces mass.
Viscous self interacting dark matter and cosmic acceleration

NASA Astrophysics Data System (ADS)

Atreya, Abhishek; Bhatt, Jitesh R.; Mishra, Arvind

2018-02-01

Self interacting dark matter (SIDM) provides us with a consistent solution to certain astrophysical observations in conflict with collision-less cold DM paradigm. In this work we estimate the shear viscosity (η) and bulk viscosity (ζ) of SIDM, within kinetic theory formalism, for galactic and cluster size SIDM halos. To that extent we make use of the recent constraints on SIDM cross-section for the dwarf galaxies, LSB galaxies and clusters. We also estimate the change in solution of Einstein's equation due to these viscous effects and find that σ/m constraints on SIDM from astrophysical data provide us with sufficient viscosity to account for the observed cosmic acceleration at present epoch, without the need of any additional dark energy component. Using the estimates of dark matter density for galactic and cluster size halo we find that the mean free path of dark matter ~ few Mpc. Thus the smallest scale at which the viscous effect start playing the role is cluster scale. Astrophysical data for dwarf, LSB galaxies and clusters also seems to suggest the same. The entire analysis is independent of any specific particle physics motivated model for SIDM.
Curvaton as dark matter with secondary inflation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Jinn-Ouk; Kitajima, Naoya; Terada, Takahiro, E-mail: jinn-ouk.gong@apctp.org, E-mail: naoya.kitajima@apctp.org, E-mail: terada@kias.re.kr

2017-03-01

We consider a novel cosmological scenario in which a curvaton is long-lived and plays the role of cold dark matter (CDM) in the presence of a short, secondary inflation. Non-trivial evolution of the large scale cosmological perturbation in the curvaton scenario can affect the duration of the short term inflation, resulting in the inhomogeneous end of inflation. Non-linear parameters of the curvature perturbation are predicted to be f {sub NL} ≈ 5/4 and g {sub NL} ≈ 0. The curvaton abundance can be well diluted by the short-term inflation and accordingly, it does not have to decay into the Standardmore » Model particles. Then the curvaton can account for the present CDM with the isocurvature perturbation being sufficiently suppressed because both the adiabatic and CDM isocurvature perturbations have the same origin. As an explicit example, we consider the thermal inflation scenario and a string axion as a candidate for this curvaton-dark matter. We further discuss possibilities to identify the curvaton-dark matter with the QCD axion.« less

Theoretical implications of the galactic radial acceleration relation of McGaugh, Lelli, and Schombert

NASA Astrophysics Data System (ADS)

Nesbet, Robert K.

2018-05-01

Velocities in stable circular orbits about galaxies, a measure of centripetal gravitation, exceed the expected Kepler/Newton velocity as orbital radius increases. Standard Λ cold dark matter (ΛCDM) attributes this anomaly to galactic dark matter. McGaugh et al. have recently shown for 153 disc galaxies that observed radial acceleration is an apparently universal function of classical acceleration computed for observed galactic baryonic mass density. This is consistent with the empirical modified Newtonian dynamics (MOND) model, not requiring dark matter. It is shown here that suitably constrained ΛCDM and conformal gravity (CG) also produce such a universal correlation function. ΛCDM requires a very specific dark matter distribution, while the implied CG non-classical acceleration must be independent of galactic mass. All three constrained radial acceleration functions agree with the empirical baryonic v4 Tully-Fisher relation. Accurate rotation data in the nominally flat velocity range could distinguish between MOND, ΛCDM, and CG.
The evolving intergalactic medium - The uncollapsed baryon fraction in a cold dark matter universe

NASA Technical Reports Server (NTRS)

Shapiro, Paul R.; Giroux, Mark L.; Babul, Arif

1991-01-01

The time-varying density of the intergalactic medium (IGM) is calculated by coupling detailed numerical calculations of the thermal and ionization balance and radiative transfer in a uniform IGM of H and He to the linearized equations for the growth of density fluctuations in both gases and a dark component in a cold dark matter universe. The IGM density is identified with the collapsed baryon fraction. It is found that even if the IGM is never reheated, a significant fraction of the baryons remain uncollapsed at redshifts of four. If instead the collapsed fraction releases enough ionizing radiation or thermal energy to reionize the IGM by z greater than four as required by the Gunn-Peterson (GP) constraint, the uncollapsed fraction at z of four is even higher. The known quasar distribution is insufficient to supply the ionizing radiation necessary to satisfy the GP constraint in this case and, if stars are instead responsible, a substantial metallicity must have been produced by z of four.
High Angular Momentum Halo Gas: A Feedback and Code-independent Prediction of LCDM

NASA Astrophysics Data System (ADS)

Stewart, Kyle R.; Maller, Ariyeh H.; Oñorbe, Jose; Bullock, James S.; Joung, M. Ryan; Devriendt, Julien; Ceverino, Daniel; Kereš, Dušan; Hopkins, Philip F.; Faucher-Giguère, Claude-André

2017-07-01

We investigate angular momentum acquisition in Milky Way-sized galaxies by comparing five high resolution zoom-in simulations, each implementing identical cosmological initial conditions but utilizing different hydrodynamic codes: Enzo, Art, Ramses, Arepo, and Gizmo-PSPH. Each code implements a distinct set of feedback and star formation prescriptions. We find that while many galaxy and halo properties vary between the different codes (and feedback prescriptions), there is qualitative agreement on the process of angular momentum acquisition in the galaxy’s halo. In all simulations, cold filamentary gas accretion to the halo results in ˜4 times more specific angular momentum in cold halo gas (λ cold ≳ 0.1) than in the dark matter halo. At z > 1, this inflow takes the form of inspiraling cold streams that are co-directional in the halo of the galaxy and are fueled, aligned, and kinematically connected to filamentary gas infall along the cosmic web. Due to the qualitative agreement among disparate simulations, we conclude that the buildup of high angular momentum halo gas and the presence of these inspiraling cold streams are robust predictions of Lambda Cold Dark Matter galaxy formation, though the detailed morphology of these streams is significantly less certain. A growing body of observational evidence suggests that this process is borne out in the real universe.
Dark-matter QCD-axion searches

DOE PAGES

Rosenberg, Leslie J.

2015-01-12

In the late 20th century, cosmology became a precision science. At the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There’s no known such elementary particle, so the strong presumption is the darkmore » matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10 -(6–3) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. But, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. Our paper is a selective overview of the current generation of sensitive axion searches. Finally, not all techniques and experiments are discussed, but I hope to give a sense of the current experimental landscape of the search for dark-matter axions.« less
Probing the sign-changeable interaction between dark energy and dark matter with current observations

NASA Astrophysics Data System (ADS)

Guo, Juan-Juan; Zhang, Jing-Fei; Li, Yun-He; He, Dong-Ze; Zhang, Xin

2018-03-01

We consider the models of vacuum energy interacting with cold dark matter in this study, in which the coupling can change sigh during the cosmological evolution. We parameterize the running coupling b by the form b( a) = b 0 a+ b e(1- a), where at the early-time the coupling is given by a constant b e and today the coupling is described by another constant b 0. We explore six specific models with (i) Q = b( a) H 0 ρ 0, (ii) Q = b( a) H 0 ρ de, (iii) Q = b( a) H 0 ρ c, (iv) Q = b( a) Hρ 0, (v) Q = b( a) H ρ de, and (vi) Q = b( a) Hρ c. The current observational data sets we use to constrain the models include the JLA compilation of type Ia supernova data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the Hubble constant direct measurement. We find that, for all the models, we have b 0 < 0 and b e > 0 at around the 1 σ level, and b 0 and b e are in extremely strong anti-correlation. Our results show that the coupling changes sign during the evolution at about the 1 σ level, i.e., the energy transfer is from dark matter to dark energy when dark matter dominates the universe and the energy transfer is from dark energy to dark matter when dark energy dominates the universe.
Results from the Wilkinson Microwave Anisotropy Probe

NASA Technical Reports Server (NTRS)

Komatsu, E.; Bennett, Charles L.; Komatsu, Eiichiro

2015-01-01

The Wilkinson Microwave Anisotropy Probe (WMAP) mapped the distribution of temperature and polarization over the entire sky in five microwave frequency bands. These full-sky maps were used to obtain measurements of temperature and polarization anisotropy of the cosmic microwave background with the unprecedented accuracy and precision. The analysis of two-point correlation functions of temperature and polarization data gives determinations of the fundamental cosmological parameters such as the age and composition of the universe, as well as the key parameters describing the physics of inflation, which is further constrained by three-point correlation functions. WMAP observations alone reduced the flat ? cold dark matter (Lambda Cold Dark Matter) cosmological model (six) parameter volume by a factor of > 68, 000 compared with pre-WMAP measurements. The WMAP observations (sometimes in combination with other astrophysical probes) convincingly show the existence of non-baryonic dark matter, the cosmic neutrino background, flatness of spatial geometry of the universe, a deviation from a scale-invariant spectrum of initial scalar fluctuations, and that the current universe is undergoing an accelerated expansion. The WMAP observations provide the strongest ever support for inflation; namely, the structures we see in the universe originate from quantum fluctuations generated during inflation.
Constraints on cold dark matter theories from observations of massive x-ray-luminous clusters of galaxies at high redshift

NASA Technical Reports Server (NTRS)

Luppino, G. A.; Gioia, I. M.

1995-01-01

During the course of a gravitational lensing survey of distant, X-ray selected Einstein Observatory Extended Medium Sensitivity Survey (EMSS) clusters of galaxies, we have studied six X-ray-luminous (L(sub x) greater than 5 x 10(exp 44)(h(sub 50)(exp -2))ergs/sec) clusters at redshifts exceeding z = 0.5. All of these clusters are apparently massive. In addition to their high X-ray luminosity, two of the clusters at z approximately 0.6 exhibit gravitationally lensed arcs. Furthermore, the highest redshift cluster in our sample, MS 1054-0321 at z = 0.826, is both extremely X-ray luminous (L(sub 0.3-3.5keV)=9.3 x 10(exp 44)(h(sub 50)(exp -2))ergs/sec) and exceedingly rich with an optical richness comparable to an Abell Richness Class 4 cluster. In this Letter, we discuss the cosmological implications of the very existence of these clusters for hierarchical structure formation theories such as standard Omega = 1 CDM (cold dark matter), hybrid Omega = 1 C + HDM (hot dark matter), and flat, low-density Lambda + CDM models.
A gamma-ray constraint on the nature of dark matter

NASA Technical Reports Server (NTRS)

Silk, Joseph; Bloemen, Hans

1987-01-01

If even a small component of the Galactic spheroid consists of the weakly interacting majorana fermions that are cold-dark-matter candidate particles for the Galactic halo, there should be a substantial flux of annihilation gamma rays from a source of about 1-deg extent at the Galactic center. COS B observations already constrain the halo cold-dark-matter (CDM) content entrained in the inner spheroid to be less than about 10 percent. A somewhat weaker constraint applies to the CDM believed to be present in the Galactic disk, but still only about 15 percent can be in such particles. Monochromatic line photons of energy 3-10 GeV are also predicted, and future experiments may be capable of improving these limits. Since both theoretical models of galaxy formation in a CDM-dominated universe and mass models for the rotation curve in the inner Galaxy suggest that a substantial fraction of the spheroid component should be nonluminous and incorporate entrained halo CDM, the hypothesis that the halo CDM consists predominantly of weakly interacting fermions such as photinos or heavy majorana mass neutrinos or higgsinos may already be subject to observational test.
MATTER IN THE BEAM: WEAK LENSING, SUBSTRUCTURES, AND THE TEMPERATURE OF DARK MATTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahdi, Hareth S.; Elahi, Pascal J.; Lewis, Geraint F.

2016-08-01

Warm dark matter (WDM) models offer an attractive alternative to the current cold dark matter (CDM) cosmological model. We present a novel method to differentiate between WDM and CDM cosmologies, namely, using weak lensing; this provides a unique probe as it is sensitive to all of the “matter in the beam,” not just dark matter haloes and the galaxies that reside in them, but also the diffuse material between haloes. We compare the weak lensing maps of CDM clusters to those in a WDM model corresponding to a thermally produced 0.5 keV dark matter particle. Our analysis clearly shows thatmore » the weak lensing magnification, convergence, and shear distributions can be used to distinguish between CDM and WDM models. WDM models increase the probability of weak magnifications, with the differences being significant to ≳5 σ , while leaving no significant imprint on the shear distribution. WDM clusters analyzed in this work are more homogeneous than CDM ones, and the fractional decrease in the amount of material in haloes is proportional to the average increase in the magnification. This difference arises from matter that would be bound in compact haloes in CDM being smoothly distributed over much larger volumes at lower densities in WDM. Moreover, the signature does not solely lie in the probability distribution function but in the full spatial distribution of the convergence field.« less
Possible interaction between baryons and dark-matter particles revealed by the first stars

NASA Astrophysics Data System (ADS)

Barkana, Rennan

2018-03-01

The cosmic radio-frequency spectrum is expected to show a strong absorption signal corresponding to the 21-centimetre-wavelength transition of atomic hydrogen around redshift 20, which arises from Lyman-α radiation from some of the earliest stars. By observing this 21-centimetre signal—either its sky-averaged spectrum or maps of its fluctuations, obtained using radio interferometers—we can obtain information about cosmic dawn, the era when the first astrophysical sources of light were formed. The recent detection of the global 21-centimetre spectrum reveals a stronger absorption than the maximum predicted by existing models, at a confidence level of 3.8 standard deviations. Here we report that this absorption can be explained by the combination of radiation from the first stars and excess cooling of the cosmic gas induced by its interaction with dark matter. Our analysis indicates that the spatial fluctuations of the 21-centimetre signal at cosmic dawn could be an order of magnitude larger than previously expected and that the dark-matter particle is no heavier than several proton masses, well below the commonly predicted mass of weakly interacting massive particles. Our analysis also confirms that dark matter is highly non-relativistic and at least moderately cold, and primordial velocities predicted by models of warm dark matter are potentially detectable. These results indicate that 21-centimetre cosmology can be used as a dark-matter probe.
Possible interaction between baryons and dark-matter particles revealed by the first stars.

PubMed

Barkana, Rennan

2018-02-28

The cosmic radio-frequency spectrum is expected to show a strong absorption signal corresponding to the 21-centimetre-wavelength transition of atomic hydrogen around redshift 20, which arises from Lyman-α radiation from some of the earliest stars. By observing this 21-centimetre signal-either its sky-averaged spectrum or maps of its fluctuations, obtained using radio interferometers-we can obtain information about cosmic dawn, the era when the first astrophysical sources of light were formed. The recent detection of the global 21-centimetre spectrum reveals a stronger absorption than the maximum predicted by existing models, at a confidence level of 3.8 standard deviations. Here we report that this absorption can be explained by the combination of radiation from the first stars and excess cooling of the cosmic gas induced by its interaction with dark matter. Our analysis indicates that the spatial fluctuations of the 21-centimetre signal at cosmic dawn could be an order of magnitude larger than previously expected and that the dark-matter particle is no heavier than several proton masses, well below the commonly predicted mass of weakly interacting massive particles. Our analysis also confirms that dark matter is highly non-relativistic and at least moderately cold, and primordial velocities predicted by models of warm dark matter are potentially detectable. These results indicate that 21-centimetre cosmology can be used as a dark-matter probe.
The cosmic microwave background

NASA Technical Reports Server (NTRS)

Silk, Joseph

1991-01-01

Recent limits on spectral distortions and angular anisotropies in the cosmic microwave background are reviewed. The various backgrounds are described, and the theoretical implications are assessed. Constraints on inflationary cosmology dominated by cold dark matter (CDM) and on open cosmological models dominated by baryonic dark matter (BDM), with, respectively, primordial random phase scale-invariant curvature fluctuations or non-gaussian isocurvature fluctuations are described. More exotic theories are addressed, and I conclude with the 'bottom line': what theorists expect experimentalists to be measuring within the next two to three years without having to abandon their most cherished theories.
Are cosmological data sets consistent with each other within the Λ cold dark matter model?

NASA Astrophysics Data System (ADS)

Raveri, Marco

2016-02-01

We use a complete and rigorous statistical indicator to measure the level of concordance between cosmological data sets, without relying on the inspection of the marginal posterior distribution of some selected parameters. We apply this test to state of the art cosmological data sets, to assess their agreement within the Λ cold dark matter model. We find that there is a good level of concordance between all the experiments with one noticeable exception. There is substantial evidence of tension between the cosmic microwave background temperature and polarization measurements of the Planck satellite and the data from the CFHTLenS weak lensing survey even when applying ultraconservative cuts. These results robustly point toward the possibility of having unaccounted systematic effects in the data, an incomplete modeling of the cosmological predictions or hints toward new physical phenomena.
Bounds on isocurvature perturbations from cosmic microwave background and large scale structure data.

PubMed

Crotty, Patrick; García-Bellido, Juan; Lesgourgues, Julien; Riazuelo, Alain

2003-10-24

We obtain very stringent bounds on the possible cold dark matter, baryon, and neutrino isocurvature contributions to the primordial fluctuations in the Universe, using recent cosmic microwave background and large scale structure data. Neglecting the possible effects of spatial curvature, tensor perturbations, and reionization, we perform a Bayesian likelihood analysis with nine free parameters, and find that the amplitude of the isocurvature component cannot be larger than about 31% for the cold dark matter mode, 91% for the baryon mode, 76% for the neutrino density mode, and 60% for the neutrino velocity mode, at 2sigma, for uncorrelated models. For correlated adiabatic and isocurvature components, the fraction could be slightly larger. However, the cross-correlation coefficient is strongly constrained, and maximally correlated/anticorrelated models are disfavored. This puts strong bounds on the curvaton model.
A model for intergalactic filaments and galaxy formation during the first gigayear

NASA Astrophysics Data System (ADS)

Harford, A. Gayler; Hamilton, Andrew J. S.

2017-11-01

We propose a physically based, analytic model for intergalactic filaments during the first gigayear of the universe. The structure of a filament is based upon a gravitationally bound, isothermal cylinder of gas. The model successfully predicts for a cosmological simulation the total mass per unit length of a filament (dark matter plus gas) based solely upon the sound speed of the gas component, contrary to the expectation for collisionless dark matter aggregation. In the model, the gas, through its hydrodynamic properties, plays a key role in filament structure rather than being a passive passenger in a preformed dark matter potential. The dark matter of a galaxy follows the classic equation of collapse of a spherically symmetric overdensity in an expanding universe. In contrast, the gas usually collapses more slowly. The relative rates of collapse of these two components for individual galaxies can explain the varying baryon deficits of the galaxies under the assumption that matter moves along a single filament passing through the galaxy centre, rather than by spherical accretion. The difference in behaviour of the dark matter and gas can be simply and plausibly related to the model. The range of galaxies studied includes that of the so-called too big to fail galaxies, which are thought to be problematic for the standard Λ cold dark matter model of the universe. The isothermal-cylinder model suggests a simple explanation for why these galaxies are, unaccountably, missing from the night sky.
Numerical Convergence in the Dark Matter Halos Properties Using Cosmological Simulations

NASA Astrophysics Data System (ADS)

Mosquera-Escobar, X. E.; Muñoz-Cuartas, J. C.

2017-07-01

Nowadays, the accepted cosmological model is the so called -Cold Dark Matter (CDM). In such model, the universe is considered to be homogeneous and isotropic, composed of diverse components as the dark matter and dark energy, where the latter is the most abundant one. Dark matter plays an important role because it is responsible for the generation of gravitational potential wells, commonly called dark matter halos. At the end, dark matter halos are characterized by a set of parameters (mass, radius, concentration, spin parameter), these parameters provide valuable information for different studies, such as galaxy formation, gravitational lensing, etc. In this work we use the publicly available code Gadget2 to perform cosmological simulations to find to what extent the numerical parameters of the simu- lations, such as gravitational softening, integration time step and force calculation accuracy affect the physical properties of the dark matter halos. We ran a suite of simulations where these parameters were varied in a systematic way in order to explore accurately their impact on the structural parameters of dark matter halos. We show that the variations on the numerical parameters affect the structural pa- rameters of dark matter halos, such as concentration, virial radius, and concentration. We show that these modifications emerged when structures become non- linear (at redshift 2) for the scale of our simulations, such that these variations affected the formation and evolution structure of halos mainly at later cosmic times. As a quantitative result, we propose which would be the most appropriate values for the numerical parameters of the simulations, such that they do not affect the halo properties that are formed. For force calculation accuracy we suggest values smaller or equal to 0.0001, integration time step smaller o equal to 0.005 and for gravitational softening we propose equal to 1/60th of the mean interparticle distance, these values, correspond to the smaller values in the numerical parameters variations. This is an important numerical exercise, since for instance, it is believed that galaxy structural parameters are strongly dependent on dark matter halo structural parameters.
Comparison between two scalar field models using rotation curves of spiral galaxies

NASA Astrophysics Data System (ADS)

Fernández-Hernández, Lizbeth M.; Rodríguez-Meza, Mario A.; Matos, Tonatiuh

2018-04-01

Scalar fields have been used as candidates for dark matter in the universe, from axions with masses ∼ 10-5eV until ultra-light scalar fields with masses ∼ Axions behave as cold dark matter while the ultra-light scalar fields galaxies are Bose-Einstein condensate drops. The ultra-light scalar fields are also called scalar field dark matter model. In this work we study rotation curves for low surface brightness spiral galaxies using two scalar field models: the Gross-Pitaevskii Bose-Einstein condensate in the Thomas-Fermi approximation and a scalar field solution of the Klein-Gordon equation. We also used the zero disk approximation galaxy model where photometric data is not considered, only the scalar field dark matter model contribution to rotation curve is taken into account. From the best-fitting analysis of the galaxy catalog we use, we found the range of values of the fitting parameters: the length scale and the central density. The worst fitting results (values of χ red2 much greater than 1, on the average) were for the Thomas-Fermi models, i.e., the scalar field dark matter is better than the Thomas- Fermi approximation model to fit the rotation curves of the analysed galaxies. To complete our analysis we compute from the fitting parameters the mass of the scalar field models and two astrophysical quantities of interest, the dynamical dark matter mass within 300 pc and the characteristic central surface density of the dark matter models. We found that the value of the central mass within 300 pc is in agreement with previous reported results, that this mass is ≈ 107 M ⊙/pc2, independent of the dark matter model. And, on the contrary, the value of the characteristic central surface density do depend on the dark matter model.
Mimicking dark matter in Horndeski gravity

NASA Astrophysics Data System (ADS)

Rinaldi, Massimiliano

2017-06-01

Since the rediscovery of Horndeski gravity, a lot of work has been devoted to the exploration of its properties, especially in the context of dark energy. However, one sector of this theory, namely the one containing the coupling of the Einstein tensor to the kinetic term of the scalar field, shows some surprising features in the construction of black holes and neutron stars. Motivated by these new results, I explore the possibility that this sector of Horndeski gravity can mimic cold dark matter at cosmological level and also explain the flattening of galactic rotation curves. I will show that, in principle, it is possible to achieve both goals with at least two scalar fields and a minimal set of assumptions.
Dynamics of supersymmetric chameleons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brax, Philippe; Davis, Anne-Christine; Sakstein, Jeremy, E-mail: Philippe.Brax@cea.fr, E-mail: A.C.Davis@damtp.cam.ac.uk, E-mail: J.A.Sakstein@damtp.cam.ac.uk

2013-10-01

We investigate the cosmological dynamics of a class of supersymmetric chameleon models coupled to cold dark matter fermions. The model includes a cosmological constant in the form of a Fayet-Illiopoulos term, which emerges at late times due to the coupling of the chameleon to two charged scalars. Supergravity corrections ensure that the supersymmetric chameleons are efficiently screened in all astrophysical objects of interest, however this does not preclude the enhancement of gravity on linear cosmological scales. We solve the modified equations for the growth of cold dark matter density perturbations in closed form in the matter era. Using this, wemore » go on to derive the modified linear power spectrum which is characterised by two scales, the horizon size at matter-radiation equality and at the redshift when the chameleon reaches the minimum of its effective potential. We analyse the deviations from the ΛCDM predictions in the linear regime. We find that there is generically a region in the model's parameter space where the model's background cosmology coincides with that of the ΛCDM model. Furthermore, we find that characteristic deviations from ΛCDM are present on the matter power spectrum providing a clear signature of supersymmetric chameleons.« less
Why the dark matter of galaxies is clumps of micro browndwarfs and not Cold Dark Matter

NASA Astrophysics Data System (ADS)

Gibson, Carl H.

Observations of quasar microlensing by Schild 1996 show the baryonic dark matter BDM of galaxies is micro-brown-dwarfs, primordial hydrogen-helium planets formed at the plasma to gas transition 10^13 seconds, in trillion-planet clumps termed proto-globular-star-clusters PGCs. Large photon-viscosity {nu} of the plasma permits supercluster-mass gravitational fragmentation at 10^12 seconds when the horizon scale L_H = ct is matched by the Schwarz viscous scale L_SV of Gibson 1996. Voids begin expansion at sonic speeds c/ 3^1/2, where c is light speed and t is time, explaining 10^25 meter size regions observed to be devoid of all matter, either BDM or non-baryonic NBDM. Most of the NBDM is weakly-collisional, strongly-diffusive, neutrino-like particles. If cold NBDM (CDM) is assumed, it must soon become warm and diffuse because it is weakly-collisional. It cannot clump and its clumps cannot clump. CDM is ruled out with 99% confidence by local-group satellite observations of Kroupa et al. 2010. The satellites are clusters of PGCs. PGCs are recaptured by the Galaxy on an accretion disk as they freeze and diffuse from its core to form its BDM halo. Stars form by viscous mergers of primordial gas planets within PGCs. Stars die by overeating mBDs, making the first chemicals, oceans and life at 2-8 Myr.

Cosmographical Implications

NASA Astrophysics Data System (ADS)

Wright, E. L.

1992-12-01

The COBE() DMR observation of large scale anisotropy of the CMBR allows one to compare the gravitational potential measured using Delta T to the gravitational forces required to produce the observed clustering of galaxies. This comparison helps to define the allowed range of cosmological models. As shown by Wright etal 1992, the COBE Delta T agrees quite well with the bulk flow velocity measured by Bertschinger etal 1990 in a window of radius 6000 km/sec. This is the best evidence that the initial perturbation spectrum in fact followed the Harrison-Zeldovich (and inflationary) prediction that P(k) ~ k(n) with n = 1. Assuming that n ~ 1, one can deduce information about the nature of the matter in the Universe: the first conclusion is that a large amount of non-baryonic dark matter is required. The second conclusion is that a linearly evolving model dominated by Cold Dark Matter produces too little structure on 2500 km/sec scales. However, mixed Cold Plus Hot Dark Matter models, vacuum dominated models, or the Couchman & Carlberg (1992) non-linear recipe for making galaxies out of CDM all seem to reproduce the observed structures on scales from 500-6,000 km/sec while connecting to the COBE results with the expected n ~ 1 slope. () COBE is supported by NASA's Astrophysics Division. Goddard Space Flight Center (GSFC), under the scientific guidance of the COBE Science Working Group, is responsible for the development and operation of COBE.
A hydrodynamic approach to cosmology: The mixed dark matter cosmological scenario

NASA Technical Reports Server (NTRS)

Cen, Renyue; Ostriker, Jeremiah P.

1994-01-01

We compute the evolution of spatially flat, mixed cold and hot dark matter models containing both baryonic matter and two kinds of dark matter. Hydrodynamics is treated with a highly developed Eulerian hydrodynamic code (see Cen 1992). A standard particle-mesh (PM) code is also used in parallel to calculate the motion of the dark matter components. We adopt the following parameters: h equivalent to (sub 0)/100 km/s Mpc(exp -1) = 0.5, OMEGA(sub C) = 0.3, and OMEGA(sub B) = 0.06, with amplitude of the perturbation spectrum fixed by the Cosmic Background Explorer Satellite (COBE) Dark Matter Radiation (DMR) measurements (Smoot et al. 1992) being sigma (sub 8) = 0.67. Four different boxes are simulated with box sizes of L = (64, 16, 4, 1) h(exp -1) Mpc, respectively, the two small boxes providing good resolution but little valid information due to absence of large-scale power. We use 128(exp 3) approximate 10(exp 6.3) baryonic cells, 128(exp .3) cold dark matter particles, and 2 x 128(exp 3) hot dark matter particles. In addition to the dark matter we follow separately six baryonic species (H, H(+), He, He(+), He(++), e(-)) with allowance for both (nonequilibrium) collisional and radiative ionization in every cell. The background radiation field is also followed in detail with allowance made for both continuum and line processes, to allow nonequilibrium heating and cooling processes to be followed in detail. The mean final Zeldovich-Sunyaev y parameter is estimated to be y Bar = (5.4 + or - 2.7) x 10(exp -7) below currently attainable observations, with a rms fluctuation of approximately delta bar y = (0.6 + or - 3.0) x 10(exp -7) on arcminute scales. The rate of galaxy formation peaks at an even later epoch (z approximate 0.3) than in the standard (OMEGA = 1, sigma sub 8 = 0.67) cold dark matter (CDM) model (z approximate 0.5) and, at a redshift of z = 4, is nearly a factor of 100 lower than for the CDM model with the same value of sigma sub 8. With regard to mass function, the smallest objects are stabilized against collapse by thermal energy: the mass-weighted mass spectrum has a broad peak in the vicinity of M(sub B) = 10(exp 9.5) solar mass with a reasonable fit to the Schechter luminosity function if the ratio of baryon mass to blue light is approximately 4. In addition, one very large PM simulation was made in a box with size (320 h(exp - 1) Mpc) containing 3 x 200(exp 3) = 10(exp 7.4) particles. Utilizing this simulation we find that the model yields a cluster mass function which is about a factor of 4 higher than observed, but a cluster-cluster correlation length marginally lower than observed, but that both are closer to observations than in the (COBE) normalized CDM model. The one-dimensional pairwise velocity dispersion is 605 + or - 8 km/s at 1/h separation, lower than that of the DCM model normalized to COBE, but still significant higher than observations (Davis & Peebles 1983). A plausible velocity bias b(sub v) = 0.8 + or - 0.1 on this scale will reduce but not remove the discrepancy. The velocity auto-correlat ion function has a coherence length of 40/h Mpc, which is somewhat lower than the observed counterpart. In all these respects the model would be improved by decreasing the cold fraction of the dark OMEGA(sub CDM)/ (OMEGA(sub CDM) + OMEGA(sub HDB). But formation of galaxies and clusters of galaxies is much later in this model than in COBE-normalized CDM, perhaps too late. To improve on these constraints a larger ratio of OMEGA(sub CDM)/ (OMEGA(sub CDM) + OMEGA(sub HDM)) is required than the value of 0.67 adopted here. It does not seem possible to find a value for this ratio which would satisfy all tests. Overall, the model is similar both on large and intermediate scales to the standard CDM model normalized to the same value of sigma(sub B), but the problem with regard to late formation of galaxies is more severe in this model than in that CDM model. Adding hot dark matter, significantly improves the ability of the COBE-normalized CDM scenario to fit existing observations, but the model is in fact not as good as the CDM model with the same sigma(sub 8) and is still probably unsatisfactory with regard to several critical tests.
A detection of wobbling brightest cluster galaxies within massive galaxy clusters

NASA Astrophysics Data System (ADS)

Harvey, David; Courbin, F.; Kneib, J. P.; McCarthy, Ian G.

2017-12-01

A striking signal of dark matter beyond the standard model is the existence of cores in the centre of galaxy clusters. Recent simulations predict that a brightest cluster galaxy (BCG) inside a cored galaxy cluster will exhibit residual wobbling due to previous major mergers, long after the relaxation of the overall cluster. This phenomenon is absent with standard cold dark matter where a cuspy density profile keeps a BCG tightly bound at the centre. We test this hypothesis using cosmological simulations and deep observations of 10 galaxy clusters acting as strong gravitational lenses. Modelling the BCG wobble as a simple harmonic oscillator, we measure the wobble amplitude, Aw, in the BAHAMAS suite of cosmological hydrodynamical simulations, finding an upper limit for the cold dark matter paradigm of Aw < 2 kpc at the 95 per cent confidence limit. We carry out the same test on the data finding a non-zero amplitude of A_w=11.82^{+7.3}_{-3.0} kpc, with the observations dis-favouring Aw = 0 at the 3σ confidence level. This detection of BCG wobbling is evidence for a dark matter core at the heart of galaxy clusters. It also shows that strong lensing models of clusters cannot assume that the BCG is exactly coincident with the large-scale halo. While our small sample of galaxy clusters already indicates a non-zero Aw, with larger surveys, e.g. Euclid, we will be able to not only confirm the effect but also to use it to determine whether or not the wobbling finds its origin in new fundamental physics or astrophysical process.
High Angular Momentum Halo Gas: A Feedback and Code-independent Prediction of LCDM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stewart, Kyle R.; Maller, Ariyeh H.; Oñorbe, Jose

We investigate angular momentum acquisition in Milky Way-sized galaxies by comparing five high resolution zoom-in simulations, each implementing identical cosmological initial conditions but utilizing different hydrodynamic codes: Enzo, Art, Ramses, Arepo, and Gizmo-PSPH. Each code implements a distinct set of feedback and star formation prescriptions. We find that while many galaxy and halo properties vary between the different codes (and feedback prescriptions), there is qualitative agreement on the process of angular momentum acquisition in the galaxy’s halo. In all simulations, cold filamentary gas accretion to the halo results in ∼4 times more specific angular momentum in cold halo gas (more » λ {sub cold} ≳ 0.1) than in the dark matter halo. At z > 1, this inflow takes the form of inspiraling cold streams that are co-directional in the halo of the galaxy and are fueled, aligned, and kinematically connected to filamentary gas infall along the cosmic web. Due to the qualitative agreement among disparate simulations, we conclude that the buildup of high angular momentum halo gas and the presence of these inspiraling cold streams are robust predictions of Lambda Cold Dark Matter galaxy formation, though the detailed morphology of these streams is significantly less certain. A growing body of observational evidence suggests that this process is borne out in the real universe.« less
Bars in dark-matter-dominated dwarf galaxy discs

NASA Astrophysics Data System (ADS)

Marasco, A.; Oman, K. A.; Navarro, J. F.; Frenk, C. S.; Oosterloo, T.

2018-05-01

We study the shape and kinematics of simulated dwarf galaxy discs in the APOSTLE suite of Λ cold dark matter (ΛCDM) cosmological hydrodynamical simulations. We find that a large fraction of these gas-rich, star-forming discs show weak bars in their stellar component, despite being dark-matter-dominated systems. The bar pattern shape and orientation reflect the ellipticity of the dark matter potential, and its rotation is locked to the slow figure rotation of the triaxial dark halo. The bar-like nature of the potential induces non-circular motions in the gas component, including strong bisymmetric flows that can be readily seen as m = 3 harmonic perturbations in the H I line-of-sight velocity fields. Similar bisymmetric flows are seen in many galaxies of The HI Nearby Galaxy Survey (THINGS) and Local Irregulars That Trace Luminosity Extremes THINGS (LITTLE THINGS), although on average their amplitudes are a factor of ˜2 weaker than in our simulated discs. Our results indicate that bar-like patterns may arise even when baryons are not dominant, and that they are common enough to warrant careful consideration when analysing the gas kinematics of dwarf galaxy discs.
Dark interactions and cosmological fine-tuning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quartin, Miguel; Calvao, Mauricio O; Joras, Sergio E

2008-05-15

Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied, but there have been claims that observational data seem to narrow (some of) them down to something annoyingly close to the {Lambda}CDM (CDM: cold dark matter) model, thus greatly reducing their ability to deal with the problem in the first place. The smallness problem of the initial energy density of dark energy has also been a target of cosmological models in recent years. Making use of a moderately general coupling scheme,more » this paper aims to unite these different approaches and shed some light on whether this class of models has any true perspective in suppressing the aforementioned issues that plague our current understanding of the universe, in a quantitative and unambiguous way.« less
Understanding the core-halo relation of quantum wave dark matter from 3D simulations.

PubMed

Schive, Hsi-Yu; Liao, Ming-Hsuan; Woo, Tak-Pong; Wong, Shing-Kwong; Chiueh, Tzihong; Broadhurst, Tom; Hwang, W-Y Pauchy

2014-12-31

We examine the nonlinear structure of gravitationally collapsed objects that form in our simulations of wavelike cold dark matter, described by the Schrödinger-Poisson (SP) equation with a particle mass ∼10(-22) eV. A distinct gravitationally self-bound solitonic core is found at the center of every halo, with a profile quite different from cores modeled in the warm or self-interacting dark matter scenarios. Furthermore, we show that each solitonic core is surrounded by an extended halo composed of large fluctuating dark matter granules which modulate the halo density on a scale comparable to the diameter of the solitonic core. The scaling symmetry of the SP equation and the uncertainty principle tightly relate the core mass to the halo specific energy, which, in the context of cosmological structure formation, leads to a simple scaling between core mass (Mc) and halo mass (Mh), Mc∝a(-1/2)Mh(1/3), where a is the cosmic scale factor. We verify this scaling relation by (i) examining the internal structure of a statistical sample of virialized halos that form in our 3D cosmological simulations and by (ii) merging multiple solitons to create individual virialized objects. Sufficient simulation resolution is achieved by adaptive mesh refinement and graphic processing units acceleration. From this scaling relation, present dwarf satellite galaxies are predicted to have kiloparsec-sized cores and a minimum mass of ∼10(8)M⊙, capable of solving the small-scale controversies in the cold dark matter model. Moreover, galaxies of 2×10(12)M⊙ at z=8 should have massive solitonic cores of ∼2×10(9)M⊙ within ∼60 pc. Such cores can provide a favorable local environment for funneling the gas that leads to the prompt formation of early stellar spheroids and quasars.
Substructure of fuzzy dark matter haloes

NASA Astrophysics Data System (ADS)

Du, Xiaolong; Behrens, Christoph; Niemeyer, Jens C.

2017-02-01

We derive the halo mass function (HMF) for fuzzy dark matter (FDM) by solving the excursion set problem explicitly with a mass-dependent barrier function, which has not been done before. We find that compared to the naive approach of the Sheth-Tormen HMF for FDM, our approach has a higher cutoff mass and the cutoff mass changes less strongly with redshifts. Using merger trees constructed with a modified version of the Lacey & Cole formalism that accounts for suppressed small-scale power and the scale-dependent growth of FDM haloes and the semi-analytic GALACTICUS code, we study the statistics of halo substructure including the effects from dynamical friction and tidal stripping. We find that if the dark matter is a mixture of cold dark matter (CDM) and FDM, there will be a suppression on the halo substructure on small scales which may be able to solve the missing satellites problem faced by the pure CDM model. The suppression becomes stronger with increasing FDM fraction or decreasing FDM mass. Thus, it may be used to constrain the FDM model.
Modifying gravity: you cannot always get what you want.

PubMed

Starkman, Glenn D

2011-12-28

The combination of general relativity (GR) and the Standard Model of particle physics disagrees with numerous observations on scales from our Solar System up. In the canonical concordance model of Lambda cold dark matter (ΛCDM) cosmology, many of these contradictions between theory and data are removed or alleviated by the introduction of three completely independent new components of stress energy--the inflaton, dark matter and dark energy. Each of these in its turn is meant to have dominated (or to currently dominate) the dynamics of the Universe. There is, until now, no non-gravitational evidence for any of these dark sectors, nor is there evidence (though there may be motivation) for the required extension of the Standard Model. An alternative is to imagine that it is GR that must be modified to account for some or all of these disagreements. Certain coincidences of scale even suggest that one might expect not to make independent modifications of the theory to replace each of the three dark sectors. Because they must address the most different types of data, attempts to replace dark matter with modified gravity are the most controversial. A phenomenological model (or family of models), modified Newtonian dynamics, has, over the last few years, seen several covariant realizations. We discuss a number of challenges that any model that seeks to replace dark matter with modified gravity must face: the loss of Birkhoff's theorem, and the calculational simplifications it implies; the failure to explain clusters, whether static or interacting, and the consequent need to introduce dark matter of some form, whether hot dark matter neutrinos or dark fields that arise in new sectors of the modified gravity theory; the intrusion of cosmological expansion into the modified force law, which arises precisely because of the coincidence in scale between the centripetal acceleration at which Newtonian gravity fails in galaxies and the cosmic acceleration. We conclude with the observation that, although modified gravity may indeed manage to replace dark matter, it is likely to do so by becoming or at least incorporating a dark matter theory itself.
A filament of dark matter between two clusters of galaxies.

PubMed

Dietrich, Jörg P; Werner, Norbert; Clowe, Douglas; Finoguenov, Alexis; Kitching, Tom; Miller, Lance; Simionescu, Aurora

2012-07-12

It is a firm prediction of the concordance cold-dark-matter cosmological model that galaxy clusters occur at the intersection of large-scale structure filaments. The thread-like structure of this 'cosmic web' has been traced by galaxy redshift surveys for decades. More recently, the warm–hot intergalactic medium (a sparse plasma with temperatures of 10(5) kelvin to 10(7) kelvin) residing in low-redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying dark-matter skeleton, which should contain more than half of all matter, has remained elusive, because earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignments of dark and luminous matter. Here we report the detection of a dark-matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft-X-ray emission, and contributes a mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. By combining this result with X-ray observations, we can place an upper limit of 0.09 on the hot gas fraction (the mass of X-ray-emitting gas divided by the total mass) in the filament.
Comparison of the linear bias models in the light of the Dark Energy Survey

NASA Astrophysics Data System (ADS)

Papageorgiou, A.; Basilakos, S.; Plionis, M.

2018-05-01

The evolution of the linear and scale independent bias, based on the most popular dark matter bias models within the Λ cold dark matter (ΛCDM) cosmology, is confronted to that of the Dark Energy Survey (DES) luminous red galaxies (LRGs). Applying a χ2 minimization procedure between models and data, we find that all the considered linear bias models reproduce well the LRG bias data. The differences among the bias models are absorbed in the predicted mass of the dark-matter halo in which LRGs live and which ranges between ˜6 × 1012 and 1.4 × 1013 h-1 M⊙, for the different bias models. Similar results, reaching however a maximum value of ˜2 × 1013 h-1 M⊙, are found by confronting the SDSS (2SLAQ) Large Red Galaxies clustering with theoretical clustering models, which also include the evolution of bias. This later analysis also provides a value of Ωm = 0.30 ± 0.01, which is in excellent agreement with recent joint analyses of different cosmological probes and the reanalysis of the Planck data.
Large-scale structure after COBE: Peculiar velocities and correlations of cold dark matter halos

NASA Technical Reports Server (NTRS)

Zurek, Wojciech H.; Quinn, Peter J.; Salmon, John K.; Warren, Michael S.

1994-01-01

Large N-body simulations on parallel supercomputers allow one to simultaneously investigate large-scale structure and the formation of galactic halos with unprecedented resolution. Our study shows that the masses as well as the spatial distribution of halos on scales of tens of megaparsecs in a cold dark matter (CDM) universe with the spectrum normalized to the anisotropies detected by Cosmic Background Explorer (COBE) is compatible with the observations. We also show that the average value of the relative pairwise velocity dispersion sigma(sub v) - used as a principal argument against COBE-normalized CDM models-is significantly lower for halos than for individual particles. When the observational methods of extracting sigma(sub v) are applied to the redshift catalogs obtained from the numerical experiments, estimates differ significantly between different observation-sized samples and overlap observational estimates obtained following the same procedure.
Redshift space clustering of galaxies and cold dark matter model

NASA Technical Reports Server (NTRS)

Bahcall, Neta A.; Cen, Renyue; Gramann, Mirt

1993-01-01

The distorting effect of peculiar velocities on the power speturm and correlation function of IRAS and optical galaxies is studied. The observed redshift space power spectra and correlation functions of IRAS and optical the galaxies over the entire range of scales are directly compared with the corresponding redshift space distributions using large-scale computer simulations of cold dark matter (CDM) models in order to study the distortion effect of peculiar velocities on the power spectrum and correlation function of the galaxies. It is found that the observed power spectrum of IRAS and optical galaxies is consistent with the spectrum of an Omega = 1 CDM model. The problems that such a model currently faces may be related more to the high value of Omega in the model than to the shape of the spectrum. A low-density CDM model is also investigated and found to be consistent with the data.
Simulations of the Formation and Evolution of X-ray Clusters

NASA Astrophysics Data System (ADS)

Bryan, G. L.; Klypin, A.; Norman, M. L.

1994-05-01

We describe results from a set of Omega = 1 Cold plus Hot Dark Matter (CHDM) and Cold Dark Matter (CDM) simulations. We examine the formation and evolution of X-ray clusters in a cosmological setting with sufficient numbers to perform statistical analysis. We find that CDM, normalized to COBE, seems to produce too many large clusters, both in terms of the luminosity (dn/dL) and temperature (dn/dT) functions. The CHDM simulation produces fewer clusters and the temperature distribution (our numerically most secure result) matches observations where they overlap. The computed cluster luminosity function drops below observations, but we are almost surely underestimating the X-ray luminosity. Because of the lower fluctuations in CHDM, there are only a small number of bright clusters in our simulation volume; however we can use the simulated clusters to fix the relation between temperature and velocity dispersion, allowing us to use collisionless N-body codes to probe larger length scales with correspondingly brighter clusters. The hydrodynamic simulations have been performed with a hybrid particle-mesh scheme for the dark matter and a high resolution grid-based piecewise parabolic method for the adiabatic gas dynamics. This combination has been implemented for massively parallel computers, allowing us to achive grids as large as 512(3) .
Creation of a Mock Universe: Photometric Astronomy on Simulation

NASA Astrophysics Data System (ADS)

Nene, Ajinkya; Rodriguez, Aldo; Primack, Joel R.

2016-01-01

A major focus in astronomy is to understand how galaxies form and evolve in the Universe. The current model known as ΛCDM explains that galaxies form and evolve in halos composed of cold dark matter. In an effort to understand galactic processes in relation to halos, researchers have developed statistical methods to connect galaxies to their halos. One of these approaches is abundance matching: a technique in which the galaxy number density of a property is connected to a theoretical halo number density. In this study, we exploit the abundance matching technique and create a massive photometric mock catalog. We populate millions of dark matter halos in the Bolshoi-Planck Simulation with highly defined galaxies that each has: luminosities, magnitudes, fluxes, masses, and Sérsic profiles. Our catalog acts as an interface between cold dark matter theory and observations: astronomers can use this mock galaxy catalog to compare ΛCDM predictions to observations as well as constrain galaxy formation models. Using our catalog, we can make powerful predictions about both theoretical data and about future astronomical surveys. We demonstrate the usability of our catalog through angular power spectra. Specifically, we shed light on the controversial intrahalo light phenomena. We emphasize that this is the first catalog of this accuracy and size and has incredible potential for application.
[Dark matter and dark energy of the universe].

PubMed

Aguilar Peris, José

2005-01-01

At the turn of the 20th Century, the Universe was thought to consist of our solar system, the Sun, planets, satellites and comets, floating under the Milky Way. The astronomers were ignorant of the existence of galaxies, clusters, quasars and black holes. Over the last ten years the Cosmology has made remarkable progress in our understanding of the composition of the Universe: 23 per cent is in an unknown form called dark matter; 73 per cent in another form called dark energy; 3 per cent is made of free hydrogen and helium atoms; 0.5 per cent makes up all the light we see in the night including the stars, clusters and superclusters; 0.3 per cent is in free neutrino particles; and finally, 0.03 per cent is in the heavier nuclei of which the Sun, the Earth and ourselves are made. In this work we study specially the dark matter and the dark energy. The first one appears to be attached to galaxies, and astronomers agree that it is cold, meaning that the particles that make up that matter are not moving fast. Very recently astronomers discovered that a tremendous amount of the so-cahled dark energy exists and that it is pushing and accelerating the expansion of the Universe. Should this expansion continue for another 14,000 million years, the sky will darken with only a handful of galaxies remaining visible.
Power spectrum of dark matter substructure in strong gravitational lenses

NASA Astrophysics Data System (ADS)

Diaz Rivero, Ana; Cyr-Racine, Francis-Yan; Dvorkin, Cora

2018-01-01

Studying the smallest self-bound dark matter structure in our Universe can yield important clues about the fundamental particle nature of dark matter. Galaxy-scale strong gravitational lensing provides a unique way to detect and characterize dark matter substructures at cosmological distances from the Milky Way. Within the cold dark matter (CDM) paradigm, the number of low-mass subhalos within lens galaxies is expected to be large, implying that their contribution to the lensing convergence field is approximately Gaussian and could thus be described by their power spectrum. We develop here a general formalism to compute from first principles the substructure convergence power spectrum for different populations of dark matter subhalos. As an example, we apply our framework to two distinct subhalo populations: a truncated Navarro-Frenk-White subhalo population motivated by standard CDM, and a truncated cored subhalo population motivated by self-interacting dark matter (SIDM). We study in detail how the subhalo abundance, mass function, internal density profile, and concentration affect the amplitude and shape of the substructure power spectrum. We determine that the power spectrum is mostly sensitive to a specific combination of the subhalo abundance and moments of the mass function, as well as to the average tidal truncation scale of the largest subhalos included in the analysis. Interestingly, we show that the asymptotic slope of the substructure power spectrum at large wave number reflects the internal density profile of the subhalos. In particular, the SIDM power spectrum exhibits a characteristic steepening at large wave number absent in the CDM power spectrum, opening the possibility of using this observable, if at all measurable, to discern between these two scenarios.
Hierarchical phase space structure of dark matter haloes: Tidal debris, caustics, and dark matter annihilation

NASA Astrophysics Data System (ADS)

Afshordi, Niayesh; Mohayaee, Roya; Bertschinger, Edmund

2009-04-01

Most of the mass content of dark matter haloes is expected to be in the form of tidal debris. The density of debris is not constant, but rather can grow due to formation of caustics at the apocenters and pericenters of the orbit, or decay as a result of phase mixing. In the phase space, the debris assemble in a hierarchy that is truncated by the primordial temperature of dark matter. Understanding this phase structure can be of significant importance for the interpretation of many astrophysical observations and, in particular, dark matter detection experiments. With this purpose in mind, we develop a general theoretical framework to describe the hierarchical structure of the phase space of cold dark matter haloes. We do not make any assumption of spherical symmetry and/or smooth and continuous accretion. Instead, working with correlation functions in the action-angle space, we can fully account for the hierarchical structure (predicting a two-point correlation function ∝ΔJ-1.6 in the action space), as well as the primordial discreteness of the phase space. As an application, we estimate the boost to the dark matter annihilation signal due to the structure of the phase space within virial radius: the boost due to the hierarchical tidal debris is of order unity, whereas the primordial discreteness of the phase structure can boost the total annihilation signal by up to an order of magnitude. The latter is dominated by the regions beyond 20% of the virial radius, and is largest for the recently formed haloes with the least degree of phase mixing. Nevertheless, as we argue in a companion paper, the boost due to small gravitationally-bound substructure can dominate this effect at low redshifts.
Large scale structure in universes dominated by cold dark matter

NASA Technical Reports Server (NTRS)

Bond, J. Richard

1986-01-01

The theory of Gaussian random density field peaks is applied to a numerical study of the large-scale structure developing from adiabatic fluctuations in models of biased galaxy formation in universes with Omega = 1, h = 0.5 dominated by cold dark matter (CDM). The angular anisotropy of the cross-correlation function demonstrates that the far-field regions of cluster-scale peaks are asymmetric, as recent observations indicate. These regions will generate pancakes or filaments upon collapse. One-dimensional singularities in the large-scale bulk flow should arise in these CDM models, appearing as pancakes in position space. They are too rare to explain the CfA bubble walls, but pancakes that are just turning around now are sufficiently abundant and would appear to be thin walls normal to the line of sight in redshift space. Large scale streaming velocities are significantly smaller than recent observations indicate. To explain the reported 700 km/s coherent motions, mass must be significantly more clustered than galaxies with a biasing factor of less than 0.4 and a nonlinear redshift at cluster scales greater than one for both massive neutrino and cold models.
Dark energy and the quietness of the local Hubble flow

NASA Astrophysics Data System (ADS)

Axenides, M.; Perivolaropoulos, L.

2002-06-01

The linearity and quietness of the local (<10 Mpc) Hubble flow (LHF) in view of the very clumpy local universe is a long standing puzzle in standard and in open CDM (cold dark matter) cosmogony. The question addressed in this paper is whether the antigravity component of the recently discovered dark energy can cool the velocity flow enough to provide a solution to this puzzle. We calculate the growth of matter fluctuations in a flat universe containing a fraction ΩX(t0) of dark energy obeying the time independent equation of state pX=wρX. We find that dark energy can indeed cool the LHF. However the dark energy parameter values required to make the predicted velocity dispersion consistent with the observed value vrms~=40 km/s have been ruled out by other observational tests constraining the dark energy parameters w and ΩX. Therefore despite the claims of recent qualitative studies, dark energy with time independent equation of state cannot by itself explain the quietness and linearity of the local Hubble flow.

Tidal disruption of fuzzy dark matter subhalo cores

NASA Astrophysics Data System (ADS)

Du, Xiaolong; Schwabe, Bodo; Niemeyer, Jens C.; Bürger, David

2018-03-01

We study tidal stripping of fuzzy dark matter (FDM) subhalo cores using simulations of the Schrödinger-Poisson equations and analyze the dynamics of tidal disruption, highlighting the differences with standard cold dark matter. Mass loss outside of the tidal radius forces the core to relax into a less compact configuration, lowering the tidal radius. As the characteristic radius of a solitonic core scales inversely with its mass, tidal stripping results in a runaway effect and rapid tidal disruption of the core once its central density drops below 4.5 times the average density of the host within the orbital radius. Additionally, we find that the core is deformed into a tidally locked ellipsoid with increasing eccentricities until it is completely disrupted. Using the core mass loss rate, we compute the minimum mass of cores that can survive several orbits for different FDM particle masses and compare it with observed masses of satellite galaxies in the Milky Way.
INTEGRAL and Light Dark Matter

NASA Astrophysics Data System (ADS)

Cassé, M.; Fayet, P.; Schanne, S.; Cordier, B.; Paul, J.

2004-10-01

The nature of Dark Matter remains one of the outstanding questions of modern astrophysics. The success of the Cold Dark Matter cosmological model argues strongly in favor of a major component of the dark matter being in the form of elementary particles, not yet discovered. Based on earlier theoretical considerations, a possible link between the recent SPI/INTEGRAL measurement of an intense and extended emission of 511 keV photons (the hallmark of positron annihilation) from the central Galaxy, and this mysterious component of the Universe, has been established advocating the existence of a light dark matter (LDM) particle (at variance with the neutralino, in general considered as very heavy). We show that it can explain the 511 keV emission mapped with SPI/INTEGRAL without overproducing undesirable signals like high energy gamma-rays arising from π? decays, and radio synchrotron photons emitted by high energy positrons circulating in magnetic fields. Combining the annihilation line constraint with the cosmological one (i.e. that the relic LDM energy density reaches about 23% of the density of the Universe), one can restrict the main properties of the light dark matter particle. Its mass should lie between ≈ 1 and 100 MeV, and the required annihilation cross section, velocity dependent, should be significantly larger than for weak interactions, and may be induced by the virtual production of a new light neutral spin 1 boson U. On astrophysical grounds, the best target to validate the LDM proposal seems to be the observation by SPI/INTEGRAL and future gamma ray telescopes of the annihilation line from the Sagittarius dwarf galaxy and the Palomar-13 globular cluster, thought to be dominated by dark matter. Key words: Galaxy center; dark matter; gamma rays. 0Corresponding author: m.casse@cea.fr 3 Institut d'Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris, France 4 Fédération de Recherche Astroparticule et Cosmologie, Coll`ege de France, 11 Place Marcellin Berthelot, 75231 Paris, France
Formation of large-scale structure from cosmic strings and massive neutrinos

NASA Technical Reports Server (NTRS)

Scherrer, Robert J.; Melott, Adrian L.; Bertschinger, Edmund

1989-01-01

Numerical simulations of large-scale structure formation from cosmic strings and massive neutrinos are described. The linear power spectrum in this model resembles the cold-dark-matter power spectrum. Galaxy formation begins early, and the final distribution consists of isolated density peaks embedded in a smooth background, leading to a natural bias in the distribution of luminous matter. The distribution of clustered matter has a filamentary appearance with large voids.
Non-linear clustering in the cold plus hot dark matter model

NASA Astrophysics Data System (ADS)

Bonometto, Silvio A.; Borgani, Stefano; Ghigna, Sebastiano; Klypin, Anatoly; Primack, Joel R.

1995-03-01

The main aim of this work is to find out if hierarchical scaling, observed in galaxy clustering, can be dynamically explained by studying N-body simulations. Previous analyses of dark matter (DM) particle distributions indicated heavy distortions with respect to the hierarchical pattern. Here, we shall describe how such distortions are to be interpreted and why they can be fully reconciled with the observed galaxy clustering. This aim is achieved by using high-resolution (512^3 grid-points) particle-mesh (PM) N-body simulations to follow the development of non-linear clustering in a Omega=1 universe, dominated either by cold dark matter (CDM) or by a mixture of cold+hot dark matter (CHDM) with Omega_cold=0.6, and Omega_hot=0.3 and Omega_baryon=0.1 a simulation box of side 100 Mpc (h=0.5) is used. We analyse two CHDM realizations with biasing factor b=1.5 (COBE normalization), starting from different initial random numbers, and compare them with CDM simulations with b=1 (COBE-compatible) and b=1.5. We evaluate high-order correlation functions and the void probability function (VPF). Correlation functions are obtained from both counts in cells and counts of neighbours. The analysis is carried out for DM particles and for galaxies identified as massive haloes of the evolved density field. We confirm that clustering of DM particles systematically exhibits deviations from hierarchical scaling, although the deviation increases somewhat in redshift space. Deviations from the hierarchical scaling of DM particles are found to be related to the spectrum shape, in a way that indicates that such distortions arise from finite sampling effects. We identify galaxy positions in the simulations and show that, quite differently from the DM particle background, galaxies follow hierarchical scaling (S_q=xi_q/& xgr^q-1_2=consta nt) far more closely, with reduced skewness and kurtosis coefficients S_3~2.5 and S_4~7.5, in general agreement with observational results. Unlike DM, the scaling of galaxy clustering is must marginally affected by redshift distortions and is obtained for both CDM and CHDM models. Hierarchical scaling in simulations is confirmed by VPF analysis. Also in this case, we find substantial agreement with observational findings.
An ecological approach to problems of Dark Energy, Dark Matter, MOND and Neutrinos

NASA Astrophysics Data System (ADS)

Zhao, Hong Sheng

2008-11-01

Modern astronomical data on galaxy and cosmological scales have revealed powerfully the existence of certain dark sectors of fundamental physics, i.e., existence of particles and fields outside the standard models and inaccessible by current experiments. Various approaches are taken to modify/extend the standard models. Generic theories introduce multiple de-coupled fields A, B, C, each responsible for the effects of DM (cold supersymmetric particles), DE (Dark Energy) effect, and MG (Modified Gravity) effect respectively. Some theories use adopt vanilla combinations like AB, BC, or CA, and assume A, B, C belong to decoupled sectors of physics. MOND-like MG and Cold DM are often taken as antagnising frameworks, e.g. in the muddled debate around the Bullet Cluster. Here we argue that these ad hoc divisions of sectors miss important clues from the data. The data actually suggest that the physics of all dark sectors is likely linked together by a self-interacting oscillating field, which governs a chameleon-like dark fluid, appearing as DM, DE and MG in different settings. It is timely to consider an interdisciplinary approach across all semantic boundaries of dark sectors, treating the dark stress as one identity, hence accounts for several "coincidences" naturally.
Falsification of dark energy by fluid mechanics

NASA Astrophysics Data System (ADS)

Gibson, Carl H.

2011-11-01

The 2011 Nobel Prize in Physics has been awarded for the discovery from observations of increased supernovae dimness interpreted as distance, so that the Universe expansion rate has changed from a rate decreasing since the big bang to one that is now increasing, driven by anti-gravity forces of a mysterious dark energy material comprising 70% of the Universe mass-energy. Fluid mechanical considerations falsify both the accelerating expansion and dark energy concepts. Kinematic viscosity is neglected in current stan- dard models of self-gravitational structure formation, which rely on cold dark matter CDM condensations and clusterings that are also falsified by fluid mechanics. Weakly collisional CDM particles do not condense but diffuse away. Photon viscosity predicts su- perclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the plasma fragments into Earth-mass gas planets in trillion planet clumps (proto-globular-star-cluster PGCs). The hydrogen planets freeze to form the dark matter of galaxies and merge to form their stars. Dark energy is a systematic dimming error for Supernovae Ia caused by dark matter planets near hot white dwarf stars at the Chandrasekhar carbon limit. Evaporated planet atmospheres may or may not scatter light from the events depending on the line of sight.
A NEWLY FORMING COLD FLOW PROTOGALACTIC DISK, A SIGNATURE OF COLD ACCRETION FROM THE COSMIC WEB

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, D. Christopher; Matuszewski, Mateusz; Morrissey, Patrick

How galaxies form from, and are fueled by, gas from the intergalactic medium (IGM) remains one of the major unsolved problems in galaxy formation. While the classical Cold Dark Matter paradigm posits galaxies forming from cooling virialized gas, recent theory and numerical simulations have highlighted the importance of cold accretion flows—relatively cool ( T ∼ few × 104 K) unshocked gas streaming along filaments into dark matter halos, including hot, massive, high-redshift halos. These flows are thought to deposit gas and angular momentum into the circumgalactic medium resulting in disk- or ring-like structures, eventually coalescing into galaxies forming at filamentarymore » intersections. We earlier reported a bright, Ly α emitting filament near the QSO HS1549+19 at redshift z = 2.843 discovered with the Palomar Cosmic Web Imager. We now report that the bright part of this filament is an enormous ( R > 100 kpc) rotating structure of hydrogen gas with a disk-like velocity profile consistent with a 4 × 10{sup 12} M {sub ⊙} halo. The orbital time of the outer part of the what we term a “protodisk” is comparable to the virialization time and the age of the universe at this redshift. We propose that this protodisk can only have recently formed from cold gas flowing directly from the cosmic web.« less
Probing the nature of dark matter through the metal enrichment of the intergalactic medium

NASA Astrophysics Data System (ADS)

Bremer, Jonas; Dayal, Pratika; Ryan-Weber, Emma V.

2018-06-01

We focus on exploring the metal enrichment of the intergalactic medium (IGM) in cold and warm (1.5 and 3 keV) dark matter (DM) cosmologies, and the constraints this yields on the DM particle mass, using a semi-analytic model, DELPHI, that jointly tracks the DM and baryonic assembly of galaxies at z ≃ 4-20 including both supernova (SN) and (a range of) reionization feedback (models). We find that while M_{UV}≳ -15 galaxies contribute half of all IGM metals in the cold dark matter (CDM) model by z ≃ 4.5, given the suppression of low-mass haloes, larger haloes with M_{UV}≲ -15 provide about 80 per cent of the IGM metal budget in 1.5 keV warm dark matter (WDM) models using two different models for the metallicity of the interstellar medium. Our results also show that the only models compatible with two different high-redshift data sets, provided by the evolving ultraviolet luminosity function (UV LF) at z ≃ 6-10 and IGM metal density, are standard CDM and 3 keV WDM that do not include any reionization feedback; a combination of the UV LF and the Díaz et al. point provides a weaker constraint, allowing CDM and 3 and 1.5 keV WDM models with SN feedback only, as well as CDM with complete gas suppression of all haloes with v_{circ} ≲ 30 km s^{-1}. Tightening the error bars on the IGM metal enrichment, future observations, at z ≳ 5.5, could therefore represent an alternative way of shedding light on the nature of DM.
The angular momentum of disc galaxies: implications for gas accretion, outflows, and dynamical friction

NASA Astrophysics Data System (ADS)

Dutton, Aaron A.; van den Bosch, Frank C.

2012-03-01

We combine constraints on the galaxy-dark matter connection with structural and dynamical scaling relations to investigate the angular momentum content of disc galaxies. For haloes with masses in the interval 1011.3 M⊙≲Mvir≲ 1012.7 M⊙ we find that the galaxy spin parameters are basically independent of halo mass with ?. This is significantly lower than for relaxed Λcold dark matter (ΛCDM) haloes, which have an average spin parameter ?. The average ratio between the specific angular momentum of disc galaxies and their host dark matter haloes is therefore ?. This calls into question a standard assumption made in the majority of all (semi-analytical) models for (disc) galaxy formation, namely that ?. Using simple disc formation models we show that it is particularly challenging to understand why ? is independent of halo mass, while the galaxy formation efficiency (ɛGF; proportional to the ratio of galaxy mass to halo mass) reveals a strong halo mass dependence. We argue that the empirical scaling relations between ɛGF, ? and halo mass require both feedback (i.e. galactic outflows) and angular momentum transfer from the baryons to the dark matter (i.e. dynamical friction). Most importantly, the efficiency of angular momentum loss needs to decrease with increasing halo mass. Such a mass dependence may reflect a bias against forming stable discs in high-mass, low-spin haloes or a transition from cold-mode accretion in low-mass haloes to hot-mode accretion at the massive end. However, current hydrodynamical simulations of galaxy formation, which should include these processes, seem unable to reproduce the empirical relation between ɛGF and ?. We conclude that the angular momentum build-up of galactic discs remains poorly understood.
THE VELOCITY WIDTH FUNCTION OF GALAXIES FROM THE 40% ALFALFA SURVEY: SHEDDING LIGHT ON THE COLD DARK MATTER OVERABUNDANCE PROBLEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Papastergis, Emmanouil; Martin, Ann M.; Giovanelli, Riccardo

The ongoing Arecibo Legacy Fast ALFA (ALFALFA) survey is a wide-area, extragalactic HI-line survey conducted at the Arecibo Observatory. Sources have so far been extracted over {approx}3000 deg{sup 2} of sky (40% of its final area), resulting in the largest HI-selected sample to date. We measure the space density of HI-bearing galaxies as a function of their observed velocity width (uncorrected for inclination) down to w = 20 km s{sup -1}, a factor of two lower than the previous generation HI Parkes All-Sky Survey. We confirm previous results that indicate a substantial discrepancy between the observational distribution and the theoreticalmore » one expected in a cold dark matter (CDM) universe, at low widths. In particular, a comparison with synthetic galaxy samples populating state-of-the-art CDM simulations imply a factor of {approx}8 difference in the abundance of galaxies with w = 50 km s{sup -1} (increasing to a factor of {approx}100 when extrapolated to the ALFALFA limit of w = 20 km s{sup -1}). We furthermore identify possible solutions, including a keV warm dark matter scenario and the fact that HI disks in low-mass galaxies are usually not extended enough to probe the full amplitude of the galactic rotation curve. In this latter case, we can statistically infer the relationship between the measured HI rotational velocity of a galaxy and the mass of its host CDM halo. Observational verification of the presented relationship at low velocities would provide an important test of the validity of the established dark matter model.« less
The Angular Momentum of Baryons and Dark Matter Halos Revisited

NASA Technical Reports Server (NTRS)

Kimm, Taysun; Devriendt, Julien; Slyz, Adrianne; Pichon, Christophe; Kassin, Susan A.; Dubois, Yohan

2011-01-01

Recent theoretical studies have shown that galaxies at high redshift are fed by cold, dense gas filaments, suggesting angular momentum transport by gas differs from that by dark matter. Revisiting this issue using high-resolution cosmological hydrodynamics simulations with adaptive-mesh refinement (AMR), we find that at the time of accretion, gas and dark matter do carry a similar amount of specific angular momentum, but that it is systematically higher than that of the dark matter halo as a whole. At high redshift, freshly accreted gas rapidly streams into the central region of the halo, directly depositing this large amount of angular momentum within a sphere of radius r = 0.1R(sub vir). In contrast, dark matter particles pass through the central region unscathed, and a fraction of them ends up populating the outer regions of the halo (r/R(sub vir) > 0.1), redistributing angular momentum in the process. As a result, large-scale motions of the cosmic web have to be considered as the origin of gas angular momentum rather than its virialised dark matter halo host. This generic result holds for halos of all masses at all redshifts, as radiative cooling ensures that a significant fraction of baryons remain trapped at the centre of the halos. Despite this injection of angular momentum enriched gas, we predict an amount for stellar discs which is in fair agreement with observations at z=0. This arises because the total specific angular momentum of the baryons (gas and stars) remains close to that of dark matter halos. Indeed, our simulations indicate that any differential loss of angular momentum amplitude between the two components is minor even though dark matter halos continuously lose between half and two-thirds of their specific angular momentum modulus as they evolve. In light of our results, a substantial revision of the standard theory of disc formation seems to be required. We propose a new scenario where gas efficiently carries the angular momentum generated by large-scale structure motions deep inside dark matter halos, redistributing it only in the vicinity of the disc.
Dark Matter Equation of State through Cosmic History

NASA Astrophysics Data System (ADS)

Kopp, Michael; Skordis, Constantinos; Thomas, Daniel B.; Ilić, Stéphane

2018-06-01

Cold dark matter is a crucial constituent of the current concordance cosmological model. Having a vanishing equation of state (EOS), its energy density scales with the inverse cosmic volume and is thus uniquely described by a single number, its present abundance. We test the inverse cosmic volume law for dark matter (DM) by allowing its EOS to vary independently in eight redshift bins in the range z =105 and z =0 . We use the latest measurements of the cosmic microwave background radiation from the Planck satellite and supplement them with baryon acoustic oscillation (BAO) data from the 6dF and SDSS-III BOSS surveys and with the Hubble Space Telescope (HST) key project data. We find no evidence for nonzero EOS in any of the eight redshift bins. With Planck data alone, the DM abundance is most strongly constrained around matter-radiation equality ωgeq=0.119 3-0.0035+0.0036 (95% C.L.), whereas its present-day value is more weakly constrained: ωg(0 )=0.1 6-0.10+0.12 (95% C.L.). Adding BAO or HST data does not significantly change the ωgeq constraint, while ωg(0 ) tightens to 0.16 0-0.065+0.069 (95% C.L.) and 0.12 4-0.067+0.081 (95% C.L.), respectively. Our results constrain for the first time the level of "coldness" required of the DM across various cosmological epochs and show that the DM abundance is strictly positive at all times.
Dark Matter Equation of State through Cosmic History.

PubMed

Kopp, Michael; Skordis, Constantinos; Thomas, Daniel B; Ilić, Stéphane

2018-06-01

Cold dark matter is a crucial constituent of the current concordance cosmological model. Having a vanishing equation of state (EOS), its energy density scales with the inverse cosmic volume and is thus uniquely described by a single number, its present abundance. We test the inverse cosmic volume law for dark matter (DM) by allowing its EOS to vary independently in eight redshift bins in the range z=10^{5} and z=0. We use the latest measurements of the cosmic microwave background radiation from the Planck satellite and supplement them with baryon acoustic oscillation (BAO) data from the 6dF and SDSS-III BOSS surveys and with the Hubble Space Telescope (HST) key project data. We find no evidence for nonzero EOS in any of the eight redshift bins. With Planck data alone, the DM abundance is most strongly constrained around matter-radiation equality ω_{g}^{eq}=0.1193_{-0.0035}^{+0.0036} (95% C.L.), whereas its present-day value is more weakly constrained: ω_{g}^{(0)}=0.16_{-0.10}^{+0.12} (95% C.L.). Adding BAO or HST data does not significantly change the ω_{g}^{eq} constraint, while ω_{g}^{(0)} tightens to 0.160_{-0.065}^{+0.069} (95% C.L.) and 0.124_{-0.067}^{+0.081} (95% C.L.), respectively. Our results constrain for the first time the level of "coldness" required of the DM across various cosmological epochs and show that the DM abundance is strictly positive at all times.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Capela, Fabio; Ramazanov, Sabir, E-mail: fc403@cam.ac.uk, E-mail: Sabir.Ramazanov@ulb.ac.be

At large scales and for sufficiently early times, dark matter is described as a pressureless perfect fluid—dust— non-interacting with Standard Model fields. These features are captured by a simple model with two scalars: a Lagrange multiplier and another playing the role of the velocity potential. That model arises naturally in some gravitational frameworks, e.g., the mimetic dark matter scenario. We consider an extension of the model by means of higher derivative terms, such that the dust solutions are preserved at the background level, but there is a non-zero sound speed at the linear level. We associate this Modified Dust withmore » dark matter, and study the linear evolution of cosmological perturbations in that picture. The most prominent effect is the suppression of their power spectrum for sufficiently large cosmological momenta. This can be relevant in view of the problems that cold dark matter faces at sub-galactic scales, e.g., the missing satellites problem. At even shorter scales, however, perturbations of Modified Dust are enhanced compared to the predictions of more common particle dark matter scenarios. This is a peculiarity of their evolution in radiation dominated background. We also briefly discuss clustering of Modified Dust. We write the system of equations in the Newtonian limit, and sketch the possible mechanism which could prevent the appearance of caustic singularities. The same mechanism may be relevant in light of the core-cusp problem.« less
Novel test of modified Newtonian dynamics with gas rich galaxies.

PubMed

McGaugh, Stacy S

2011-03-25

The current cosmological paradigm, the cold dark matter model with a cosmological constant, requires that the mass-energy of the Universe be dominated by invisible components: dark matter and dark energy. An alternative to these dark components is that the law of gravity be modified on the relevant scales. A test of these ideas is provided by the baryonic Tully-Fisher relation (BTFR), an empirical relation between the observed mass of a galaxy and its rotation velocity. Here, I report a test using gas rich galaxies for which both axes of the BTFR can be measured independently of the theories being tested and without the systematic uncertainty in stellar mass that affects the same test with star dominated spirals. The data fall precisely where predicted a priori by the modified Newtonian dynamics. The scatter in the BTFR is attributable entirely to observational uncertainty, consistent with a single effective force law.
On the observability of coupled dark energy with cosmic voids

NASA Astrophysics Data System (ADS)

Sutter, P. M.; Carlesi, Edoardo; Wandelt, Benjamin D.; Knebe, Alexander

2015-01-01

Taking N-body simulations with volumes and particle densities tuned to match the sloan digital sky survey DR7 spectroscopic main sample, we assess the ability of current void catalogues to distinguish a model of coupled dark matter-dark energy from Λ cold dark matter cosmology using properties of cosmic voids. Identifying voids with the VIDE toolkit, we find no statistically significant differences in the ellipticities, but find that coupling produces a population of significantly larger voids, possibly explaining the recent result of Tavasoli et al. In addition, we use the universal density profile of Hamaus et al. to quantify the relationship between coupling and density profile shape, finding that the coupling produces broader, shallower, undercompensated profiles for large voids by thinning the walls between adjacent medium-scale voids. We find that these differences are potentially measurable with existing void catalogues once effects from survey geometries and peculiar velocities are taken into account.
Testing cold dark matter models using Hubble flow variations

NASA Astrophysics Data System (ADS)

Shi, Xiangdong

1999-05-01

COBE-normalized flat (matter plus cosmological constant) and open cold dark matter (CDM) models are tested by comparing their expected Hubble flow variations and the observed variations in a Type Ia supernova sample and a Tully-Fisher cluster sample. The test provides a probe of the CDM power spectrum on scales of 0.02h Mpc^-1<~ k<~ 0.2h Mpc^-1, free of the bias factor b. The results favour a low matter content universe, or a flat matter-dominated universe with a very low Hubble constant and/or a very small spectral index n^ps, with the best fits having Ο_0~ 0.3 to 0.4. The test is found to be more discriminative to the open CDM models than to the flat CDM models. For example, the test results are found to be compatible with those from the X-ray cluster abundance measurements at smaller length-scales, and consistent with the galaxy and cluster correlation analysis of Peacock & Dodds at similar length-scales, if our universe is flat; but the results are marginally incompatible with the X-ray cluster abundance measurements if our universe is open. The open CDM results are consistent with that of Peacock & Dodds only if the matter density of the universe is less than about 60 per cent of the critical density. The shortcoming of the test is discussed, so are ways to minimize it.
The peculiar velocities of rich clusters in the hot and cold dark matter scenarios

NASA Technical Reports Server (NTRS)

Rhee, George F.; West, Michael J.; Villumsen, Jens V.

1993-01-01

We present the results of a study of the peculiar velocities of rich clusters of galaxies. The peculiar motion of rich clusters in various cosmological scenarios is of interest for a number of reasons. Observationally, one can measure the peculiar motion of clusters to greater distances than galaxies because cluster peculiar motions can be determined to greater accuracy. One can also test the slope of distance indicator relations using clusters to see if galaxy properties vary with environment. We have used N-body simulations to measure the amplitude and rms cluster peculiar velocity as a function of bias parameter in the hot and cold dark matter scenarios. In addition to measuring the mean and rms peculiar velocity of clusters in the two models, we determined whether the peculiar velocity vector of a given cluster is well aligned with the gravity vector due to all the particles in the simulation and the gravity vector due to the particles present only in the clusters. We have investigated the peculiar velocities of rich clusters of galaxies in the cold dark matter and hot dark matter galaxy formation scenarios. We have derived peculiar velocities and associated errors for the scenarios using four values of the bias parameter ranging from b = 1 to b = 2.5. The growth of the mean peculiar velocity with scale factor has been determined and compared to that predicted by linear theory. In addition, we have compared the orientation of force and velocity in these simulations to see if a program such as that proposed by Bertschinger and Dekel (1989) for elliptical galaxy peculiar motions can be applied to clusters. The method they describe enables one to recover the density field from large scale redshift distance samples. The method makes it possible to do this when only radial velocities are known by assuming that the velocity field is curl free. Our analysis suggests that this program if applied to clusters is only realizable for models with a low value of the bias parameter, i.e., models in which the peculiar velocities of clusters are large enough that the errors do not render the analysis impracticable.
Weighing neutrinos in the scenario of vacuum energy interacting with cold dark matter: application of the parameterized post-Friedmann approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Rui-Yun; Li, Yun-He; Zhang, Jing-Fei

We constrain the neutrino mass in the scenario of vacuum energy interacting with cold dark matter by using current cosmological observations. To avoid the large-scale instability problem in interacting dark energy models, we employ the parameterized post-Friedmann (PPF) approach to do the calculation of perturbation evolution, for the Q = β H ρ{sub c} and Q = β H ρ{sub Λ} models. The current observational data sets used in this work include Planck (cosmic microwave background), BSH (baryon acoustic oscillations, type Ia supernovae, and Hubble constant), and LSS (redshift space distortions and weak lensing). According to the constraint results, wemore » find that β > 0 at more than 1σ level for the Q = β H ρ{sub c} model, which indicates that cold dark matter decays into vacuum energy; while β = 0 is consistent with the current data at 1σ level for the Q = β H ρ{sub Λ} model. Taking the ΛCDM model as a baseline model, we find that a smaller upper limit, ∑ m {sub ν} < 0.11 eV (2σ), is induced by the latest BAO BOSS DR12 data and the Hubble constant measurement H {sub 0} = 73.00 ± 1.75 km s{sup −1} Mpc{sup −1}. For the Q = β H ρ{sub c} model, we obtain ∑ m {sub ν}<0.20 eV (2σ) from Planck+BSH. For the Q = β H ρ{sub Λ} model, ∑ m {sub ν}<0.10 eV (2σ) and ∑ m {sub ν}<0.14 eV (2σ) are derived from Planck+BSH and Planck+BSH+LSS, respectively. We show that these smaller upper limits on ∑ m {sub ν} are affected more or less by the tension between H {sub 0} and other observational data.« less
Galaxy formation through hierarchical clustering

NASA Astrophysics Data System (ADS)

White, Simon D. M.; Frenk, Carlos S.

1991-09-01

Analytic methods for studying the formation of galaxies by gas condensation within massive dark halos are presented. The present scheme applies to cosmogonies where structure grows through hierarchical clustering of a mixture of gas and dissipationless dark matter. The simplest models consistent with the current understanding of N-body work on dissipationless clustering, and that of numerical and analytic work on gas evolution and cooling are adopted. Standard models for the evolution of the stellar population are also employed, and new models for the way star formation heats and enriches the surrounding gas are constructed. Detailed results are presented for a cold dark matter universe with Omega = 1 and H(0) = 50 km/s/Mpc, but the present methods are applicable to other models. The present luminosity functions contain significantly more faint galaxies than are observed.

PICASSO, COUPP and PICO - Search for dark matter with bubble chambers

DOE PAGES

Amole, C.; Ardid, M.; Asner, D. M.; ...

2015-05-29

The PICASSO and COUPP collaborations use superheated liquid detectors to search for cold dark matter through the direct detection of weakly interacting massive particles (WIMPs). These experiments, located in the underground laboratory of SNOLAB, Canada, detect phase transitions triggered by nuclear recoils in the keV range induced by interactions with WIMPs. We present details of the construction and operation of these detectors as well as the results, obtained by several years of observations. We also introduce PICO, which is a joint effort of the two collaborations to build a second generation ton-scale bubble chamber with 250 liters of active liquid.
Cold dark matter. 2: Spatial and velocity statistics

NASA Technical Reports Server (NTRS)

Gelb, James M.; Bertschinger, Edmund

1994-01-01

We examine high-resolution gravitational N-body simulations of the omega = 1 cold dark matter (CDM) model in order to determine whether there is any normalization of the initial density fluctuation spectrum that yields acceptable results for galaxy clustering and velocities. Dense dark matter halos in the evolved mass distribution are identified with luminous galaxies; the most massive halos are also considered as sites for galaxy groups, with a range of possibilities explored for the group mass-to-light ratios. We verify the earlier conclusions of White et al. (1987) for the low-amplitude (high-bias) CDM model-the galaxy correlation function is marginally acceptable but that there are too many galaxies. We also show that the peak biasing method does not accurately reproduce the results obtained using dense halos identified in the simulations themselves. The Cosmic Background Explorer (COBE) anisotropy implies a higher normalization, resulting in problems with excessive pairwise galaxy velocity dispersion unless a strong velocity bias is present. Although we confirm the strong velocity bias of halos reported by Couchman & Carlberg (1992), we show that the galaxy motions are still too large on small scales. We find no amplitude for which the CDM model can reconcile simultaneously and galaxy correlation function, the low pairwise velocity dispersion, and the richness distribution of groups and clusters. With the normalization implied by COBE, the CDM spectrum has too much power on small scales if omega = 1.
Cosmic string wakes

NASA Technical Reports Server (NTRS)

Stebbins, Albert; Veeraraghavan, Shoba; Silk, Joseph; Brandenberger, Robert; Turok, Neil

1987-01-01

Accretion of matter onto wakes left behind by horizon-sized pieces of cosmic string is investigated, and the effects of wakes on the large-scale structure of the universe are determined. Accretion of cold matter onto wakes, the effects of a long string on fluids with finite velocity dispersion or sound speeds, the interactions between loops and wakes, and the conditions for wakes to survive disruption by loops are discussed. It is concluded that the most important wakes are those which were formed at the time of equal matter and radiation density. This leads to sheetlike overdense regions of galaxies with a mean separation in agreement with the scale of the bubbles of de Lapparent, Geller, and Huchra (1986). However, for the value of G(mu) favored from galaxy formation considerations in a universe with cold dark matter, a wake accretes matter from a distance of only about 1.5 Mpc, which is much less than the distance between the wakes.
Cold dark matter. 1: The formation of dark halos

NASA Technical Reports Server (NTRS)

Gelb, James M.; Bertschinger, Edmund

1994-01-01

We use numerical simulations of critically closed cold dark matter (CDM) models to study the effects of numerical resolution on observable quantities. We study simulations with up to 256(exp 3) particles using the particle-mesh (PM) method and with up to 144(exp 3) particles using the adaptive particle-particle-mesh (P3M) method. Comparisons of galaxy halo distributions are made among the various simulations. We also compare distributions with observations, and we explore methods for identifying halos, including a new algorithm that finds all particles within closed contours of the smoothed density field surrounding a peak. The simulated halos show more substructure than predicted by the Press-Schechter theory. We are able to rule out all omega = 1 CDM models for linear amplitude sigma(sub 8) greater than or approximately = 0.5 because the simulations produce too many massive halos compared with the observations. The simulations also produce too many low-mass halos. The distribution of halos characterized by their circular velocities for the P3M simulations is in reasonable agreement with the observations for 150 km/s less than or = V(sub circ) less than or = 350 km/s.
Galaxy clusters and cold dark matter - A low-density unbiased universe?

NASA Technical Reports Server (NTRS)

Bahcall, Neta A.; Cen, Renyue

1992-01-01

Large-scale simulations of a universe dominated by cold dark matter (CDM) are tested against two fundamental properties of clusters of galaxies: the cluster mass function and the cluster correlation function. We find that standard biased CDM models are inconsistent with these observations for any bias parameter b. A low-density, low-bias CDM-type model, with or without a cosmological constant, appears to be consistent with both the cluster mass function and the cluster correlations. The low-density model agrees well with the observed correlation function of the Abell, Automatic Plate Measuring Facility (APM), and Edinburgh-Durham cluster catalogs. The model is in excellent agreement with the observed dependence of the correlation strength on cluster mean separation, reproducing the measured universal dimensionless cluster correlation. The low-density model is also consistent with other large-scale structure observations, including the APM angular galaxy-correlations, and for lambda = 1-Omega with the COBE results of the microwave background radiation fluctuations.
Our Cannibalistic Galaxy

NASA Astrophysics Data System (ADS)

Majewski, S. R.

2004-12-01

It is now evident that our Milky Way has cannibalistic tendencies. Recently found examples of satellite star systems being digested by our galaxy demonstrate that Milky Way-like spiral galaxies continue to grow through the piecemeal accumulation of mass from smaller neighbors, as predicted by Cold Dark Matter (CDM) models of structure formation. Cross-sections of the Milky Way halo reveal it to be networked with long-lived, coherent debris streams of stars and star clusters that attest to its accretive formation. These dynamically cold streams, created from the tidal disruption of satellite star systems, in turn provide useful tools to explore both the nature of Galactic dwarf satellites as well as the the dark matter distribution of the Milky Way; the results of such work, however, yield some unexpected results compared to current CDM models. (Research described has been supported by NASA/JPL, the National Science Foundation, The David and Lucile Packard Foundation, the Research Corporation, and the F.H. Levinson Fund of the Peninsula Community Foundation.)
The least-action method, cold dark matter, and omega

NASA Technical Reports Server (NTRS)

Dunn, A. M.; Laflamme, R.

1995-01-01

Peebles has suggested an interesting technique, called the least-action method, to trace positions of galaxies back in time. This method applied on the Local Group galaxies seems to indicate that we live in an omega approximately = 0.1 universe. We have studied a cold dark matter (CDM) N-body simulation with omega = 0.2 and H = 50 km/s/Mpc and compared trajectories traced back by the least-action method with the ones given by the center of mass of the CDM halos. We show that the agreement between these sets of trajectories is at best qualitative. We also show that the line-of-sight peculiar velocities of halos are underestimated. This discrepancy is due to orphans, i.e., CDM particles which do not end up in halos. We vary the value of omega in the least-action method until the line-of-sight velocities agree with the CDM ones. The best value for this omega underestimates one of the CDM simulations by a factor of 4-5.
Mass-Discrepancy Acceleration Relation: A Natural Outcome of Galaxy Formation in Cold Dark Matter Halos.

PubMed

Ludlow, Aaron D; Benítez-Llambay, Alejandro; Schaller, Matthieu; Theuns, Tom; Frenk, Carlos S; Bower, Richard; Schaye, Joop; Crain, Robert A; Navarro, Julio F; Fattahi, Azadeh; Oman, Kyle A

2017-04-21

We analyze the total and baryonic acceleration profiles of a set of well-resolved galaxies identified in the eagle suite of hydrodynamic simulations. Our runs start from the same initial conditions but adopt different prescriptions for unresolved stellar and active galactic nuclei feedback, resulting in diverse populations of galaxies by the present day. Some of them reproduce observed galaxy scaling relations, while others do not. However, regardless of the feedback implementation, all of our galaxies follow closely a simple relationship between the total and baryonic acceleration profiles, consistent with recent observations of rotationally supported galaxies. The relation has small scatter: Different feedback implementations-which produce different galaxy populations-mainly shift galaxies along the relation rather than perpendicular to it. Furthermore, galaxies exhibit a characteristic acceleration g_{†}, above which baryons dominate the mass budget, as observed. These observations, consistent with simple modified Newtonian dynamics, can be accommodated within the standard cold dark matter paradigm.
Dark-matter haloes and the M-σ relation for supermassive black holes

NASA Astrophysics Data System (ADS)

Larkin, Adam C.; McLaughlin, Dean E.

2016-10-01

We develop models of two-component spherical galaxies to establish scaling relations linking the properties of spheroids at z = 0 (total stellar masses, effective radii Re and velocity dispersions within Re) to the properties of their dark-matter haloes at both z = 0 and higher redshifts. Our main motivation is the widely accepted idea that the accretion-driven growth of supermassive black holes (SMBHs) in protogalaxies is limited by quasar-mode feedback and gas blow-out. The SMBH masses, MBH, should then be connected to the dark-matter potential wells at the redshift zqso of the blow-out. We specifically consider the example of a power-law dependence on the maximum circular speed in a protogalactic dark-matter halo: M_{BH}∝ V^4_{d,pk}, as could be expected if quasar-mode feedback were momentum-driven. For haloes with a given Vd,pk at a given zqso ≥ 0, our model scaling relations give a typical stellar velocity dispersion σap(Re) at z = 0. Thus, they transform a theoretical MBH-Vd,pk relation into a prediction for an observable MBH-σap(Re) relation. We find the latter to be distinctly non-linear in log-log space. Its shape depends on the generic redshift evolution of haloes in a Λ cold dark matter cosmology and the systematic variation of stellar-to-dark matter mass fraction at z = 0, in addition to any assumptions about the physics underlying the MBH-Vd,pk relation. Despite some clear limitations of the form we use for MBH versus Vd,pk, and even though we do not include any SMBH growth through dry mergers at low redshift, our results for MBH-σap(Re) compare well to data for local early types if we take zqso ˜ 2-4.
Pressure from dark matter annihilation and the rotation curve of spiral galaxies

NASA Astrophysics Data System (ADS)

Wechakama, M.; Ascasibar, Y.

2011-05-01

The rotation curves of spiral galaxies are one of the basic predictions of the cold dark matter paradigm, and their shape in the innermost regions has been hotly debated over the last decades. The present work shows that dark matter annihilation into electron-positron pairs may affect the observed rotation curve by a significant amount. We adopt a model-independent approach, where all the electrons and positrons are injected with the same initial energy E0˜mdmc2 in the range from 1 MeV to 1 TeV and the injection rate is constrained by INTEGRAL, Fermi and HESS data. The pressure of the relativistic electron-positron gas is determined by solving the diffusion-loss equation, considering inverse Compton scattering, synchrotron radiation, Coulomb collisions, bremsstrahlung and ionization. For values of the gas density and magnetic field that are representative of the Milky Way, it is estimated that pressure gradients are strong enough to balance gravity in the central parts if E0 < 1 GeV. The exact value depends somewhat on the astrophysical parameters, and it changes dramatically with the slope of the dark matter density profile. For very steep slopes, as those expected from adiabatic contraction, the rotation curves of spiral galaxies would be affected on ˜kpc scales for most values of E0. By comparing the predicted rotation curves with observations of dwarf and low surface brightness galaxies, we show that the pressure from dark matter annihilation may improve the agreement between theory and observations in some cases, but it also imposes severe constraints on the model parameters (most notably, the inner slope of halo density profile, as well as the mass and the annihilation cross-section of dark matter particles into electron-positron pairs).
Remapping dark matter halo catalogues between cosmological simulations

NASA Astrophysics Data System (ADS)

Mead, A. J.; Peacock, J. A.

2014-05-01

We present and test a method for modifying the catalogue of dark matter haloes produced from a given cosmological simulation, so that it resembles the result of a simulation with an entirely different set of parameters. This extends the method of Angulo & White, which rescales the full particle distribution from a simulation. Working directly with the halo catalogue offers an advantage in speed, and also allows modifications of the internal structure of the haloes to account for non-linear differences between cosmologies. Our method can be used directly on a halo catalogue in a self-contained manner without any additional information about the overall density field; although the large-scale displacement field is required by the method, this can be inferred from the halo catalogue alone. We show proof of concept of our method by rescaling a matter-only simulation with no baryon acoustic oscillation (BAO) features to a more standard Λ cold dark matter model containing a cosmological constant and a BAO signal. In conjunction with the halo occupation approach, this method provides a basis for the rapid generation of mock galaxy samples spanning a wide range of cosmological parameters.
Gamma-Ray Emission from Galaxy Clusters : DARK MATTER AND COSMIC-RAYS

NASA Astrophysics Data System (ADS)

Pinzke, Anders

The quest for the first detection of a galaxy cluster in the high energy gamma-ray regime is ongoing, and even though clusters are observed in several other wave-bands, there is still no firm detection in gamma-rays. To complement the observational efforts we estimate the gamma-ray contributions from both annihilating dark matter and cosmic-ray (CR) proton as well as CR electron induced emission. Using high-resolution simulations of galaxy clusters, we find a universal concave shaped CR proton spectrum independent of the simulated galaxy cluster. Specifically, the gamma-ray spectra from decaying neutral pions, which are produced by CR protons, dominate the cluster emission. Furthermore, based on our derived flux and luminosity functions, we identify the galaxy clusters with the brightest galaxy clusters in gamma-rays. While this emission is challenging to detect using the Fermi satellite, major observations with Cherenkov telescopes in the near future may put important constraints on the CR physics in clusters. To extend these predictions, we use a dark matter model that fits the recent electron and positron data from Fermi, PAMELA, and H.E.S.S. with remarkable precision, and make predictions about the expected gamma-ray flux from nearby clusters. In order to remain consistent with the EGRET upper limit on the gamma-ray emission from Virgo, we constrain the minimum mass of substructures for cold dark matter halos. In addition, we find comparable levels of gamma-ray emission from CR interactions and dark matter annihilations without Sommerfeld enhancement.
Physics of superheavy dark matter in supergravity

NASA Astrophysics Data System (ADS)

Addazi, Andrea; Marciano, Antonino; Ketov, Sergei V.; Khlopov, Maxim Yu.

New trends in inflationary model building and dark matter production in supergravity are considered. Starobinsky inflation is embedded into 𝒩 = 1 supergravity, avoiding instability problems, when the inflaton belongs to a vector superfield associated with a U(1) gauge symmetry, instead of a chiral superfield. This gauge symmetry can be spontaneously broken by the super-Higgs mechanism resulting in a massive vector supermultiplet including the (real scalar) inflaton field. Both supersymmetry (SUSY) and the R-symmetry can also be spontaneously broken by the Polonyi mechanism at high scales close to the inflationary scale. In this case, Polonyi particles and gravitinos become superheavy, and can be copiously produced during inflation by the Schwinger mechanism sourced by the universe expansion. The Polonyi mass slightly exceeds twice the gravitino mass, so that Polonyi particles are unstable and decay into gravitinos. Considering the mechanisms of superheavy gravitino production, we find that the right amount of cold dark matter composed of gravitinos can be achieved. In our scenario, the parameter space of the inflaton potential is directly related to the dark matter one, providing a new unifying framework of inflation and dark matter genesis. A multi-superfield extension of the supergravity framework with a single (inflaton) superfield can result in a formation of primordial nonlinear structures like mini- and stellar-mass black holes, primordial nongaussianity, and the running spectral index of density fluctuations. This framework can be embedded into the SUSY GUTs inspired by heterotic string compactifications on Calabi-Yau three-folds, thus unifying particle physics with quantum gravity.
Detecting dark-matter waves with a network of precision-measurement tools

NASA Astrophysics Data System (ADS)

Derevianko, Andrei

2018-04-01

Virialized ultralight fields (VULFs) are viable cold dark-matter candidates and include scalar and pseudoscalar bosonic fields, such as axions and dilatons. Direct searches for VULFs rely on low-energy precision-measurement tools. While previous proposals have focused on detecting coherent oscillations of the VULF signals at the VULF Compton frequencies for individual devices, here I consider a network of such devices. Virialized ultralight fields are essentially dark-matter waves and as such they carry both temporal and spatial phase information. Thereby, the discovery reach can be improved by using networks of precision-measurement tools. To formalize this idea, I derive a spatiotemporal two-point correlation function for the ultralight dark-matter fields in the framework of the standard halo model. Due to VULFs being Gaussian random fields, the derived two-point correlation function fully determines N -point correlation functions. For a network of ND devices within the coherence length of the field, the sensitivity compared to a single device can be improved by a factor of √{ND}. Further, I derive a VULF dark-matter signal profile for an individual device. The resulting line shape is strongly asymmetric due to the parabolic dispersion relation for massive nonrelativistic bosons. I discuss the aliasing effect that extends the discovery reach to VULF frequencies higher than the experimental sampling rate. I present sensitivity estimates and develop a stochastic field signal-to-noise ratio statistic. Finally, I consider an application of the formalism developed to atomic clocks and their networks.
Update on the MiniCLEAN dark matter experiment

DOE PAGES

Rielage, K.; Akashi-Ronquest, M.; Bodmer, M.; ...

2015-03-24

The direct search for dark matter is entering a period of increased sensitivity to the hypothetical Weakly Interacting Massive Particle (WIMP). One such technology that is being examined is a scintillation only noble liquid experiment, MiniCLEAN. MiniCLEAN utilizes over 500 kg of liquid cryogen to detect nuclear recoils from WIMP dark matter and serves as a demonstration for a future detector of order 50 to 100 tonnes. The liquid cryogen is interchangeable between argon and neon to study the A² dependence of the potential signal and examine backgrounds. MiniCLEAN utilizes a unique modular design with spherical geometry to maximize themore » light yield using cold photomultiplier tubes in a single-phase detector. Pulse shape discrimination techniques are used to separate nuclear recoil signals from electron recoil backgrounds. MiniCLEAN will be spiked with additional ³⁹Ar to demonstrate the effective reach of the pulse shape discrimination capability. Assembly of the experiment is underway at SNOLAB and an update on the project is given.« less
Smooth halos in the cosmic web

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaite, José, E-mail: jose.gaite@upm.es

Dark matter halos can be defined as smooth distributions of dark matter placed in a non-smooth cosmic web structure. This definition of halos demands a precise definition of smoothness and a characterization of the manner in which the transition from smooth halos to the cosmic web takes place. We introduce entropic measures of smoothness, related to measures of inequality previously used in economy and with the advantage of being connected with standard methods of multifractal analysis already used for characterizing the cosmic web structure in cold dark matter N-body simulations. These entropic measures provide us with a quantitative description ofmore » the transition from the small scales portrayed as a distribution of halos to the larger scales portrayed as a cosmic web and, therefore, allow us to assign definite sizes to halos. However, these ''smoothness sizes'' have no direct relation to the virial radii. Finally, we discuss the influence of N-body discreteness parameters on smoothness.« less
Rotation curves of galaxies and the stellar mass-to-light ratio

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Khodadadi, Aziz; Ghari, Amir; Zonoozi, Akram Hasani; Kroupa, Pavel

2018-03-01

Mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c - Mvir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration and virial mass. Although accounting for a NFW dark halo profile can explain rotation curve observations, the implied c - Mvir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L -color correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L - ratios of 51 galaxies (30% of our sample) have unphysically negative values in the framework of the ΛCDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of ΛCDM cosmological structure formation, is not an appropriate profile for the dark halos of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disk galaxies.
Rotation curves of galaxies and the stellar mass-to-light ratio

NASA Astrophysics Data System (ADS)

Haghi, Hosein; Khodadadi, Aziz; Ghari, Amir; Zonoozi, Akram Hasani; Kroupa, Pavel

2018-07-01

Mass models of a sample of 171 low- and high-surface brightness galaxies are presented in the context of the cold dark matter (CDM) theory using the NFW dark matter halo density distribution to extract a new concentration-viral mass relation (c-Mvir). The rotation curves (RCs) are calculated from the total baryonic matter based on the 3.6 μm-band surface photometry, the observed distribution of neutral hydrogen, and the dark halo, in which the three adjustable parameters are the stellar mass-to-light ratio, halo concentration, and virial mass. Although accounting for a NFW dark halo profile can explain RC observations, the implied c-Mvir relation from RC analysis strongly disagrees with that resulting from different cosmological simulations. Also, the M/L-colour correlation of the studied galaxies is inconsistent with that expected from stellar population synthesis models with different stellar initial mass functions. Moreover, we show that the best-fitting stellar M/L ratios of 51 galaxies (30 per cent of our sample) have unphysically negative values in the framework of the ΛCDM theory. This can be interpreted as a serious crisis for this theory. This suggests either that the commonly used NFW halo profile, which is a natural result of ΛCDM cosmological structure formation, is not an appropriate profile for the dark haloes of galaxies, or, new dark matter physics or alternative gravity models are needed to explain the rotational velocities of disc galaxies.
Mixed axion/neutralino dark matter in the SUSY DFSZ axion model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bae, Kyu Jung; Baer, Howard; Chun, Eung Jin, E-mail: bae@nhn.ou.edu, E-mail: baer@nhn.ou.edu, E-mail: ejchun@kias.re.kr

2013-12-01

We examine mixed axion/neutralino cold dark matter production in the SUSY DFSZ axion model where an axion superfield couples to Higgs superfields. We calculate a wide array of axino and saxion decay modes along with their decay temperatures, and thermal and non-thermal production rates. For a SUSY benchmark model with a standard underabundance (SUA) of Higgsino-like dark matter (DM), we find for the PQ scale f{sub a}∼<10{sup 12} GeV that the DM abundance is mainly comprised of axions as the saxion/axino decay occurs before the standard neutralino freeze-out and thus its abundance remains suppressed. For 10{sup 12}∼10{sup 14} GeV, bothmore » neutralino dark matter and dark radiation are typically overproduced. For judicious parameter choices, these can be suppressed and the combined neutralino/axion abundance brought into accord with measured values. A SUSY benchmark model with a standard overabundance (SOA) of bino DM is also examined and typically remains excluded due at least to too great a neutralino DM abundance for f{sub a}∼<10{sup 15} GeV. For f{sub a}∼>10{sup 15} GeV and lower saxion masses, large entropy production from saxion decay can dilute all relics and the SOA model can be allowed by all constraints.« less
Evolution of Mass and Velocity Field in the Cosmic Web: Comparison between Baryonic and Dark Matter

NASA Astrophysics Data System (ADS)

Zhu, Weishan; Feng, Long-Long

2017-03-01

We investigate the evolution of the cosmic web since z = 5 in grid-based cosmological hydrodynamical simulations, focusing on the mass and velocity fields of both baryonic and cold dark matter. The tidal tensor of density is used as the main method for web identification, with λ th = 0.2-1.2. The evolution trends in baryonic and dark matter are similar, although moderate differences are observed. Sheets appear early, and their large-scale pattern may have been set up by z = 3. In terms of mass, filaments supersede sheets as the primary collapsing structures from z ˜ 2-3. Tenuous filaments assembled with each other to form prominent ones at z < 2. In accordance with the construction of the frame of the sheets, the cosmic divergence velocity, v div, was already well-developed above 2-3 Mpc by z = 3. Afterwards, the curl velocity, v curl, grew dramatically along with the rising of filaments, becoming comparable to v div, for <2-3 Mpc at z = 0. The scaling of v curl can be described by the hierarchical turbulence model. The alignment between the vorticity and the eigenvectors of the shear tensor in the baryonic matter field resembles that in the dark matter field, and is even moderately stronger between {\\boldsymbol{ω }} and {{\\boldsymbol{e}}}1, and ω and {{\\boldsymbol{e}}}3. Compared with dark matter, there is slightly less baryonic matter found residing in filaments and clusters, and its vorticity developed more significantly below 2-3 Mpc. These differences may be underestimated because of the limited resolution and lack of star formation in our simulation. The impact of the change of dominant structures in overdense regions at z ˜ 2-3 on galaxy formation and evolution is shortly discussed.

Dark matter candidates: a ten-point test

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taoso, Marco; Masiero, Antonio; Bertone, Gianfranco, E-mail: taoso@pd.infn.it, E-mail: bertone@iap.fr, E-mail: antonio.masiero@pd.infn.it

An extraordinarily rich zoo of non-baryonic dark matter candidates has been proposed over the last three decades. Here we present a ten-point test that a new particle has to pass in order to be considered a viable DM candidate. (I) Does it match the appropriate relic density? (II) Is it cold? (III) Is it neutral? (IV) Is it consistent with BBN? (V) Does it leave stellar evolution unchanged? (VI) Is it compatible with constraints on self-interactions? (VII) Is it consistent with direct DM searches? (VIII) Is it compatible with gamma-ray constraints? (IX) Is it compatible with other astrophysical bounds? (X)more » Can it be probed experimentally?.« less
A galaxy lacking dark matter

NASA Astrophysics Data System (ADS)

van Dokkum, Pieter; Danieli, Shany; Cohen, Yotam; Merritt, Allison; Romanowsky, Aaron J.; Abraham, Roberto; Brodie, Jean; Conroy, Charlie; Lokhorst, Deborah; Mowla, Lamiya; O'Sullivan, Ewan; Zhang, Jielai

2018-03-01

Studies of galaxy surveys in the context of the cold dark matter paradigm have shown that the mass of the dark matter halo and the total stellar mass are coupled through a function that varies smoothly with mass. Their average ratio Mhalo/Mstars has a minimum of about 30 for galaxies with stellar masses near that of the Milky Way (approximately 5 × 1010 solar masses) and increases both towards lower masses and towards higher masses. The scatter in this relation is not well known; it is generally thought to be less than a factor of two for massive galaxies but much larger for dwarf galaxies. Here we report the radial velocities of ten luminous globular-cluster-like objects in the ultra-diffuse galaxy NGC1052–DF2, which has a stellar mass of approximately 2 × 108 solar masses. We infer that its velocity dispersion is less than 10.5 kilometres per second with 90 per cent confidence, and we determine from this that its total mass within a radius of 7.6 kiloparsecs is less than 3.4 × 108 solar masses. This implies that the ratio Mhalo/Mstars is of order unity (and consistent with zero), a factor of at least 400 lower than expected. NGC1052–DF2 demonstrates that dark matter is not always coupled with baryonic matter on galactic scales.
A galaxy lacking dark matter.

PubMed

van Dokkum, Pieter; Danieli, Shany; Cohen, Yotam; Merritt, Allison; Romanowsky, Aaron J; Abraham, Roberto; Brodie, Jean; Conroy, Charlie; Lokhorst, Deborah; Mowla, Lamiya; O'Sullivan, Ewan; Zhang, Jielai

2018-03-28

Studies of galaxy surveys in the context of the cold dark matter paradigm have shown that the mass of the dark matter halo and the total stellar mass are coupled through a function that varies smoothly with mass. Their average ratio M halo /M stars has a minimum of about 30 for galaxies with stellar masses near that of the Milky Way (approximately 5 × 10 10 solar masses) and increases both towards lower masses and towards higher masses. The scatter in this relation is not well known; it is generally thought to be less than a factor of two for massive galaxies but much larger for dwarf galaxies. Here we report the radial velocities of ten luminous globular-cluster-like objects in the ultra-diffuse galaxy NGC1052-DF2, which has a stellar mass of approximately 2 × 10 8 solar masses. We infer that its velocity dispersion is less than 10.5 kilometres per second with 90 per cent confidence, and we determine from this that its total mass within a radius of 7.6 kiloparsecs is less than 3.4 × 10 8 solar masses. This implies that the ratio M halo /M stars is of order unity (and consistent with zero), a factor of at least 400 lower than expected. NGC1052-DF2 demonstrates that dark matter is not always coupled with baryonic matter on galactic scales.
Discovery of a New Fundamental Plane Dictating Galaxy Cluster Evolution from Gravitational Lensing

NASA Astrophysics Data System (ADS)

Fujita, Yutaka; Umetsu, Keiichi; Rasia, Elena; Meneghetti, Massimo; Donahue, Megan; Medezinski, Elinor; Okabe, Nobuhiro; Postman, Marc

2018-04-01

In cold dark-matter (CDM) cosmology, objects in the universe have grown under the effect of gravity of dark matter. The intracluster gas in a galaxy cluster was heated when the dark-matter halo formed through gravitational collapse. The potential energy of the gas was converted to thermal energy through this process. However, this process and the thermodynamic history of the gas have not been clearly characterized in connection with the formation and evolution of the internal structure of dark-matter halos. Here, we show that observational CLASH data of high-mass galaxy clusters lie on a plane in the three-dimensional logarithmic space of their characteristic radius r s , mass M s , and X-ray temperature T X with a very small orthogonal scatter. The tight correlation indicates that the gas temperature was determined at a specific cluster formation time, which is encoded in r s and M s . The plane is tilted with respect to T X ∝ M s /r s , which is the plane expected in the case of simplified virial equilibrium. We show that this tilt can be explained by a similarity solution, which indicates that clusters are not isolated but continuously growing through matter accretion from their outer environments. Numerical simulations reproduce the observed plane and its angle. This result holds independently of the gas physics implemented in the code, revealing the fundamental origin of this plane.
Halo abundance and assembly history with extreme-axion wave dark matter at z ≥ 4

NASA Astrophysics Data System (ADS)

Schive, Hsi-Yu; Chiueh, Tzihong

2018-01-01

Wave dark matter (ψDM) composed of extremely light bosons (mψ ˜ 10 - 22 eV), with quantum pressure suppressing structures below a kpc-scale de Broglie wavelength, has become a viable dark matter candidate. Compared to the conventional free-particle ψDM (FPψDM), the extreme-axion ψDM model (EAψDM) proposed by Zhang & Chiueh features a larger cut-off wavenumber and a broad spectral bump in the matter transfer function. Here, we conduct cosmological simulations to compare the halo abundances and assembly histories at z = 4-11 between three different scenarios: FPψDM, EAψDM and cold dark matter (CDM). We show that EAψDM produces significantly more abundant low-mass haloes than FPψDM with the same mψ, and therefore could alleviate the tension in mψ required by the Lyα forest data and by the kpc-scale dwarf galaxy cores. We also find that, compared to the CDM counterparts, massive EAψDM haloes are, on average, 3-4 times more massive at z = 10-11 due to their earlier formation, undergo a slower mass accretion at 7 ≲ z ≲ 11, and then show a rapidly rising major merger rate exceeding CDM by ˜ 50 per cent at 4 ≲ z ≲ 7. This fact suggests that EAψDM haloes may exhibit more prominent starbursts at z ≲ 7.
Galaxy halo formation in the absence of violent relaxation and a universal density profile of the halo center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baushev, A. N., E-mail: baushev@gmail.com; Institut für Physik und Astronomie, Universität Potsdam, D-14476 Potsdam-Golm

2014-05-01

While N-body simulations testify to a cuspy profile of the central region of dark matter halos, observations favor a shallow, cored density profile of the central region of at least some spiral galaxies and dwarf spheroidals. We show that a central profile, very close to the observed one, inevitably forms in the center of dark matter halos if we make a supposition about a moderate energy relaxation of the system during the halo formation. If we assume the energy exchange between dark matter particles during the halo collapse is not too intensive, the profile is universal: it depends almost notmore » at all on the properties of the initial perturbation and is very akin, but not identical, to the Einasto profile with a small Einasto index n ∼ 0.5. We estimate the size of the 'central core' of the distribution, i.e., the extent of the very central region with a respectively gentle profile, and show that the cusp formation is unlikely, even if the dark matter is cold. The obtained profile is in good agreement with observational data for at least some types of galaxies but clearly disagrees with N-body simulations.« less
A general explanation on the correlation of dark matter halo spin with the large-scale environment

NASA Astrophysics Data System (ADS)

Wang, Peng; Kang, Xi

2017-06-01

Both simulations and observations have found that the spin of halo/galaxy is correlated with the large-scale environment, and particularly the spin of halo flips in filament. A consistent picture of halo spin evolution in different environments is still lacked. Using N-body simulation, we find that halo spin with its environment evolves continuously from sheet to cluster, and the flip of halo spin happens both in filament and nodes. The flip in filament can be explained by halo formation time and migrating time when its environment changes from sheet to filament. For low-mass haloes, they form first in sheets and migrate into filaments later, so their mass and spin growth inside filament are lower, and the original spin is still parallel to filament. For high-mass haloes, they migrate into filaments first, and most of their mass and spin growth are obtained in filaments, so the resulted spin is perpendicular to filament. Our results well explain the overall evolution of cosmic web in the cold dark matter model and can be tested using high-redshift data. The scenario can also be tested against alternative models of dark matter, such as warm/hot dark matter, where the structure formation will proceed in a different way.
High energy seesaw models, GUTs and Leptogenesis

NASA Astrophysics Data System (ADS)

Di Bari, Pasquale

2017-09-01

I review high energy (type I) seesaw models and in particular how they can be nicely embedded within grand-unified models and reproduce the observed matter-antimatter asymmetry with leptogenesis. I also discuss how high energy (type I) seesaw models can provide a candidate for very heavy cold dark matter, within the TeV-EeV range, whose decays might explain part of the IceCube high energy neutrino events in addition to an astrophysical component.
Wide-Field Lensing Mass Maps from Dark Energy Survey Science Verification Data

DOE PAGES

Chang, C.

2015-07-29

We present a mass map reconstructed from weak gravitational lensing shear measurements over 139 deg 2 from the Dark Energy Survey science verification data. The mass map probes both luminous and dark matter, thus providing a tool for studying cosmology. We also find good agreement between the mass map and the distribution of massive galaxy clusters identified using a red-sequence cluster finder. Potential candidates for superclusters and voids are identified using these maps. We measure the cross-correlation between the mass map and a magnitude-limited foreground galaxy sample and find a detection at the 6.8σ level with 20 arc min smoothing.more » These measurements are consistent with simulated galaxy catalogs based on N-body simulations from a cold dark matter model with a cosmological constant. This suggests low systematics uncertainties in the map. Finally, we summarize our key findings in this Letter; the detailed methodology and tests for systematics are presented in a companion paper.« less
Pairwise velocities in the "Running FLRW" cosmological model

NASA Astrophysics Data System (ADS)

Bibiano, Antonio; Croton, Darren J.

2017-05-01

We present an analysis of the pairwise velocity statistics from a suite of cosmological N-body simulations describing the 'Running Friedmann-Lemaître-Robertson-Walker' (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends Λ cold dark matter (CDM) with a time-evolving vacuum energy density, ρ _Λ. To enforce local conservation of matter, a time-evolving gravitational coupling is also included. Our results constitute the first study of velocities in the R-FLRW cosmology, and we also compare with other dark energy simulations suites, repeating the same analysis. We find a strong degeneracy between the pairwise velocity and σ8 at z = 0 for almost all scenarios considered, which remains even when we look back to epochs as early as z = 2. We also investigate various coupled dark energy models, some of which show minimal degeneracy, and reveal interesting deviations from ΛCDM that could be readily exploited by future cosmological observations to test and further constrain our understanding of dark energy.
Wide-Field Lensing Mass Maps from Dark Energy Survey Science Verification Data.

PubMed

Chang, C; Vikram, V; Jain, B; Bacon, D; Amara, A; Becker, M R; Bernstein, G; Bonnett, C; Bridle, S; Brout, D; Busha, M; Frieman, J; Gaztanaga, E; Hartley, W; Jarvis, M; Kacprzak, T; Kovács, A; Lahav, O; Lin, H; Melchior, P; Peiris, H; Rozo, E; Rykoff, E; Sánchez, C; Sheldon, E; Troxel, M A; Wechsler, R; Zuntz, J; Abbott, T; Abdalla, F B; Allam, S; Annis, J; Bauer, A H; Benoit-Lévy, A; Brooks, D; Buckley-Geer, E; Burke, D L; Capozzi, D; Carnero Rosell, A; Carrasco Kind, M; Castander, F J; Crocce, M; D'Andrea, C B; Desai, S; Diehl, H T; Dietrich, J P; Doel, P; Eifler, T F; Evrard, A E; Fausti Neto, A; Flaugher, B; Fosalba, P; Gruen, D; Gruendl, R A; Gutierrez, G; Honscheid, K; James, D; Kent, S; Kuehn, K; Kuropatkin, N; Maia, M A G; March, M; Martini, P; Merritt, K W; Miller, C J; Miquel, R; Neilsen, E; Nichol, R C; Ogando, R; Plazas, A A; Romer, A K; Roodman, A; Sako, M; Sanchez, E; Sevilla, I; Smith, R C; Soares-Santos, M; Sobreira, F; Suchyta, E; Tarle, G; Thaler, J; Thomas, D; Tucker, D; Walker, A R

2015-07-31

We present a mass map reconstructed from weak gravitational lensing shear measurements over 139 deg2 from the Dark Energy Survey science verification data. The mass map probes both luminous and dark matter, thus providing a tool for studying cosmology. We find good agreement between the mass map and the distribution of massive galaxy clusters identified using a red-sequence cluster finder. Potential candidates for superclusters and voids are identified using these maps. We measure the cross-correlation between the mass map and a magnitude-limited foreground galaxy sample and find a detection at the 6.8σ level with 20 arc min smoothing. These measurements are consistent with simulated galaxy catalogs based on N-body simulations from a cold dark matter model with a cosmological constant. This suggests low systematics uncertainties in the map. We summarize our key findings in this Letter; the detailed methodology and tests for systematics are presented in a companion paper.
Core or Cusps: The Central Dark Matter Profile of a Strong Lensing Cluster with a Bright Central Image at Redshift 1 [Core or Cusps: The Central Dark Matter Profile of a Redshift One Strong Lensing Cluster with a Bright Central Image

DOE PAGES

Collett, Thomas E.; Buckley-Geer, Elizabeth; Lin, Huan; ...

2017-07-10

Here, we report on SPT-CLJ2011-5228, a giant system of arcs created by a cluster at z = 1.06. The arc system is notable for the presence of a bright central image. The source is a Lyman break galaxy at z s = 2.39 and the mass enclosed within the Einstein ring of radius 14 arcsec ismore » $$\\sim {10}^{14.2}\\ {M}_{\\odot }$$. We perform a full reconstruction of the light profile of the lensed images to precisely infer the parameters of the mass distribution. The brightness of the central image demands that the central total density profile of the lens be shallow. By fitting the dark matter as a generalized Navarro–Frenk–White profile—with a free parameter for the inner density slope—we find that the break radius is $${270}_{-76}^{+48}$$ kpc, and that the inner density falls with radius to the power –0.38 ± 0.04 at 68% confidence. Such a shallow profile is in strong tension with our understanding of relaxed cold dark matter halos; dark matter-only simulations predict that the inner density should fall as $${r}^{-1}$$. The tension can be alleviated if this cluster is in fact a merger; a two-halo model can also reconstruct the data, with both clumps (density varying as $${r}^{-0.8}$$ and $${r}^{-1.0}$$) much more consistent with predictions from dark matter-only simulations. At the resolution of our Dark Energy Survey imaging, we are unable to choose between these two models, but we make predictions for forthcoming Hubble Space Telescope imaging that will decisively distinguish between them.« less
Core or Cusps: The Central Dark Matter Profile of a Strong Lensing Cluster with a Bright Central Image at Redshift 1 [Core or Cusps: The Central Dark Matter Profile of a Redshift One Strong Lensing Cluster with a Bright Central Image

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collett, Thomas E.; Buckley-Geer, Elizabeth; Lin, Huan

Here, we report on SPT-CLJ2011-5228, a giant system of arcs created by a cluster at z = 1.06. The arc system is notable for the presence of a bright central image. The source is a Lyman break galaxy at z s = 2.39 and the mass enclosed within the Einstein ring of radius 14 arcsec ismore » $$\\sim {10}^{14.2}\\ {M}_{\\odot }$$. We perform a full reconstruction of the light profile of the lensed images to precisely infer the parameters of the mass distribution. The brightness of the central image demands that the central total density profile of the lens be shallow. By fitting the dark matter as a generalized Navarro–Frenk–White profile—with a free parameter for the inner density slope—we find that the break radius is $${270}_{-76}^{+48}$$ kpc, and that the inner density falls with radius to the power –0.38 ± 0.04 at 68% confidence. Such a shallow profile is in strong tension with our understanding of relaxed cold dark matter halos; dark matter-only simulations predict that the inner density should fall as $${r}^{-1}$$. The tension can be alleviated if this cluster is in fact a merger; a two-halo model can also reconstruct the data, with both clumps (density varying as $${r}^{-0.8}$$ and $${r}^{-1.0}$$) much more consistent with predictions from dark matter-only simulations. At the resolution of our Dark Energy Survey imaging, we are unable to choose between these two models, but we make predictions for forthcoming Hubble Space Telescope imaging that will decisively distinguish between them.« less
Core or Cusps: The Central Dark Matter Profile of a Strong Lensing Cluster with a Bright Central Image at Redshift 1

NASA Astrophysics Data System (ADS)

Collett, Thomas E.; Buckley-Geer, Elizabeth; Lin, Huan; Bacon, David; Nichol, Robert C.; Nord, Brian; Morice-Atkinson, Xan; Amara, Adam; Birrer, Simon; Kuropatkin, Nikolay; More, Anupreeta; Papovich, Casey; Romer, Kathy K.; Tessore, Nicolas; Abbott, Tim M. C.; Allam, Sahar; Annis, James; Benoit-Lévy, Aurlien; Brooks, David; Burke, David L.; Carrasco Kind, Matias; Castander, Francisco Javier J.; D'Andrea, Chris B.; da Costa, Luiz N.; Desai, Shantanu; Diehl, H. Thomas; Doel, Peter; Eifler, Tim F.; Flaugher, Brenna; Frieman, Josh; Gerdes, David W.; Goldstein, Daniel A.; Gruen, Daniel; Gschwend, Julia; Gutierrez, Gaston; James, David J.; Kuehn, Kyler; Kuhlmann, Steve; Lahav, Ofer; Li, Ting S.; Lima, Marcos; Maia, Marcio A. G.; March, Marisa; Marshall, Jennifer L.; Martini, Paul; Melchior, Peter; Miquel, Ramon; Plazas, Andrs A.; Rykoff, Eli S.; Sanchez, Eusebio; Scarpine, Vic; Schindler, Rafe; Schubnell, Michael; Sevilla-Noarbe, Ignacio; Smith, Mathew; Sobreira, Flavia; Suchyta, Eric; Swanson, Molly E. C.; Tarle, Gregory; Tucker, Douglas L.; Walker, Alistair R.

2017-07-01

We report on SPT-CLJ2011-5228, a giant system of arcs created by a cluster at z = 1.06. The arc system is notable for the presence of a bright central image. The source is a Lyman break galaxy at z s = 2.39 and the mass enclosed within the Einstein ring of radius 14 arcsec is ˜ {10}14.2 {M}⊙ . We perform a full reconstruction of the light profile of the lensed images to precisely infer the parameters of the mass distribution. The brightness of the central image demands that the central total density profile of the lens be shallow. By fitting the dark matter as a generalized Navarro-Frenk-White profile—with a free parameter for the inner density slope—we find that the break radius is {270}-76+48 kpc, and that the inner density falls with radius to the power -0.38 ± 0.04 at 68% confidence. Such a shallow profile is in strong tension with our understanding of relaxed cold dark matter halos; dark matter-only simulations predict that the inner density should fall as {r}-1. The tension can be alleviated if this cluster is in fact a merger; a two-halo model can also reconstruct the data, with both clumps (density varying as {r}-0.8 and {r}-1.0) much more consistent with predictions from dark matter-only simulations. At the resolution of our Dark Energy Survey imaging, we are unable to choose between these two models, but we make predictions for forthcoming Hubble Space Telescope imaging that will decisively distinguish between them.
Core or Cusps: The Central Dark Matter Profile of a Strong Lensing Cluster with a Bright Central Image at Redshift 1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collett, Thomas E.; Buckley-Geer, Elizabeth; Lin, Huan

We report on SPT-CLJ2011-5228, a giant system of arcs created by a cluster atmore » $z=1.06$. The arc system is notable for the presence of a bright central image. The source is a Lyman Break galaxy at $$z_s=2.39$$ and the mass enclosed within the 14 arc second radius Einstein ring is $$10^{14.2}$$ solar masses. We perform a full light profile reconstruction of the lensed images to precisely infer the parameters of the mass distribution. The brightness of the central image demands that the central total density profile of the lens be shallow. By fitting the dark matter as a generalized Navarro-Frenk-White profile---with a free parameter for the inner density slope---we find that the break radius is $$270^{+48}_{-76}$$ kpc, and that the inner density falls with radius to the power $$-0.38\\pm0.04$$ at 68 percent confidence. Such a shallow profile is in strong tension with our understanding of relaxed cold dark matter halos; dark matter only simulations predict the inner density should fall as $$r^{-1}$$. The tension can be alleviated if this cluster is in fact a merger; a two halo model can also reconstruct the data, with both clumps (density going as $$r^{-0.8}$$ and $$r^{-1.0}$$) much more consistent with predictions from dark matter only simulations. At the resolution of our Dark Energy Survey imaging, we are unable to choose between these two models, but we make predictions for forthcoming Hubble Space Telescope imaging that will decisively distinguish between them.« less
Linear perturbation theory for tidal streams and the small-scale CDM power spectrum

NASA Astrophysics Data System (ADS)

Bovy, Jo; Erkal, Denis; Sanders, Jason L.

2017-04-01

Tidal streams in the Milky Way are sensitive probes of the population of low-mass dark matter subhaloes predicted in cold dark matter (CDM) simulations. We present a new calculus for computing the effect of subhalo fly-bys on cold streams based on the action-angle representation of streams. The heart of this calculus is a line-of-parallel-angle approach that calculates the perturbed distribution function of a stream segment by undoing the effect of all relevant impacts. This approach allows one to compute the perturbed stream density and track in any coordinate system in minutes for realizations of the subhalo distribution down to 105 M⊙, accounting for the stream's internal dispersion and overlapping impacts. We study the statistical properties of density and track fluctuations with large suites of simulations of the effect of subhalo fly-bys. The one-dimensional density and track power spectra along the stream trace the subhalo mass function, with higher mass subhaloes producing power only on large scales, while lower mass subhaloes cause structure on smaller scales. We also find significant density and track bispectra that are observationally accessible. We further demonstrate that different projections of the track all reflect the same pattern of perturbations, facilitating their observational measurement. We apply this formalism to data for the Pal 5 stream and make a first rigorous determination of 10^{+11}_{-6} dark matter subhaloes with masses between 106.5 and 109 M⊙ within 20 kpc from the Galactic centre [corresponding to 1.4^{+1.6}_{-0.9} times the number predicted by CDM-only simulations or to fsub(r < 20 kpc) ≈ 0.2 per cent] assuming that the Pal 5 stream is 5 Gyr old. Improved data will allow measurements of the subhalo mass function down to 105 M⊙, thus definitively testing whether dark matter is clumpy on the smallest scales relevant for galaxy formation.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Zackrisson, Erik; Rydberg, Claes-Erik; Oestlin, Goeran

The first stars in the history of the universe are likely to form in the dense central regions of {approx}10{sup 5}-10{sup 6} M{sub sun} cold dark matter halos at z {approx} 10-50. The annihilation of dark matter particles in these environments may lead to the formation of so-called dark stars, which are predicted to be cooler, larger, more massive, and potentially more long-lived than conventional population III stars. Here, we investigate the prospects of detecting high-redshift dark stars with the upcoming James Webb Space Telescope (JWST). We find that all dark stars with masses up to 10{sup 3} M{sub sun}more » are intrinsically too faint to be detected by JWST at z > 6. However, by exploiting foreground galaxy clusters as gravitational telescopes do, certain varieties of cool (T{sub eff} {<=} 30, 000 K) dark stars should be within reach at redshifts up to z {approx} 10. If the lifetimes of dark stars are sufficiently long, many such objects may also congregate inside the first galaxies. We demonstrate that this could give rise to peculiar features in the integrated spectra of galaxies at high redshifts, provided that dark stars make up at least {approx}1% of the total stellar mass in such objects.« less
Extensive investigation of the generalized dark matter model

NASA Astrophysics Data System (ADS)

Kopp, Michael; Skordis, Constantinos; Thomas, Dan B.

2016-08-01

The cold dark matter (CDM) model, wherein the dark matter is treated as a pressureless perfect fluid, provides a good fit to galactic and cosmological data. With the advent of precision cosmology, it should be asked whether this simplest model needs to be extended, and whether doing so could improve our understanding of the properties of dark matter. One established parametrization for generalizing the CDM fluid is the generalized dark matter (GDM) model, in which dark matter is an imperfect fluid with pressure and shear viscosity that fulfill certain postulated closure equations. We investigate these closure equations and the three new parametric functions they contain: the background equation of state w , the speed of sound cs2 and the viscosity cvis2. Taking these functions to be constant parameters, we analyze an exact solution of the perturbed Einstein equations in a flat GDM-dominated universe and discuss the main effects of the three parameters on the cosmic microwave background (CMB). Our analysis suggests that the CMB alone is not able to distinguish between the GDM sound speed and viscosity parameters, but that other observables, such as the matter power spectrum, are required to break this degeneracy. In order to elucidate further the meaning of the GDM closure equations, we also consider other descriptions of imperfect fluids that have a nonperturbative definition and relate these to the GDM model. In particular, we consider scalar fields, an effective field theory (EFT) of fluids, an EFT of large-scale structure, nonequilibrium thermodynamics and tightly coupled fluids. These descriptions could be used to extend the GDM model into the nonlinear regime of structure formation, which is necessary if the wealth of data available on those scales is to be employed in constraining the model. We also derive the initial conditions for adiabatic and isocurvature perturbations in the presence of GDM and standard cosmological fluids and provide the result in a form ready for implementation in Einstein-Boltzmann solvers.
Cosmology with a stiff matter era

NASA Astrophysics Data System (ADS)

Chavanis, Pierre-Henri

2015-11-01

We consider the possibility that the Universe is made of a dark fluid described by a quadratic equation of state P =K ρ2 , where ρ is the rest-mass density and K is a constant. The energy density ɛ =ρ c2+K ρ2 is the sum of two terms: a rest-mass term ρ c2 that mimics "dark matter" (P =0 ) and an internal energy term u =K ρ2=P that mimics a "stiff fluid" (P =ɛ ) in which the speed of sound is equal to the speed of light. In the early universe, the internal energy dominates and the dark fluid behaves as a stiff fluid (P ˜ɛ , ɛ ∝a-6). In the late universe, the rest-mass energy dominates and the dark fluid behaves as pressureless dark matter (P ≃0 , ɛ ∝a-3). We provide a simple analytical solution of the Friedmann equations for a universe undergoing a stiff matter era, a dark matter era, and a dark energy era due to the cosmological constant. This analytical solution generalizes the Einstein-de Sitter solution describing the dark matter era, and the Λ CDM model describing the dark matter era and the dark energy era. Historically, the possibility of a primordial stiff matter era first appeared in the cosmological model of Zel'dovich where the primordial universe is assumed to be made of a cold gas of baryons. A primordial stiff matter era also occurs in recent cosmological models where dark matter is made of relativistic self-gravitating Bose-Einstein condensates (BECs). When the internal energy of the dark fluid mimicking stiff matter is positive, the primordial universe is singular like in the standard big bang theory. It expands from an initial state with a vanishing scale factor and an infinite density. We consider the possibility that the internal energy of the dark fluid is negative (while, of course, its total energy density is positive), so that it mimics anti-stiff matter. This happens, for example, when the BECs have an attractive self-interaction with a negative scattering length. In that case, the primordial universe is nonsingular and bouncing like in loop quantum cosmology. At t =0 , the scale factor is finite and the energy density is equal to zero. The universe first has a phantom behavior where the energy density increases with the scale factor, then a normal behavior where the energy density decreases with the scale factor. For the sake of generality, we consider a cosmological constant of arbitrary sign. When the cosmological constant is positive, the Universe asymptotically reaches a de Sitter regime where the scale factor increases exponentially rapidly with time. This can account for the accelerating expansion of the Universe that we observe at present. When the cosmological constant is negative (anti-de Sitter), the evolution of the Universe is cyclic. Therefore, depending on the sign of the internal energy of the dark fluid and on the sign of the cosmological constant, we obtain analytical solutions of the Friedmann equations describing singular and nonsingular expanding, bouncing, or cyclic universes.
Is cosmic acceleration slowing down?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shafieloo, Arman; Sahni, Varun; Starobinsky, Alexei A.

2009-11-15

We investigate the course of cosmic expansion in its recent past using the Constitution SN Ia sample, along with baryon acoustic oscillations (BAO) and cosmic microwave background (CMB) data. Allowing the equation of state of dark energy (DE) to vary, we find that a coasting model of the universe (q{sub 0}=0) fits the data about as well as Lambda cold dark matter. This effect, which is most clearly seen using the recently introduced Om diagnostic, corresponds to an increase of Om and q at redshifts z < or approx. 0.3. This suggests that cosmic acceleration may have already peaked andmore » that we are currently witnessing its slowing down. The case for evolving DE strengthens if a subsample of the Constitution set consisting of SNLS+ESSENCE+CfA SN Ia data is analyzed in combination with BAO+CMB data. The effect we observe could correspond to DE decaying into dark matter (or something else)« less

Gravitational redshift of galaxies in clusters as predicted by general relativity.

PubMed

Wojtak, Radosław; Hansen, Steen H; Hjorth, Jens

2011-09-28

The theoretical framework of cosmology is mainly defined by gravity, of which general relativity is the current model. Recent tests of general relativity within the Lambda Cold Dark Matter (ΛCDM) model have found a concordance between predictions and the observations of the growth rate and clustering of the cosmic web. General relativity has not hitherto been tested on cosmological scales independently of the assumptions of the ΛCDM model. Here we report an observation of the gravitational redshift of light coming from galaxies in clusters at the 99 per cent confidence level, based on archival data. Our measurement agrees with the predictions of general relativity and its modification created to explain cosmic acceleration without the need for dark energy (the f(R) theory), but is inconsistent with alternative models designed to avoid the presence of dark matter. © 2011 Macmillan Publishers Limited. All rights reserved
Cosmological structure formation in Decaying Dark Matter models

NASA Astrophysics Data System (ADS)

Cheng, Dalong; Chu, M.-C.; Tang, Jiayu

2015-07-01

The standard cold dark matter (CDM) model predicts too many and too dense small structures. We consider an alternative model that the dark matter undergoes two-body decays with cosmological lifetime τ into only one type of massive daughters with non-relativistic recoil velocity Vk. This decaying dark matter model (DDM) can suppress the structure formation below its free-streaming scale at time scale comparable to τ. Comparing with warm dark matter (WDM), DDM can better reduce the small structures while being consistent with high redshfit observations. We study the cosmological structure formation in DDM by performing self-consistent N-body simulations and point out that cosmological simulations are necessary to understand the DDM structures especially on non-linear scales. We propose empirical fitting functions for the DDM suppression of the mass function and the concentration-mass relation, which depend on the decay parameters lifetime τ, recoil velocity Vk and redshift. The fitting functions lead to accurate reconstruction of the the non-linear power transfer function of DDM to CDM in the framework of halo model. Using these results, we set constraints on the DDM parameter space by demanding that DDM does not induce larger suppression than the Lyman-α constrained WDM models. We further generalize and constrain the DDM models to initial conditions with non-trivial mother fractions and show that the halo model predictions are still valid after considering a global decayed fraction. Finally, we point out that the DDM is unlikely to resolve the disagreement on cluster numbers between the Planck primary CMB prediction and the Sunyaev-Zeldovich (SZ) effect number count for τ ~ H0-1.
The evolution of X-ray clusters in a cold plus hot dark matter universe

NASA Technical Reports Server (NTRS)

Bryan, Greg L.; Klypin, Anatoly; Loken, Chris; Norman, Michael L.; Burns, Jack O.

1994-01-01

We present the first self-consistently computed results on the evolution of X-ray properties of galaxy clusters in a cold + hot dark matter (CHDM) model. We have performed a hydrodynamic plus N-body simulation for the COBE-compatible CHDM model with standard mass components: Omega(sub hot) = 0.3, Omega (sub cold) = 0.6 and Omega(sub baryon) = 0.1 (h = 0.5). In contrast with the CDM model, which fails to reproduce the observed temperature distribution function dN/dT (Bryan et al. 1994b), the CHDM model fits the observational dN/dT quite well. Our results on X-ray luminosity are less firm but even more intriguing. We find that the resulting X-ray luminosity functions at redshifts z = 0.0, 0.2, 0.4, 0.7 are well fit by observations, where they overlap. The fact that both temperatures and luminosities provide a reasonable fit to the available observational data indicates that, unless we are missing some essential physics, there is neither room nor need for a large fraction of gas in rich clusters: 10% (or less) in baryons is sufficient to explain their X-ray properties. We also see a tight correlation between X-ray luminosity and gas temperature.
The median density of the Universe

NASA Astrophysics Data System (ADS)

Stücker, Jens; Busch, Philipp; White, Simon D. M.

2018-07-01

Despite the fact that the mean matter density of the Universe has been measured to an accuracy of a few per cent within the standard Λcold dark matter (ΛCDM) paradigm, its median density is not known even to the order of magnitude. Typical points lie in low-density regions and are not part of a collapsed structure of any scale. Locally, the dark matter distribution is then simply a stretched version of that in the early Universe. In this single-stream regime, the distribution of unsmoothed density is sensitive to the initial power spectrum on all scales, in particular on very small scales, and hence to the nature of the dark matter. It cannot be estimated reliably using conventional cosmological simulations because of the enormous dynamic range involved, but a suitable excursion set procedure can be used instead. For the Planck cosmological parameters, a 100 GeV WIMP, corresponding to a free-streaming mass ˜10-6M⊙, results in a median density of ˜4 × 10-3 in units of the mean density, whereas a 10 μeV axion with free-streaming mass ˜10-12M⊙ gives ˜3 × 10-3, and warm dark matter (WDM) with a (thermal relic) mass of 1 keV gives ˜8 × 10-2. In CDM (but not in WDM) universes, single-stream regions are predicted to be topologically isolated by the excursion set formalism. A test by direct N-body simulations seems to confirm this prediction, although it is still subject to finite size and resolution effects. Unfortunately, it is unlikely that any of these properties is observable and so suitable for constraining the properties of dark matter.
Alternative to particle dark matter

NASA Astrophysics Data System (ADS)

Khoury, Justin

2015-01-01

We propose an alternative to particle dark matter that borrows ingredients of modified Newtonian dynamics (MOND) while adding new key components. The first new feature is a dark matter fluid, in the form of a scalar field with small equation of state and sound speed. This component is critical in reproducing the success of cold dark matter for the expansion history and the growth of linear perturbations, but does not cluster significantly on nonlinear scales. Instead, the missing mass problem on nonlinear scales is addressed by a modification of the gravitational force law. The force law approximates MOND at large and intermediate accelerations, and therefore reproduces the empirical success of MOND at fitting galactic rotation curves. At ultralow accelerations, the force law reverts to an inverse-square law, albeit with a larger Newton's constant. This latter regime is important in galaxy clusters and is consistent with their observed isothermal profiles, provided the characteristic acceleration scale of MOND is mildly varying with scale or mass, such that it is 12 times higher in clusters than in galaxies. We present an explicit relativistic theory in terms of two scalar fields. The first scalar field is governed by a Dirac-Born-Infeld action and behaves as a dark matter fluid on large scales. The second scalar field also has single-derivative interactions and mediates a fifth force that modifies gravity on nonlinear scales. Both scalars are coupled to matter via an effective metric that depends locally on the fields. The form of this effective metric implies the equality of the two scalar gravitational potentials, which ensures that lensing and dynamical mass estimates agree. Further work is needed in order to make both the acceleration scale of MOND and the fraction at which gravity reverts to an inverse-square law explicitly dynamical quantities, varying with scale or mass.
Vector dark energy and high-z massive clusters

NASA Astrophysics Data System (ADS)

Carlesi, Edoardo; Knebe, Alexander; Yepes, Gustavo; Gottlöber, Stefan; Jiménez, Jose Beltrán.; Maroto, Antonio L.

2011-12-01

The detection of extremely massive clusters at z > 1 such as SPT-CL J0546-5345, SPT-CL J2106-5844 and XMMU J2235.3-2557 has been considered by some authors as a challenge to the standard Λ cold dark matter cosmology. In fact, assuming Gaussian initial conditions, the theoretical expectation of detecting such objects is as low as ≤1 per cent. In this paper we discuss the probability of the existence of such objects in the light of the vector dark energy paradigm, showing by means of a series of N-body simulations that chances of detection are substantially enhanced in this non-standard framework.
Reionization in sterile neutrino cosmologies

NASA Astrophysics Data System (ADS)

Bose, Sownak; Frenk, Carlos S.; Hou, Jun; Lacey, Cedric G.; Lovell, Mark R.

2016-12-01

We investigate the process of reionization in a model in which the dark matter is a warm elementary particle such as a sterile neutrino. We focus on models that are consistent with the dark matter decay interpretation of the recently detected line at 3.5 keV in the X-ray spectra of galaxies and clusters. In warm dark matter models, the primordial spectrum of density perturbations has a cut-off on the scale of dwarf galaxies. Structure formation therefore begins later than in the standard cold dark matter (CDM) model and very few objects form below the cut-off mass scale. To calculate the number of ionizing photons, we use the Durham semi-analytic model of galaxy formation, GALFORM. We find that even the most extreme 7 keV sterile neutrino we consider is able to reionize the Universe early enough to be compatible with the bounds on the epoch of reionization from Planck. This, perhaps surprising, result arises from the rapid build-up of high redshift galaxies in the sterile neutrino models which is also reflected in a faster evolution of their far-UV luminosity function between 10 > z > 7 than in CDM. The dominant sources of ionizing photons are systematically more massive in the sterile neutrino models than in CDM. As a consistency check on the models, we calculate the present-day luminosity function of satellites of Milky Way-like galaxies. When the satellites recently discovered in the Dark Energy Survey are taken into account, strong constraints are placed on viable sterile neutrino models.
Does lower Omega allow a resolution of the large-scale structure problem?

NASA Technical Reports Server (NTRS)

Silk, Joseph; Vittorio, Nicola

1987-01-01

The intermediate angular scale anisotropy of the cosmic microwave background, peculiar velocities, density correlations, and mass fluctuations for both neutrino and baryon-dominated universes with Omega less than one are evaluated. The large coherence length associated with a low-Omega, hot dark matter-dominated universe provides substantial density fluctuations on scales up to 100 Mpc: there is a range of acceptable models that are capable of producing large voids and superclusters of galaxies and the clustering of galaxy clusters, with Omega roughly 0.3, without violating any observational constraint. Low-Omega, cold dark matter-dominated cosmologies are also examined. All of these models may be reconciled with the inflationary requirement of a flat universe by introducing a cosmological constant 1-Omega.
The Dynamics of the Local Group in the Era of Precision Astrometry

NASA Astrophysics Data System (ADS)

Besla, Gurtina; Garavito-Camargo, Nicolas; Patel, Ekta

2018-06-01

Our understanding of the dynamics of our Local Group of galaxies has changed dramatically over the past few years owing to significant advancements in astrometry and our theoretical understanding of galaxy structure. New surveys now enable us to map the 3D structure of our Milky Way and the dynamics of tracers of its dark matter distribution, like globular clusters, satellite galaxies and streams, with unprecedented precision. Some results have met with controversy, challenging preconceived notions of the orbital dynamics of key components of the Local Group. I will provide an overview of this evolving picture of our Local Group and outline how we can test the cold dark matter paradigm in the era of Gaia, LSST and JWST.
DICE/ColDICE: 6D collisionless phase space hydrodynamics using a lagrangian tesselation

NASA Astrophysics Data System (ADS)

Sousbie, Thierry

2018-01-01

DICE is a C++ template library designed to solve collisionless fluid dynamics in 6D phase space using massively parallel supercomputers via an hybrid OpenMP/MPI parallelization. ColDICE, based on DICE, implements a cosmological and physical VLASOV-POISSON solver for cold systems such as dark matter (CDM) dynamics.
Gluino coannihilation revisited

DOE PAGES

Ellis, John; Luo, Feng; Olive, Keith A.

2015-09-21

In this study, some variants of the MSSM feature a strip in parameter space where the lightest neutralino χ is identified as the lightest supersymmetric particle (LSP), the gluino g ~ is the next-to-lightest supersymmetric particle (NLSP) and is nearly degenerate with χ, and the relic cold dark matter density is brought into the range allowed by astrophysics and cosmology by coannihilation with the gluino NLSP. We calculate the relic density along this gluino coannihilation strip in the MSSM, including the effects of gluino-gluino bound states and initial-state Sommerfeld enhancement, and taking into account the decoupling of the gluino andmore » LSP densities that occurs for large values of the squark mass m q ~. We find that bound-state effects can increase the maximum m χ for which the relic cold dark matter density lies within the range favoured by astrophysics and cosmology by as much as ~50% if m q ~/m g ~=1.1 , and that the LSP may weigh up to ~8 TeV for a wide range of m q ~/m g ~≲100 .« less
The formation of cosmic structure in a texture-seeded cold dark matter cosmogony

NASA Technical Reports Server (NTRS)

Gooding, Andrew K.; Park, Changbom; Spergel, David N.; Turok, Neil; Gott, Richard, III

1992-01-01

The growth of density fluctuations induced by global texture in an Omega = 1 cold dark matter (CDM) cosmogony is calculated. The resulting power spectra are in good agreement with each other, with more power on large scales than in the standard inflation plus CDM model. Calculation of related statistics (two-point correlation functions, mass variances, cosmic Mach number) indicates that the texture plus CDM model compares more favorably than standard CDM with observations of large-scale structure. Texture produces coherent velocity fields on large scales, as observed. Excessive small-scale velocity dispersions, and voids less empty than those observed may be remedied by including baryonic physics. The topology of the cosmic structure agrees well with observation. The non-Gaussian texture induced density fluctuations lead to earlier nonlinear object formation than in Gaussian models and may also be more compatible with recent evidence that the galaxy density field is non-Gaussian on large scales. On smaller scales the density field is strongly non-Gaussian, but this appears to be primarily due to nonlinear gravitational clustering. The velocity field on smaller scales is surprisingly Gaussian.
Galactic disks, infall, and the global value of Omega

NASA Technical Reports Server (NTRS)

Toth, G.; Ostriker, J. P.

1992-01-01

Stringent limits on the current rate of infall of satellite systems onto spiral galaxies are set on the basis of the thinness and coldness of Galactic disks. For infalling satellites on isotropically oriented circular orbits, it is shown that, due to scattering, the thermal energy gain of the disk exceeds the satellite energy loss from dynamical friction by a factor of 1.6, with 25 percent deposited in z motion and 75 percent in planar motions. It is found that no more than 4 percent of the Galactic mass inside the solar radius can have accreted within the last 5 billion years, or else its scale and its Toomre Q-parameter would exceed observed values. In standard cold-dark-matter-dominated models for the growth of structure with Omega sub tot of 1, the mass accreted in dark matter lumps rises faster than t exp 2/3 and would exceed 28 percent in the last 5 Gyr. It is proposed that heating from satellite infall accounts for a substantial fraction of the increase of velocity dispersion and scale height with age that is observed in the Galaxy.
New astrophysical bounds on ultralight axionlike particles

DOE PAGES

Banik, Nilanjan; Christopherson, Adam J.; Sikivie, Pierre; ...

2017-02-15

Motivated by tension between the predictions of ordinary cold dark matter (CDM) and observations at galactic scales, ultralight axionlike particles (ULALPs) with mass of the order 10 -22 eV have been proposed as an alternative CDM candidate. We consider cold and collisionless ULALPs produced in the early Universe by the vacuum realignment mechanism and constituting most of CDM. The ULALP fluid is commonly described by classical field equations. However, we show that, like QCD axions, the ULALPs thermalize by gravitational self-interactions and form a Bose-Einstein condensate, a quantum phenomenon. ULALPs, like QCD axions, explain the observational evidence for caustic ringsmore » of dark matter because they thermalize and go to the lowest energy state available to them. This is one of rigid rotation on the turnaround sphere. Here, by studying the heating effect of infalling ULALPs on galactic disk stars and the thickness of the nearby caustic ring as observed from a triangular feature in the infrared astronomical satellite map of our galactic disk, we obtain lower-mass bounds on the ULALP mass of order 10 -23 and 10 -20 eV, respectively.« less
Simulated cosmic microwave background maps at 0.5 deg resolution: Unresolved features

NASA Technical Reports Server (NTRS)

Kogut, A.; Hinshaw, G.; Bennett, C. L.

1995-01-01

High-contrast peaks in the cosmic microwave background (CMB) anisotropy can appear as unresolved sources to observers. We fit simluated CMB maps generated with a cold dark matter model to a set of unresolved features at instrumental resolution 0.5 deg-1.5 deg to derive the integral number density per steradian n (greater than absolute value of T) of features brighter than threshold temperature absolute value of T and compare the results to recent experiments. A typical medium-scale experiment observing 0.001 sr at 0.5 deg resolution would expect to observe one feature brighter than 85 micro-K after convolution with the beam profile, with less than 5% probability to observe a source brighter than 150 micro-K. Increasing the power-law index of primordial density perturbations n from 1 to 1.5 raises these temperature limits absolute value of T by a factor of 2. The MSAM features are in agreement with standard cold dark matter models and are not necessarily evidence for processes beyond the standard model.
Formation of the Galactic Stellar Halo: Origin of the Metallicity-Eccentricity Relation.

PubMed

Bekki; Chiba

2000-05-01

Motivated by the recently improved knowledge on the kinematic and chemical properties of the Galactic metal-poor stars, we present the numerical simulation for the formation of the Galactic stellar halo to interpret the observational results. As a model for the Galaxy contraction, we adopt the currently standard theory of galaxy formation based on the hierarchical assembly of the cold dark matter fluctuations. We find, for the simulated stars with &sqbl0;Fe&solm0;H&sqbr0;
Resonant sterile neutrino dark matter in the local and high-z Universe

NASA Astrophysics Data System (ADS)

Bozek, Brandon; Boylan-Kolchin, Michael; Horiuchi, Shunsaku; Garrison-Kimmel, Shea; Abazajian, Kevork; Bullock, James S.

2016-06-01

Sterile neutrinos comprise an entire class of dark matter models that, depending on their production mechanism, can be hot, warm, or cold dark matter (CDM). We simulate the Local Group and representative volumes of the Universe in a variety of sterile neutrino models, all of which are consistent with the possible existence of a radiative decay line at ˜3.5 keV. We compare models of production via resonances in the presence of a lepton asymmetry (suggested by Shi & Fuller 1999) to `thermal' models. We find that properties in the highly non-linear regime - e.g. counts of satellites and internal properties of haloes and subhaloes - are insensitive to the precise fall-off in power with wavenumber, indicating that non-linear evolution essentially washes away differences in the initial (linear) matter power spectrum. In the quasi-linear regime at higher redshifts, however, quantitative differences in the 3D matter power spectra remain, raising the possibility that such models can be tested with future observations of the Lyman-α forest. While many of the sterile neutrino models largely eliminate multiple small-scale issues within the CDM paradigm, we show that these models may be ruled out in the near future via discoveries of additional dwarf satellites in the Local Group.
Anisotropic Galaxy-Galaxy Lensing in the Illustris-1 Simulation

NASA Astrophysics Data System (ADS)

Brainerd, Tereasa G.

2017-06-01

In Cold Dark Matter universes, the dark matter halos of galaxies are expected to be triaxial, leading to a surface mass density that is not circularly symmetric. In principle, this "flattening" of the dark matter halos of galaxies should be observable as an anisotropy in the weak galaxy-galaxy lensing signal. The degree to which the weak lensing signal is observed to be anisotropic, however, will depend strongly on the degree to which mass (i.e., the dark matter) is aligned with light in the lensing galaxies. That is, the anisotropy will be maximized when the major axis of the projected mass distribution is well aligned with the projected light distribution of the lens galaxies. Observational studies of anisotropic galaxy-galaxy lensing have found an anisotropic weak lensing signal around massive, red galaxies. Detecting the signal around blue, disky galaxies has, however, been more elusive. A possible explanation for this is that mass and light are well aligned within red galaxies and poorly aligned within blue galaxies (an explanation that is supported by studies of the locations of satellites of large, relatively isolated galaxies). Here we compute the weak lensing signal of isolated central galaxies in the Illustris-1 simulation. We compute the anisotropy of the weak lensing signal using two definitions of the geometry: [1] the major axis of the projected dark matter mass distribution and [2] the major axis of the projected stellar mass. On projected scales less than 15% of the virial radius, an anisotropy of order 10% is found for both definitions of the geometry. On larger scales, the anisotropy computed relative to the major axis of the projected light distribution is less than the anisotropy computed relative to the major axis of the projected dark matter. On projected scales of order the virial radius, the anisotropy obtained when using the major axis of the light is an order of magnitude less than the anisotropy obtained when using the major axis of the dark matter. The suppression of the anisotropy when using the major axis of the light to define the geometry is indicative of a significant misalignment of mass and light in the Illustris-1 galaxies at large physical radii.
Radiative Natural Supersymmetry with Mixed Axion/Higgsino Cold Dark Matter

NASA Astrophysics Data System (ADS)

Baer, Howard

Models of natural supersymmetry seek to solve the little hierarchy problem by positing a spectrum of light higgsinos ≲ 200 GeV and light top squarks ≲ 500 GeV along with very heavy squarks and TeV-scale gluinos. Such models have low electroweak finetuning and are safe from LHC searches. However, in the context of the MSSM, they predict too low a value of m h and the relic density of thermally produced higgsino-like WIMPs falls well below dark matter (DM) measurements. Allowing for high scale soft SUSY breaking Higgs mass m H u > m 0 leads to natural cancellations during RG running, and to radiatively induced low finetuning at the electroweak scale. This model of radiative natural SUSY (RNS), with large mixing in the top squark sector, allows for finetuning at the 5-10 % level with TeV-scale top squarks and a 125 GeV light Higgs scalar h. If the strong CP problem is solved via the PQ mechanism, then we expect an axion-higgsino admixture of dark matter, where either or both the DM particles might be directly detected.
Radiative natural supersymmetry with mixed axion/higgsino cold dark matter

NASA Astrophysics Data System (ADS)

Baer, Howard

2013-05-01

Models of natural supersymmetry seek to solve the little hierarchy problem by positing a spectrum of light higgsinos <~ 200 GeV and light top squarks <~ 500 GeV along with very heavy squarks and TeV-scale gluinos. Such models have low electroweak finetuning and are safe from LHC searches. However, in the context of the MSSM, they predict too low a value of mh and the relic density of thermally produced higgsino-like WIMPs falls well below dark matter (DM) measurements. Allowing for high scale soft SUSY breaking Higgs mass mHu > m0 leads to natural cancellations during RG running, and to radiatively induced low finetuning at the electroweak scale. This model of radiative natural SUSY (RNS), with large mixing in the top squark sector, allows for finetuning at the 5-10% level with TeV-scale top squarks and a 125 GeV light Higgs scalar h. If the strong CP problem is solved via the PQ mechanism, then we expect an axion-higgsino admixture of dark matter, where either or both the DM particles might be directly detected.

The three-point function as a probe of models for large-scale structure

NASA Astrophysics Data System (ADS)

Frieman, Joshua A.; Gaztanaga, Enrique

1994-04-01

We analyze the consequences of models of structure formation for higher order (n-point) galaxy correlation functions in the mildly nonlinear regime. Several variations of the standard Omega = 1 cold dark matter model with scale-invariant primordial perturbations have recently been introduced to obtain more power on large scales, Rp is approximately 20/h Mpc, e.g., low matter-density (nonzero cosmological constant) models, 'tilted' primordial spectra, and scenarios with a mixture of cold and hot dark matter. They also include models with an effective scale-dependent bias, such as the cooperative galaxy formation scenario of Bower et al. We show that higher-order (n-point) galaxy correlation functions can provide a useful test of such models and can discriminate between models with true large-scale power in the density field and those where the galaxy power arises from scale-dependent bias: a bias with rapid scale dependence leads to a dramatic decrease of the the hierarchical amplitudes QJ at large scales, r is greater than or approximately Rp. Current observational constraints on the three-point amplitudes Q3 and S3 can place limits on the bias parameter(s) and appear to disfavor, but not yet rule out, the hypothesis that scale-dependent bias is responsible for the extra power observed on large scales.
A new approach to simulating collisionless dark matter fluids

NASA Astrophysics Data System (ADS)

Hahn, Oliver; Abel, Tom; Kaehler, Ralf

2013-09-01

Recently, we have shown how current cosmological N-body codes already follow the fine grained phase-space information of the dark matter fluid. Using a tetrahedral tessellation of the three-dimensional manifold that describes perfectly cold fluids in six-dimensional phase space, the phase-space distribution function can be followed throughout the simulation. This allows one to project the distribution function into configuration space to obtain highly accurate densities, velocities and velocity dispersions. Here, we exploit this technique to show first steps on how to devise an improved particle-mesh technique. At its heart, the new method thus relies on a piecewise linear approximation of the phase-space distribution function rather than the usual particle discretization. We use pseudo-particles that approximate the masses of the tetrahedral cells up to quadrupolar order as the locations for cloud-in-cell (CIC) deposit instead of the particle locations themselves as in standard CIC deposit. We demonstrate that this modification already gives much improved stability and more accurate dynamics of the collisionless dark matter fluid at high force and low mass resolution. We demonstrate the validity and advantages of this method with various test problems as well as hot/warm dark matter simulations which have been known to exhibit artificial fragmentation. This completely unphysical behaviour is much reduced in the new approach. The current limitations of our approach are discussed in detail and future improvements are outlined.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Ellis, John; Evans, Jason L.; Nagata, Natsumi

We reconsider the minimal SU( 5) grand unified theory (GUT) in the context of no-scale supergravity inspired by string compactification scenarios, assuming that the soft supersymmetry-breaking parameters satisfy universality conditions at some input scale M in above the GUT scale M GUT. When setting up such a no-scale super-GUT model, special attention must be paid to avoiding the Scylla of rapid proton decay and the Charybdis of an excessive density of cold dark matter, while also having an acceptable mass for the Higgs boson. Furthermore, we do not find consistent solutions if none of the matter and Higgs fields aremore » assigned to twisted chiral supermultiplets, even in the presence of Giudice–Masiero terms. But, consistent solutions may be found if at least one fiveplet of GUT Higgs fields is assigned to a twisted chiral supermultiplet, with a suitable choice of modular weights. Spin-independent dark matter scattering may be detectable in some of these consistent solutions.« less
Voids as alternatives to dark energy and the propagation of γ rays through the universe.

PubMed

DeLavallaz, Arnaud; Fairbairn, Malcolm

2012-04-27

We test the opacity of a void universe to TeV energy γ rays having obtained the extragalactic background light in that universe using a simple model and the observed constraints on the star formation rate history. We find that the void universe has significantly more opacity than a Λ cold dark matter universe, putting it at odds with observations of BL-Lac objects. We argue that while this method of distinguishing between the two cosmologies contains uncertainties, it circumvents any debates over fine-tuning.
Cosmic strings and superconducting cosmic strings

NASA Technical Reports Server (NTRS)

Copeland, Edmund

1988-01-01

The possible consequences of forming cosmic strings and superconducting cosmic strings in the early universe are discussed. Lecture 1 describes the group theoretic reasons for and the field theoretic reasons why cosmic strings can form in spontaneously broken gauge theories. Lecture 2 discusses the accretion of matter onto string loops, emphasizing the scenario with a cold dark matter dominated universe. In lecture 3 superconducting cosmic strings are discussed, as is a mechanism which leads to the formation of structure from such strings.
Secondary ionization in a flat universe

NASA Technical Reports Server (NTRS)

Atrio-Barandela, F.; Doroshkevich, A. G.

1994-01-01

We analyze the effect of a secondary ionization on the evolution of temperature fluctuations in cosmic background radiation. The main results presented in this paper are appropriate analytic expressions of the transfer function relating temperature fluctuations to matter density perturbations at recombination for all possible recombination histories. Furthermore, we particularize our calculation to the standard cold dark matter model, where we study the erasure of primordial temperature fluctuations and calculate the magnitude and angular scale of the damping induced by a late recombination.
On the late-time cosmology of a condensed scalar field

NASA Astrophysics Data System (ADS)

Ghalee, Amir

2016-04-01

We study the late-time cosmology of a scalar field with a kinetic term non-minimally coupled to gravity. It is demonstrated that the scalar field dominate the radiation matter and the cold dark matter (CDM). Moreover, we show that eventually the scalar field will be condensed and results in an accelerated expansion. The metric perturbations around the condensed phase of the scalar field are investigated and it has been shown that the ghost instability and gradient instability do not exist.
Gravitational vacuum energy in our recently accelerating universe

NASA Astrophysics Data System (ADS)

Bludman, Sidney

2009-04-01

We review current observations of the homogeneous cosmological expansion which, because they measure only kinematic variables, cannot determine the dynamics driving the recent accelerated expansion. The minimal fit to the data, the flat ACDM model, consisting of cold dark matter and a cosmological constant, interprets 4? geometrically as a classical spacetime curvature constant of nature, avoiding any reference to quantum vacuum energy. (The observed Uehling and Casimir effects measure forces due to QED vacuum polarization, but not any quantum material vacuum energies.) An Extended Anthropic Principle, that Dark Energy and Dark Gravity be indistinguishable, selects out flat ACDM. Prospective cosmic shear and galaxy clustering observations of the growth of fluctuations are intended to test whether the 'dark energy' driving the recent cosmological acceleration is static or moderately dynamic. Even if dynamic, observational differences between an additional negative-pressure material component within general relativity (Dark Energy) and low-curvature modifications of general relativity (Dark Gravity) will be extremely small.
Natural X-ray lines from the low scale supersymmetry breaking

NASA Astrophysics Data System (ADS)

Kang, Zhaofeng; Ko, P.; Li, Tianjun; Liu, Yandong

2015-03-01

In the supersymmetric models with low scale supersymmetry (SUSY) breaking where the gravitino mass is around keV, we show that the 3.5 keV X-ray lines can be explained naturally through several different mechanisms: (I) a keV scale dark gaugino plays the role of sterile neutrino in the presence of bilinear R-parity violation. Because the light dark gaugino obtains Majorana mass only via gravity mediation, it is a decaying warm dark matter (DM) candidate; (II) the compressed cold DM states, whose mass degeneracy is broken by gravity mediated SUSY breaking, emit such a line via the heavier one decay into the lighter one plus photon(s). A highly supersymmetric dark sector may readily provide such kind of system; (III) the light axino, whose mass again is around the gravitino mass, decays to neutrino plus gamma in the R-parity violating SUSY. Moreover, we comment on dark radiation from dark gaugino.
Universal subhalo accretion in cold and warm dark matter cosmologies

NASA Astrophysics Data System (ADS)

Kubik, Bogna; Libeskind, Noam I.; Knebe, Alexander; Courtois, Hélène; Yepes, Gustavo; Gottlöber, Stefan; Hoffman, Yehuda

2017-12-01

The influence of the large-scale structure on host haloes may be studied by examining the angular infall pattern of subhaloes. In particular, since warm dark matter (WDM) and cold dark matter (CDM) cosmologies predict different abundances and internal properties for haloes at the low-mass end of the mass function, it is interesting to examine if there are differences in how these low-mass haloes are accreted. The accretion events are defined as the moment a halo becomes a substructure, namely when it crosses its host's virial radius. We quantify the cosmic web at each point by the shear tensor and examine where, with respect to its eigenvectors, such accretion events occur in ΛCDM and ΛWDM (1 keV sterile neutrino) cosmological models. We find that the CDM and WDM subhaloes are preferentially accreted along the principal axis of the shear tensor corresponding to the direction of weakest collapse. The beaming strength is modulated by the host and subhalo masses and by the redshift at which the accretion event occurs. Although strongest for the most massive hosts and subhaloes at high redshift, the preferential infall is found to be always aligned with the axis of weakest collapse, thus we say that it has universal nature. We compare the strength of beaming in the ΛWDM cosmology with the one found in the ΛCDM scenario. While the main findings remain the same, the accretion in the ΛWDM model for the most massive host haloes appears more beamed than in ΛCDM cosmology across all the redshifts.
Imprints of non-standard dark energy and dark matter models on the 21cm intensity map power spectrum

NASA Astrophysics Data System (ADS)

Carucci, Isabella P.; Corasaniti, Pier-Stefano; Viel, Matteo

2017-12-01

We study the imprint of non-standard dark energy (DE) and dark matter (DM) models on the 21cm intensity map power spectra from high-redshift neutral hydrogen (HI) gas. To this purpose we use halo catalogs from N-body simulations of dynamical DE models and DM scenarios which are as successful as the standard Cold Dark Matter model with Cosmological Constant (ΛCDM) at interpreting available cosmological observations. We limit our analysis to halo catalogs at redshift z=1 and 2.3 which are common to all simulations. For each catalog we model the HI distribution by using a simple prescription to associate the HI gas mass to N-body halos. We find that the DE models leave a distinct signature on the HI spectra across a wide range of scales, which correlates with differences in the halo mass function and the onset of the non-linear regime of clustering. In the case of the non-standard DM model significant differences of the HI spectra with respect to the ΛCDM model only arise from the suppressed abundance of low mass halos. These cosmological model dependent features also appear in the 21cm spectra. In particular, we find that future SKA measurements can distinguish the imprints of DE and DM models at high statistical significance.
Initial conditions for accurate N-body simulations of massive neutrino cosmologies

NASA Astrophysics Data System (ADS)

Zennaro, M.; Bel, J.; Villaescusa-Navarro, F.; Carbone, C.; Sefusatti, E.; Guzzo, L.

2017-04-01

The set-up of the initial conditions in cosmological N-body simulations is usually implemented by rescaling the desired low-redshift linear power spectrum to the required starting redshift consistently with the Newtonian evolution of the simulation. The implementation of this practical solution requires more care in the context of massive neutrino cosmologies, mainly because of the non-trivial scale-dependence of the linear growth that characterizes these models. In this work, we consider a simple two-fluid, Newtonian approximation for cold dark matter and massive neutrinos perturbations that can reproduce the cold matter linear evolution predicted by Boltzmann codes such as CAMB or CLASS with a 0.1 per cent accuracy or below for all redshift relevant to non-linear structure formation. We use this description, in the first place, to quantify the systematic errors induced by several approximations often assumed in numerical simulations, including the typical set-up of the initial conditions for massive neutrino cosmologies adopted in previous works. We then take advantage of the flexibility of this approach to rescale the late-time linear power spectra to the simulation initial redshift, in order to be as consistent as possible with the dynamics of the N-body code and the approximations it assumes. We implement our method in a public code (REPS rescaled power spectra for initial conditions with massive neutrinos https://github.com/matteozennaro/reps) providing the initial displacements and velocities for cold dark matter and neutrino particles that will allow accurate, I.e. 1 per cent level, numerical simulations for this cosmological scenario.
Hydrodynamical simulations of coupled and uncoupled quintessence models - II. Galaxy clusters

NASA Astrophysics Data System (ADS)

Carlesi, Edoardo; Knebe, Alexander; Lewis, Geraint F.; Yepes, Gustavo

2014-04-01

We study the z = 0 properties of clusters (and large groups) of galaxies within the context of interacting and non-interacting quintessence cosmological models, using a series of adiabatic SPH simulations. Initially, we examine the average properties of groups and clusters, quantifying their differences in ΛCold Dark Matter (ΛCDM), uncoupled Dark Energy (uDE) and coupled Dark Energy (cDE) cosmologies. In particular, we focus upon radial profiles of the gas density, temperature and pressure, and we also investigate how the standard hydrodynamic equilibrium hypothesis holds in quintessence cosmologies. While we are able to confirm previous results about the distribution of baryons, we also find that the main discrepancy (with differences up to 20 per cent) can be seen in cluster pressure profiles. We then switch attention to individual structures, mapping each halo in quintessence cosmology to its ΛCDM counterpart. We are able to identify a series of small correlations between the coupling in the dark sector and halo spin, triaxiality and virialization ratio. When looking at spin and virialization of dark matter haloes, we find a weak (5 per cent) but systematic deviation in fifth force scenarios from ΛCDM.
The Rh = ct universe in alternative theories of gravity

NASA Astrophysics Data System (ADS)

Sultana, Joseph; Kazanas, Demosthenes

2017-12-01

The Λ cold dark matter (ΛCDM) model (one comprising of a cosmological constant Λ and cold dark matter) is generally considered the standard model in cosmology. One of the alternatives that has received attention in the last few years is the Rh = ct universe, which provides an age for the Universe similar to that of ΛCDM and whose (vanishing) deceleration parameter is apparently not inconsistent with observations. Like the ΛCDM, the Rh = ct universe is based on a Friedmann-Robertson-Walker cosmology with the total energy density ρ and pressure p of the cosmic fluid satisfying the simple equation of state ρ + 3p = 0, i.e. a vanishing total active gravitational mass. In an earlier paper, we examined the possible sources for the Rh = ct universe within general relativity, and we have shown that it still contains a dark energy component, albeit not in the form of a cosmological constant. The growing interest in gravitational theories, alternative to Einstein's general relativity, in cosmology, is mainly driven by the need for cosmological models that attain a late-time accelerated expansion without the presence of a cosmological constant as in the ΛCDM, and thereby avoiding the problems associated with it. In this paper, we discuss some of these common alternative theories and show that the Rh = ct is also a solution to some of them.
LOW-MASS SUPPRESSION OF THE SATELLITE LUMINOSITY FUNCTION DUE TO THE SUPERSONIC BARYON-COLD-DARK-MATTER RELATIVE VELOCITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bovy, Jo; Dvorkin, Cora

We study the effect of the supersonic baryon-cold-dark-matter (CDM) flow, which has recently been shown to have a large effect on structure formation during the dark ages 10 {approx}< z {approx}< 1000, on the abundance of luminous, low-mass satellite galaxies around galaxies like the Milky Way. As the supersonic baryon-CDM flow significantly suppresses both the number of halos formed and the amount of baryons accreted onto such halos of masses 10{sup 6} < M{sub halo}/M{sub Sun} < 10{sup 8} at z {approx}> 10, a large effect results on the stellar luminosity function before reionization. As halos of these masses aremore » believed to have very little star formation after reionization due to the effects of photoheating by the ultraviolet background, this effect persists to the present day. We calculate that the number of low-mass 10{sup 6} < M{sub halo}/M{sub Sun} < 5 Multiplication-Sign 10{sup 7} halos that host luminous satellite galaxies today is typically suppressed by 50%, with values ranging up to 90% in regions where the initial supersonic velocity is high. We show that this previously ignored cosmological effect resolves some of the tension between the observed and predicted number of low-mass satellites in the Milky Way, reducing the need for other mass-dependent star-formation suppression before reionization.« less
Small-scale structure and 21cm fluctuations by primordial black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Jinn-Ouk; Kitajima, Naoya, E-mail: jinn-ouk.gong@apctp.org, E-mail: kitajima.naoya@f.mbox.nagoya-u.ac.jp

We discuss early structure formation of small scales sourced by primordial black holes (PBHs) which constitute a small part of present cold dark matter component. We calculate the mass function and power spectrum of haloes originated from the Poisson fluctuations of PBH number and show that the number of small haloes is significantly modified in the presence of PBHs even if their fraction accounts for only 10{sup −4}–10{sup −3} of total dark matter abundance. We then compute the subsequent 21cm signature from those haloes. We find that PBHs can provide major contributions at high redshifts within the detectability of futuremore » experiments such as Square Kilometer Array, and provide a forecast constraint on the PBH fraction.« less
A giant protogalactic disk linked to the cosmic web

NASA Astrophysics Data System (ADS)

Martin, D. Christopher; Matuszewski, Mateusz; Morrissey, Patrick; Neill, James D.; Moore, Anna; Cantalupo, Sebastiano; Prochaska, J. Xavier; Chang, Daphne

2015-08-01

The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that `cold accretion flows'--relatively cool (temperatures of the order of 104 kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos--are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections. Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging. Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a dark-matter halo with a mass of 1013 solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow.
A giant protogalactic disk linked to the cosmic web.

PubMed

Martin, D Christopher; Matuszewski, Mateusz; Morrissey, Patrick; Neill, James D; Moore, Anna; Cantalupo, Sebastiano; Prochaska, J Xavier; Chang, Daphne

2015-08-13

The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that 'cold accretion flows'--relatively cool (temperatures of the order of 10(4) kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos--are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections. Recently, a large and luminous filament, consistent with such a cold accretion flow, was discovered near the quasi-stellar object QSO UM287 at redshift 2.279 using narrow-band imaging. Unfortunately, imaging is not sufficient to constrain the physical characteristics of the filament, to determine its kinematics, to explain how it is linked to nearby sources, or to account for its unusual brightness, more than a factor of ten above what is expected for a filament. Here we report a two-dimensional spectroscopic investigation of the emitting structure. We find that the brightest emission region is an extended rotating hydrogen disk with a velocity profile that is characteristic of gas in a dark-matter halo with a mass of 10(13) solar masses. This giant protogalactic disk appears to be connected to a quiescent filament that may extend beyond the virial radius of the halo. The geometry is strongly suggestive of a cold accretion flow.
Modified Holographic Ricci Dark Energy in Chameleon Brans-Dicke Cosmology and Its Thermodynamic Consequence

NASA Astrophysics Data System (ADS)

Jawad, A.; Chattopadhyay, S.; Bhattacharya, S.; Pasqua, A.

2015-04-01

The objective of this paper is to discuss the Chameleon Brans-Dicke gravity with non-minimally matter coupling of scalar field. We take modified Holographic Ricci dark energy model in this gravity with its energy density in interaction with energy density of cold dark matter. We assume power-law ansatz for scale factor and scalar field to discuss potential as well as coupling functions in the evolving universe. These reconstructed functions are plotted versus scalar field and time for different values of power component of scale factor n. We observe that potential and coupling functions represent increasing behavior, in particular, consistent results for a specific value of n. Finally, we have examined validity of the generalized second law of thermodynamics and we have observed its validity for all values of n. The financial Supported from Department of Science and Technology, Govt. of India under Project Grant No. SR/FTP/PS-167/2011 is thankfully acknowledged by SC
Chameleon dark energy models with characteristic signatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gannouji, Radouane; Department of Physics, Faculty of Science, Tokyo University of Science, 1-3, Kagurazaka, Shinjuku-ku, Tokyo 162-8601; Moraes, Bruno

2010-12-15

In chameleon dark energy models, local gravity constraints tend to rule out parameters in which observable cosmological signatures can be found. We study viable chameleon potentials consistent with a number of recent observational and experimental bounds. A novel chameleon field potential, motivated by f(R) gravity, is constructed where observable cosmological signatures are present both at the background evolution and in the growth rate of the perturbations. We study the evolution of matter density perturbations on low redshifts for this potential and show that the growth index today {gamma}{sub 0} can have significant dispersion on scales relevant for large scale structures.more » The values of {gamma}{sub 0} can be even smaller than 0.2 with large variations of {gamma} on very low redshifts for the model parameters constrained by local gravity tests. This gives a possibility to clearly distinguish these chameleon models from the {Lambda}-cold-dark-matter ({Lambda}CDM) model in future high-precision observations.« less

Simulations of the formation, evolution and clustering of galaxies and quasars.

PubMed

Springel, Volker; White, Simon D M; Jenkins, Adrian; Frenk, Carlos S; Yoshida, Naoki; Gao, Liang; Navarro, Julio; Thacker, Robert; Croton, Darren; Helly, John; Peacock, John A; Cole, Shaun; Thomas, Peter; Couchman, Hugh; Evrard, August; Colberg, Jörg; Pearce, Frazer

2005-06-02

The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability. Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations. Here we present a simulation of the growth of dark matter structure using 2,160(3) particles, following them from redshift z = 127 to the present in a cube-shaped region 2.230 billion lightyears on a side. In postprocessing, we also follow the formation and evolution of the galaxies and quasars. We show that baryon-induced features in the initial conditions of the Universe are reflected in distorted form in the low-redshift galaxy distribution, an effect that can be used to constrain the nature of dark energy with future generations of observational surveys of galaxies.
Anthropic versus cosmological solutions to the coincidence problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barreira, A.; Avelino, P. P.; Departamento de Fisica da Faculdade de Ciencias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto

2011-05-15

In this paper, we investigate possible solutions to the coincidence problem in flat phantom dark-energy models with a constant dark-energy equation of state and quintessence models with a linear scalar field potential. These models are representative of a broader class of cosmological scenarios in which the universe has a finite lifetime. We show that, in the absence of anthropic constraints, including a prior probability for the models inversely proportional to the total lifetime of the universe excludes models very close to the {Lambda} cold dark matter model. This relates a cosmological solution to the coincidence problem with a dynamical dark-energymore » component having an equation-of-state parameter not too close to -1 at the present time. We further show that anthropic constraints, if they are sufficiently stringent, may solve the coincidence problem without the need for dynamical dark energy.« less
Reionization and Galaxy Formation in Warm Dark Matter Cosmologies

NASA Astrophysics Data System (ADS)

Dayal, Pratika; Choudhury, Tirthankar Roy; Bromm, Volker; Pacucci, Fabio

2017-02-01

We compare model results from a semi-analytic (merger-tree based) framework for high-redshift (z ≃ 5-20) galaxy formation against reionization indicators, including the Planck electron scattering optical depth (τ es) and the ionizing photon emissivity ({\\dot{n}}{ion}), to shed light on the reionization history and sources in Cold (CDM) and Warm Dark Matter (WDM; particle masses of {m}x = 1.5, 3, and 5 keV) cosmologies. This model includes all of the key processes of star formation, supernova feedback, the merger/accretion/ejection driven evolution of gas and stellar mass and the effect of the ultra-violet background (UVB), created during reionization, in photo-evaporating the gas content of galaxies in halos with M h ≲ 109 {M}⊙ . We find that the delay in the start of reionization in light (1.5 keV) WDM models can be compensated by a steeper redshift evolution of the ionizing photon escape fraction and a faster mass assembly, resulting in reionization ending at comparable redshifts (z ≃ 5.5) in all the dark matter models considered. We find that the bulk of the reionization photons come from galaxies with a halo mass of M h ≲ 109 {M}⊙ and a UV magnitude of -15 ≲ M UV ≲ -10 in CDM. The progressive suppression of low-mass halos with decreasing {m}x leads to a shift in the “reionization” population to larger halo masses of M h ≳ 109 {M}⊙ and -17 ≲ M UV ≲ -13 for 1.5 keV WDM. We find that current observations of τ es and the ultra violet luminosity function are equally compatible with all the (cold and warm) dark matter models considered in this work. Quantifying the impact of the UVB on galaxy observables (luminosity functions, stellar mass densities, and stellar to halo mass ratios) for different DM models, we propose that global indicators including the redshift evolution of the stellar mass density and the stellar mass-halo mass relation, observable with the James Webb Space Telescope, can be used to distinguish between CDM and WDM (1.5 keV) cosmologies.
Fully stripped? The dynamics of dark and luminous matter in the massive cluster collision MACSJ0553.4-3342

NASA Astrophysics Data System (ADS)

Ebeling, H.; Qi, J.; Richard, J.

2017-11-01

We present the results of a multiwavelength investigation of the very X-ray luminous galaxy cluster MACSJ0553.4-3342 (z = 0.4270; hereafter MACSJ0553). Combining high-resolution data obtained with the Hubble Space Telescope and the Chandra X-ray Observatory with ground-based galaxy spectroscopy, our analysis establishes the system unambiguously as a binary, post-collision merger of massive clusters. Key characteristics include perfect alignment of luminous and dark matter for one component, a separation of almost 650 kpc (in projection) between the dark-matter peak of the other subcluster and the second X-ray peak, extremely hot gas (kT > 15 keV) at either end of the merger axis, a potential cold front in the east, an unusually low gas mass fraction of approximately 0.075 for the western component, a velocity dispersion of 1490_{-130}^{+104} km s-1, and no indication of significant substructure along the line of sight. We propose that the MACSJ0553 merger proceeds not in the plane of the sky, but at a large inclination angle, is observed very close to turnaround, and that the eastern X-ray peak is the cool core of the slightly less massive western component that was fully stripped and captured by the eastern subcluster during the collision. If correct, this hypothesis would make MACSJ0553 a superb target for a competitive study of ram-pressure stripping and the collisional behaviour of luminous and dark matter during cluster formation.
Finite Temperature Density Profile in SFDM

NASA Astrophysics Data System (ADS)

Robles, Victor H.; Matos, T.

Recent high-quality observations of low surface brightness (LSB) galaxies have shown that their dark matter (DM) halos prefer flat central density profiles. On the other hand the standard cold dark matter model simulations predict a more cuspy behavior. Feedback from star formation has been widely used to reconcile simulations with observations, this might be successful in field dwarf galaxies but its success in high mass LSB galaxies remains unclear. Additionally, including too much feedback in the simulations is a double-edged sword, in order to obtain a cored DM distribution from an initially cuspy one, feedback recipes require to remove a large quantity of baryons from the center of galaxies, however, other feedback recipes produce twice more satellite galaxies of a given luminosity and with much smaller mass to light ratios from those that are observed. Therefore, one DM profile that produces cores naturally and that does not require large amounts of feedback would be preferable. We find both requirements to be satisfied in the scalar field dark matter model. Here, we consider that the dark matter is an auto-interacting real scalar field in a thermal bath of temperature T with an initial Z 2 symmetric potential, as the universe expands the temperature drops so that the Z 2 symmetry is spontaneously broken and the field rolls down to a new minimum. We give an exact analytic solution to the Newtonian limit of this system and show both, that it satisfies the two desired requirements and that the rotation curve profile is not longer universal.
A hydrodynamic treatment of the cold dark matter cosmological scenario

NASA Technical Reports Server (NTRS)

Cen, Renyue; Ostriker, Jeremiah

1992-01-01

The evolution of structure in a postrecombination Friedmann-Robertson-Walker universe containing both gaseous baryons and cold dark matter (CDM) is studied by means of an Eulerian code coupled with a standard particle-mesh code. Ionization state and radiative opacity are calculated in detail, and the hydrodynamic simulations make it possible to compute properties of gas distribution on scales larger than three cell sizes. The model yields a soft X-ray background consistent with the latest cosmic nucleosynthesis values, and can accurately reproduce the galaxy-galaxy two-point correlation. The rate of galaxy formation peaks at a relatively late epoch. With regard to mass function, the smallest objects are stabilized against collapse by thermal energy: the mass-weighted mass spectrum peaks in the vicinity of m(b) = 10 exp 9.2 solar masses with a reasonable fit to the Schecter luminosity function if the baryon mass to blue light ratio is approximately 4. Overall, the simulations provide strong support for the CMD scenario. Of particular interest is that, while the baryons are not biased on scales greater than 1/h Mpc, the galaxies are, and that the 'galaxies' have a correlation function of the required slope and the correct amplitude.
High-z objects and cold dark matter cosmogonies - Constraints on the primordial power spectrum on small scales

NASA Technical Reports Server (NTRS)

Kashlinsky, A.

1993-01-01

Modified cold dark matter (CDM) models were recently suggested to account for large-scale optical data, which fix the power spectrum on large scales, and the COBE results, which would then fix the bias parameter, b. We point out that all such models have deficit of small-scale power where density fluctuations are presently nonlinear, and should then lead to late epochs of collapse of scales M between 10 exp 9 - 10 exp 10 solar masses and (1-5) x 10 exp 14 solar masses. We compute the probabilities and comoving space densities of various scale objects at high redshifts according to the CDM models and compare these with observations of high-z QSOs, high-z galaxies and the protocluster-size object found recently by Uson et al. (1992) at z = 3.4. We show that the modified CDM models are inconsistent with the observational data on these objects. We thus suggest that in order to account for the high-z objects, as well as the large-scale and COBE data, one needs a power spectrum with more power on small scales than CDM models allow and an open universe.
The Formation of Milky Way-mass Disk Galaxies in the First 500 Million Years of a Cold Dark Matter Universe

NASA Astrophysics Data System (ADS)

Feng, Yu; Di Matteo, Tiziana; Croft, Rupert; Tenneti, Ananth; Bird, Simeon; Battaglia, Nicholas; Wilkins, Stephen

2015-07-01

Whether or not among the myriad tiny protogalaxies there exists a population with similarities to present-day galaxies is an open question. We show, using BlueTides, the first hydrodynamic simulation large enough to resolve the relevant scales, that the first massive galaxies to form are predicted to have extensive rotationally supported disks. Although their morphology resembles in some ways Milky Way types seen at much lower redshifts, these high-redshift galaxies are smaller, denser, and richer in gas than their low-redshift counterparts. From a kinematic analysis of a statistical sample of 216 galaxies at redshift z = 8-10, we have found that disk galaxies make up 70% of the population of galaxies with stellar mass {10}10{M}⊙ or greater. Cold dark matter cosmology therefore makes specific predictions for the population of large galaxies 500 million years after the Big Bang. We argue that wide-field satellite telescopes (e.g., WFIRST) will in the near future discover these first massive disk galaxies. The simplicity of their structure and formation history should make new tests of cosmology possible.
Axion as a Cold Dark Matter Candidate: Proof to Fully Nonlinear Order

DOE Office of Scientific and Technical Information (OSTI.GOV)

Noh, Hyerim; Hwang, Jai-chan; Park, Chan-Gyung

2017-09-01

We present proof of the axion as a cold dark matter (CDM) candidate to the fully nonlinear order perturbations based on Einstein’s gravity. We consider the axion as a coherently oscillating massive classical scalar field without interaction. We present the fully nonlinear and exact, except for ignoring the transverse-tracefree tensor-type perturbation, hydrodynamic equations for an axion fluid in Einstein’s gravity. We show that the axion has the characteristic pressure and anisotropic stress; the latter starts to appear from the second-order perturbation. But these terms do not directly affect the hydrodynamic equations in our axion treatment. Instead, what behaves as themore » effective pressure term in relativistic hydrodynamic equations is the perturbed lapse function and the relativistic result coincides exactly with the one known in the previous non-relativistic studies. The effective pressure term leads to a Jeans scale that is of the solar-system scale for conventional axion mass. As the fully nonlinear and relativistic hydrodynamic equations for an axion fluid coincide exactly with the ones of a zero-pressure fluid in the super-Jeans scale, we have proved the CDM nature of such an axion in that scale.« less
Subhalo demographics in the Illustris simulation: effects of baryons and halo-to-halo variation

NASA Astrophysics Data System (ADS)

Chua, Kun Ting Eddie; Pillepich, Annalisa; Rodriguez-Gomez, Vicente; Vogelsberger, Mark; Bird, Simeon; Hernquist, Lars

2017-12-01

We study the abundance of subhaloes in the hydrodynamical cosmological simulation Illustris, which includes both baryons and dark matter in a cold dark matter volume 106.5 Mpc a side. We compare Illustris to its dark-matter only (DMO) analogue, Illustris-Dark and quantify the effects of baryonic processes on the demographics of subhaloes in the host mass range 1011-3 × 1014 M⊙. We focus on both the evolved (z = 0) subhalo cumulative mass functions (SHMF) and the statistics of subhaloes ever accreted, i.e. infall SHMF. We quantify the variance in subhalo abundance at fixed host mass and investigate the physical reasons responsible for such scatter. We find that in Illustris, baryonic physics impacts both the infall and z = 0 subhalo abundance by tilting the DMO function and suppressing the abundance of low-mass subhaloes. The breaking of self-similarity in the subhalo abundance at z = 0 is enhanced by the inclusion of baryonic physics. The non-monotonic alteration of the evolved subhalo abundances can be explained by the modification of the concentration-mass relation of Illustris hosts compared to Illustris-Dark. Interestingly, the baryonic implementation in Illustris does not lead to an increase in the halo-to-halo variation compared to Illustris-Dark. In both cases, the normalized intrinsic scatter today is larger for Milky Way-like haloes than for cluster-sized objects. For Milky Way-like haloes, it increases from about eight per cent at infall to about 25 per cent at the current epoch. In both runs, haloes of fixed mass formed later host more subhaloes than early formers.
Beyond concordance cosmology with magnification of gravitational-wave standard sirens.

PubMed

Camera, Stefano; Nishizawa, Atsushi

2013-04-12

We show how future gravitational-wave detectors would be able to discriminate between the concordance Λ cold dark matter cosmological model and up-to-date competing alternatives, e.g., dynamical dark energy (DE) models or modified gravity (MG) theories. Our method consists of using the weak-lensing magnification effect that affects a standard-siren signal because of its traveling through the Universe's large scale structure. As a demonstration, we present constraints on DE and MG from proposed gravitational-wave detectors, namely Einstein Telescope and DECI-Hertz Interferometer Gravitational-Wave Observatory and Big-Bang Observer.
Measuring spacetime: from the big bang to black holes.

PubMed

Tegmark, Max

2002-05-24

Space is not a boring static stage on which events unfold over time, but a dynamic entity with curvature, fluctuations, and a rich life of its own. Spectacular measurements of the cosmic microwave background, gravitational lensing, type Ia supernovae, large-scale structure, spectra of the Lyman alpha forest, stellar dynamics, and x-ray binaries are probing the properties of spacetime over 22 orders of magnitude in scale. Current measurements are consistent with an infinite flat everlasting universe containing about 30% cold dark matter, 65% dark energy, and at least two distinct populations of black holes.
THE INNER STRUCTURE OF DWARF-SIZED HALOS IN WARM AND COLD DARK MATTER COSMOLOGIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

González-Samaniego, A.; Avila-Reese, V.; Colín, P.

2016-03-10

By means of N-body + hydrodynamic zoom-in simulations we study the evolution of the inner dark matter and stellar mass distributions of central dwarf galaxies formed in halos of virial masses M{sub v} = (2–3) × 10{sup 10} h{sup −1} M{sub ⊙} at z = 0, both in a warm dark matter (WDM) and cold dark matter (CDM) cosmology. The half-mode mass in the WDM power spectrum of our simulations is M{sub f} = 2 × 10{sup 10} h{sup −1} M{sub ⊙}. In the dark matter (DM) only simulations halo density profiles are well described by the Navarro–Frenk–White parametric fit in both cosmologies, though the WDM halos have concentrations lower bymore » factors of 1.5–2.0 than their CDM counterparts. In the hydrodynamic simulations, the effects of baryons significantly flatten the inner density, velocity dispersion, and pseudo phase space density profiles of the WDM halos but not of the CDM ones. The density slope, measured at ≈0.02R{sub v}, α{sub 0.02}, becomes shallow in periods of 2–5 Gyr in the WDM runs. We explore whether this flattening process correlates with the global star formation (SF), M{sub s}/M{sub v} ratio, gas outflow, and internal specific angular momentum histories. We do not find any clear trends, but when α{sub 0.02} is shallower than −0.5, M{sub s}/M{sub v} is always between 0.25% and 1%. We conclude that the main reason for the formation of the shallow core is the presence of strong gas mass fluctuations inside the inner halo, which are a consequence of the feedback driven by a very bursty and sustained SF history in shallow gravitational potentials. Our WDM halos, which assemble late and are less concentrated than the CDM ones, obey these conditions. There are also (rare) CDM systems with extended mass assembly histories that obey these conditions and form shallow cores. The dynamical heating and expansion processes behind the DM core flattening apply also to the stars in such a way that the stellar age and metallicity gradients of the dwarfs are softened, their stellar half-mass radii strongly grow with time, and their central surface densities decrease.« less
The three-point function as a probe of models for large-scale structure

NASA Technical Reports Server (NTRS)

Frieman, Joshua A.; Gaztanaga, Enrique

1993-01-01

The consequences of models of structure formation for higher-order (n-point) galaxy correlation functions in the mildly non-linear regime are analyzed. Several variations of the standard Omega = 1 cold dark matter model with scale-invariant primordial perturbations were recently introduced to obtain more power on large scales, R(sub p) is approximately 20 h(sup -1) Mpc, e.g., low-matter-density (non-zero cosmological constant) models, 'tilted' primordial spectra, and scenarios with a mixture of cold and hot dark matter. They also include models with an effective scale-dependent bias, such as the cooperative galaxy formation scenario of Bower, etal. It is shown that higher-order (n-point) galaxy correlation functions can provide a useful test of such models and can discriminate between models with true large-scale power in the density field and those where the galaxy power arises from scale-dependent bias: a bias with rapid scale-dependence leads to a dramatic decrease of the hierarchical amplitudes Q(sub J) at large scales, r is approximately greater than R(sub p). Current observational constraints on the three-point amplitudes Q(sub 3) and S(sub 3) can place limits on the bias parameter(s) and appear to disfavor, but not yet rule out, the hypothesis that scale-dependent bias is responsible for the extra power observed on large scales.
On the stability of satellite planes - I. Effects of mass, velocity, halo shape and alignment

NASA Astrophysics Data System (ADS)

Fernando, Nuwanthika; Arias, Veronica; Guglielmo, Magda; Lewis, Geraint F.; Ibata, Rodrigo A.; Power, Chris

2017-02-01

The recently discovered vast thin plane of dwarf satellites orbiting the Andromeda Galaxy (M31) adds to the mystery of the small-scale distribution of the Local Group's galaxy population. Such well-defined planar structures are apparently rare occurrences in cold dark matter cosmological simulations, and we lack a coherent explanation of their formation and existence. In this paper, we explore the long-term survivability of thin planes of dwarfs in galactic haloes, focusing, in particular, on systems mimicking the observed Andromeda distribution. The key results show that, in general, planes of dwarf galaxies are fragile, sensitive to the shape of the dark matter halo and other perturbing effects. In fact, long-lived planes of satellites only exist in polar orbits in spherical dark matter haloes, presenting a challenge to the observed Andromeda plane that is significantly tilted with respect to the optical disc. Our conclusion is that, in the standard cosmological models, planes of satellites are generally short lived, and hence we must be located at a relatively special time in the evolution of the Andromeda Plane, lucky enough to see its coherent pattern.
Matter density perturbation and power spectrum in running vacuum model

NASA Astrophysics Data System (ADS)

Geng, Chao-Qiang; Lee, Chung-Chi

2017-01-01

We investigate the matter density perturbation δm and power spectrum P(k) in the running vacuum model, with the cosmological constant being a function of the Hubble parameter, given by Λ = Λ0 + 6σHH0 + 3νH2, in which the linear and quadratic terms of H would originate from the QCD vacuum condensation and cosmological renormalization group, respectively. Taking the dark energy perturbation into consideration, we derive the evolution equation for δm and find a specific scale dcr = 2π/kcr, which divides the evolution of the universe into the sub-interaction and super-interaction regimes, corresponding to k ≪ kcr and k ≫ kcr, respectively. For the former, the evolution of δm has the same behaviour as that in the Λ cold dark model, while for the latter, the growth of δm is frozen (greatly enhanced) when ν + σ > (<)0 due to the couplings between radiation, matter and dark energy. It is clear that the observational data rule out the cases with ν < 0 and ν + σ < 0, while the allowed window for the model parameters is extremely narrow with ν , |σ | ≲ O(10^{-7}).
First star formation in ultralight particle dark matter cosmology

NASA Astrophysics Data System (ADS)

Hirano, Shingo; Sullivan, James M.; Bromm, Volker

2018-01-01

The formation of the first stars in the high-redshift Universe is a sensitive probe of the small-scale, particle physics nature of dark matter (DM). We carry out cosmological simulations of primordial star formation in ultralight, axion-like particle DM cosmology, with masses of 10-22 and 10-21 eV, with de Broglie wavelengths approaching galactic scales (˜ kpc). The onset of star formation is delayed, and shifted to more massive host structures. For the lightest DM particle mass explored here, first stars form at z ˜ 7 in structures with ˜109 M⊙, compared to the standard minihalo environment within the Λ cold dark matter (ΛCDM) cosmology, where z ˜ 20-30 and ˜105-106 M⊙. Despite this greatly altered DM host environment, the thermodynamic behaviour of the metal-free gas as it collapses into the DM potential well asymptotically approaches a very similar evolutionary track. Thus, the fragmentation properties are predicted to remain the same as in ΛCDM cosmology, implying a similar mass scale for the first stars. These results predict intense starbursts in the axion cosmologies, which may be amenable to observations with the James Webb Space Telescope.
The rise and fall of a challenger: the Bullet Cluster in Λ cold dark matter simulations

NASA Astrophysics Data System (ADS)

Thompson, Robert; Davé, Romeel; Nagamine, Kentaro

2015-09-01

The Bullet Cluster has provided some of the best evidence for the Λ cold dark matter (ΛCDM) model via direct empirical proof of the existence of collisionless dark matter, while posing a serious challenge owing to the unusually high inferred pairwise velocities of its progenitor clusters. Here, we investigate the probability of finding such a high-velocity pair in large-volume N-body simulations, particularly focusing on differences between halo-finding algorithms. We find that algorithms that do not account for the kinematics of infalling groups yield vastly different statistics and probabilities. When employing the ROCKSTAR halo finder that considers particle velocities, we find numerous Bullet-like pair candidates that closely match not only the high pairwise velocity, but also the mass, mass ratio, separation distance, and collision angle of the initial conditions that have been shown to produce the Bullet Cluster in non-cosmological hydrodynamic simulations. The probability of finding a high pairwise velocity pair among haloes with Mhalo ≥ 1014 M⊙ is 4.6 × 10-4 using ROCKSTAR, while it is ≈34 × lower using a friends-of-friends (FoF)-based approach as in previous studies. This is because the typical spatial extent of Bullet progenitors is such that FoF tends to group them into a single halo despite clearly distinct kinematics. Further requiring an appropriately high average mass among the two progenitors, we find the comoving number density of potential Bullet-like candidates to be of the order of ≈10-10 Mpc-3. Our findings suggest that ΛCDM straightforwardly produces massive, high relative velocity halo pairs analogous to Bullet Cluster progenitors, and hence the Bullet Cluster does not present a challenge to the ΛCDM model.
Tidal stripping and the structure of dwarf galaxies in the Local Group

NASA Astrophysics Data System (ADS)

Fattahi, Azadeh; Navarro, Julio F.; Frenk, Carlos S.; Oman, Kyle A.; Sawala, Till; Schaller, Matthieu

2018-05-01

The shallow faint-end slope of the galaxy mass function is usually reproduced in Λ cold dark matter (ΛCDM) galaxy formation models by assuming that the fraction of baryons that turn into stars drops steeply with decreasing halo mass and essentially vanishes in haloes with maximum circular velocities Vmax < 20-30 km s-1. Dark-matter-dominated dwarfs should therefore have characteristic velocities of about that value, unless they are small enough to probe only the rising part of the halo circular velocity curve (i.e. half-mass radii, r1/2 ≪ 1 kpc). Many dwarfs have properties in disagreement with this prediction: they are large enough to probe their halo Vmax but their characteristic velocities are well below 20 km s-1. These `cold faint giants' (an extreme example is the recently discovered Crater 2 Milky Way satellite) can only be reconciled with our ΛCDM models if they are the remnants of once massive objects heavily affected by tidal stripping. We examine this possibility using the APOSTLE cosmological hydrodynamical simulations of the Local Group. Assuming that low-velocity-dispersion satellites have been affected by stripping, we infer their progenitor masses, radii, and velocity dispersions, and find them in remarkable agreement with those of isolated dwarfs. Tidal stripping also explains the large scatter in the mass discrepancy-acceleration relation in the dwarf galaxy regime: tides remove preferentially dark matter from satellite galaxies, lowering their accelerations below the amin ˜ 10-11 m s-2 minimum expected for isolated dwarfs. In many cases, the resulting velocity dispersions are inconsistent with the predictions from Modified Newtonian Dynamics, a result that poses a possibly insurmountable challenge to that scenario.
Tidal features of classical Milky Way satellites in a Λ cold dark matter universe

NASA Astrophysics Data System (ADS)

Wang, M.-Y.; Fattahi, Azadeh; Cooper, Andrew P.; Sawala, Till; Strigari, Louis E.; Frenk, Carlos S.; Navarro, Julio F.; Oman, Kyle; Schaller, Matthieu

2017-07-01

We use the APOSTLE (A Project Of Simulating The Local Environment) cosmological hydrodynamic simulations to examine the effects of tidal stripping on cold dark matter subhaloes that host three of the most luminous Milky Way dwarf satellite galaxies: Fornax, Sculptor and Leo I. We identify simulated satellites that match the observed spatial and kinematic distributions of stars in these galaxies, and track their evolution after infall. We find ˜30 per cent of subhaloes hosting satellites with present-day stellar mass 106-108 M⊙ experience >20 per cent stellar mass-loss after infall. Fornax analogues have earlier infall times compared to Sculptor and Leo I analogues. Star formation in Fornax analogues continues for ˜3-6 Gyr after infall, whereas Sculptor and Leo I analogues stop forming stars <2-3 Gyr after infall. Fornax analogues typically show more significant stellar mass-loss and exhibit stellar tidal tails, whereas Sculptor and Leo I analogues, which are more deeply embedded in their host dark matter haloes at infall, do not show substantial mass-loss due to tides. When additionally comparing the orbital motion of the host subaloes to the measured proper motion of Fornax, we find the matching more difficult; host subhaloes tend to have pericentres smaller than that measured for Fornax itself. From the kinematic and orbital data, we estimate that Fornax has lost 10-20 per cent of its infall stellar mass. Our best estimate for the surface brightness of a stellar tidal stream associated with Fornax is Σ ˜ 32.6 mag arcsec-2, which may be detectable with deep imaging surveys such as DES and LSST.

Hidden from view: coupled dark sector physics and small scales

NASA Astrophysics Data System (ADS)

Elahi, Pascal J.; Lewis, Geraint F.; Power, Chris; Carlesi, Edoardo; Knebe, Alexander

2015-09-01

We study cluster mass dark matter (DM) haloes, their progenitors and surroundings in a coupled dark matter-dark energy (DE) model and compare it to quintessence and Λ cold dark matter (ΛCDM) models with adiabatic zoom simulations. When comparing cosmologies with different expansions histories, growth functions and power spectra, care must be taken to identify unambiguous signatures of alternative cosmologies. Shared cosmological parameters, such as σ8, need not be the same for optimal fits to observational data. We choose to set our parameters to ΛCDM z = 0 values. We find that in coupled models, where DM decays into DE, haloes appear remarkably similar to ΛCDM haloes despite DM experiencing an additional frictional force. Density profiles are not systematically different and the subhalo populations have similar mass, spin, and spatial distributions, although (sub)haloes are less concentrated on average in coupled cosmologies. However, given the scatter in related observables (V_max,R_{V_max}), this difference is unlikely to distinguish between coupled and uncoupled DM. Observations of satellites of Milky Way and M31 indicate a significant subpopulation reside in a plane. Coupled models do produce planar arrangements of satellites of higher statistical significance than ΛCDM models; however, in all models these planes are dynamically unstable. In general, the non-linear dynamics within and near large haloes masks the effects of a coupled dark sector. The sole environmental signature we find is that small haloes residing in the outskirts are more deficient in baryons than their ΛCDM counterparts. The lack of a pronounced signal for a coupled dark sector strongly suggests that such a phenomena would be effectively hidden from view.
Status of the MiniCLEAN dark matter experiment

NASA Astrophysics Data System (ADS)

Rielage, Keith

2009-10-01

MiniCLEAN utilizes over 400 kg of liquid cryogen to detect nuclear recoils from WIMP dark matter with a projected sensitivity of 2x10-45 cm^2 for a mass of 100 GeV. The liquid cryogen is interchangeable between argon and neon to study the A^2 dependence of the potential signal and examine backgrounds. MiniCLEAN utilizes a unique modular design with spherical geometry to maximize the light yield using cold photomultiplier tubes in a single-phase detector. Pulse shape discrimination techniques are used to separate nuclear recoil signals from electron recoil backgrounds. Particular attention is being paid to mitigating the backgrounds from contamination of surfaces by radon daughters during assembly. The design and assembly status of the experiment will be discussed. The projected timeline and future plans for staging the experiment at SNOLAB in Sudbury, Canada will be presented.
The super-NFW model: an analytic dynamical model for cold dark matter haloes and elliptical galaxies

NASA Astrophysics Data System (ADS)

Lilley, Edward J.; Evans, N. Wyn; Sanders, Jason L.

2018-05-01

An analytic galaxy model with ρ ˜ r-1 at small radii and ρ ˜ r-3.5 at large radii is presented. The asymptotic density fall-off is slower than the Hernquist model, but faster than the Navarro-Frenk-White (NFW) profile for dark matter haloes, and so in accord with recent evidence from cosmological simulations. The model provides the zeroth-order term in a biorthornomal basis function expansion, meaning that axisymmetric, triaxial, and lopsided distortions can easily be added (much like the Hernquist model itself which is the zeroth-order term of the Hernquist-Ostriker expansion). The properties of the spherical model, including analytic distribution functions which are either isotropic, radially anisotropic, or tangentially anisotropic, are discussed in some detail. The analogue of the mass-concentration relation for cosmological haloes is provided.
Gravity and count probabilities in an expanding universe

NASA Technical Reports Server (NTRS)

Bouchet, Francois R.; Hernquist, Lars

1992-01-01

The time evolution of nonlinear clustering on large scales in cold dark matter, hot dark matter, and white noise models of the universe is investigated using N-body simulations performed with a tree code. Count probabilities in cubic cells are determined as functions of the cell size and the clustering state (redshift), and comparisons are made with various theoretical models. We isolate the features that appear to be the result of gravitational instability, those that depend on the initial conditions, and those that are likely a consequence of numerical limitations. More specifically, we study the development of skewness, kurtosis, and the fifth moment in relation to variance, the dependence of the void probability on time as well as on sparseness of sampling, and the overall shape of the count probability distribution. Implications of our results for theoretical and observational studies are discussed.
Interpretation of the cosmic microwave background radiation anisotropy detected by the COBE Differential Microwave Radiometer

NASA Technical Reports Server (NTRS)

Wright, E. L.; Meyer, S. S.; Bennett, C. L.; Boggess, N. W.; Cheng, E. S.; Hauser, M. G.; Kogut, A.; Lineweaver, C.; Mather, J. C.; Smoot, G. F.

1992-01-01

The large-scale cosmic background anisotropy detected by the COBE Differential Microwave Radiometer (DMR) instrument is compared to the sensitive previous measurements on various angular scales, and to the predictions of a wide variety of models of structure formation driven by gravitational instability. The observed anisotropy is consistent with all previously measured upper limits and with a number of dynamical models of structure formation. For example, the data agree with an unbiased cold dark matter (CDM) model with H0 = 50 km/s Mpc and Delta-M/M = 1 in a 16 Mpc radius sphere. Other models, such as CDM plus massive neutrinos (hot dark matter (HDM)), or CDM with a nonzero cosmological constant are also consistent with the COBE detection and can provide the extra power seen on 5-10,000 km/s scales.
Observations of MilkyWay Dwarf Spheroidal galaxies with the Fermi-LAT detector and

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abdo, A.A.; Ackermann, M.; Ajello, M.

We report on the observations of 14 dwarf spheroidal galaxies with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope, which is conducting an all-sky {gamma}-ray survey in the 20 MeV to >300 GeV energy range, provides a new opportunity to test particle dark matter models through the expected {gamma}-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dwarf spheroidal galaxies, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearbymore » and among the most extreme dark matter dominated environments. No significant {gamma}-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the {gamma}-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10{sup -9} photons cm{sup -2}s{sup -1}. Using recent stellar kinematic data, the {gamma}-ray flux limits are combined with improved determinations of the dark matter density profile in 8 of the 14 candidate dwarfs to place limits on the pair annihilation cross-section ofWIMPs in several widely studied extensions of the standard model, including its supersymmetric extension and other models that received recent attention. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g. in models where supersymmetry breaking occurs via anomaly mediation. The {gamma}-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e{sup +}e{sup -} data, including low-mass wino-like neutralinos and models with TeV masses pair-annihilating into muon-antimuon pairs.« less
No-scale SU( 5) super-GUTs

DOE PAGES

Ellis, John; Evans, Jason L.; Nagata, Natsumi; ...

2017-04-12

We reconsider the minimal SU( 5) grand unified theory (GUT) in the context of no-scale supergravity inspired by string compactification scenarios, assuming that the soft supersymmetry-breaking parameters satisfy universality conditions at some input scale M in above the GUT scale M GUT. When setting up such a no-scale super-GUT model, special attention must be paid to avoiding the Scylla of rapid proton decay and the Charybdis of an excessive density of cold dark matter, while also having an acceptable mass for the Higgs boson. Furthermore, we do not find consistent solutions if none of the matter and Higgs fields aremore » assigned to twisted chiral supermultiplets, even in the presence of Giudice–Masiero terms. But, consistent solutions may be found if at least one fiveplet of GUT Higgs fields is assigned to a twisted chiral supermultiplet, with a suitable choice of modular weights. Spin-independent dark matter scattering may be detectable in some of these consistent solutions.« less
Efficient calculation of cosmological neutrino clustering in the non-linear regime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archidiacono, Maria; Hannestad, Steen, E-mail: archi@phys.au.dk, E-mail: sth@phys.au.dk

2016-06-01

We study in detail how neutrino perturbations can be followed in linear theory by using only terms up to l =2 in the Boltzmann hierarchy. We provide a new approximation to the third moment and demonstrate that the neutrino power spectrum can be calculated to a precision of better than ∼ 5% for masses up to ∼ 1 eV and k ∼< 10 h /Mpc. The matter power spectrum can be calculated far more precisely and typically at least a factor of a few better than with existing approximations. We then proceed to study how the neutrino power spectrum canmore » be reliably calculated even in the non-linear regime by using the non-linear gravitational potential, sourced by dark matter overdensities, as it is derived from semi-analytic methods based on N -body simulations in the Boltzmann evolution hierarchy. Our results agree extremely well with results derived from N -body simulations that include cold dark matter and neutrinos as independent particles with different properties.« less
Structure formation simulations with momentum exchange: alleviating tensions between high-redshift and low-redshift cosmological probes

NASA Astrophysics Data System (ADS)

Baldi, Marco; Simpson, Fergus

2017-02-01

Persisting tensions between the cosmological constraints derived from low-redshift probes and the ones obtained from temperature and polarization anisotropies of the cosmic microwave background (CMB) - although not yet providing compelling evidence against the Λcold dark matter model - seem to consistently indicate a slower growth of density perturbations as compared to the predictions of the standard cosmological scenario. Such behaviour is not easily accommodated by the simplest extensions of General Relativity, such as f(R) models, which generically predict an enhanced growth rate. In this work, we present the outcomes of a suite of large N-body simulations carried out in the context of a cosmological model featuring a non-vanishing scattering cross-section between the dark matter and the dark energy fields, for two different parametrizations of the dark energy equation of state. Our results indicate that these dark scattering models have very mild effects on many observables related to large-scale structures formation and evolution, while providing a significant suppression of the amplitude of linear density perturbations and the abundance of massive clusters. Our simulations therefore confirm that these models offer a promising route to alleviate existing tensions between low-redshift measurements and those of the CMB.
Effects of coupled dark energy on the Milky Way and its satellites

NASA Astrophysics Data System (ADS)

Penzo, Camilla; Macciò, Andrea V.; Baldi, Marco; Casarini, Luciano; Oñorbe, Jose; Dutton, Aaron A.

2016-09-01

We present the first numerical simulations in coupled dark energy cosmologies with high enough resolution to investigate the effects of the coupling on galactic and subgalactic scales. We choose two constant couplings and a time-varying coupling function and we run simulations of three Milky Way-sized haloes (˜1012 M⊙), a lower mass halo (6 × 1011 M⊙) and a dwarf galaxy halo (5 × 109 M⊙). We resolve each halo with several million dark matter particles. On all scales, the coupling causes lower halo concentrations and a reduced number of substructures with respect to Λ cold dark matter (ΛCDM). We show that the reduced concentrations are not due to different formation times. We ascribe them to the extra terms that appear in the equations describing the gravitational dynamics. On the scale of the Milky Way satellites, we show that the lower concentrations can help in reconciling observed and simulated rotation curves, but the coupling values necessary to have a significant difference from ΛCDM are outside the current observational constraints. On the other hand, if other modifications to the standard model allowing a higher coupling (e.g. massive neutrinos) are considered, coupled dark energy can become an interesting scenario to alleviate the small-scale issues of the ΛCDM model.
The halo model in a massive neutrino cosmology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Massara, Elena; Villaescusa-Navarro, Francisco; Viel, Matteo, E-mail: emassara@sissa.it, E-mail: villaescusa@oats.inaf.it, E-mail: viel@oats.inaf.it

2014-12-01

We provide a quantitative analysis of the halo model in the context of massive neutrino cosmologies. We discuss all the ingredients necessary to model the non-linear matter and cold dark matter power spectra and compare with the results of N-body simulations that incorporate massive neutrinos. Our neutrino halo model is able to capture the non-linear behavior of matter clustering with a ∼20% accuracy up to very non-linear scales of k = 10 h/Mpc (which would be affected by baryon physics). The largest discrepancies arise in the range k = 0.5 – 1 h/Mpc where the 1-halo and 2-halo terms are comparable and are present also inmore » a massless neutrino cosmology. However, at scales k < 0.2 h/Mpc our neutrino halo model agrees with the results of N-body simulations at the level of 8% for total neutrino masses of < 0.3 eV. We also model the neutrino non-linear density field as a sum of a linear and clustered component and predict the neutrino power spectrum and the cold dark matter-neutrino cross-power spectrum up to k = 1 h/Mpc with ∼30% accuracy. For masses below 0.15 eV the neutrino halo model captures the neutrino induced suppression, casted in terms of matter power ratios between massive and massless scenarios, with a 2% agreement with the results of N-body/neutrino simulations. Finally, we provide a simple application of the halo model: the computation of the clustering of galaxies, in massless and massive neutrinos cosmologies, using a simple Halo Occupation Distribution scheme and our halo model extension.« less
Ground-based Opportunities for Astrometry

DTIC Science & Technology

2013-01-01

those stars (Dinescu eta/. 2005) leads to a measurement of the tangential velocity of the Sagittarius dwarf and a definitive orbit. Several other...Currently accepted Lambda cold-dark-matter (CDM) cosmological models (see also Chapter 28) predict several hundred merging dwarf galaxies within 1...nination of tations with I) diagrams. o parallaxes lial velocity tarius dwarf of possible eta/. 2005) a definitive ttion of their uti on. :Is
Search for Low-Mass Dark Matter wtih SuperCDMS Soudan and Study of Shorted Electric Field Configurations in CDMS Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneck, Kristiana

The area of dark matter is one of the most interesting and exciting topics in physics today. Existing at the intersection of particle physics and astrophysics, the existence of a new dark matter particle can be used to explain many astrophysical and cosmological observations, as well as to reconcile outstanding issues in the standard model of particle physics. Experiments such as SuperCDMS are built to detect dark matter in the lab by looking for low-energy nuclear recoils produced by collisions between dark matter particles and atoms in terrestrial detectors. SuperCDMS Soudan is particularly well-suited to follow up on possible hintsmore » of low-mass dark matter seen by other recent experiments because of its low thresholds and excellent background discrimination. Analyzing SuperCDMS Soudan data to look for low-mass dark matter comes with particular challenges because of the low signal-to-noise very near threshold. However, with a detailed background model developed by scaling high-energy events down into the low-energy signal region, SuperCDMS Soudan produced worldleading limits on the existence of low-mass dark matter. In addition, a few SuperCDMS Soudan detectors experienced cold hardware problems that can affect the data collected. Of particular interest is one detector considered for the low-mass WIMP search that has one of its charge electrodes shorted to chassis ground. Three events were observed in this detector upon unblinding the SuperCDMS Soudan low-energy data, even though <1 event was expected based on pre-unblinding calulations. However, the data collected by the shorted detector may have been compromised since an electrode shorted to ground will modify the electric field in the detector. The SuperCDMS Detector Monte Carlo (DMC) provides an excellent way to model the effects of the modified electric field, so a new model of the expected backgrounds in the low-mass WIMP search is developed using the DMC to try to explain how the short may have affected the data collected. This thesis is organized as follows: Chapter 1 gives a broad introduction to dark matter, discussing the astrophysical and cosmological evidence for its existence, listing several possible particle physics candidates, and outlining several experimental strategies to look for dark matter. Chapter 2 is an overview of CDMS detector technology and the experimental setup at the Soudan Underground Laboratory, with a focus on how data coming out of Soudan is analyzed. Chapter 3 presents results from a search for low-mass dark matter at SuperCDMS Soudan and discusses the interpretation of the results. Chapter 4 contains follow-up work that uses the CDMS Detector Monte Carlo (DMC) to understand the possible systematics associated with a detector that had one of its charge electrodes shorted to ground. This chapter represents the first time the DMC has been used to inform ongoing CDMS analysis. Chapter 5 takes a brief detour into the world of effective field theory (EFT), examining the consequences of an expanded set of possible WIMP-nucleon interactions in the EFT framework. Finally, Chapter 6 wraps up the material of the previous chapters and discusses how the research presented in this thesis can be applied as CDMS moves toward SuperCDMS SNOLAB.« less
Rotation curves of high-resolution LSB and SPARC galaxies with fuzzy and multistate (ultralight boson) scalar field dark matter

NASA Astrophysics Data System (ADS)

Bernal, T.; Fernández-Hernández, L. M.; Matos, T.; Rodríguez-Meza, M. A.

2018-04-01

Cold dark matter (CDM) has shown to be an excellent candidate for the dark matter (DM) of the Universe at large scales; however, it presents some challenges at the galactic level. The scalar field dark matter (SFDM), also called fuzzy, wave, Bose-Einstein condensate, or ultralight axion DM, is identical to CDM at cosmological scales but different at the galactic ones. SFDM forms core haloes, it has a natural cut-off in its matter power spectrum, and it predicts well-formed galaxies at high redshifts. In this work we reproduce the rotation curves of high-resolution low surface brightness (LSB) and SPARC galaxies with two SFDM profiles: (1) the soliton+NFW profile in the fuzzy DM (FDM) model, arising empirically from cosmological simulations of real, non-interacting scalar field (SF) at zero temperature, and (2) the multistate SFDM (mSFDM) profile, an exact solution to the Einstein-Klein-Gordon equations for a real, self-interacting SF, with finite temperature into the SF potential, introducing several quantum states as a realistic model for an SFDM halo. From the fits with the soliton+NFW profile, we obtained for the boson mass 0.212 < mψ/(10-23 eV/c2) < 27.0 and for the core radius 0.326 < rc/kpc < 8.96. From the combined analysis with the LSB galaxies, we obtained mψ = 0.554 × 10-23 eV, a result in tension with the severe cosmological constraints. Also, we show the analytical mSFDM model fits the observations as well as or better than the empirical soliton+NFW profile, and it reproduces naturally the wiggles present in some galaxies, being a theoretically motivated framework additional or alternative to the FDM profile.
Imprints of dark energy on cosmic structure formation - I. Realistic quintessence models and the non-linear matter power spectrum

NASA Astrophysics Data System (ADS)

Alimi, J.-M.; Füzfa, A.; Boucher, V.; Rasera, Y.; Courtin, J.; Corasaniti, P.-S.

2010-01-01

Quintessence has been proposed to account for dark energy (DE) in the Universe. This component causes a typical modification of the background cosmic expansion, which, in addition to its clustering properties, can leave a potentially distinctive signature on large-scale structures. Many previous studies have investigated this topic, particularly in relation to the non-linear regime of structure formation. However, no careful pre-selection of viable quintessence models with high precision cosmological data was performed. Here we show that this has led to a misinterpretation (and underestimation) of the imprint of quintessence on the distribution of large-scale structures. To this purpose, we perform a likelihood analysis of the combined Supernova Ia UNION data set and Wilkinson Microwave Anisotropy Probe 5-yr data to identify realistic quintessence models. These are specified by different model parameter values, but still statistically indistinguishable from the vanilla Λ cold dark matter (ΛCDM). Differences are especially manifest in the predicted amplitude and shape of the linear matter power spectrum though these remain within the uncertainties of the Sloan Digital Sky Survey data. We use these models as a benchmark for studying the clustering properties of dark matter haloes by performing a series of high-resolution N-body simulations. In this first paper, we specifically focus on the non-linear matter power spectrum. We find that realistic quintessence models allow for relevant differences of the dark matter distribution with respect to the ΛCDM scenario well into the non-linear regime, with deviations of up to 40 per cent in the non-linear power spectrum. Such differences are shown to depend on the nature of DE, as well as the scale and epoch considered. At small scales (k ~ 1-5hMpc-1, depending on the redshift), the structure formation process is about 20 per cent more efficient than in ΛCDM. We show that these imprints are a specific record of the cosmic structure formation history in DE cosmologies and therefore cannot be accounted for in standard fitting functions of the non-linear matter power spectrum.
Subhalo Tracing in Simulations and Subhalo Observation in Gamma-rays

NASA Astrophysics Data System (ADS)

Han, J. X.

2014-05-01

Current major observations of the Universe favor the concordant ΛCDM cosmology, in which the matter content is dominated by cold dark matter (CDM). In this CDM universe, small perturbations from the initial condition grow into clumps of virilized structure called dark matter haloes. Small haloes form early and later merge to form bigger haloes. As a result, dark matter haloes host plenty of substructures called subhaloes which are the self-bound remnants of their progenitor haloes. These subhaloes could be studied in detail with the help of numerical simulations, which then could provide input into theories of galaxy formation, and also influence the way dark matter could be detected. To find and trace dark matter subhaloes in simulations, we develop a new code, the Hierarchical Bound-Tracing (HBT for short) code, based on the merger hierarchy of dark matter haloes. Application of this code to a recent benchmark test of finding subhaloes demonstrates that HBT stands as one of the best codes to trace the evolutionary history of subhaloes. The success of this code lies in its careful treatment of the complex physical processes associated with the evolution of subhaloes, and in its robust unbinding algorithm with an adaptive source subhalo management. We keep a full record of the merger hierarchy of haloes and subhaloes, and allow growth of satellite subhaloes through accretion from its ``satellite-of-satellites'', hence allowing mergers among satellites. Local accretion of background mass is omitted, while rebinding of stripped mass is allowed. The justification of these treatments is provided by case studies of the lives of individual subhaloes, and by the success in finding the complete subhalo catalogue. We compare our result to other popular subhalo finders. It is shown that HBT is able to well resolve subhaloes in high density environment, and keep strict physical track of subhaloes' merger history. This code is fully parallelized, and freely available upon request to the authors. If the cold dark matter consists of weakly interacting massive particles, their annihilation within subhaloes could lead to diffuse GeV emission that would dominate over the annihilation signal of the host halo. We have carried out a search for this kind of GeV emission from three nearby galaxy clusters: Coma, Virgo, and Fornax. We first remove known extragalactic and galactic diffuse gamma-ray backgrounds and point sources from the Fermi 2-year catalogue, and find a significant residual diffuse emission in all three clusters. We then investigate whether this emission is due to (i) unresolved point sources; (ii) dark matter annihilation; or (iii) cosmic rays (CRs). Using 45 months of Fermi-LAT data, we detect several new point sources (not present in the Fermi 2-year point source catalogue) which contaminate the signal previously analyzed by Han et al. Including these and accounting for the effects of undetected point sources, we find no significant detection of extended emission from the three clusters studied. Instead, we determine upper limits on emission due to dark matter annihilation and cosmic rays. For Fornax and Virgo the limits on CR emission are consistent with theoretical models, but for Coma the upper limit is a factor of 2 below the theoretical expectation. Allowing for systematic uncertainties associated with the treatment of CR, the upper limits on the cross section for dark matter annihilation from our clusters are more stringent than those from the analyses of dwarf galaxies in the Milky Way. Adopting a boost factor of ˜10^3 from subhalos on cluster luminosity as suggested by recent theoretical models, we rule out the thermal cross section for supersymmetric dark matter particles for masses as large as 100 GeV (depending on the annihilation channel). There are recent claims of the detection of a 130 GeV line signal from regions around the galactic center, which can be explained as annihilation of dark matter into monotonic photon pairs. However, in the subhalo-dominated halo annihilation profile, significant contributions should come from the outer regions of the galactic halo. We scan the 4-year public Fermi data at high galactic latitudes (|b|>30°) for a line signal by using the 100-200 GeV events. No evidence for a line signal has been identified within the energy range from 109 to 149 GeV. We adopt the standard P7V6 energy dispersion function, and take into account the inclination, conversion type, as well as the energy dependence of the dispersion. We also try an alternative dispersion function used by Ackermann et al. (2012), and find little difference in the results. Without considering boosts from subhaloes, our cross-section upper-limits are slightly higher than those from Ackermann et al. (2012) and Huang et al. (2012) who used a larger dataset (with |b|>10° data-cut), and permit a line signal as found in Weniger (2012). However, when annihilation signals from subhalos are also modelled, the 130 GeV signal can be ruled out at >95% confidence.
THE EFFECT OF WARM DARK MATTER ON GALAXY PROPERTIES: CONSTRAINTS FROM THE STELLAR MASS FUNCTION AND THE TULLY-FISHER RELATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Xi; Maccio, Andrea V.; Dutton, Aaron A.

2013-04-10

In this paper, we combine high-resolution N-body simulations with a semi-analytical model of galaxy formation to study the effects of a possible warm dark matter (WDM) component on the observable properties of galaxies. We compare three WDM models with a dark matter (DM) mass of 0.5, 0.75, and 2.0 keV with the standard cold dark matter case. For a fixed set of parameters describing the baryonic physics, the WDM models predict fewer galaxies at low (stellar) masses, as expected due to the suppression of power on small scales, while no substantial difference is found at the high-mass end. However, thesemore » differences in the stellar mass function vanish when a different set of parameters is used to describe the (largely unknown) galaxy formation processes. We show that it is possible to break this degeneracy between DM properties and the parameterization of baryonic physics by combining observations on the stellar mass function with the Tully-Fisher relation (the relation between stellar mass and the rotation velocity at large galactic radii as probed by resolved H I rotation curves). WDM models with a too warm candidate (m{sub {nu}} < 0.75 keV) cannot simultaneously reproduce the stellar mass function and the Tully-Fisher relation. We conclude that accurate measurements of the galaxy stellar mass function and the link between galaxies and DM halos down to the very low mass end can give very tight constraints on the nature of DM candidates.« less
Modelling the line-of-sight contribution in substructure lensing

NASA Astrophysics Data System (ADS)

Despali, Giulia; Vegetti, Simona; White, Simon D. M.; Giocoli, Carlo; van den Bosch, Frank C.

2018-04-01

We investigate how Einstein rings and magnified arcs are affected by small-mass dark-matter haloes placed along the line of sight to gravitational lens systems. By comparing the gravitational signature of line-of-sight haloes with that of substructures within the lensing galaxy, we derive a mass-redshift relation that allows us to rescale the detection threshold (i.e. lowest detectable mass) for substructures to a detection threshold for line-of-sight haloes at any redshift. We then quantify the line-of-sight contribution to the total number density of low-mass objects that can be detected through strong gravitational lensing. Finally, we assess the degeneracy between substructures and line-of-sight haloes of different mass and redshift to provide a statistical interpretation of current and future detections, with the aim of distinguishing between cold dark matter and warm dark matter. We find that line-of-sight haloes statistically dominate with respect to substructures, by an amount that strongly depends on the source and lens redshifts, and on the chosen dark-matter model. Substructures represent about 30 percent of the total number of perturbers for low lens and source redshifts (as for the SLACS lenses), but less than 10 per cent for high-redshift systems. We also find that for data with high enough signal-to-noise ratio and angular resolution, the non-linear effects arising from a double-lens-plane configuration are such that one is able to observationally recover the line-of-sight halo redshift with an absolute error precision of 0.15 at the 68 per cent confidence level.
Addressing the too big to fail problem with baryon physics and sterile neutrino dark matter

NASA Astrophysics Data System (ADS)

Lovell, Mark R.; Gonzalez-Perez, Violeta; Bose, Sownak; Boyarsky, Alexey; Cole, Shaun; Frenk, Carlos S.; Ruchayskiy, Oleg

2017-07-01

N-body dark matter simulations of structure formation in the Λ cold dark matter (ΛCDM) model predict a population of subhaloes within Galactic haloes that have higher central densities than inferred for the Milky Way satellites, a tension known as the 'too big to fail' problem. Proposed solutions include baryonic effects, a smaller mass for the Milky Way halo and warm dark matter (WDM). We test these possibilities using a semi-analytic model of galaxy formation to generate luminosity functions for Milky Way halo-analogue satellite populations, the results of which are then coupled to the Jiang & van den Bosch model of subhalo stripping to predict the subhalo Vmax functions for the 10 brightest satellites. We find that selecting the brightest satellites (as opposed to the most massive) and modelling the expulsion of gas by supernovae at early times increases the likelihood of generating the observed Milky Way satellite Vmax function. The preferred halo mass is 6 × 1011 M⊙, which has a 14 per cent probability to host a Vmax function like that of the Milky Way satellites. We conclude that the Milky Way satellite Vmax function is compatible with a CDM cosmology, as previously found by Sawala et al. using hydrodynamic simulations. Sterile neutrino-WDM models achieve a higher degree of agreement with the observations, with a maximum 50 per cent chance of generating the observed Milky Way satellite Vmax function. However, more work is required to check that the semi-analytic stripping model is calibrated correctly for each sterile neutrino cosmology.
Halo ellipticity of GAMA galaxy groups from KiDS weak lensing

NASA Astrophysics Data System (ADS)

van Uitert, Edo; Hoekstra, Henk; Joachimi, Benjamin; Schneider, Peter; Bland-Hawthorn, Joss; Choi, Ami; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Hopkins, Andrew M.; Klaes, Dominik; Kuijken, Konrad; Nakajima, Reiko; Napolitano, Nicola R.; Schrabback, Tim; Valentijn, Edwin; Viola, Massimo

2017-06-01

We constrain the average halo ellipticity of ˜2600 galaxy groups from the Galaxy And Mass Assembly (GAMA) survey, using the weak gravitational lensing signal measured from the overlapping Kilo Degree Survey (KiDS). To do so, we quantify the azimuthal dependence of the stacked lensing signal around seven different proxies for the orientation of the dark matter distribution, as it is a priori unknown which one traces the orientation best. On small scales, the major axis of the brightest group/cluster member (BCG) provides the best proxy, leading to a clear detection of an anisotropic signal. In order to relate that to a halo ellipticity, we have to adopt a model density profile. We derive new expressions for the quadrupole moments of the shear field given an elliptical model surface mass density profile. Modelling the signal with an elliptical Navarro-Frenk-White profile on scales R < 250 kpc, and assuming that the BCG is perfectly aligned with the dark matter, we find an average halo ellipticity of ɛh = 0.38 ± 0.12, in fair agreement with results from cold dark matter only simulations. On larger scales, the lensing signal around the BCGs becomes isotropic and the distribution of group satellites provides a better proxy for the halo's orientation instead, leading to a 3σ-4σ detection of a non-zero halo ellipticity at 250 < R < 750 kpc. Our results suggest that the distribution of stars enclosed within a certain radius forms a good proxy for the orientation of the dark matter within that radius, which has also been observed in hydrodynamical simulations.

Constraining self-interacting dark matter with scaling laws of observed halo surface densities

NASA Astrophysics Data System (ADS)

Bondarenko, Kyrylo; Boyarsky, Alexey; Bringmann, Torsten; Sokolenko, Anastasia

2018-04-01

The observed surface densities of dark matter halos are known to follow a simple scaling law, ranging from dwarf galaxies to galaxy clusters, with a weak dependence on their virial mass. Here we point out that this can not only be used to provide a method to determine the standard relation between halo mass and concentration, but also to use large samples of objects in order to place constraints on dark matter self-interactions that can be more robust than constraints derived from individual objects. We demonstrate our method by considering a sample of about 50 objects distributed across the whole halo mass range, and by modelling the effect of self-interactions in a way similar to what has been previously done in the literature. Using additional input from simulations then results in a constraint on the self-interaction cross section per unit dark matter mass of about σ/mχlesssim 0.3 cm2/g. We expect that these constraints can be significantly improved in the future, and made more robust, by i) an improved modelling of the effect of self-interactions, both theoretical and by comparison with simulations, ii) taking into account a larger sample of objects and iii) by reducing the currently still relatively large uncertainties that we conservatively assign to the surface densities of individual objects. The latter can be achieved in particular by using kinematic observations to directly constrain the average halo mass inside a given radius, rather than fitting the data to a pre-selected profile and then reconstruct the mass. For a velocity-independent cross-section, our current result is formally already somewhat smaller than the range 0.5‑5 cm2/g that has been invoked to explain potential inconsistencies between small-scale observations and expectations in the standard collisionless cold dark matter paradigm.
The Formation of the First Cosmic Structures and the Physics of the z ~ 20 Universe

NASA Astrophysics Data System (ADS)

O'Leary, Ryan M.; McQuinn, Matthew

2012-11-01

We perform a suite of cosmological simulations in the ΛCDM paradigm of the formation of the first structures in the universe prior to astrophysical reheating and reionization (15 <~ z < 200). These are the first simulations initialized in a manner that self-consistently accounts for the impact of pressure on the rate of growth of modes, temperature fluctuations in the gas, and the dark matter-baryon supersonic velocity difference. Even with these improvements, these are still difficult times to simulate accurately as the Jeans length of the cold intergalactic gas must be resolved while also capturing a representative sample of the universe. We explore the box size and resolution requirements to meet these competing objectives. Our simulations support the finding of recent studies that the dark matter-baryon velocity difference has a surprisingly large impact on the accretion of gas onto the first star-forming minihalos (which have masses of ~106 M ⊙). In fact, the halo gas is often significantly downwind of such halos and with lower densities in the simulations in which the baryons have a bulk flow with respect to the dark matter, modulating the formation of the first stars by the local value of this velocity difference. We also show that dynamical friction plays an important role in the nonlinear evolution of the dark matter-baryon differential velocity, acting to erase this velocity difference quickly in overdense gas, as well as sourcing visually apparent bow shocks and Mach cones throughout the universe. We use simulations with both the GADGET and Enzo cosmological codes to test the robustness of these conclusions. The comparison of these codes' simulations also provides a relatively controlled test of these codes themselves, allowing us to quantify some of the tradeoffs between the algorithms. For example, we find that particle coupling in GADGET between the gas and dark matter particles results in spurious growth that mimics nonlinear growth in the matter power spectrum for standard initial setups. This coupling is alleviated by using adaptive gravitational softening for the gas. In a companion paper, we use the simulations presented here to make detailed estimates for the impact of the dark matter-baryon velocity differential on redshifted 21 cm radiation. The initial conditions generator used in this study, CICSASS, can be publicly downloaded.
Axions, Inflation and String Theory

NASA Astrophysics Data System (ADS)

Mack, Katherine J.; Steinhardt, P. J.

2009-01-01

The QCD axion is the leading contender to rid the standard model of the strong-CP problem. If the Peccei-Quinn symmetry breaking occurs before inflation, which is likely in string theory models, axions manifest themselves cosmologically as a form of cold dark matter with a density determined by the axion's initial conditions and by the energy scale of inflation. Constraints on the dark matter density and on the amplitude of CMB isocurvature perturbations currently demand an exponential degree of fine-tuning of both axion and inflationary parameters beyond what is required for particle physics. String theory models generally produce large numbers of axion-like fields; the prospect that any of these fields exist at scales close to that of the QCD axion makes the problem drastically worse. I will discuss the challenge of accommodating string-theoretic axions in standard inflationary cosmology and show that the fine-tuning problems cannot be fully addressed by anthropic principle arguments.
Astrometric cosmology .

NASA Astrophysics Data System (ADS)

Lattanzi, M. G.

The accurate measurement of the motions of stars in our Galaxy can provide access to the cosmological signatures in the disk and halo, while astrometric experiments from within our Solar System can uniquely probe possible deviations from General Relativity. This article will introduce to the fact that astrometry has the potential, thanks also to impressive technological advancements, to become a key player in the field of local cosmology. For example, accurate absolute kinematics at the scale of the Milky Way can, for the first time in situ, account for the predictions made by the cold dark matter model for the Galactic halo, and eventually map out the distribution of dark matter, or other formation mechanisms, required to explain the signatures recently identified in the old component of the thick disk. Final notes dwell on to what extent Gaia can fulfill the expectations of astrometric cosmology and on what must instead be left to future, specifically designed, astrometric experiments.
Simulating the formation of cosmic structure.

PubMed

Frenk, C S

2002-06-15

A timely combination of new theoretical ideas and observational discoveries has brought about significant advances in our understanding of cosmic evolution. Computer simulations have played a key role in these developments by providing the means to interpret astronomical data in the context of physical and cosmological theory. In the current paradigm, our Universe has a flat geometry, is undergoing accelerated expansion and is gravitationally dominated by elementary particles that make up cold dark matter. Within this framework, it is possible to simulate in a computer the emergence of galaxies and other structures from small quantum fluctuations imprinted during an epoch of inflationary expansion shortly after the Big Bang. The simulations must take into account the evolution of the dark matter as well as the gaseous processes involved in the formation of stars and other visible components. Although many unresolved questions remain, a coherent picture for the formation of cosmic structure is now beginning to emerge.
Dynamical evolution of topology of large-scale structure. [in distribution of galaxies

NASA Technical Reports Server (NTRS)

Park, Changbom; Gott, J. R., III

1991-01-01

The nonlinear effects of statistical biasing and gravitational evolution on the genus are studied. The biased galaxy subset is picked for the first time by actually identifying galaxy-sized peaks above a fixed threshold in the initial conditions, and their subsequent evolution is followed. It is found that in the standard cold dark matter (CDM) model the statistical biasing in the locations of galaxies produces asymmetry in the genus curve and coupling with gravitational evolution gives rise to a shift in the genus curve to the left in moderately nonlinear regimes. Gravitational evolution alone reduces the amplitude of the genus curve due to strong phase correlations in the density field and also produces asymmetry in the curve. Results on the genus of the mass density field for both CDM and hot dark matter models are consistent with previous work by Melott, Weinberg, and Gott (1987).
Linear velocity fields in non-Gaussian models for large-scale structure

NASA Technical Reports Server (NTRS)

Scherrer, Robert J.

1992-01-01

Linear velocity fields in two types of physically motivated non-Gaussian models are examined for large-scale structure: seed models, in which the density field is a convolution of a density profile with a distribution of points, and local non-Gaussian fields, derived from a local nonlinear transformation on a Gaussian field. The distribution of a single component of the velocity is derived for seed models with randomly distributed seeds, and these results are applied to the seeded hot dark matter model and the global texture model with cold dark matter. An expression for the distribution of a single component of the velocity in arbitrary local non-Gaussian models is given, and these results are applied to such fields with chi-squared and lognormal distributions. It is shown that all seed models with randomly distributed seeds and all local non-Guassian models have single-component velocity distributions with positive kurtosis.
Particle Astrophysics after COBE- Blois 92- Summary Talk

NASA Astrophysics Data System (ADS)

Primack, J. R.

The IV Rencontres de Blois, on Particle Astrophysics, held at the Ch\\^ateau de Blois, June 15-20, 1992, was a meeting well-timed for a reconsideration of the issues in particle astrophysics in the light of the COBE discovery of the cosmic microwave background (CMB) fluctuations. This is a summary of what I thought were the most interesting things discussed at Blois: (1) The near-success of Cold Dark Matter (CDM) in predicting the COBE fluctuation amplitude, which favors the hypothesis that structure formed in the universe through gravitational collapse. (2) The indications that $\\Omega\\approx1$ and that the power spectrum has a little more power on supercluster and larger scales than CDM. These are suggested by the IRAS and CfA redshift surveys and POTENT galaxy peculiar velocity analysis, and also by the COBE data. (3) The consequent demise of CDM and the rise of hybrid schemes such as Cold+Hot Dark Matter (C+HDM). (4) The possible implications for neutrino masses and mixings, and for cosmology, of the recent results on solar neutrinos. (5) The first discovery of TeV $\\gamma$ rays from an extragalactic source, which was announced at Blois. I also summarize here a number of the exciting ongoing and planned experiments and observations discussed at Blois: CERN experiments on $\
EDITORIAL: Focus on Dark Matter and Particle Physics

NASA Astrophysics Data System (ADS)

Aprile, Elena; Profumo, Stefano

2009-10-01

The quest for the nature of dark matter has reached a historical point in time, with several different and complementary experiments on the verge of conclusively exploring large portions of the parameter space of the most theoretically compelling particle dark matter models. This focus issue on dark matter and particle physics brings together a broad selection of invited articles from the leading experimental and theoretical groups in the field. The leitmotif of the collection is the need for a multi-faceted search strategy that includes complementary experimental and theoretical techniques with the common goal of a sound understanding of the fundamental particle physical nature of dark matter. These include theoretical modelling, high-energy colliders and direct and indirect searches. We are confident that the works collected here present the state of the art of this rapidly changing field and will be of interest to both experts in the topic of dark matter as well as to those new to this exciting field. Focus on Dark Matter and Particle Physics Contents DARK MATTER AND ASTROPHYSICS Scintillator-based detectors for dark matter searches I S K Kim, H J Kim and Y D Kim Cosmology: small-scale issues Joel R Primack Big Bang nucleosynthesis and particle dark matter Karsten Jedamzik and Maxim Pospelov Particle models and the small-scale structure of dark matter Torsten Bringmann DARK MATTER AND COLLIDERS Dark matter in the MSSM R C Cotta, J S Gainer, J L Hewett and T G Rizzo The role of an e+e- linear collider in the study of cosmic dark matter M Battaglia Collider, direct and indirect detection of supersymmetric dark matter Howard Baer, Eun-Kyung Park and Xerxes Tata INDIRECT PARTICLE DARK MATTER SEARCHES:EXPERIMENTS PAMELA and indirect dark matter searches M Boezio et al An indirect search for dark matter using antideuterons: the GAPS experiment C J Hailey Perspectives for indirect dark matter search with AMS-2 using cosmic-ray electrons and positrons B Beischer, P von Doetinchem, H Gast, T Kirn and S Schael Axion searches with helioscopes and astrophysical signatures for axion(-like) particles K Zioutas, M Tsagri, Y Semertzidis, T Papaevangelou, T Dafni and V Anastassopoulos The indirect search for dark matter with IceCube Francis Halzen and Dan Hooper DIRECT DARK MATTER SEARCHES:EXPERIMENTS Gaseous dark matter detectors G Sciolla and C J Martoff Search for dark matter with CRESST Rafael F Lang and Wolfgang Seidel DIRECT AND INDIRECT PARTICLE DARK MATTER SEARCHES:THEORY Dark matter annihilation around intermediate mass black holes: an update Gianfranco Bertone, Mattia Fornasa, Marco Taoso and Andrew R Zentner Update on the direct detection of dark matter in MSSM models with non-universal Higgs masses John Ellis, Keith A Olive and Pearl Sandick Dark stars: a new study of the first stars in the Universe Katherine Freese, Peter Bodenheimer, Paolo Gondolo and Douglas Spolyar Determining the mass of dark matter particles with direct detection experiments Chung-Lin Shan The detection of subsolar mass dark matter halos Savvas M Koushiappas Neutrino coherent scattering rates at direct dark matter detectors Louis E Strigari Gamma rays from dark matter annihilation in the central region of the Galaxy Pasquale Dario Serpico and Dan Hooper DARK MATTER MODELS The dark matter interpretation of the 511 keV line Céline Boehm Axions as dark matter particles Leanne D Duffy and Karl van Bibber Sterile neutrinos Alexander Kusenko Dark matter candidates Lars Bergström Minimal dark matter: model and results Marco Cirelli and Alessandro Strumia Shedding light on the dark sector with direct WIMP production Partha Konar, Kyoungchul Kong, Konstantin T Matchev and Maxim Perelstein Axinos as dark matter particles Laura Covi and Jihn E Kim
The XENON100 Dark Matter Experiment: Design, Construction, Calibration and 2010 Search Results with Improved Measurement of the Scintillation Response of Liquid Xenon to Low-Energy Nuclear Recoils

NASA Astrophysics Data System (ADS)

Plante, Guillaume

An impressive array of astrophysical observations suggest that 83% of the matter in the universe is in a form of non-luminous, cold, collisionless, non-baryonic dark matter. Several extensions of the Standard Model of particle physics aimed at solving the hierarchy problem predict stable weakly interacting massive particles (WIMPs) that could naturally have the right cosmological relic abundance today to compose most of the dark matter if their interactions with normal matter are on the order of a weak scale cross section. These candidates also have the added benefit that their properties and interaction rates can be computed in a well defined particle physics model. A considerable experimental effort is currently under way to uncover the nature of dark matter. One method of detecting WIMP dark matter is to look for its interactions in terrestrial detectors where it is expected to scatter off nuclei. In 2007, the XENON10 experiment took the lead over the most sensitive direct detection dark matter search in operation, the CDMS II experiment, by probing spin-independent WIMP-nucleon interaction cross sections down to sigmachi N ˜ 5 x 10-44 cm 2 at 30 GeV/c2. Liquefied noble gas detectors are now among the technologies at the forefront of direct detection experiments. Liquid xenon (LXe), in particular, is a well suited target for WIMP direct detection. It is easily scalable to larger target masses, allows discrimination between nuclear recoils and electronic recoils, and has an excellent stopping power to shield against external backgrounds. A particle losing energy in LXe creates both ionization electrons and scintillation light. In a dual-phase LXe time projection chamber (TPC) the ionization electrons are drifted and extracted into the gas phase where they are accelerated to amplify the charge signal into a proportional scintillation signal. These two signals allow the three-dimensional localization of events with millimeter precision and the ability to fiducialize the target volume, yielding an inner core with a very low background. Additionally, the ratio of ionization and scintillation can be used to discriminate between nuclear recoils, from neutrons or WIMPs, and electronic recoils, from gamma or beta backgrounds. In these detectors, the energy scale is based on the scintillation signal of nuclear recoils and consequently the precise knowledge of the scintillation efficiency of nuclear recoils in LXe is of prime importance. Inspired by the success of the XENON10 experiment, the XENON collaboration designed and built a new, ten times larger, with a one hundred times lower background, LXe TPC to search for dark matter. It is currently the most sensitive direct detection experiment in operation. In order to shed light on the response of LXe to low energy nuclear recoils a new single phase detector designed specifically for the measurement of the scintillation efficiency of nuclear recoils was also built. In 2011, the XENON100 dark matter results from 100 live days set the most stringent limit on the spin-independent WIMP-nucleon interaction cross section over a wide range of masses, down to sigma chi N ˜ 7 x 10-45 cm2 at 50 GeV/c2, almost an order of magnitude improvement over XENON10 in less than four years. This thesis describes the research conducted in the context of the XENON100 dark matter search experiment. I describe the initial simulation results and ideas that influenced the design of the XENON100 detector, the construction and assembly steps that lead into its concrete realization, the detector and its subsystems, a subset of the calibration results of the detector, and finally dark matter exclusion limits. I also describe in detail the new improved measurement of the important quantity for the interpretation of results from LXe dark matter searches, the scintillation efficiency of low-energy nuclear recoils in LXe.
"Missing Mass" Found in Recycled Dwarf Galaxies

NASA Astrophysics Data System (ADS)

2007-05-01

Astronomers studying dwarf galaxies formed from the debris of a collision of larger galaxies found the dwarfs much more massive than expected, and think the additional material is "missing mass" that theorists said should not be present in this kind of dwarf galaxy. Multiwavelength Image of NGC 5291 Multiwavelength image of NGC 5291 and dwarf galaxies around it. CREDIT: P-A Duc, CEA-CNRS/NRAO/AUI/NSF/NASA. Click on image for page of more graphics and full information The scientists used the National Science Foundation's Very Large Array (VLA) radio telescope to study a galaxy called NGC 5291, 200 million light-years from Earth. This galaxy collided with another 360 million years ago, and the collision shot streams of gas and stars outward. Later, the dwarf galaxies formed from the ejected debris. "Our detailed studies of three 'recycled' dwarf galaxies in this system showed that the dwarfs have twice as much unseen matter as visible matter. This was surprising, because they were expected to have very little unseen matter," said Frederic Bournaud, of the French astrophysics laboratory AIM of the French CEA and CNRS. Bournaud and his colleagues announced their discovery in the May 10 online issue of the journal Science. "Dark matter," which astronomers can detect only by its gravitational effects, comes, they believe, in two basic forms. One form is the familiar kind of matter seen in stars, planets, and humans -- called baryonic matter -- that does not emit much light or other type of radiation. The other form, called non-baryonic dark matter, comprises nearly a third of the Universe but its nature is unknown. The visible portion of spiral galaxies, like our own Milky Way, lies mostly in a flattened disk, usually with a bulge in the center. This visible portion, however, is surrounded by a much larger halo of dark matter. When spiral galaxies collide, the material expelled outward by the interaction comes from the galaxies' disks. For this reason, astronomers did not expect that "recycled" dwarf galaxies formed from this collision debris would contain much, if any, dark matter. When Bournaud and his international team of scientists used the VLA to study three dwarf galaxies formed from the debris of NGC 5291's collision, they were surprised to find two to three times the amount of dark matter as visible matter in the dwarfs. They determined the dwarfs' masses by measuring the Doppler shift of radio waves emitted by atomic Hydrogen at a frequency of 1420 MHz. The amount of shift in the frequency indicated the rotational speed in the galaxy. That, in turn, allowed the scientists to calculate the dwarf's mass. Images from two NASA satellites provided vital information about the dwarf galaxies. "Using ultraviolet images from the Galex satellite and infrared data collected by the Spitzer satellite, we had previously shown that the dwarfs all along the debris stream were star-forming galaxies," said Pierre-Alain Duc, also of the AIM laboratory (CEA/CNRS). What is the dark matter in the dwarfs? The astronomers don't believe it is the mysterious non-baryonic type, but rather cold Hydrogen molecules that are extremely difficult to detect. When the astronomers performed computer models of the collision of NGC 5291 to simulate the formation of the system seen today, the models left the resulting recycled dwarfs with almost no dark matter. These computer models had started off with all the dark matter in the galaxy's larger halo. "The result of the computer models means that the additional mass we see in the real dwarfs came from the disks, not the haloes, of the larger galaxies that collided," Bournaud said. That additional mass, the scientists believe, almost certainly is "normal" baryonic matter, probably cold molecular Hydrogen. While the discovery about NGC 5291's neighboring dwarf galaxies sheds new light on the composition of spiral galaxies, it doesn't tell the scientists anything about the non-baryonic dark matter, whose nature remains a mystery. "Still, this new information about the matter comprising galactic disks should help us work toward a better understanding of their formation and evolution," Bournaud concluded. Bournaud and Duc worked with Mederic Boquien, also of the AIM laboratory (CEA/CNRS); Elias Brinks of the University of Hertfordshire in the UK; Phillipe Amram of the Astronomical Observatory of Marseille-Provence; Ute Lisenfeld of the University of Granada, Spain; Barbel S. Koribalski of the Australia Telescope National Facility; Fabian Walter of the Max Planck Institute for Astronomy in Heidelberg, Germany; and Vassilis Charmandaris of the University of Crete, Greece. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The California Institute of Technology leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory, a division of Caltech, manages the mission and built the science instrument, and also manages the Spitzer Space Telescope.
Astronomical bounds on a cosmological model allowing a general interaction in the dark sector

NASA Astrophysics Data System (ADS)

Pan, Supriya; Mukherjee, Ankan; Banerjee, Narayan

2018-06-01

Non-gravitational interaction between two barotropic dark fluids, namely the pressureless dust and the dark energy in a spatially flat Friedmann-Lemaître-Robertson-Walker model, has been discussed. It is shown that for the interactions that are linear in terms the energy densities of the dark components and their first order derivatives, the net energy density is governed by a second-order differential equation with constant coefficients. Taking a generalized interaction, which includes a number of already known interactions as special cases, the dynamics of the universe is described for three types of the dark energy equation of state, namely that of interacting quintessence, interacting vacuum energy density, and interacting phantom. The models have been constrained using the standard cosmological probes, Supernovae Type Ia data from joint light curve analysis and the observational Hubble parameter data. Two geometric tests, the cosmographic studies, and the Om diagnostic have been invoked so as to ascertain the behaviour of the present model vis-a-vis the Λ-cold dark matter model. We further discussed the interacting scenarios taking into account the thermodynamic considerations.
Measurement of a Cosmographic Distance Ratio with Galaxy and Cosmic Microwave Background Lensing.

PubMed

Miyatake, Hironao; Madhavacheril, Mathew S; Sehgal, Neelima; Slosar, Anže; Spergel, David N; Sherwin, Blake; van Engelen, Alexander

2017-04-21

We measure the gravitational lensing shear signal around dark matter halos hosting constant mass galaxies using light sources at z∼1 (background galaxies) and at the surface of last scattering at z∼1100 (the cosmic microwave background). The galaxy shear measurement uses data from the CFHTLenS survey, and the microwave background shear measurement uses data from the Planck satellite. The ratio of shears from these cross-correlations provides a purely geometric distance measurement across the longest possible cosmological lever arm. This is because the matter distribution around the halos, including uncertainties in galaxy bias and systematic errors such as miscentering, cancels in the ratio for halos in thin redshift slices. We measure this distance ratio in three different redshift slices of the constant mass (CMASS) sample and combine them to obtain a 17% measurement of the distance ratio, r=0.390_{-0.062}^{+0.070}, at an effective redshift of z=0.53. This is consistent with the predicted ratio from the Planck best-fit cold dark matter model with a cosmological constant cosmology of r=0.419.
Joint measurement of lensing–galaxy correlations using SPT and DES SV data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baxter, E.; Clampitt, J.; Giannantonio, T.

We measure the correlation of galaxy lensing and cosmic microwave background lensing with a set of galaxies expected to trace the matter density field. The measurements are performed using pre-survey Dark Energy Survey (DES) Science Verification optical imaging data and millimetre-wave data from the 2500 sq. deg. South Pole Telescope Sunyaev–Zel'dovich (SPT-SZ) survey. The two lensing–galaxy correlations are jointly fit to extract constraints on cosmological parameters, constraints on the redshift distribution of the lens galaxies, and constraints on the absolute shear calibration of DES galaxy-lensing measurements. We show that an attractive feature of these fits is that they are fairlymore » insensitive to the clustering bias of the galaxies used as matter tracers. The measurement presented in this work confirms that DES and SPT data are consistent with each other and with the currently favoured Λ cold dark matter cosmological model. It also demonstrates that joint lensing–galaxy correlation measurement considered here contains a wealth of information that can be extracted using current and future surveys.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Miyatake, Hironao; Madhavacheril, Mathew S.; Sehgal, Neelima

We measure the gravitational lensing shear signal around dark matter halos hosting constant mass galaxies using light sources at z~1 (background galaxies) and at the surface of last scattering at z~1100 (the cosmic microwave background). The galaxy shear measurement uses data from the CFHTLenS survey, and the microwave background shear measurement uses data from the Planck satellite. The ratio of shears from these cross-correlations provides a purely geometric distance measurement across the longest possible cosmological lever arm. This is because the matter distribution around the halos, including uncertainties in galaxy bias and systematic errors such as miscentering, cancels in themore » ratio for halos in thin redshift slices. We measure this distance ratio in three different redshift slices of the constant mass (CMASS) sample and combine them to obtain a 17% measurement of the distance ratio, r = 0.390 +0.070 –0.062, at an effective redshift of z = 0.53. As a result, this is consistent with the predicted ratio from the Planck best-fit cold dark matter model with a cosmological constant cosmology of r = 0.419.« less
XENON100 Dark Matter Search: Scintillation Response of Liquid Xenon to Electronic Recoils

NASA Astrophysics Data System (ADS)

Lim, Kyungeun Elizabeth

Dark matter is one of the missing pieces necessary to complete the puzzle of the universe. Numerous astrophysical observations at all scales suggest that 23 % of the universe is made of nonluminous, cold, collisionless, nonbaryonic, yet undiscovered dark matter. Weakly Interacting Massive Particles (WIMPs) are the most well-motivated dark matter candidates and significant efforts have been made to search for WIMPs. The XENON100 dark matter experiment is currently the most sensitive experiment in the global race for the first direct detection of WIMP dark matter. XENON100 is a dual-phase (liquid-gas) time projection chamber containing a total of 161 kg of liquid xenon (LXe) with a 62kg WIMP target mass. It has been built with radiopure materials to achieve an ultra-low electromagnetic background and operated at the Laboratori Nazionali del Gran Sasso in Italy. WIMPs are expected to scatter off xenon nuclei in the target volume. Simultaneous measurement of ionization and scintillation produced by nuclear recoils allows for the detection of WIMPs in XENON100. Data from the XENON100 experiment have resulted in the most stringent limits on the spin-independent elastic WIMP-nucleon scattering cross sections for most of the significant WIMP masses. As the experimental precision increases, a better understanding of the scintillation and ionization response of LXe to low energy (< 10 keV) particles is crucial for the interpretation of data from LXe based WIMP searches. A setup has been built and operated at Columbia University to measure the scintillation response of LXe to both electronic and nuclear recoils down to energies of a few keV, in particular for the XENON100 experiment. In this thesis, I present the research carried out in the context of the XENON100 dark matter search experiment. For the theoretical foundation of the XENON100 experiment, the first two chapters are dedicated to the motivation for and detection medium choice of the XENON100 experiment, respectively. A general review about dark matter focusing on WIMPs and their direct detection with liquid noble gas detectors is presented in Chap. 1. LXe as an attractive WIMP detection medium is explained in Chap. 2. The XENON100 detector design, the detector, and its subsystems are detailed in Chap. 3. The calibration of the detector and the characterized detector response used for the discrimination of a WIMP-like signal against background are explained in Chap. 4. In an effort to understand the background, anomalous electronic recoils were studied extensively and are described in Chap. 5. In order to obtain a better understanding of the electronic recoil background of XENON100, including an estimation of the electronic recoil background contribution, as well as to interpret dark matter results such as annual modulation, measurement of the scintillation yield of low-energy electrons in LXe was performed in 2011, with the dedicated setup mentioned above. The results from this measurement are discussed in Chap. 6. Finally, the results for the latest science data from XENON100 to search for WIMPs, comprising 225 live-days taken over 13 months during 2011 and 2012 are explained in Chap. 7.
Exclusion limits on the WIMP nucleon elastic scattering cross-section from the Cryogenic Dark Matter Search

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golwala, Sunil Ramanlal

2000-01-01

Extensive evidence indicates that a large fraction of the matter in the universe is nonluminous, nonbaryonic, and “cold” — nonrelativistic at the time matter began to dominate the energy density of the universe. Weakly Interacting Massive Particles (WIMPs) are an excellent candidate for nonbaryonic, cold dark matter. Minimal supersymmetry provides a natural WIMP candidate in the form of the lightest superpartner, with a typical mass Mδ ~ 100 GeV c-2 . WIMPs are expected to have collapsed into a roughly isothermal, spherical halo within which the visible portion of our galaxy resides. They would scatter off nuclei via the weakmore » interaction, potentially allowingtheir direct detection. The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for WIMPs via their elastic-scatteringinteractions with nuclei while discriminatingagainst interactions of background particles. The former yield nuclear recoils while the latter produce electron recoils. The ionization yield (the ratio of ionization production to recoil energy in a semiconductor) of a particle interaction differs greatly for nuclear and electron recoils. CDMS detectors measure phonon and electron-hole-pair production to determine recoil energy and ionization yield for each event and thereby discriminate nuclear recoils from electron recoils. This dissertation reports new limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV c-2 WIMP mass and, at > 75% CL, the entire 3σ allowed region for the WIMP signal reported by the DAMA experiment. The experimental apparatus, detector performance, and data analysis are fully described.« less
Self-consistent construction of virialized wave dark matter halos

NASA Astrophysics Data System (ADS)

Lin, Shan-Chang; Schive, Hsi-Yu; Wong, Shing-Kwong; Chiueh, Tzihong

2018-05-01

Wave dark matter (ψ DM ), which satisfies the Schrödinger-Poisson equation, has recently attracted substantial attention as a possible dark matter candidate. Numerical simulations have, in the past, provided a powerful tool to explore this new territory of possibility. Despite their successes in revealing several key features of ψ DM , further progress in simulations is limited, in that cosmological simulations so far can only address formation of halos below ˜2 ×1011 M⊙ and substantially more massive halos have become computationally very challenging to obtain. For this reason, the present work adopts a different approach in assessing massive halos by constructing wave-halo solutions directly from the wave distribution function. This approach bears certain similarities with the analytical construction of the particle-halo (cold dark matter model). Instead of many collisionless particles, one deals with one single wave that has many noninteracting eigenstates. The key ingredient in the wave-halo construction is the distribution function of the wave power, and we use several halos produced by structure formation simulations as templates to determine the wave distribution function. Among different models, we find the fermionic King model presents the best fits and we use it for our wave-halo construction. We have devised an iteration method for constructing the nonlinear halo and demonstrate its stability by three-dimensional simulations. A Milky Way-sized halo has also been constructed, and the inner halo is found to be flatter than the NFW profile. These wave-halos have small-scale interferences both in space and time producing time-dependent granules. While the spatial scale of granules varies little, the correlation time is found to increase with radius by 1 order of magnitude across the halo.
The imprint of dark matter haloes on the size and velocity dispersion evolution of early-type galaxies

NASA Astrophysics Data System (ADS)

Posti, Lorenzo; Nipoti, Carlo; Stiavelli, Massimo; Ciotti, Luca

2014-05-01

Early-type galaxies (ETGs) are observed to be more compact, on average, at z ≳ 2 than at z ≃ 0, at fixed stellar mass. Recent observational works suggest that such size evolution could reflect the similar evolution of the host dark matter halo density as a function of the time of galaxy quenching. We explore this hypothesis by studying the distribution of halo central velocity dispersion (σ0) and half-mass radius (rh) as functions of halo mass M and redshift z, in a cosmological Λ cold dark matter N-body simulation. In the range 0 ≲ z ≲ 2.5, we find σ0∝M0.31-0.37 and rh∝M0.28-0.32, close to the values expected for homologous virialized systems. At fixed M in the range 1011 M⊙ ≲ M ≲ 5.5 × 1014 M⊙ we find σ0 ∝ (1 + z)0.35 and rh ∝ (1 + z)-0.7. We show that such evolution of the halo scaling laws is driven by individual haloes growing in mass following the evolutionary tracks σ0 ∝ M0.2 and rh ∝ M0.6, consistent with simple dissipationless merging models in which the encounter orbital energy is accounted for. We compare the N-body data with ETGs observed at 0 ≲ z ≲ 3 by populating the haloes with a stellar component under simple but justified assumptions: the resulting galaxies evolve consistently with the observed ETGs up to z ≃ 2, but the model has difficulty in reproducing the fast evolution observed at z ≳ 2. We conclude that a substantial fraction of the size evolution of ETGs can be ascribed to a systematic dependence on redshift of the dark matter haloes structural properties.
Conformal complex singlet extension of the Standard Model: scenario for dark matter and a second Higgs boson

NASA Astrophysics Data System (ADS)

Wang, Zhi-Wei; Steele, T. G.; Hanif, T.; Mann, R. B.

2016-08-01

We consider a conformal complex singlet extension of the Standard Model with a Higgs portal interaction. The global U(1) symmetry of the complex singlet can be either broken or unbroken and we study each scenario. In the unbroken case, the global U(1) symmetry protects the complex singlet from decaying, leading to an ideal cold dark matter candidate with approximately 100 GeV mass along with a significant proportion of thermal relic dark matter abundance. In the broken case, we have developed a renormalization-scale optimization technique to significantly narrow the parameter space and in some situations, provide unique predictions for all the model's couplings and masses. We have found there exists a second Higgs boson with a mass of approximately 550 GeV that mixes with the known 125 GeV Higgs with a large mixing angle sin θ ≈ 0.47 consistent with current experimental limits. The imaginary part of the complex singlet in the broken case could provide axion dark matter for a wide range of models. Upon including interactions of the complex scalar with an additional vector-like fermion, we explore the possibility of a diphoton excess in both the unbroken and the broken cases. In the unbroken case, the model can provide a natural explanation for diphoton excess if extra terms are introduced providing extra contributions to the singlet mass. In the broken case, we find a set of coupling solutions that yield a second Higgs boson of mass 720 GeV and an 830 GeV extra vector-like fermion F , which is able to address the 750 GeV LHC diphoton excess. We also provide criteria to determine the symmetry breaking pattern in both the Higgs and hidden sectors.

The impact of ΛCDM substructure and baryon-dark matter transition on the image positions of quad galaxy lenses

NASA Astrophysics Data System (ADS)

Gomer, Matthew R.; Williams, Liliya L. R.

2018-04-01

The positions of multiple images in galaxy lenses are related to the galaxy mass distribution. Smooth elliptical mass profiles were previously shown to be inadequate in reproducing the quad population. In this paper, we explore the deviations from such smooth elliptical mass distributions. Unlike most other work, we use a model-free approach based on the relative polar image angles of quads, and their position in 3D space with respect to the fundamental surface of quads (FSQ). The FSQ is defined by quads produced by elliptical lenses. We have generated thousands of quads from synthetic populations of lenses with substructure consistent with Lambda cold dark matter (ΛCDM) simulations, and found that such perturbations are not sufficient to match the observed distribution of quads relative to the FSQ. The result is unchanged even when subhalo masses are increased by a factor of 10, and the most optimistic lensing selection bias is applied. We then produce quads from galaxies created using two components, representing baryons and dark matter. The transition from the mass being dominated by baryons in inner radii to being dominated by dark matter in outer radii can carry with it asymmetries, which would affect relative image angles. We run preliminary experiments using lenses with two elliptical mass components with non-identical axial ratios and position angles, perturbations from ellipticity in the form of non-zero Fourier coefficients a4 and a6, and artificially offset ellipse centres as a proxy for asymmetry at image radii. We show that combination of these effects is a promising way of accounting for quad population properties. We conclude that the quad population provides a unique and sensitive tool for constraining detailed mass distribution in the centres of galaxies.
Ellipsoidal universe can solve the cosmic microwave background quadrupole problem.

PubMed

Campanelli, L; Cea, P; Tedesco, L

2006-09-29

The recent 3 yr Wilkinson Microwave Anisotropy Probe data have confirmed the anomaly concerning the low quadrupole amplitude compared to the best-fit Lambda-cold dark matter prediction. We show that by allowing the large-scale spatial geometry of our universe to be plane symmetric with eccentricity at decoupling or order 10(-2), the quadrupole amplitude can be drastically reduced without affecting higher multipoles of the angular power spectrum of the temperature anisotropy.
Comment on ''Interacting holographic dark energy model and generalized second law of thermodynamics in a non-flat universe{sup ,} by M.R. Setare (JCAP 01 (2007) 023)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karami, K., E-mail: kkarami@uok.ac.ir

2010-01-01

Author of ref. 1, M.R. Setare (JCAP 01 (2007) 023), by redefining the event horizon measured from the sphere of the horizon as the system's IR cut-off for an interacting holographic dark energy model in a non-flat universe, showed that the generalized second law of thermodynamics is satisfied for the special range of the deceleration parameter. His paper includes an erroneous calculation of the entropy of the cold dark matter. Also there are some missing terms and some misprints in the equations of his paper. Here we present that his conclusion is not true and the generalized second law ismore » violated for the present time independently of the deceleration parameter.« less
Cosmological constraints from a combination of galaxy clustering and lensing - III. Application to SDSS data

NASA Astrophysics Data System (ADS)

Cacciato, Marcello; van den Bosch, Frank C.; More, Surhud; Mo, Houjun; Yang, Xiaohu

2013-04-01

We simultaneously constrain cosmology and galaxy bias using measurements of galaxy abundances, galaxy clustering and galaxy-galaxy lensing taken from the Sloan Digital Sky Survey. We use the conditional luminosity function (which describes the halo occupation statistics as a function of galaxy luminosity) combined with the halo model (which describes the non-linear matter field in terms of its halo building blocks) to describe the galaxy-dark matter connection. We explicitly account for residual redshift-space distortions in the projected galaxy-galaxy correlation functions, and marginalize over uncertainties in the scale dependence of the halo bias and the detailed structure of dark matter haloes. Under the assumption of a spatially flat, vanilla Λ cold dark matter (ΛCDM) cosmology, we focus on constraining the matter density, Ωm, and the normalization of the matter power spectrum, σ8, and we adopt 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) priors for the spectral index, n, the Hubble parameter, h, and the baryon density, Ωb. We obtain that Ωm = 0.278+ 0.023- 0.026 and σ8 = 0.763+ 0.064- 0.049 (95 per cent CL). These results are robust to uncertainties in the radial number density distribution of satellite galaxies, while allowing for non-Poisson satellite occupation distributions results in a slightly lower value for σ8 (0.744+ 0.056- 0.047). These constraints are in excellent agreement (at the 1σ level) with the cosmic microwave background constraints from WMAP. This demonstrates that the use of a realistic and accurate model for galaxy bias, down to the smallest non-linear scales currently observed in galaxy surveys, leads to results perfectly consistent with the vanilla ΛCDM cosmology.
Combined cosmological tests of a bivalent tachyonic dark energy scalar field model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keresztes, Zoltán; Gergely, László Á., E-mail: zkeresztes@titan.physx.u-szeged.hu, E-mail: gergely@physx.u-szeged.hu

A recently investigated tachyonic scalar field dark energy dominated universe exhibits a bivalent future: depending on initial parameters can run either into a de Sitter exponential expansion or into a traversable future soft singularity followed by a contraction phase. We also include in the model (i) a tiny amount of radiation, (ii) baryonic matter (Ω{sub b}h{sup 2} = 0.022161, where the Hubble constant is fixed as h = 0.706) and (iii) cold dark matter (CDM). Out of a variety of six types of evolutions arising in a more subtle classification, we identify two in which in the past the scalar field effectively degenerates intomore » a dust (its pressure drops to an insignificantly low negative value). These are the evolutions of type IIb converging to de Sitter and type III hitting the future soft singularity. We confront these background evolutions with various cosmological tests, including the supernova type Ia Union 2.1 data, baryon acoustic oscillation distance ratios, Hubble parameter-redshift relation and the cosmic microwave background (CMB) acoustic scale. We determine a subset of the evolutions of both types which at 1σ confidence level are consistent with all of these cosmological tests. At perturbative level we derive the CMB temperature power spectrum to find the best agreement with the Planck data for Ω{sub CDM} = 0.22. The fit is as good as for the ΛCDM model at high multipoles, but the power remains slightly overestimated at low multipoles, for both types of evolutions. The rest of the CDM is effectively generated by the tachyonic field, which in this sense acts as a combined dark energy and dark matter model.« less
Impeded Dark Matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kopp, Joachim; Liu, Jia; Slatyer, Tracy

Here, we consider dark matter models in which the mass splitting between the dark matter particles and their annihilation products is tiny. Compared to the previously proposed Forbidden Dark Matter scenario, the mass splittings we consider are much smaller, and are allowed to be either positive or negative. To emphasize this modification, we dub our scenario \\Impeded Dark Matter". We also demonstrate that Impeded Dark Matter can be easily realized without requiring tuning of model parameters. For negative mass splitting, we demonstrate that the annihilation cross-section for Impeded Dark Matter depends linearly on the dark matter velocity or may evenmore » be kinematically forbidden, making this scenario almost insensitive to constraints from the cosmic microwave background and from observations of dwarf galaxies. Accordingly, it may be possible for Impeded Dark Matter to yield observable signals in clusters or the Galactic center, with no corresponding signal in dwarfs. Furthermore, for positive mass splitting, we show that the annihilation cross-section is suppressed by the small mass splitting, which helps light dark matter to survive increasingly stringent constraints from indirect searches. As specific realizations for Impeded Dark Matter, we introduce a model of vector dark matter from a hidden SU(2) sector, and a composite dark matter scenario based on a QCD-like dark sector.« less
Impeded Dark Matter

DOE PAGES

Kopp, Joachim; Liu, Jia; Slatyer, Tracy; ...

2016-12-12

Here, we consider dark matter models in which the mass splitting between the dark matter particles and their annihilation products is tiny. Compared to the previously proposed Forbidden Dark Matter scenario, the mass splittings we consider are much smaller, and are allowed to be either positive or negative. To emphasize this modification, we dub our scenario \\Impeded Dark Matter". We also demonstrate that Impeded Dark Matter can be easily realized without requiring tuning of model parameters. For negative mass splitting, we demonstrate that the annihilation cross-section for Impeded Dark Matter depends linearly on the dark matter velocity or may evenmore » be kinematically forbidden, making this scenario almost insensitive to constraints from the cosmic microwave background and from observations of dwarf galaxies. Accordingly, it may be possible for Impeded Dark Matter to yield observable signals in clusters or the Galactic center, with no corresponding signal in dwarfs. Furthermore, for positive mass splitting, we show that the annihilation cross-section is suppressed by the small mass splitting, which helps light dark matter to survive increasingly stringent constraints from indirect searches. As specific realizations for Impeded Dark Matter, we introduce a model of vector dark matter from a hidden SU(2) sector, and a composite dark matter scenario based on a QCD-like dark sector.« less
Working Group Report: Dark Matter Complementarity (Dark Matter in the Coming Decade: Complementary Paths to Discovery and Beyond)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arrenberg, Sebastian; et al.,

2013-10-31

In this Report we discuss the four complementary searches for the identity of dark matter: direct detection experiments that look for dark matter interacting in the lab, indirect detection experiments that connect lab signals to dark matter in our own and other galaxies, collider experiments that elucidate the particle properties of dark matter, and astrophysical probes sensitive to non-gravitational interactions of dark matter. The complementarity among the different dark matter searches is discussed qualitatively and illustrated quantitatively in several theoretical scenarios. Our primary conclusion is that the diversity of possible dark matter candidates requires a balanced program based on allmore » four of those approaches.« less
The pursuit of dark matter at colliders—an overview

NASA Astrophysics Data System (ADS)

Penning, Björn

2018-06-01

Dark matter is one of the main puzzles in fundamental physics and the goal of a diverse, multi-pronged research programme. Underground and astrophysical searches look for dark matter particles in the cosmos, either by interacting directly or by searching for dark matter annihilation. Particle colliders, in contrast, might produce dark matter in the laboratory and are able to probe most basic dark-matter–matter interactions. They are sensitive to low dark matter masses, provide complementary information at higher masses and are subject to different systematic uncertainties. Collider searches are therefore an important part of an inter-disciplinary dark matter search strategy. This article highlights the experimental and phenomenological development in collider dark matter searches of recent years and their connection with the wider field.
Using the Moon As A Low-Noise Seismic Detector For Strange Quark Nuggets

NASA Technical Reports Server (NTRS)

Banerdt, W. Bruce; Chui, Talso; Griggs, Cornelius E.; Herrin, Eugene T.; Nakamura, Yosio; Paik, Ho Jung; Penanen, Konstantin; Rosenbaum, Doris; Teplitz, Vigdor L.; Young, Joseph

2006-01-01

Strange quark matter made of up, down and strange quarks has been postulated by Witten [1]. Strange quark matter would be nearly charge neutral and would have density of nuclear matter (10(exp 14) gm/cu cm). Witten also suggested that nuggets of strange quark matter, or strange quark nuggets (SQNs), could have formed shortly after the Big Bang, and that they would be viable candidates for cold dark matter. As suggested by de Rujula and Glashow [2], an SQN may pass through a celestial body releasing detectable seismic energy along a straight line. The Moon, being much quieter seismically than the Earth, would be a favorable place to search for such events. We review previous searches for SQNs to illustrate the parameter space explored by using the Moon as a low-noise detector of SQNs. We also discuss possible detection schemes using a single seismometer, and using an International Lunar Seismic Network.
Hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit: General formalism and perturbations analysis

NASA Astrophysics Data System (ADS)

Suárez, Abril; Chavanis, Pierre-Henri

2015-07-01

Using a generalization of the Madelung transformation, we derive the hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit. We consider a complex self-interacting scalar field with a λ |φ |4 potential. We study the evolution of the spatially homogeneous background in the fluid representation and derive the linearized equations describing the evolution of small perturbations in a static and in an expanding Universe. We compare the results with simplified models in which the gravitational potential is introduced by hand in the Klein-Gordon equation, and assumed to satisfy a (generalized) Poisson equation. Nonrelativistic hydrodynamic equations based on the Schrödinger-Poisson equations or on the Gross-Pitaevskii-Poisson equations are recovered in the limit c →+∞. We study the evolution of the perturbations in the matter era using the nonrelativistic limit of our formalism. Perturbations whose wavelength is below the Jeans length oscillate in time while perturbations whose wavelength is above the Jeans length grow linearly with the scale factor as in the cold dark matter model. The growth of perturbations in the scalar field model is substantially faster than in the cold dark matter model. When the wavelength of the perturbations approaches the cosmological horizon (Hubble length), a relativistic treatment is mandatory. In that case, we find that relativistic effects attenuate or even prevent the growth of perturbations. This paper exposes the general formalism and provides illustrations in simple cases. Other applications of our formalism will be considered in companion papers.
Monitoring xenon purity in the LUX detector with a mass spectrometry system

NASA Astrophysics Data System (ADS)

Balajthy, Jon; LUX Experiment Collaboration

2015-04-01

The LUX dark matter search experiment is a 350 kg two-phase liquid/gas xenon time projection chamber located at the 4850 ft level of the Sanford Underground Research Facility in Lead, SD. To monitor for radioactive impurities such as krypton and impurities which limit charge yield such as oxygen, LUX uses a xenon sampling system consisting of a mass spectrometer and a liquid nitrogen cold trap. The cold trap separates the gaseous impurities from a small sample of xenon and allows them to pass to the mass spectrometer for analysis. We report here on results from the LUX xenon sampling program. We also report on methods to enhance the sensitivity of the cold trap technique in preparation for the next-generation LUX-ZEPLIN experiment which will have even more stringent purity requirements.
Fast Simulations of Gas Sloshing and Cold Front Formation

NASA Technical Reports Server (NTRS)

Roediger, E.; ZuHone, J. A.

2011-01-01

We present a simplified and fast method for simulating minor mergers between galaxy clusters. Instead of following the evolution of the dark matter halos directly by the N-body method, we employ a rigid potential approximation for both clusters. The simulations are run in the rest frame of the more massive cluster and account for the resulting inertial accelerations in an optimised way. We test the reliability of this method for studies of minor merger induced gas sloshing by performing a one-to-one comparison between our simulations and hydro+N-body ones. We find that the rigid potential approximation reproduces the sloshing-related features well except for two artefacts: the temperature just outside the cold fronts is slightly over-predicted, and the outward motion of the cold fronts is delayed by typically 200 Myr. We discuss reasons for both artefacts.
Fast Simulations of Gas Sloshing and Cold Front Formation

NASA Technical Reports Server (NTRS)

Roediger, E.; ZuHone, J. A.

2012-01-01

We present a simplified and fast method for simulating minor mergers between galaxy clusters. Instead of following the evolution of the dark matter halos directly by the N-body method, we employ a rigid potential approximation for both clusters. The simulations are run in the rest frame of the more massive cluster and account for the resulting inertial accelerations in an optimised way. We test the reliability of this method for studies of minor merger induced gas sloshing by performing a one-to-one comparison between our simulations and hydro+N-body ones. We find that the rigid potential approximation reproduces the sloshing-related features well except for two artifacts: the temperature just outside the cold fronts is slightly over-predicted, and the outward motion of the cold fronts is delayed by typically 200 Myr. We discuss reasons for both artifacts.
The intrinsic matter bispectrum in ΛCDM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tram, Thomas; Crittenden, Robert; Koyama, Kazuya

2016-05-01

We present a fully relativistic calculation of the matter bispectrum at second order in cosmological perturbation theory assuming a Gaussian primordial curvature perturbation. For the first time we perform a full numerical integration of the bispectrum for both baryons and cold dark matter using the second-order Einstein-Boltzmann code, SONG. We review previous analytical results and provide an improved analytic approximation for the second-order kernel in Poisson gauge which incorporates Newtonian nonlinear evolution, relativistic initial conditions, the effect of radiation at early times and the cosmological constant at late times. Our improved kernel provides a percent level fit to the fullmore » numerical result at late times for most configurations, including both equilateral shapes and the squeezed limit. We show that baryon acoustic oscillations leave an imprint in the matter bispectrum, making a significant impact on squeezed shapes.« less
N-body dark matter haloes with simple hierarchical histories

NASA Astrophysics Data System (ADS)

Jiang, Lilian; Helly, John C.; Cole, Shaun; Frenk, Carlos S.

2014-05-01

We present a new algorithm which groups the subhaloes found in cosmological N-body simulations by structure finders such as SUBFIND into dark matter haloes whose formation histories are strictly hierarchical. One advantage of these `Dhaloes' over the commonly used friends-of-friends (FoF) haloes is that they retain their individual identity in the cases when FoF haloes are artificially merged by tenuous bridges of particles or by an overlap of their outer diffuse haloes. Dhaloes are thus well suited for modelling galaxy formation and their merger trees form the basis of the Durham semi-analytic galaxy formation model, GALFORM. Applying the Dhalo construction to the Λ cold dark matter Millennium II Simulation, we find that approximately 90 per cent of Dhaloes have a one-to-one, bijective match with a corresponding FoF halo. The remaining 10 per cent are typically secondary components of large FoF haloes. Although the mass functions of both types of haloes are similar, the mass of Dhaloes correlates much more tightly with the virial mass, M200, than FoF haloes. Approximately 80 per cent of FoF and bijective and non-bijective Dhaloes are relaxed according to standard criteria. For these relaxed haloes, all three types have similar concentration-M200 relations and, at fixed mass, the concentration distributions are described accurately by log-normal distributions.
Codecaying Dark Matter.

PubMed

Dror, Jeff Asaf; Kuflik, Eric; Ng, Wee Hao

2016-11-18

We propose a new mechanism for thermal dark matter freeze-out, called codecaying dark matter. Multicomponent dark sectors with degenerate particles and out-of-equilibrium decays can codecay to obtain the observed relic density. The dark matter density is exponentially depleted through the decay of nearly degenerate particles rather than from Boltzmann suppression. The relic abundance is set by the dark matter annihilation cross section, which is predicted to be boosted, and the decay rate of the dark sector particles. The mechanism is viable in a broad range of dark matter parameter space, with a robust prediction of an enhanced indirect detection signal. Finally, we present a simple model that realizes codecaying dark matter.
The Linear Bias in the Zeldovich Approximation and a Relation between the Number Density and the Linear Bias of Dark Halos

NASA Astrophysics Data System (ADS)

Fan, Zuhui

2000-01-01

The linear bias of the dark halos from a model under the Zeldovich approximation is derived and compared with the fitting formula of simulation results. While qualitatively similar to the Press-Schechter formula, this model gives a better description for the linear bias around the turnaround point. This advantage, however, may be compromised by the large uncertainty of the actual behavior of the linear bias near the turnaround point. For a broad class of structure formation models in the cold dark matter framework, a general relation exists between the number density and the linear bias of dark halos. This relation can be readily tested by numerical simulations. Thus, instead of laboriously checking these models one by one, numerical simulation studies can falsify a whole category of models. The general validity of this relation is important in identifying key physical processes responsible for the large-scale structure formation in the universe.
Entropy corrected holographic dark energy models in modified gravity

NASA Astrophysics Data System (ADS)

Jawad, Abdul; Azhar, Nadeem; Rani, Shamaila

We consider the power law and the entropy corrected holographic dark energy (HDE) models with Hubble horizon in the dynamical Chern-Simons modified gravity. We explore various cosmological parameters and planes in this framework. The Hubble parameter lies within the consistent range at the present and later epoch for both entropy corrected models. The deceleration parameter explains the accelerated expansion of the universe. The equation of state (EoS) parameter corresponds to quintessence and cold dark matter (ΛCDM) limit. The ωΛ-ωΛ‧ approaches to ΛCDM limit and freezing region in both entropy corrected models. The statefinder parameters are consistent with ΛCDM limit and dark energy (DE) models. The generalized second law of thermodynamics remain valid in all cases of interacting parameter. It is interesting to mention here that our results of Hubble, EoS parameter and ωΛ-ωΛ‧ plane show consistency with the present observations like Planck, WP, BAO, H0, SNLS and nine-year WMAP.
Experimental search for hidden photon CDM in the eV mass range with a dish antenna

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, J.; Horie, T.; Inoue, Y.

2015-09-15

A search for hidden photon cold dark matter (HP CDM) using a new technique with a dish antenna is reported. From the result of the measurement, we found no evidence for the existence of HP CDM and set an upper limit on the photon-HP mixing parameter χ of ∼6×10{sup −12} for the hidden photon mass m{sub γ}=3.1±1.2 eV.

Distorted neutrino oscillations from time varying cosmic fields

NASA Astrophysics Data System (ADS)

Krnjaic, Gordan; Machado, Pedro A. N.; Necib, Lina

2018-04-01

Cold, ultralight (≪eV ) bosonic fields can induce fast temporal variation in neutrino couplings, thereby distorting neutrino oscillations. In this paper, we exploit this effect to introduce a novel probe of neutrino time variation and dark matter at long-baseline experiments. We study several representative observables and find that current and future experiments, including DUNE and JUNO, are sensitive to a wide range of model parameters over many decades in mass reach and time-variation periodicity.
Is the vast polar structure of dwarf galaxies a serious problem for Λ cold dark matter?

NASA Astrophysics Data System (ADS)

Lipnicky, Andrew; Chakrabarti, Sukanya

2017-06-01

The dwarf galaxies around the Milky Way are distributed in a so-called vast polar structure (VPOS) that may be in conflict with Λ cold dark matter (ΛCDM) simulations. Here, we seek to determine if the VPOS poses a serious challenge to the ΛCDM paradigm on galactic scales. Specifically, we investigate if the VPOS remains coherent as a function of time. Using the measured Hubble Space Telescope (HST) proper motions and associated uncertainties, we integrate the orbits of the classical Milky Way satellites backwards in time and find that the structure disperses well before a dynamical time. We also examine, in particular, Leo I and Leo II using their most recent proper motion data, both of which have extreme kinematic properties, but these satellites do not appear to drive the polar fit that is seen at the present day. We have studied the effect of the uncertainties on the HST proper motions on the coherence of the VPOS as a function of time. We find that 8 of the 11 classical dwarfs have reliable proper motions; for these eight, the VPOS also loses significance in less than a dynamical time, indicating that the VPOS is not a dynamically stable structure. Obtaining more accurate proper motion measurements of Ursa Minor, Sculptor and Carina would bolster these conclusions.
Detecting dark matter with imploding pulsars in the galactic center.

PubMed

Bramante, Joseph; Linden, Tim

2014-11-07

The paucity of old millisecond pulsars observed at the galactic center of the Milky Way could be the result of dark matter accumulating in and destroying neutron stars. In regions of high dark matter density, dark matter clumped in a pulsar can exceed the Schwarzschild limit and collapse into a natal black hole which destroys the pulsar. We examine what dark matter models are consistent with this hypothesis and find regions of parameter space where dark matter accumulation can significantly degrade the neutron star population within the galactic center while remaining consistent with observations of old millisecond pulsars in globular clusters and near the solar position. We identify what dark matter couplings and masses might cause a young pulsar at the galactic center to unexpectedly extinguish. Finally, we find that pulsar collapse age scales inversely with the dark matter density and linearly with the dark matter velocity dispersion. This implies that maximum pulsar age is spatially dependent on position within the dark matter halo of the Milky Way. In turn, this pulsar age spatial dependence will be dark matter model dependent.
Perturbative unitarity constraints on gauge portals

NASA Astrophysics Data System (ADS)

El Hedri, Sonia; Shepherd, William; Walker, Devin G. E.

2017-12-01

Dark matter that was once in thermal equilibrium with the Standard Model is generally prohibited from obtaining all of its mass from the electroweak phase transition. This implies a new scale of physics and mediator particles to facilitate dark matter annihilation. In this work, we focus on dark matter that annihilates through a generic gauge boson portal. We show how partial wave unitarity places upper bounds on the dark gauge boson, dark Higgs and dark matter masses. Outside of well-defined fine-tuned regions, we find an upper bound of 9 TeV for the dark matter mass when the dark Higgs and dark gauge bosons both facilitate the dark matter annihilations. In this scenario, the upper bound on the dark Higgs and dark gauge boson masses are 10 TeV and 16 TeV, respectively. When only the dark gauge boson facilitates dark matter annihilations, we find an upper bound of 3 TeV and 6 TeV for the dark matter and dark gauge boson, respectively. Overall, using the gauge portal as a template, we describe a method to not only place upper bounds on the dark matter mass but also on the new particles with Standard Model quantum numbers. We briefly discuss the reach of future accelerator, direct and indirect detection experiments for this class of models.
Dark matter annihilation at the galactic center

NASA Astrophysics Data System (ADS)

Linden, Tim

Observations by the WMAP and PLANCK satellites have provided extraordinarily accurate observations on the densities of baryonic matter, dark matter, and dark energy in the universe. These observations indicate that our universe is composed of approximately five times as much dark matter as baryonic matter. However, efforts to detect a particle responsible for the energy density of dark matter have been unsuccessful. Theoretical models have indicated that a leading candidate for the dark matter is the lightest supersymmetric particle, which may be stable due to a conserved R-parity. This dark matter particle would still be capable of interacting with baryons via weak-force interactions in the early universe, a process which was found to naturally explain the observed relic abundance of dark matter today. These residual annihilations can persist, albeit at a much lower rate, in the present universe, providing a detectable signal from dark matter annihilation events which occur throughout the universe. Simulations calculating the distribution of dark matter in our galaxy almost universally predict the galactic center of the Milky Way Galaxy (GC) to provide the brightest signal from dark matter annihilation due to its relative proximity and large simulated dark matter density. Recent advances in telescope technology have allowed for the first multiwavelength analysis of the GC, with suitable effective exposure, angular resolution, and energy resolution in order to detect dark matter particles with properties similar to those predicted by the WIMP miracle. In this work, I describe ongoing efforts which have successfully detected an excess in gamma-ray emission from the region immediately surrounding the GC, which is difficult to describe in terms of standard diffuse emission predicted in the GC region. While the jury is still out on any dark matter interpretation of this excess, I describe several related observations which may indicate a dark matter origin. Finally, I discuss the role of future telescopes in differentiating a dark matter model from astrophysical emission.
Precombination Cloud Collapse and Baryonic Dark Matter

NASA Technical Reports Server (NTRS)

Hogan, Craig J.

1993-01-01

A simple spherical model of dense baryon clouds in the hot big bang 'strongly nonlinear primordial isocurvature baryon fluctuations' is reviewed and used to describe the dependence of cloud behavior on the model parameters, baryon mass, and initial over-density. Gravitational collapse of clouds before and during recombination is considered including radiation diffusion and trapping, remnant type and mass, and effects on linear large-scale fluctuation modes. Sufficiently dense clouds collapse early into black holes with a minimum mass of approx. 1 solar mass, which behave dynamically like collisionless cold dark matter. Clouds below a critical over-density, however, delay collapse until recombination, remaining until then dynamically coupled to the radiation like ordinary diffuse baryons, and possibly producing remnants of other kinds and lower mass. The mean density in either type of baryonic remnant is unconstrained by observed element abundances. However, mixed or unmixed spatial variations in abundance may survive in the diffuse baryon and produce observable departures from standard predictions.
CHAM: a fast algorithm of modelling non-linear matter power spectrum in the sCreened HAlo Model

NASA Astrophysics Data System (ADS)

Hu, Bin; Liu, Xue-Wen; Cai, Rong-Gen

2018-05-01

We present a fast numerical screened halo model algorithm (CHAM, which stands for the sCreened HAlo Model) for modelling non-linear power spectrum for the alternative models to Λ cold dark matter. This method has three obvious advantages. First of all, it is not being restricted to a specific dark energy/modified gravity model. In principle, all of the screened scalar-tensor theories can be applied. Secondly, the least assumptions are made in the calculation. Hence, the physical picture is very easily understandable. Thirdly, it is very predictable and does not rely on the calibration from N-body simulation. As an example, we show the case of the Hu-Sawicki f(R) gravity. In this case, the typical CPU time with the current parallel PYTHON script (eight threads) is roughly within 10 min. The resulting spectra are in a good agreement with N-body data within a few percentage accuracy up to k ˜ 1 h Mpc-1.
Technical results from the surface run of the LUX dark matter experiment

DOE PAGES

Akerib, D. S.; Bai, X.; Bernard, E.; ...

2013-03-07

We present the results of the three-month above-ground commissioning run of the Large Underground Xenon (LUX) experiment at the Sanford Underground Research Facility located in Lead, South Dakota, USA. LUX is a 370 kg liquid xenon detector that will search for cold dark matter in the form of Weakly Interacting Massive Particles (WIMPs). The commissioning run, conducted with the detector immersed in a water tank, validated the integration of the various sub-systems in preparation of the underground deployment. Using the data collected, we report excellent light collection properties, achieving 8.4 photoelectrons per keV for 662 keV electron recoils without anmore » applied electric field, measured in the center of the WIMP target. Here, we also find good energy and position resolution in relatively high-energy interactions from a variety of internal and external sources. Finally, we have used the commissioning data to tune the optical properties of our simulation and report updated sensitivity projections for spin-independent WIMP-nucleon scattering.« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Rielage, K.; Akashi-Ronquest, M.; Bodmer, M.

The direct search for dark matter is entering a period of increased sensitivity to the hypothetical Weakly Interacting Massive Particle (WIMP). One such technology that is being examined is a scintillation only noble liquid experiment, MiniCLEAN. MiniCLEAN utilizes over 500 kg of liquid cryogen to detect nuclear recoils from WIMP dark matter and serves as a demonstration for a future detector of order 50 to 100 tonnes. The liquid cryogen is interchangeable between argon and neon to study the A² dependence of the potential signal and examine backgrounds. MiniCLEAN utilizes a unique modular design with spherical geometry to maximize themore » light yield using cold photomultiplier tubes in a single-phase detector. Pulse shape discrimination techniques are used to separate nuclear recoil signals from electron recoil backgrounds. MiniCLEAN will be spiked with additional ³⁹Ar to demonstrate the effective reach of the pulse shape discrimination capability. Assembly of the experiment is underway at SNOLAB and an update on the project is given.« less
Quark seesaw mechanism, dark U (1 ) symmetry, and the baryon-dark matter coincidence

NASA Astrophysics Data System (ADS)

Gu, Pei-Hong; Mohapatra, Rabindra N.

2017-09-01

We attempt to understand the baryon-dark matter coincidence problem within the quark seesaw extension of the standard model where parity invariance is used to solve the strong C P problem. The S U (2 )L×S U (2 )R×U (1 )B -L gauge symmetry of this model is extended by a dark U (1 )X group plus inclusion of a heavy neutral vector-like fermion χL ,R charged under the dark group which plays the role of dark matter. All fermions are Dirac type in this model. Decay of heavy scalars charged under U (1 )X leads to simultaneous asymmetry generation of the dark matter and baryons after sphaleron effects are included. The U (1 )X group not only helps to stabilize the dark matter but also helps in the elimination of the symmetric part of the dark matter via χ -χ ¯ annihilation. For dark matter mass near the proton mass, it explains why the baryon and dark matter abundances are of similar magnitude (the baryon-dark matter coincidence problem). This model is testable in low threshold (sub-keV) direct dark matter search experiments.
Cold Dark Matter Cosmogony with Hydrodynamics and Galaxy Formation: Galaxy Properties at Redshift Zero

NASA Astrophysics Data System (ADS)

Cen, Renyue; Ostriker, Jeremiah P.

1993-11-01

We have supplemented our code, which computes the evolution of the physical state of a representative piece of the universe, to include not only the dynamics of dark matter (with a standard PM code) and the hydrodynamics of the gaseous component (including detailed collisional and radiative processes), but also galaxy formation on a heuristic but plausible basis. If, within a cell, the gas is Jeans-unstable, collapsing and cooling rapidly, it is transformed to galaxy subunits, which are then followed with a collisionless code. We study two representative boxes with sizes L = (80, 8) h-1 Mpc, in both cases utilizing a mesh of 2003 cells containing 2003 dark matter particles and having nominal resolutions of (400, 40) h-1 kpc, respectively, with true resolution approximately 2.5 times worse. We adopt the standard cold dark matter (CDM) perturbation spectrum with an amplitude of σ8 ≡ = (δM/M)rms,8 = 0.77, a compromise between the COBE normalization σ8 = 1.05 and that indicated by the small-scale velocity dispersion (perhaps σ8 = 0.45). We find a mass function which is similar to that observed. There is a strong correlation between galactic age and environment. Identifying the oldest fraction with elliptical and 50 galaxies, we find a density morphology relation of the same type as is observed as well as a correlation between gas mass/total mass ratio and morphology that is similar to observations. In addition, we find that low-mass galaxies contain relatively more dark matter than giants. We present analytic fits to our derived results for "bias," the dependence of ρgal/ <ρgal> on ρtot/<ρtot>. Spatial structures resemble quantitatively those seen in redshift surveys, with galaxies concentrated in clusters and on filaments (or sheets) which surround quite empty voids. The void probability statistics indicate that this model is consistent with magnitude-limited real data. The small-scale velocity field is too large compared with the observed velocity correlation function. The distribution of proper velocities fits an exponential (not a Maxwellian) P(υ) 2 ∝ υ2e-υ/σexp with σexp = 225 km s-1. For galaxies separated by 1 h-1 Mpc we find a one-dimensional velocity dispersion of 670 km s-1 (490 km s-1 for the most massive subset) compared with 340±40 km s-1 as measured by Davis & Peebles (1983). Adoption of the COBE normalization causes the problem to become worse; the CDM prediction is then approximately (920±160) km s-1. If we look at the genus curves of all our galaxies, they fit the random-phase expectation, but a magnitude-limited sample emphasizes the older, more massive galaxies which have collected at a vertices. This explains the observed "meatball shift" of the genus curves found in observed samples.
REVIEWS OF TOPICAL PROBLEMS: The search for dark matter particles

NASA Astrophysics Data System (ADS)

Ryabov, Vladimir A.; Tsarev, Vladimir A.; Tskhovrebov, Andrei M.

2008-11-01

Evidence of dark matter in the Universe is discussed and the most popular candidates for dark matter particles are reviewed. The review is mainly devoted to numerous experiments, both underway and planned, on the search for dark matter particles. Various experimental methods are discussed, including those involving direct registration of dark matter particles with the detector and those where the products of dark matter decay and annihilation are registered.
Measuring the Value Added of Management: A Knowledge Value Added Approach

DTIC Science & Technology

2006-12-31

Dark Matter ” ................................................................3 Difficult-to-track Dark Matter Outputs .................................................5 Computing Metaphor..........................................................................6 Dark Matter Correlates with Market Performance ..............................8 Outputs of Dark Matter .......................................................................9 Operationalizing: The Measurement of Dark
A Database of COBE-normalized Cold Dark Matter Simulations

NASA Astrophysics Data System (ADS)

Martel, Hugo; Matzner, Richard

2000-02-01

We have simulated the formation and evolution of large-scale structure in the universe, for 68 different COBE-normalized cosmological models. For each cosmological model, we have performed between one and three simulations, for a total of 160 simulations. This constitutes the largest database of cosmological simulations ever assembled, and the largest cosmological parameter space ever covered by such simulations. We are making this database available to the astronomical community. We provide instructions for accessing the database and for converting the data from computational units to physical units. The database includes tilted cold dark matter (TCDM) models, tilted open cold dark matter (TOCDM) models, and tilted Λ cold dark matter (TΛCDM) models. (For several simulations, the primordial exponent n of the power spectrum is near unity, hence these simulations can be considered as ``untilted.'') The simulations cover a four-dimensional cosmological parameter phase space, the parameters being the present density parameter Ω0, cosmological constant λ0, and Hubble constant H0, and the rms density fluctuation σ8 at scale 8 h-1 Mpc. All simulations were performed using a P3M algorithm with 643 particles on a 1283 mesh, in a cubic volume of comoving size 128 Mpc. Each simulation starts at a redshift of 24 and is carried up to the present. More simulations will be added to the database in the future. We have performed a limited amount of data reduction and analysis of the final states of the simulations. We computed the rms density fluctuation, the two-point correlation function, the velocity moments, and the properties of clusters. Our results are the following:1. The numerical value σnum8 of the rms density fluctuation differs from the value σcont8 obtained by integrating the power spectrum at early times and extrapolating linearly up the present. This results from the combined effects of discreteness in the numerical representation of the power spectrum, the presence of a Gaussian factor in the initial conditions, and late-time nonlinear evolution. The first of these three effects is negligible. The second and third are comparable, and can both modify the value of σ8 by up to 10%. Nonlinear effects, however, are important only for models with σ8>0.6, and can result in either an increase or a decrease in σ8.2. The observed galaxy two-point correlation function is well reproduced (assuming an unbiased relation between galaxies and mass) by models with σ8~0.8, nearly independently of the values of the other parameters, Ω0, λ0, and H0. For models with σ8>0.8, the correlation function is too large and its slope is too steep. For models with σ8<0.8, the correlation function is too small and its slope is too shallow.3. At small separations, r<1 Mpc, the velocity moments indicate that small clusters have reached virial equilibrium, while still accreting matter from the field. The velocity moments depend essentially upon Ω0 and σ8, and not λ0 and H0. The pairwise particle velocity dispersions are much larger than the observed pairwise galaxy velocity dispersion, for nearly all models. Velocity bias between galaxies and dark matter is needed to reconcile the simulations with observations.4. The cluster multiplicity function is decreasing for models with σ8~0.3. It has a horizontal plateau for models with σ8 in the range 0.4-0.9. For models with σ8>0.9, it has a U shape, which is probably a numerical artifact caused by the finite number of particles used in the simulations. For all models, clusters have densities in the range 100-1000 times the mean background density, the spin parameters λ are in the range 0.008-0.2, with the median near 0.05, and about 2/3 of the clusters are prolate. Rotationally supported disks do not form in these simulations.
Asymmetric capture of Dirac dark matter by the Sun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blennow, Mattias; Clementz, Stefan

2015-08-18

Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles andmore » anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.« less
EXPLAINING THE OBSERVED VELOCITY DISPERSION OF DWARF GALAXIES BY BARYONIC MASS LOSS DURING THE FIRST COLLAPSE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gritschneder, Matthias; Lin, Douglas N. C., E-mail: gritschneder@ucolick.org

2013-03-01

In the widely adopted {Lambda} cold dark matter ({Lambda}CDM) scenario for galaxy formation, dwarf galaxies are the building blocks of larger galaxies. Since they formed at relatively early epochs when the background density was relatively high, they are expected to retain their integrity as satellite galaxies when they merge to form larger entities. Although many dwarf spheroidal galaxies are found in the galactic halo around the Milky Way, their phase-space density (or velocity dispersion) appears to be significantly smaller than that expected for satellite dwarf galaxies in the {Lambda}CDM scenario. In order to account for this discrepancy, we consider themore » possibility that they may have lost a significant fraction of their baryonic matter content during the first infall at the Hubble expansion turnaround. Such mass loss arises naturally due to the feedback by relatively massive stars that formed in their centers briefly before the maximum contraction. Through a series of N-body simulations, we show that the timely loss of a significant fraction of the dSphs initial baryonic matter content can have profound effects on their asymptotic half-mass radius, velocity dispersion, phase-space density, and the mass fraction between residual baryonic and dark matter.« less
Direct nutritional link between 600-m deep cold-water corals and surface productivity

NASA Astrophysics Data System (ADS)

Soetaert, Karline; Mohn, Christian; Rengstorff, Anna; Grehan, Anthony; van Oevelen, Dick

2016-04-01

Cold-water corals (CWC) form deep-sea reefs that are found in all of the world's oceans, with an areal extent at par with that of tropical coral reefs, and are recognised hotspots of biodiversity and metabolic activity. Yet, it remains largely enigmatic how these rich CWC reefs can thrive in a cold and dark environment that is considered to be strongly food-limited. Here, we use a novel benthic-pelagic modeling approach, which involves coupling models of hydrodynamics, biogeochemistry and habitat suitability, to unravel organic matter delivery to reef mounds at a water depth of 600 m that are capped with a thriving CWC reef community at Rockall Bank (NE Atlantic). Model simulations show that the interaction between 300-m high reef mounds and spring tidal currents induces episodic downwelling events that establish a vertical coupling between 600-m deep CWC with surface productivity. We therefore conclude that there is a positive feedback between CWC mound growth and organic matter supply. This episodic downwelling strongly enhances carbon sequestration to the deep ocean and the ubiquitous occurrence of topographic rises along the ocean margins suggests that a topographically-induced benthic-pelagic carbon pump could be of global importance.
Simulation and Preliminary Design of a Cold Stream Experiment on Omega EP

NASA Astrophysics Data System (ADS)

Coffing, Shane; Angulo, Adrianna; Trantham, Matt; Malamud, Guy; Kuranz, Carolyn; Drake, R. P.

2017-10-01

Galaxies form within dark matter halos, accreting gas that may clump and eventually form stars. Infalling matter gradually increases the density of the halo, and, if cooling is insufficient, rising pressure forms a shock that slows the infalling gas, reducing star formation. However, galaxies with sufficient cooling become prolific star formers. A recent theory suggests that so called ``stream fed galaxies'' are able to acquire steady streams of cold gas via galactic ``filaments'' that penetrate the halo. The cold, dense filament flowing into a hot, less dense environment is potentially Kelvin-Helmholtz unstable. This instability may hinder the ability of the stream to deliver gas deeply enough into the halo. To study this process, we have begun preliminary design of a well-scaled laser experiment on Omega EP. We present here early simulation results and the physics involved. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, Grant Number DE-NA0002956, and the National Laser User Facility Program, Grant Number DE-NA0002719, and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-NA0001944.
Baryogenesis from strong CP violation and the QCD axion.

PubMed

Servant, Géraldine

2014-10-24

We show that strong CP violation from the QCD axion can be responsible for the matter antimatter asymmetry of the Universe in the context of cold electroweak baryogenesis if the electroweak phase transition is delayed below the GeV scale. This can occur naturally if the Higgs couples to a O(100) GeV dilaton, as expected in some models where the Higgs is a pseudo-Nambu-Goldstone boson of a new strongly interacting sector at the TeV scale. The existence of such a second scalar resonance with a mass and properties similar to the Higgs boson will soon be tested at the LHC. In this context, the QCD axion would not only solve the strong CP problem, but also the matter antimatter asymmetry and dark matter.
Perturbative unitarity constraints on gauge portals

DOE PAGES

El Hedri, Sonia; Shepherd, William; Walker, Devin G. E.

2017-10-03

Dark matter that was once in thermal equilibrium with the Standard Model is generally prohibited from obtaining all of its mass from the electroweak phase transition. This implies a new scale of physics and mediator particles to facilitate dark matter annihilation. In this work, we focus on dark matter that annihilates through a generic gauge boson portal. We show how partial wave unitarity places upper bounds on the dark gauge boson, dark Higgs and dark matter masses. Outside of well-defined fine-tuned regions, we find an upper bound of 9 TeV for the dark matter mass when the dark Higgs andmore » dark gauge bosons both facilitate the dark matter annihilations. In this scenario, the upper bound on the dark Higgs and dark gauge boson masses are 10 TeV and 16 TeV, respectively. When only the dark gauge boson facilitates dark matter annihilations, we find an upper bound of 3 TeV and 6 TeV for the dark matter and dark gauge boson, respectively. Overall, using the gauge portal as a template, we describe a method to not only place upper bounds on the dark matter mass but also on the new particles with Standard Model quantum numbers. Here, we briefly discuss the reach of future accelerator, direct and indirect detection experiments for this class of models.« less

Perturbative unitarity constraints on gauge portals

DOE Office of Scientific and Technical Information (OSTI.GOV)

El Hedri, Sonia; Shepherd, William; Walker, Devin G. E.

Dark matter that was once in thermal equilibrium with the Standard Model is generally prohibited from obtaining all of its mass from the electroweak phase transition. This implies a new scale of physics and mediator particles to facilitate dark matter annihilation. In this work, we focus on dark matter that annihilates through a generic gauge boson portal. We show how partial wave unitarity places upper bounds on the dark gauge boson, dark Higgs and dark matter masses. Outside of well-defined fine-tuned regions, we find an upper bound of 9 TeV for the dark matter mass when the dark Higgs andmore » dark gauge bosons both facilitate the dark matter annihilations. In this scenario, the upper bound on the dark Higgs and dark gauge boson masses are 10 TeV and 16 TeV, respectively. When only the dark gauge boson facilitates dark matter annihilations, we find an upper bound of 3 TeV and 6 TeV for the dark matter and dark gauge boson, respectively. Overall, using the gauge portal as a template, we describe a method to not only place upper bounds on the dark matter mass but also on the new particles with Standard Model quantum numbers. Here, we briefly discuss the reach of future accelerator, direct and indirect detection experiments for this class of models.« less
A dark matter scaling relation from mirror dark matter

NASA Astrophysics Data System (ADS)

Foot, R.

2014-12-01

Mirror dark matter, and other similar dissipative dark matter candidates, need an energy source to stabilize dark matter halos around spiral galaxies. It has been suggested previously that ordinary supernovae can potentially supply the required energy. By matching the energy supplied to the halo from supernovae to that lost due to radiative cooling, we here derive a rough scaling relation, RSN ∝ρ0r02 (RSN is the supernova rate and ρ0 ,r0 the dark matter central density and core radius). Such a relation is consistent with dark matter properties inferred from studies of spiral galaxies with halo masses larger than 3 ×1011M⊙. We speculate that other observed galaxy regularities might be explained within the framework of such dissipative dark matter.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Bozorgnia, Nassim; Gelmini, Graciela B.; Gondolo, Paolo, E-mail: n.bozorgnia@uva.nl, E-mail: gelmini@physics.ucla.edu, E-mail: paolo@physics.utah.edu

Directional dark matter detection attempts to measure the direction of motion of nuclei recoiling after having interacted with dark matter particles in the halo of our Galaxy. Due to Earth's motion with respect to the Galaxy, the dark matter flux is concentrated around a preferential direction. An anisotropy in the recoil direction rate is expected as an unmistakable signature of dark matter. The average nuclear recoil direction is expected to coincide with the average direction of dark matter particles arriving to Earth. Here we point out that for a particular type of dark matter, inelastic exothermic dark matter, the meanmore » recoil direction as well as a secondary feature, a ring of maximum recoil rate around the mean recoil direction, could instead be opposite to the average dark matter arrival direction. Thus, the detection of an average nuclear recoil direction opposite to the usually expected direction would constitute a spectacular experimental confirmation of this type of dark matter.« less
Dark side of the Universe after Planck data

NASA Astrophysics Data System (ADS)

Cheng, Cheng; Huang, Qing-Guo

2014-02-01

Recently released Planck data imply a smaller Hubble constant H0 than that from the Hubble Space Telescope project (HST) and a larger percentage of the matter components Ωm compared to the Supernova Legacy Survey (SNLS) in the Λ cold dark matter (CDM) model. In this paper we found that even though the tension on H0 between Planck and HST can be relaxed if the dark radiation is introduced [ΔNeff=0.536-0.224+0.229 at 68% CL from the data sets of Planck+WMAP polarization (WP)+baryon acoustic oscillation (BAO)+the combination of supernova Union2.1 compilation of 580 Supernovae (Union2.1)+HST], Ωm from Planck is still not nicely compatible with that from SNLS. The tensions between Planck and other astrophysical data sets can be significantly relaxed in the wCDM model, and the combination of these data sets prefers a phantomlike dark energy at more than 95% CL: w =-1.15±0.07 and w=-1.16±0.06 at 68% CL from Planck+WP+BAO+Union2.1+HST and Planck+WP+BAO+SNLS+HST, respectively. From the statistical point of view, there is no evidence for a time-evolving equation of state (Δχ2=-0.3 compared to a constant equation of state for the combination of Planck+WP+BAO+SNLS+HST).
Galaxy formation with BECDM - I. Turbulence and relaxation of idealized haloes

NASA Astrophysics Data System (ADS)

Mocz, Philip; Vogelsberger, Mark; Robles, Victor H.; Zavala, Jesús; Boylan-Kolchin, Michael; Fialkov, Anastasia; Hernquist, Lars

2017-11-01

We present a theoretical analysis of some unexplored aspects of relaxed Bose-Einstein condensate dark matter (BECDM) haloes. This type of ultralight bosonic scalar field dark matter is a viable alternative to the standard cold dark matter (CDM) paradigm, as it makes the same large-scale predictions as CDM and potentially overcomes CDM's small-scale problems via a galaxy-scale de Broglie wavelength. We simulate BECDM halo formation through mergers, evolved under the Schrödinger-Poisson equations. The formed haloes consist of a soliton core supported against gravitational collapse by the quantum pressure tensor and an asymptotic r-3 NFW-like profile. We find a fundamental relation of the core-to-halo mass with the dimensionless invariant Ξ ≡ |E|/M3/(Gm/ℏ)2 or Mc/M ≃ 2.6Ξ1/3, linking the soliton to global halo properties. For r ≥ 3.5 rc core radii, we find equipartition between potential, classical kinetic and quantum gradient energies. The haloes also exhibit a conspicuous turbulent behaviour driven by the continuous reconnection of vortex lines due to wave interference. We analyse the turbulence 1D velocity power spectrum and find a k-1.1 power law. This suggests that the vorticity in BECDM haloes is homogeneous, similar to thermally-driven counterflow BEC systems from condensed matter physics, in contrast to a k-5/3 Kolmogorov power law seen in mechanically-driven quantum systems. The mode where the power spectrum peaks is approximately the soliton width, implying that the soliton-sized granules carry most of the turbulent energy in BECDM haloes.
Discrepancies between CFHTLenS cosmic shear and Planck: new physics or systematic effects?

NASA Astrophysics Data System (ADS)

Kitching, Thomas D.; Verde, Licia; Heavens, Alan F.; Jimenez, Raul

2016-06-01

There is currently a discrepancy in the measured value of the amplitude of matter clustering, parametrized using σ8, inferred from galaxy weak lensing, and cosmic microwave background (CMB) data, which could be an indication of new physics, such as massive neutrinos or a modification to the gravity law, or baryon feedback. In this paper we make the assumption that the cosmological parameters are well determined by Planck, and use weak lensing data to investigate the implications for baryon feedback and massive neutrinos, as well as possible contributions from intrinsic alignments and biases in photometric redshifts. We apply a non-parametric approach to model the baryonic feedback on the dark matter clustering, which is flexible enough to reproduce the OWLS (OverWhelmingly Large Simulations) and Illustris simulation results. The statistic we use, 3D cosmic shear, is a method that extracts cosmological information from weak lensing data using a spherical-Bessel function power spectrum approach. We analyse the CFHTLenS weak lensing data and, assuming best-fitting cosmological parameters from the Planck CMB experiment, find that there is no evidence for baryonic feedback on the dark matter power spectrum, but there is evidence for a bias in the photometric redshifts in the CFHTLenS data, consistent with a completely independent analysis by Choi et al., based on spectroscopic redshifts, and that these conclusions are robust to assumptions about the intrinsic alignment systematic. We also find an upper limit, of <0.28 eV (1σ), to the sum of neutrino masses conditional on other Λ-cold-dark-matter parameters being fixed.
Galaxy formation with BECDM - I. Turbulence and relaxation of idealized haloes.

PubMed

Mocz, Philip; Vogelsberger, Mark; Robles, Victor H; Zavala, Jesús; Boylan-Kolchin, Michael; Fialkov, Anastasia; Hernquist, Lars

2017-11-01

We present a theoretical analysis of some unexplored aspects of relaxed Bose-Einstein condensate dark matter (BECDM) haloes. This type of ultralight bosonic scalar field dark matter is a viable alternative to the standard cold dark matter (CDM) paradigm, as it makes the same large-scale predictions as CDM and potentially overcomes CDM's small-scale problems via a galaxy-scale de Broglie wavelength. We simulate BECDM halo formation through mergers, evolved under the Schrödinger-Poisson equations. The formed haloes consist of a soliton core supported against gravitational collapse by the quantum pressure tensor and an asymptotic r -3 NFW-like profile. We find a fundamental relation of the core-to-halo mass with the dimensionless invariant Ξ ≡ | E |/ M 3 /( Gm/ħ ) 2 or M c / M ≃ 2.6Ξ 1/3 , linking the soliton to global halo properties. For r ≥ 3.5 r c core radii, we find equipartition between potential, classical kinetic and quantum gradient energies. The haloes also exhibit a conspicuous turbulent behaviour driven by the continuous reconnection of vortex lines due to wave interference. We analyse the turbulence 1D velocity power spectrum and find a k -1.1 power law. This suggests that the vorticity in BECDM haloes is homogeneous, similar to thermally-driven counterflow BEC systems from condensed matter physics, in contrast to a k -5/3 Kolmogorov power law seen in mechanically-driven quantum systems. The mode where the power spectrum peaks is approximately the soliton width, implying that the soliton-sized granules carry most of the turbulent energy in BECDM haloes.
DOE Office of Scientific and Technical Information (OSTI.GOV)

Blennow, Mattias; Clementz, Stefan, E-mail: emb@kth.se, E-mail: scl@kth.se

Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles andmore » anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.« less
Secretly asymmetric dark matter

NASA Astrophysics Data System (ADS)

Agrawal, Prateek; Kilic, Can; Swaminathan, Sivaramakrishnan; Trendafilova, Cynthia

2017-01-01

We study a mechanism where the dark matter number density today arises from asymmetries generated in the dark sector in the early Universe, even though the total dark matter number remains zero throughout the history of the Universe. The dark matter population today can be completely symmetric, with annihilation rates above those expected from thermal weakly interacting massive particles. We give a simple example of this mechanism using a benchmark model of flavored dark matter. We discuss the experimental signatures of this setup, which arise mainly from the sector that annihilates the symmetric component of dark matter.
Modified dark matter: Relating dark energy, dark matter and baryonic matter

NASA Astrophysics Data System (ADS)

Edmonds, Douglas; Farrah, Duncan; Minic, Djordje; Ng, Y. Jack; Takeuchi, Tatsu

Modified dark matter (MDM) is a phenomenological model of dark matter, inspired by gravitational thermodynamics. For an accelerating universe with positive cosmological constant (Λ), such phenomenological considerations lead to the emergence of a critical acceleration parameter related to Λ. Such a critical acceleration is an effective phenomenological manifestation of MDM, and it is found in correlations between dark matter and baryonic matter in galaxy rotation curves. The resulting MDM mass profiles, which are sensitive to Λ, are consistent with observational data at both the galactic and cluster scales. In particular, the same critical acceleration appears both in the galactic and cluster data fits based on MDM. Furthermore, using some robust qualitative arguments, MDM appears to work well on cosmological scales, even though quantitative studies are still lacking. Finally, we comment on certain nonlocal aspects of the quanta of modified dark matter, which may lead to novel nonparticle phenomenology and which may explain why, so far, dark matter detection experiments have failed to detect dark matter particles.
Dilaton-assisted dark matter.

PubMed

Bai, Yang; Carena, Marcela; Lykken, Joseph

2009-12-31

A dilaton could be the dominant messenger between standard model fields and dark matter. The measured dark matter relic abundance relates the dark matter mass and spin to the conformal breaking scale. The dark matter-nucleon spin-independent cross section is predicted in terms of the dilaton mass. We compute the current constraints on the dilaton from LEP and Tevatron experiments, and the gamma-ray signal from dark matter annihilation to dilatons that could be observed by Fermi Large Area Telescope.
Dark matter detection in supersymmetric models with non-universal gaugino masses

NASA Astrophysics Data System (ADS)

Park, Eun-Kyung

SUSY is one of the most promising new physics ideas, and will soon be tested at high energy accelerators like the CERN LHC. Moreover SUSY provides a good candidate for cold dark matter (CDM). In this dissertation, we investigated phenomenology of SUSY models with non-universal gaugino masses (NUGM) at colliding experiments using event generators such as ISAJET and examined direct and indirect detection rates of relic neutralino CDM in the universe. The motivation of these models is that in most of mSUGRA parameter space, the relic density WZ1˜ h2 is considerably larger than the WMAP measurement, and it is well known that if non-universal gaugino masses are allowed, then qualitatively new possibilities arise that are not realized in the mSUGRA model. Our first NUGM attempt is to allow a mixed wino-bino lightest SUSY particle (LSP) by lowering SU(2) gaugino mass M2 at the weak scale from its mSUGRA value while keeping the hypercharge gaugino mass M1 fixed (Mixed Wino Dark Matter). In this model, wino-like Z˜1 with sufficiently low M2 compared to M1 enhances Z˜1Z˜ 1 → W+1W-1 annihilations to reach the WMAP measured relic density. The second attempt is study on the NUGM model with different signs of M 1 and M2 (Bino-Wino Co-Annihilation Scenario). In this case, there is little mixing, so that Z˜1 remains nearly a pure bino or a pure wino. By increasing M1 ≃ M 2, enhanced bino-wino co-annihilation can achieve the relic neutralino abundance. The final attempt of NUGM models is lowering the SU(3) gaugino mass to diminish the effect of the large top quark Yukawa coupling in the running of the higgs mass, so that the value of superpotential mu parameter gets efficiently low to give rise to mixed higgsino dark matter (Mixed Higgsino Dark Matter). Consequences of these NUGM model studies show us that relaxing universality of gaugino masses in SUSY models leads to enhanced direct and indirect dark matter detection rates and reduced mZ2˜-m Z1˜ mass gap so that the LHC and ILC can distinguish each NUGM model from others. Finally, we found that models with well-tempered neutralinos, where the composition of the neutralino is adjusted to give observed relic density, yield target cross sections which are detectable at proposed experiments.
The part and the whole: voids, supervoids, and their ISW imprint

NASA Astrophysics Data System (ADS)

Kovács, András

2018-04-01

The integrated Sachs-Wolfe (ISW) imprint of extreme structures in the cosmic web probes the dynamical nature of dark energy. Looking through typical cosmic voids, no anomalous signal has been reported. On the contrary, supervoids, associated with large-scale fluctuations in the gravitational potential, have shown potentially disturbing excess signals. In this study, we used the Jubilee ISW simulation to demonstrate how the stacked signal depends on the void definition. We found that large underdensities, with at least ≈5 merged sub-voids, show a peculiar ISW imprint shape with central cold spots and surrounding hot rings, offering a natural way to define supervoids in the cosmic web. We then inspected the real-world Baryon Oscillations Spectroscopic Survey data release 12 (BOSS DR12) data using the simulated imprints as templates. The imprinted profile of BOSS supervoids appears to be more compact than in simulations, requiring an extra α ≈ 0.7 re-scaling of filter sizes. The data reveal an excess ISW-like signal with AISW ≈ 9 amplitude at the ≈2.5σ significance level, unlike previous studies that used isolated voids and reported good consistency with AISW = 1. The tension with the Jubilee-based Λ cold dark matter predictions is ≳2σ, in consistency with independent analyses of supervoids in Dark Energy Survey data. We show that such a very large enhancement of the AISW parameter hints at a possible causal relation between the cosmic microwave background Cold Spot and the Eridanus supervoid. The origin of these findings remains unclear.
Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud

NASA Technical Reports Server (NTRS)

Drlica-Wagner, Alex; Gomez-Vargas, German A.; Hewitt, John W.; Linden, Tim; Tibaldo, Luigi

2014-01-01

Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use gamma-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant gamma-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (approximately 3 x 10 (sup -26) cubic centimeters per second) for dark matter masses less than or approximately 30 gigaelectronvolts annihilating via the B/B- bar oscillation or tau/antitau channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.
Searching For Dark Matter Annihilation In The Smith High-Velocity Cloud

DOE PAGES

Drlica-Wagner, Alex; Gómez-Vargas, Germán A.; Hewitt, John W.; ...

2014-06-27

Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use γ-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant γ-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation crossmore » section assuming a spatially extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section (~3 × 10 -26 cm3 s -1) for dark matter masses . 30 GeV annihilating via the b¯b or τ⁺τ⁻ channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.« less
Measurement of a cosmographic distance ratio with galaxy and cosmic microwave background lensing

DOE PAGES

Miyatake, Hironao; Madhavacheril, Mathew S.; Sehgal, Neelima; ...

2017-04-17

We measure the gravitational lensing shear signal around dark matter halos hosting constant mass galaxies using light sources at z~1 (background galaxies) and at the surface of last scattering at z~1100 (the cosmic microwave background). The galaxy shear measurement uses data from the CFHTLenS survey, and the microwave background shear measurement uses data from the Planck satellite. The ratio of shears from these cross-correlations provides a purely geometric distance measurement across the longest possible cosmological lever arm. This is because the matter distribution around the halos, including uncertainties in galaxy bias and systematic errors such as miscentering, cancels in themore » ratio for halos in thin redshift slices. We measure this distance ratio in three different redshift slices of the constant mass (CMASS) sample and combine them to obtain a 17% measurement of the distance ratio, r = 0.390 +0.070 –0.062, at an effective redshift of z = 0.53. As a result, this is consistent with the predicted ratio from the Planck best-fit cold dark matter model with a cosmological constant cosmology of r = 0.419.« less
Unifying leptogenesis, dark matter and high-energy neutrinos with right-handed neutrino mixing via Higgs portal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bari, Pasquale Di; Ludl, Patrick Otto; Palomares-Ruiz, Sergio

2016-11-21

We revisit a model in which neutrino masses and mixing are described by a two right-handed (RH) neutrino seesaw scenario, implying a strictly hierarchical light neutrino spectrum. A third decoupled RH neutrino, N{sub DM} with mass M{sub DM}, plays the role of cold dark matter (DM) and is produced by the mixing with a source RH neutrino, N{sub S} with mass M{sub S}, induced by Higgs portal interactions. The same interactions are also responsible for N{sub DM} decays. We discuss in detail the constraints coming from DM abundance and stability conditions showing that in the hierarchical case, for M{sub DM}≫M{submore » S}, there is an allowed window on M{sub DM} values necessarily implying a contribution, from DM decays, to the high-energy neutrino flux recently detected by IceCube. We also show how the model can explain the matter-antimatter asymmetry of the Universe via leptogenesis in the quasi-degenerate limit. In this case, the DM mass should be within the range 300 GeV ≲M{sub S}« less
DOE Office of Scientific and Technical Information (OSTI.GOV)

Baghram, Shant; Abolhasani, Ali Akbar; Firouzjahi, Hassan

We study the predictions of anomalous inflationary models on the abundance of structures in large scale structure observations. The anomalous features encoded in primordial curvature perturbation power spectrum are (a): localized feature in momentum space, (b): hemispherical asymmetry and (c): statistical anisotropies. We present a model-independent expression relating the number density of structures to the changes in the matter density variance. Models with localized feature can alleviate the tension between observations and numerical simulations of cold dark matter structures on galactic scales as a possible solution to the missing satellite problem. In models with hemispherical asymmetry we show that themore » abundance of structures becomes asymmetric depending on the direction of observation to sky. In addition, we study the effects of scale-dependent dipole amplitude on the abundance of structures. Using the quasars data and adopting the power-law scaling k{sup n{sub A}-1} for the amplitude of dipole we find the upper bound n{sub A} < 0.6 for the spectral index of the dipole asymmetry. In all cases there is a critical mass scale M{sub c} in which for M M{sub c}) the enhancement in variance induced from anomalous feature decreases (increases) the abundance of dark matter structures in Universe.« less
Dissipative dark matter and the rotation curves of dwarf galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foot, R., E-mail: rfoot@unimelb.edu.au

2016-07-01

There is ample evidence from rotation curves that dark matter halos around disk galaxies have nontrivial dynamics. Of particular significance are: a) the cored dark matter profile of disk galaxies, b) correlations of the shape of rotation curves with baryonic properties, and c) Tully-Fisher relations. Dark matter halos around disk galaxies may have nontrivial dynamics if dark matter is strongly self interacting and dissipative. Multicomponent hidden sector dark matter featuring a massless 'dark photon' (from an unbroken dark U(1) gauge interaction) which kinetically mixes with the ordinary photon provides a concrete example of such dark matter. The kinetic mixing interactionmore » facilitates halo heating by enabling ordinary supernovae to be a source of these 'dark photons'. Dark matter halos can expand and contract in response to the heating and cooling processes, but for a sufficiently isolated halo could have evolved to a steady state or 'equilibrium' configuration where heating and cooling rates locally balance. This dynamics allows the dark matter density profile to be related to the distribution of ordinary supernovae in the disk of a given galaxy. In a previous paper a simple and predictive formula was derived encoding this relation. Here we improve on previous work by modelling the supernovae distribution via the measured UV and H α fluxes, and compare the resulting dark matter halo profiles with the rotation curve data for each dwarf galaxy in the LITTLE THINGS sample. The dissipative dark matter concept is further developed and some conclusions drawn.« less
Non scale-invariant density perturbations from chaotic extended inflation

NASA Technical Reports Server (NTRS)

Mollerach, Silvia; Matarrese, Sabino

1991-01-01

Chaotic inflation is analyzed in the frame of scalar-tensor theories of gravity. Fluctuations in the energy density arise from quantum fluctuations of the Brans-Dicke field and of the inflation field. The spectrum of perturbations is studied for a class of models: it is non scale-invarient and, for certain values of the parameters, it has a peak. If the peak appears at astrophysically interesting scales, it may help to reconcile the Cold Dark Matter scenario for structure formation with large scale observations.

Experimental search for hidden photon CDM in the eV mass range with a dish antenna

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, J.; Horie, T.; Minowa, M.

2015-09-01

A search for hidden photon cold dark matter (HP CDM) using a new technique with a dish antenna is reported. From the result of the measurement, we found no evidence for the existence of HP CDM and set an upper limit on the photon-HP mixing parameter χ of ∼ 6× 10{sup −12} for the hidden photon mass m{sub γ} = 3.1 ± 1.2 eV.
Distorted neutrino oscillations from time varying cosmic fields

DOE PAGES

Krnjaic, Gordan; Machado, Pedro A. N.; Necib, Lina

2018-04-16

Cold, ultralight (more » $$\\ll$$ eV) bosonic fields can induce fast temporal variation in neutrino couplings, thereby distorting neutrino oscillations. In this paper, we exploit this effect to introduce a novel probe of neutrino time variation and dark matter at long-baseline experiments. We study several representative observables and find that current and future experiments, including DUNE and JUNO, are sensitive to a wide range of model parameters over many decades in mass reach and time-variation periodicity.« less
Distorted neutrino oscillations from time varying cosmic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krnjaic, Gordan; Machado, Pedro A. N.; Necib, Lina

Cold, ultralight (more » $$\\ll$$ eV) bosonic fields can induce fast temporal variation in neutrino couplings, thereby distorting neutrino oscillations. In this paper, we exploit this effect to introduce a novel probe of neutrino time variation and dark matter at long-baseline experiments. We study several representative observables and find that current and future experiments, including DUNE and JUNO, are sensitive to a wide range of model parameters over many decades in mass reach and time-variation periodicity.« less
Apocalypse soon

NASA Astrophysics Data System (ADS)

Jackson, J. C.

1998-05-01

Based upon a simple vacuum Lagrangian, comprising cosmological and quadratic scalar field terms, a cosmological model is presented the history of which is indistinguishable from that of an innocuous low-density cold dark matter (CDM) universe, but the future of which is very much shorter. For sensible values of the deceleration parameter (0
Implications of two-component dark matter induced by forbidden channels and thermal freeze-out

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aoki, Mayumi; Toma, Takashi, E-mail: mayumi@hep.s.kanazawa-u.ac.jp, E-mail: takashi.toma@tum.de

2017-01-01

We consider a model of two-component dark matter based on a hidden U(1) {sub D} symmetry, in which relic densities of the dark matter are determined by forbidden channels and thermal freeze-out. The hidden U(1) {sub D} symmetry is spontaneously broken to a residual Z{sub 4} symmetry, and the lightest Z{sub 4} charged particle can be a dark matter candidate. Moreover, depending on the mass hierarchy in the dark sector, we have two-component dark matter. We show that the relic density of the lighter dark matter component can be determined by forbidden annihilation channels which require larger couplings compared tomore » the normal freeze-out mechanism. As a result, a large self-interaction of the lighter dark matter component can be induced, which may solve small scale problems of ΛCDM model. On the other hand, the heavier dark matter component is produced by normal freeze-out mechanism. We find that interesting implications emerge between the two dark matter components in this framework. We explore detectabilities of these dark matter particles and show some parameter space can be tested by the SHiP experiment.« less
Collapsed Dark Matter Structures

NASA Astrophysics Data System (ADS)

Buckley, Matthew R.; DiFranzo, Anthony

2018-02-01

The distributions of dark matter and baryons in the Universe are known to be very different: The dark matter resides in extended halos, while a significant fraction of the baryons have radiated away much of their initial energy and fallen deep into the potential wells. This difference in morphology leads to the widely held conclusion that dark matter cannot cool and collapse on any scale. We revisit this assumption and show that a simple model where dark matter is charged under a "dark electromagnetism" can allow dark matter to form gravitationally collapsed objects with characteristic mass scales much smaller than that of a Milky-Way-type galaxy. Though the majority of the dark matter in spiral galaxies would remain in the halo, such a model opens the possibility that galaxies and their associated dark matter play host to a significant number of collapsed substructures. The observational signatures of such structures are not well explored but potentially interesting.
Collapsed Dark Matter Structures.

PubMed

Buckley, Matthew R; DiFranzo, Anthony

2018-02-02

The distributions of dark matter and baryons in the Universe are known to be very different: The dark matter resides in extended halos, while a significant fraction of the baryons have radiated away much of their initial energy and fallen deep into the potential wells. This difference in morphology leads to the widely held conclusion that dark matter cannot cool and collapse on any scale. We revisit this assumption and show that a simple model where dark matter is charged under a "dark electromagnetism" can allow dark matter to form gravitationally collapsed objects with characteristic mass scales much smaller than that of a Milky-Way-type galaxy. Though the majority of the dark matter in spiral galaxies would remain in the halo, such a model opens the possibility that galaxies and their associated dark matter play host to a significant number of collapsed substructures. The observational signatures of such structures are not well explored but potentially interesting.
The Evolving Search for the Nature of Dark Energy | Berkeley Lab

Science.gov Websites

percent of its contents is ordinary matter, 24 percent is dark matter, and all the rest is dark energy ordinary matter, 24 percent is dark matter, and all the rest is dark energy - unless there's a flaw in our Universe, and it's pushing all the rest - ordinary matter and dark matter - farther apart at an ever
Weak lensing by galaxy troughs in DES Science Verification data

DOE PAGES

Gruen, D.; Friedrich, O.; Amara, A.; ...

2015-11-29

In this study, we measure the weak lensing shear around galaxy troughs, i.e. the radial alignment of background galaxies relative to underdensities in projections of the foreground galaxy field over a wide range of redshift in Science Verification data from the Dark Energy Survey. Our detection of the shear signal is highly significant (10σ–15σ for the smallest angular scales) for troughs with the redshift range z ϵ [0.2, 0.5] of the projected galaxy field and angular diameters of 10 arcmin…1°. These measurements probe the connection between the galaxy, matter density, and convergence fields. By assuming galaxies are biased tracers ofmore » the matter density with Poissonian noise, we find agreement of our measurements with predictions in a fiducial Λ cold dark matter model. The prediction for the lensing signal on large trough scales is virtually independent of the details of the underlying model for the connection of galaxies and matter. Our comparison of the shear around troughs with that around cylinders with large galaxy counts is consistent with a symmetry between galaxy and matter over- and underdensities. In addition, we measure the two-point angular correlation of troughs with galaxies which, in contrast to the lensing signal, is sensitive to galaxy bias on all scales. The lensing signal of troughs and their clustering with galaxies is therefore a promising probe of the statistical properties of matter underdensities and their connection to the galaxy field.« less
A global fit of the γ-ray galactic center excess within the scalar singlet Higgs portal model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cuoco, Alessandro; Eiteneuer, Benedikt; Heisig, Jan

2016-06-28

We analyse the excess in the γ-ray emission from the center of our galaxy observed by Fermi-LAT in terms of dark matter annihilation within the scalar Higgs portal model. In particular, we include the astrophysical uncertainties from the dark matter distribution and allow for unspecified additional dark matter components. We demonstrate through a detailed numerical fit that the strength and shape of the γ-ray spectrum can indeed be described by the model in various regions of dark matter masses and couplings. Constraints from invisible Higgs decays, direct dark matter searches, indirect searches in dwarf galaxies and for γ-ray lines, andmore » constraints from the dark matter relic density reduce the parameter space to dark matter masses near the Higgs resonance. We find two viable regions: one where the Higgs-dark matter coupling is of O(10{sup −2}), and an additional dark matter component beyond the scalar WIMP of our model is preferred, and one region where the Higgs-dark matter coupling may be significantly smaller, but where the scalar WIMP constitutes a significant fraction or even all of dark matter. Both viable regions are hard to probe in future direct detection and collider experiments.« less
Massive graviton dark matter with environment dependent mass: A natural explanation of the dark matter-baryon ratio

NASA Astrophysics Data System (ADS)

Aoki, Katsuki; Mukohyama, Shinji

2017-11-01

We propose a scenario that can naturally explain the observed dark matter-baryon ratio in the context of bimetric theory with a chameleon field. We introduce two additional gravitational degrees of freedom, the massive graviton and the chameleon field, corresponding to dark matter and dark energy, respectively. The chameleon field is assumed to be nonminimally coupled to dark matter, i.e., the massive graviton, through the graviton mass terms. We find that the dark matter-baryon ratio is dynamically adjusted to the observed value due to the energy transfer by the chameleon field. As a result, the model can explain the observed dark matter-baryon ratio independently from the initial abundance of them.
Dark sequential Z ' portal: Collider and direct detection experiments

NASA Astrophysics Data System (ADS)

Arcadi, Giorgio; Campos, Miguel D.; Lindner, Manfred; Masiero, Antonio; Queiroz, Farinaldo S.

2018-02-01

We revisit the status of a Majorana fermion as a dark matter candidate when a sequential Z' gauge boson dictates the dark matter phenomenology. Direct dark matter detection signatures rise from dark matter-nucleus scatterings at bubble chamber and liquid xenon detectors, and from the flux of neutrinos from the Sun measured by the IceCube experiment, which is governed by the spin-dependent dark matter-nucleus scattering. On the collider side, LHC searches for dilepton and monojet + missing energy signals play an important role. The relic density and perturbativity requirements are also addressed. By exploiting the dark matter complementarity we outline the region of parameter space where one can successfully have a Majorana dark matter particle in light of current and planned experimental sensitivities.
Flavored dark matter beyond Minimal Flavor Violation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agrawal, Prateek; Blanke, Monika; Gemmler, Katrin

We study the interplay of flavor and dark matter phenomenology for models of flavored dark matter interacting with quarks. We allow an arbitrary flavor structure in the coupling of dark matter with quarks. This coupling is assumed to be the only new source of violation of the Standard Model flavor symmetry extended by a U(3) χ associated with the dark matter. We call this ansatz Dark Minimal Flavor Violation (DMFV) and highlight its various implications, including an unbroken discrete symmetry that can stabilize the dark matter. As an illustration we study a Dirac fermionic dark matter χ which transforms asmore » triplet under U(3) χ , and is a singlet under the Standard Model. The dark matter couples to right-handed down-type quarks via a colored scalar mediator Φ with a coupling λ. We identify a number of “flavor-safe” scenarios for the structure of λ which are beyond Minimal Flavor Violation. Also, for dark matter and collider phenomenology we focus on the well-motivated case of b-flavored dark matter. Furthermore, the combined flavor and dark matter constraints on the parameter space of λ turn out to be interesting intersections of the individual ones. LHC constraints on simplified models of squarks and sbottoms can be adapted to our case, and monojet searches can be relevant if the spectrum is compressed.« less
Flavored dark matter beyond Minimal Flavor Violation

DOE PAGES

Agrawal, Prateek; Blanke, Monika; Gemmler, Katrin

2014-10-13

We study the interplay of flavor and dark matter phenomenology for models of flavored dark matter interacting with quarks. We allow an arbitrary flavor structure in the coupling of dark matter with quarks. This coupling is assumed to be the only new source of violation of the Standard Model flavor symmetry extended by a U(3) χ associated with the dark matter. We call this ansatz Dark Minimal Flavor Violation (DMFV) and highlight its various implications, including an unbroken discrete symmetry that can stabilize the dark matter. As an illustration we study a Dirac fermionic dark matter χ which transforms asmore » triplet under U(3) χ , and is a singlet under the Standard Model. The dark matter couples to right-handed down-type quarks via a colored scalar mediator Φ with a coupling λ. We identify a number of “flavor-safe” scenarios for the structure of λ which are beyond Minimal Flavor Violation. Also, for dark matter and collider phenomenology we focus on the well-motivated case of b-flavored dark matter. Furthermore, the combined flavor and dark matter constraints on the parameter space of λ turn out to be interesting intersections of the individual ones. LHC constraints on simplified models of squarks and sbottoms can be adapted to our case, and monojet searches can be relevant if the spectrum is compressed.« less
The COBE normalization for standard cold dark matter

NASA Technical Reports Server (NTRS)

Bunn, Emory F.; Scott, Douglas; White, Martin

1995-01-01

The Cosmic Background Explorer Satellite (COBE) detection of microwave anisotropies provides the best way of fixing the amplitude of cosmological fluctuations on the largest scales. This normalization is usually given for an n = 1 spectrum, including only the anisotropy caused by the Sachs-Wolfe effect. This is certainly not a good approximation for a model containing any reasonable amount of baryonic matter. In fact, even tilted Sachs-Wolfe spectra are not a good fit to models like cold dark matter (CDM). Here, we normalize standard CDM (sCDM) to the two-year COBE data and quote the best amplitude in terms of the conventionally used measures of power. We also give normalizations for some specific variants of this standard model, and we indicate how the normalization depends on the assumed values on n, Omega(sub B) and H(sub 0). For sCDM we find the mean value of Q = 19.9 +/- 1.5 micro-K, corresponding to sigma(sub 8) = 1.34 +/- 0.10, with the normalization at large scales being B = (8.16 +/- 1.04) x 10(exp 5)(Mpc/h)(exp 4), and other numbers given in the table. The measured rms temperature fluctuation smoothed on 10 deg is a little low relative to this normalization. This is mainly due to the low quadrupole in the data: when the quadrupole is removed, the measured value of sigma(10 deg) is quite consistent with the best-fitting the mean value of Q. The use of the mean value of Q should be preferred over sigma(10 deg), when its value can be determined for a particular theory, since it makes full use of the data.
Mystery of the Hidden Cosmos [Complex Dark Matter

DOE PAGES

Dobrescu, Bogdan A.; Lincoln, Don

2015-06-16

Scientists know there must be more matter in the universe than what is visible. Searches for this dark matter have focused on a single unseen particle, but decades of experiments have been unsuccessful at finding it. Exotic possibilities for dark matter are looking increasingly plausible. Rather than just one particle, dark matter could contain an entire world of particles and forces that barely interact with normal matter. Complex dark matter could form dark atoms and molecules and even clump together to make hidden galactic disks that overlap with the spiral arms of the Milky Way and other galaxies. Experiments aremore » under way to search for evidence of such a dark sector.« less
Dark Matter Decay between Phase Transitions at the Weak Scale.

PubMed

Baker, Michael J; Kopp, Joachim

2017-08-11

We propose a new alternative to the weakly interacting massive particle paradigm for dark matter. Rather than being determined by thermal freeze-out, the dark matter abundance in this scenario is set by dark matter decay, which is allowed for a limited amount of time just before the electroweak phase transition. More specifically, we consider fermionic singlet dark matter particles coupled weakly to a scalar mediator S_{3} and to auxiliary dark sector fields, charged under the standard model gauge groups. Dark matter freezes out while still relativistic, so its abundance is initially very large. As the Universe cools down, the scalar mediator develops a vacuum expectation value (VEV), which breaks the symmetry that stabilizes dark matter. This allows dark matter to mix with charged fermions and decay. During this epoch, the dark matter abundance is reduced to give the value observed today. Later, the SM Higgs field also develops a VEV, which feeds back into the S_{3} potential and restores the dark sector symmetry. In a concrete model we show that this "VEV flip-flop" scenario is phenomenologically successful in the most interesting regions of its parameter space. We also comment on detection prospects at the LHC and elsewhere.
Dark Matter Decay between Phase Transitions at the Weak Scale

NASA Astrophysics Data System (ADS)

Baker, Michael J.; Kopp, Joachim

2017-08-01

We propose a new alternative to the weakly interacting massive particle paradigm for dark matter. Rather than being determined by thermal freeze-out, the dark matter abundance in this scenario is set by dark matter decay, which is allowed for a limited amount of time just before the electroweak phase transition. More specifically, we consider fermionic singlet dark matter particles coupled weakly to a scalar mediator S3 and to auxiliary dark sector fields, charged under the standard model gauge groups. Dark matter freezes out while still relativistic, so its abundance is initially very large. As the Universe cools down, the scalar mediator develops a vacuum expectation value (VEV), which breaks the symmetry that stabilizes dark matter. This allows dark matter to mix with charged fermions and decay. During this epoch, the dark matter abundance is reduced to give the value observed today. Later, the SM Higgs field also develops a VEV, which feeds back into the S3 potential and restores the dark sector symmetry. In a concrete model we show that this "VEV flip-flop" scenario is phenomenologically successful in the most interesting regions of its parameter space. We also comment on detection prospects at the LHC and elsewhere.
Radial oscillations of strange quark stars admixed with condensed dark matter

NASA Astrophysics Data System (ADS)

Panotopoulos, G.; Lopes, Ilídio

2017-10-01

We compute the 20 lowest frequency radial oscillation modes of strange stars admixed with condensed dark matter. We assume a self-interacting bosonic dark matter, and we model dark matter inside the star as a Bose-Einstein condensate. In this case the equation of state is a polytropic one with index 1 +1 /n =2 and a constant K that is computed in terms of the mass of the dark matter particle and the scattering length. Assuming a mass and a scattering length compatible with current observational bounds for self-interacting dark matter, we have integrated numerically first the Tolman-Oppenheimer-Volkoff equations for the hydrostatic equilibrium, and then the equations for the perturbations ξ =Δ r /r and η =Δ P /P . For a compact object with certain mass and radius we have considered here three cases, namely no dark matter at all and two different dark matter scenarios. Our results show that (i) the separation between consecutive modes increases with the amount of dark matter, and (ii) the effect is more pronounced for higher order modes. These effects are relevant even for a strange star made of 5% dark matter.
Testing the Bose-Einstein Condensate dark matter model at galactic cluster scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harko, Tiberiu; Liang, Pengxiang; Liang, Shi-Dong

The possibility that dark matter may be in the form of a Bose-Einstein Condensate (BEC) has been extensively explored at galactic scale. In particular, good fits for the galactic rotations curves have been obtained, and upper limits for the dark matter particle mass and scattering length have been estimated. In the present paper we extend the investigation of the properties of the BEC dark matter to the galactic cluster scale, involving dark matter dominated astrophysical systems formed of thousands of galaxies each. By considering that one of the major components of a galactic cluster, the intra-cluster hot gas, is describedmore » by King's β-model, and that both intra-cluster gas and dark matter are in hydrostatic equilibrium, bound by the same total mass profile, we derive the mass and density profiles of the BEC dark matter. In our analysis we consider several theoretical models, corresponding to isothermal hot gas and zero temperature BEC dark matter, non-isothermal gas and zero temperature dark matter, and isothermal gas and finite temperature BEC, respectively. The properties of the finite temperature BEC dark matter cluster are investigated in detail numerically. We compare our theoretical results with the observational data of 106 galactic clusters. Using a least-squares fitting, as well as the observational results for the dark matter self-interaction cross section, we obtain some upper bounds for the mass and scattering length of the dark matter particle. Our results suggest that the mass of the dark matter particle is of the order of μ eV, while the scattering length has values in the range of 10{sup −7} fm.« less

Three-dimensional motions in the Sculptor dwarf galaxy as a glimpse of a new era

NASA Astrophysics Data System (ADS)

Massari, D.; Breddels, M. A.; Helmi, A.; Posti, L.; Brown, A. G. A.; Tolstoy, E.

2018-02-01

The three-dimensional motions of stars in small galaxies beyond our own are minute, yet they are crucial for understanding the nature of gravity and dark matter1,2. Even for the dwarf galaxy Sculptor—one of the best-studied systems, which is inferred to be strongly dark matter dominated3,4—there are conflicting reports5-7 on its mean motion around the Milky Way, and the three-dimensional internal motions of its stars have never been measured. Here, we present precise proper motions of Sculptor's stars based on data from the Gaia mission8 and Hubble Space Telescope. Our measurements show that Sculptor moves around the Milky Way on a high-inclination elongated orbit that takes it much further out than previously thought. For Sculptor's internal velocity dispersions, we find σR = 11.5 ± 4.3 km s-1 and σT = 8.5 ± 3.2 km s-1 along the projected radial and tangential directions. Thus, the stars in our sample move preferentially on radial orbits as quantified by the anisotropy parameter, which we find to be β 0.8 6-0.83+0.12 at a location beyond the core radius. Taken at face value, this high radial anisotropy requires abandoning conventional models9 for Sculptor's mass distribution. Our sample is dominated by metal-rich stars and for these we find βM R 0.9 5-0.27+0.04—a value consistent with multi-component spherical models where Sculptor is embedded in a cuspy dark halo10, as might be expected for cold dark matter.
Constraining the Nature of Dark Matter with the Star-formation History of the Faintest Local Group Dwarf Galaxy Satellites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chau, Alice; Mayer, Lucio; Governato, Fabio

Λ warm dark matter (ΛWDM), realized by collisionless particles of 1–3 keV, has been proposed as an alternative scenario to Λ-Cold-Dark Matter (ΛCDM) for the dwarf galaxy scale discrepancies. We present an approach to test the viability of such WDM models using star-formation histories (SFHs) of the dwarf spheroidal galaxies (dSphs) in the Local Group. We compare their high-time-resolution SFHs with the collapse redshift of their dark halos in CDM and WDM. Collapse redshift is inferred after determining the subhalo infall mass. This is based on the dwarf current mass inferred from stellar kinematics, combined with cosmological simulation results onmore » subhalo evolution. WDM subhalos close to the filtering mass scale, forming significantly later than CDM, are the most difficult to reconcile with early truncation of star formation ( z ≥ 3). The ultra-faint dwarfs (UFDs) provide the most stringent constraints. Using six UFDs and eight classical dSphs, we show that a 1 keV particle is strongly disfavored, consistently with other reported methods. Excluding other models is only hinted for a few UFDs. Other UFDs for which the lack of robust constraints on halo mass prevents us from carrying out our analysis rigorously, show a very early onset of star formation that will strengthen the constraints delivered by our method in the future. We discuss the various caveats, notably the low number of dwarfs with accurately determined SFHs and the uncertainties when determining the subhalo infall mass, most notably the baryonic physics. Our preliminary analysis may serve as a pathfinder for future investigations that will combine accurate SFHs for local dwarfs with direct analysis of WDM simulations with baryons.« less
Superconducting Detectors for Superlight Dark Matter.

PubMed

Hochberg, Yonit; Zhao, Yue; Zurek, Kathryn M

2016-01-08

We propose and study a new class of superconducting detectors that are sensitive to O(meV) electron recoils from dark matter-electron scattering. Such devices could detect dark matter as light as the warm dark-matter limit, m(X)≳1 keV. We compute the rate of dark-matter scattering off of free electrons in a (superconducting) metal, including the relevant Pauli blocking factors. We demonstrate that classes of dark matter consistent with terrestrial and cosmological or astrophysical constraints could be detected by such detectors with a moderate size exposure.
Superconducting Detectors for Superlight Dark Matter

NASA Astrophysics Data System (ADS)

Hochberg, Yonit; Zhao, Yue; Zurek, Kathryn M.

2016-01-01

We propose and study a new class of superconducting detectors that are sensitive to O (meV ) electron recoils from dark matter-electron scattering. Such devices could detect dark matter as light as the warm dark-matter limit, mX≳1 keV . We compute the rate of dark-matter scattering off of free electrons in a (superconducting) metal, including the relevant Pauli blocking factors. We demonstrate that classes of dark matter consistent with terrestrial and cosmological or astrophysical constraints could be detected by such detectors with a moderate size exposure.
The Dark Energy Survey: more than dark energy – an overview

DOE PAGES

Abbott, T.

2016-03-21

This overview article describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters ( grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovaemore » and other transients. The main goals of DES are to characterise dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the solar system, the Milky Way, galaxy evolution, quasars, and other topics. In addition, we show that if the cosmological model is assumed to be Lambda+ Cold Dark Matter (LCDM) then important astrophysics can be deduced from the primary DES probes. Lastly, highlights from DES early data include the discovery of 34 Trans Neptunian Objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).« less
The Dark Energy Survey: More than dark energy - An overview

DOE PAGES

Abbott, T.

2016-03-21

This overview article describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters ( grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovaemore » and other transients. The main goals of DES are to characterise dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the solar system, the Milky Way, galaxy evolution, quasars, and other topics. In addition, we show that if the cosmological model is assumed to be Lambda+ Cold Dark Matter (LCDM) then important astrophysics can be deduced from the primary DES probes. Lastly, highlights from DES early data include the discovery of 34 Trans Neptunian Objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).« less
The Dark Energy Survey: more than dark energy – an overview

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vikram, Vinu; Abbott, T; Abdalla, F. B.

This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovaemore » and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from ‘Science Verification’, and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be Λ+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).« less
The Dark Energy Survey: more than dark energy – an overview

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbott, T.

This overview article describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters ( grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovaemore » and other transients. The main goals of DES are to characterise dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the solar system, the Milky Way, galaxy evolution, quasars, and other topics. In addition, we show that if the cosmological model is assumed to be Lambda+ Cold Dark Matter (LCDM) then important astrophysics can be deduced from the primary DES probes. Lastly, highlights from DES early data include the discovery of 34 Trans Neptunian Objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).« less
Dark matter as ultralight axion-like particle in E6 × U(1)X GUT with QCD axion

NASA Astrophysics Data System (ADS)

Corianò, Claudio; Frampton, Paul H.

2018-07-01

Axion-like fields are naturally generated by a mechanism of anomaly cancellation of one or more anomalous gauge abelian symmetries at the Planck scale, emerging as duals of a two-form from the massless bosonic sector of string theory. This suggests an analogy of the Green-Schwarz mechanism of anomaly cancellation, at field theory level, which results in one or more Stueckelberg pseudoscalars. In the case of a single Stueckelberg pseudoscalar b, vacuum misalignments at phase transitions in the early Universe at the GUT scale provide a small mass - due to instanton suppression of the periodic potential - for a component of b, denoted as χ and termed the "axi-Higgs", which is a physical axion-like particle. The coupling of the axi-Higgs to the gauge sector via Wess-Zumino terms is suppressed by the Planck mass, which guarantees its decoupling, while its angle of misalignment is related to MGUT. We build a gauged E6 × U (1) model with anomalous U (1). It contains both an automatic invisible QCD axion and an ultra-light axi-Higgs. The invisible axion present in the model solves the strong CP problem and has mass in the conventional range while the axi-Higgs, which can act as dark matter, is sufficiently light (10-22 eV
First test of Verlinde's theory of emergent gravity using weak gravitational lensing measurements

NASA Astrophysics Data System (ADS)

Brouwer, Margot M.; Visser, Manus R.; Dvornik, Andrej; Hoekstra, Henk; Kuijken, Konrad; Valentijn, Edwin A.; Bilicki, Maciej; Blake, Chris; Brough, Sarah; Buddelmeijer, Hugo; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Holwerda, Benne W.; Hopkins, Andrew M.; Klaes, Dominik; Liske, Jochen; Loveday, Jon; McFarland, John; Nakajima, Reiko; Sifón, Cristóbal; Taylor, Edward N.

2017-04-01

Verlinde proposed that the observed excess gravity in galaxies and clusters is the consequence of emergent gravity (EG). In this theory, the standard gravitational laws are modified on galactic and larger scales due to the displacement of dark energy by baryonic matter. EG gives an estimate of the excess gravity (described as an apparent dark matter density) in terms of the baryonic mass distribution and the Hubble parameter. In this work, we present the first test of EG using weak gravitational lensing, within the regime of validity of the current model. Although there is no direct description of lensing and cosmology in EG yet, we can make a reasonable estimate of the expected lensing signal of low-redshift galaxies by assuming a background Lambda cold dark matter cosmology. We measure the (apparent) average surface mass density profiles of 33 613 isolated central galaxies and compare them to those predicted by EG based on the galaxies' baryonic masses. To this end, we employ the ˜180 deg2 overlap of the Kilo-Degree Survey with the spectroscopic Galaxy And Mass Assembly survey. We find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed galaxy-galaxy lensing profiles in four different stellar mass bins. Although this performance is remarkable, this study is only a first step. Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.
Light sterile neutrinos, dark matter, and new resonances in a U(1) extension of the MSSM

NASA Astrophysics Data System (ADS)

Hebbar, A.; Lazarides, G.; Shafi, Q.

2017-09-01

We present ψ'MSSM, a model based on a U(1) ψ' extension of the minimal supersymmetric standard model. The gauge symmetry U(1)ψ', also known as U(1)N,is a linear combination of the U(1) χ and U(1)ψ subgroups of E6. The model predicts the existence of three sterile neutrinos with masses ≲0.1 eV , if the U(1)ψ' breaking scale is of order 10 TeV. Their contribution to the effective number of neutrinos at nucleosynthesis is Δ Nν≃0.29. The model can provide a variety of possible cold dark matter candidates including the lightest sterile sneutrino. If the U(1) ψ' breaking scale is increased to 1 03 TeV , the sterile neutrinos, which are stable on account of a Z2symmetry, become viable warm dark matter candidates. The observed value of the standard model Higgs boson mass can be obtained with relatively light stop quarks thanks to the D-term contribution from U(1)ψ'. The model predicts diquark and diphoton resonances which may be found at an updated LHC. The well-known μ problem is resolved and the observed baryon asymmetry of the universe can be generated via leptogenesis. The breaking of U(1)ψ' produces superconducting strings that may be present in our galaxy. A U(1) R symmetry plays a key role in keeping the proton stable and providing the light sterile neutrinos.
Alternative Gravity Rotation Curves for the LITTLE THINGS Survey

NASA Astrophysics Data System (ADS)

O’Brien, James G.; Chiarelli, Thomas L.; Dentico, Jeremy; Stulge, Modestas; Stefanski, Brian; Moss, Robert; Chaykov, Spasen

2018-01-01

Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral galaxies of all morphologies. Dwarf galaxies serve as an increasingly interesting case of rotation curve dynamics due to their typically rising rotation curve as opposed to the flattening curve of large spirals. Dwarf galaxies usually vary in galactic structure and mostly terminate at small radial distances. This, coupled with the fact that Cold Dark Matter theories struggle with the universality of galactic rotation curves, allow for exclusive features of alternative gravitational models to be analyzed. Recently, The H I Nearby Galactic Survey (THINGS) has been extended to include a sample of 25 dwarf galaxies now known as the LITTLE THINGS Survey. Here, we show an application of alternative gravitational models to the LITTLE THINGS survey, specifically focusing on conformal gravity (CG) and Modified Newtonian Dynamics (MOND). In this work, we provide an analysis and discussion of the rotation curve predictions of each theory to the sample. Furthermore, we show how these two alternative gravitational models account for the recently observed universal trends in centripetal accelerations in spiral galaxies. This work highlights the similarities and differences of the predictions of the two theories in dwarf galaxies. The sample is not large or diverse enough to strongly favor a single theory, but we posit that both CG and MOND can provide an accurate description of the galactic dynamics in the LITTLE THINGS sample without the need for dark matter.
Galaxy spin as a formation probe: the stellar-to-halo specific angular momentum relation

NASA Astrophysics Data System (ADS)

Posti, Lorenzo; Pezzulli, Gabriele; Fraternali, Filippo; Di Teodoro, Enrico M.

2018-03-01

We derive the stellar-to-halo specific angular momentum relation (SHSAMR) of galaxies at z = 0 by combining (i) the standard Λcold dark matter tidal torque theory, (ii) the observed relation between stellar mass and specific angular momentum (the Fall relation), and (iii) various determinations of the stellar-to-halo mass relation (SHMR). We find that the ratio fj = j*/jh of the specific angular momentum of stars to that of the dark matter (i) varies with mass as a double power law, (ii) always has a peak in the mass range explored and iii) is three to five times larger for spirals than for ellipticals. The results have some dependence on the adopted SHMR and we provide fitting formulae in each case. For any choice of the SHMR, the peak of fj occurs at the same mass where the stellar-to-halo mass ratio f* = M*/Mh has a maximum. This is mostly driven by the straightness and tightness of the Fall relation, which requires fj and f* to be correlated with each other roughly as f_j∝ f_\\ast ^{2/3}, as expected if the outer and more angular momentum rich parts of a halo failed to accrete on to the central galaxy and form stars (biased collapse). We also confirm that the difference in the angular momentum of spirals and ellipticals at a given mass is too large to be ascribed only to different spins of the parent dark-matter haloes (spin bias).
Holographic vortices in the presence of dark matter sector

NASA Astrophysics Data System (ADS)

Rogatko, Marek; Wysokinski, Karol I.

2015-12-01

The dark matter seem to be an inevitable ingredient of the total matter configuration in the Universe and the knowledge how the dark matter affects the properties of superconductors is of vital importance for the experiments aimed at its direct detection. The homogeneous magnetic field acting perpendicularly to the surface of (2+1) dimensional s-wave holographic superconductor in the theory with dark matter sector has been modeled by the additional U(1)-gauge field representing dark matter and coupled to the Maxwell one. As expected the free energy for the vortex configuration turns out to be negative. Importantly its value is lower in the presence of dark matter sector. This feature can explain why in the Early Universe first the web of dark matter appeared and next on these gratings the ordinary matter forming cluster of galaxies has formed.
Dissipative dark matter halos: The steady state solution

NASA Astrophysics Data System (ADS)

Foot, R.

2018-02-01

Dissipative dark matter, where dark matter particle properties closely resemble familiar baryonic matter, is considered. Mirror dark matter, which arises from an isomorphic hidden sector, is a specific and theoretically constrained scenario. Other possibilities include models with more generic hidden sectors that contain massless dark photons [unbroken U (1 ) gauge interactions]. Such dark matter not only features dissipative cooling processes but also is assumed to have nontrivial heating sourced by ordinary supernovae (facilitated by the kinetic mixing interaction). The dynamics of dissipative dark matter halos around rotationally supported galaxies, influenced by heating as well as cooling processes, can be modeled by fluid equations. For a sufficiently isolated galaxy with a stable star formation rate, the dissipative dark matter halos are expected to evolve to a steady state configuration which is in hydrostatic equilibrium and where heating and cooling rates locally balance. Here, we take into account the major cooling and heating processes, and numerically solve for the steady state solution under the assumptions of spherical symmetry, negligible dark magnetic fields, and that supernova sourced energy is transported to the halo via dark radiation. For the parameters considered, and assumptions made, we were unable to find a physically realistic solution for the constrained case of mirror dark matter halos. Halo cooling generally exceeds heating at realistic halo mass densities. This problem can be rectified in more generic dissipative dark matter models, and we discuss a specific example in some detail.
The segregation of baryons and dark matter during halo assembly

NASA Astrophysics Data System (ADS)

Liao, Shihong; Gao, Liang; Frenk, Carlos S.; Guo, Qi; Wang, Jie

2017-09-01

The standard galaxy formation theory assumes that baryons and dark matter are initially well mixed before becoming segregated due to radiative cooling. We use non-radiative hydrodynamical simulations to explicitly examine this assumption and find that baryons and dark matter can also be segregated due to different characteristics of gas and dark matter during the buildup of the halo. As a result, baryons in many haloes do not originate from the same Lagrangian region as the dark matter. When using the fraction of corresponding dark matter and gas particles in the initial conditions (the 'paired fraction') as a proxy of the dark matter and gas segregation strength of a halo, on average about 25 per cent of the baryonic and dark matter of the final halo are segregated in the initial conditions. This is at odds with the assumption of the standard galaxy formation model. A consequence of this effect is that the baryons and dark matter of the same halo initially experience different tidal torques and thus their angular momentum vectors are often misaligned. The degree of the misalignment is largely preserved during later halo assembly and can be understood with the tidal torque theory. The result challenges the precision of some semi-analytical approaches that utilize dark matter halo merger trees to infer properties of gas associated with dark matter haloes.
Hypercharged dark matter and direct detection as a probe of reheating.

PubMed

Feldstein, Brian; Ibe, Masahiro; Yanagida, Tsutomu T

2014-03-14

The lack of new physics at the LHC so far weakens the argument for TeV scale thermal dark matter. On the other hand, heavier, nonthermal dark matter is generally difficult to test experimentally. Here we consider the interesting and generic case of hypercharged dark matter, which can allow for heavy dark matter masses without spoiling testability. Planned direct detection experiments will be able to see a signal for masses up to an incredible 1010 GeV, and this can further serve to probe the reheating temperature up to about 109 GeV, as determined by the nonthermal dark matter relic abundance. The Z-mediated nature of the dark matter scattering may be determined in principle by comparing scattering rates on different detector nuclei, which in turn can reveal the dark matter mass. We will discuss the extent to which future experiments may be able to make such a determination.
THE DETECTION OF ULTRA-FAINT LOW SURFACE BRIGHTNESS DWARF GALAXIES IN THE VIRGO CLUSTER: A PROBE OF DARK MATTER AND BARYONIC PHYSICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giallongo, E.; Menci, N.; Grazian, A.

2015-11-01

We have discovered 11 ultra-faint (r ≲ 22.1) low surface brightness (LSB, central surface brightness 23 ≲ μ{sub r} ≲ 26) dwarf galaxy candidates in one deep Virgo field of just 576 arcmin{sup 2} obtained by the Large Binocular Camera at the Large Binocular Telescope. Their association with the Virgo cluster is supported by their distinct position in the central surface brightness—total magnitude plane with respect to the background galaxies of similar total magnitude. They have typical absolute magnitudes and scale sizes, if at the distance of Virgo, in the range −13 ≲ M{sub r} ≲ −9 and 250 ≲more » r{sub s} ≲ 850 pc, respectively. Their colors are consistent with a gradually declining star formation history with a specific star formation rate of the order of 10{sup −11} yr{sup −1}, i.e., 10 times lower than that of main sequence star-forming galaxies. They are older than the cluster formation age and appear to be regular in morphology. They represent the faintest extremes of the population of low luminosity LSB dwarfs that has recently been detected in wider surveys of the Virgo cluster. Thanks to the depth of our observations, we are able to extend the Virgo luminosity function down to M{sub r} ∼ −9.3 (corresponding to total masses M ∼ 10{sup 7} M{sub ⊙}), finding an average faint-end slope α ≃ −1.4. This relatively steep slope puts interesting constraints on the nature of the dark matter and, in particular, on warm dark matter (WDM) often invoked to solve the overprediction of the dwarf number density by the standard cold dark matter scenario. We derive a lower limit on the WDM particle mass >1.5 keV.« less
fire in the field: simulating the threshold of galaxy formation

NASA Astrophysics Data System (ADS)

Fitts, Alex; Boylan-Kolchin, Michael; Elbert, Oliver D.; Bullock, James S.; Hopkins, Philip F.; Oñorbe, Jose; Wetzel, Andrew; Wheeler, Coral; Faucher-Giguère, Claude-André; Kereš, Dušan; Skillman, Evan D.; Weisz, Daniel R.

2017-11-01

We present a suite of 15 cosmological zoom-in simulations of isolated dark matter haloes, all with masses of Mhalo ≈ 1010 M⊙ at z = 0, in order to understand the relationship among halo assembly, galaxy formation and feedback's effects on the central density structure in dwarf galaxies. These simulations are part of the Feedback in Realistic Environments (fire) project and are performed at extremely high resolution (mbaryon = 500 M⊙, mdm = 2500 M⊙). The resultant galaxies have stellar masses that are consistent with rough abundance matching estimates, coinciding with the faintest galaxies that can be seen beyond the virial radius of the Milky Way (M*/M⊙ ≈ 105 - 107). This non-negligible spread in stellar mass at z = 0 in haloes within a narrow range of virial masses is strongly correlated with central halo density or maximum circular velocity Vmax, both of which are tightly linked to halo formation time. Much of this dependence of M* on a second parameter (beyond Mhalo) is a direct consequence of the Mhalo ˜ 1010 M⊙ mass scale coinciding with the threshold for strong reionization suppression: the densest, earliest-forming haloes remain above the UV-suppression scale throughout their histories while late-forming systems fall below the UV-suppression scale over longer periods and form fewer stars as a result. In fact, the latest-forming, lowest-concentration halo in our suite fails to form any stars. Haloes that form galaxies with M⋆ ≳ 2 × 106 M⊙ have reduced central densities relative to dark-matter-only simulations, and the radial extent of the density modifications is well-approximated by the galaxy half-mass radius r1/2. Lower-mass galaxies do not modify their host dark matter haloes at the mass scale studied here. This apparent stellar mass threshold of M⋆ ≈ 2 × 106 - 2 × 10- 4 Mhalo is broadly consistent with previous work and provides a testable prediction of fire feedback models in Λcold dark matter.
Identifying Anomalies in Gravitational Lens Time Delays

NASA Astrophysics Data System (ADS)

Congdon, Arthur B.; Keeton, C. R.; Nordgren, C. E.

2009-05-01

Gravitational lensing has become a powerful probe of cold dark matter substructure. Earlier work using anomalous flux ratios in four-image quasar lenses has shown that lensing is sensitive to substructure which raises the exciting prospect of constraining the mass function and spatial distribution of dark matter satellites in galaxies. We examine the ability of gravitational lens time delays to reveal complex structure in lens potentials. We use Monte Carlo simulations to determine the range of time delays that can be produced by realistic smooth lens models consisting of isothermal ellipsoid galaxies with tidal shear. We can then identify outliers as "time-delay anomalies." We find evidence for anomalies in close image pairs in the cusp lenses RX J1131-1231 and B1422+231. The anomalies in RX J1131-1231 provide strong evidence for substructure in the lens potential, while at this point the apparent anomalies in B1422+231 mainly indicate that the time delay measurements need to be improved. We also find evidence for time-delay anomalies in larger-separation image pairs in four additional lenses. We suggest that these anomalies are caused by some combination of substructure and a complex lens environment. Our work argues for a large sample of strong lenses with precisely-measured time delays. The first of these objectives will be readily achievable as the next generation of optical and radio telescopes come online, while the second will require a dedicated one-meter class space-based observatory. Meeting these goals will make it possible to examine the properties of dark matter on sub-galactic scales, which is essential for distinguishing among the various dark matter candidates from particle physics. Part of this work was funded by NSF grant AST-0747311. ABC is currently supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA.

Likelihood analysis of the sub-GUT MSSM in light of LHC 13-TeV data

NASA Astrophysics Data System (ADS)

Costa, J. C.; Bagnaschi, E.; Sakurai, K.; Borsato, M.; Buchmueller, O.; Citron, M.; De Roeck, A.; Dolan, M. J.; Ellis, J. R.; Flächer, H.; Heinemeyer, S.; Lucio, M.; Santos, D. Martínez; Olive, K. A.; Richards, A.; Weiglein, G.

2018-02-01

We describe a likelihood analysis using MasterCode of variants of the MSSM in which the soft supersymmetry-breaking parameters are assumed to have universal values at some scale M_in below the supersymmetric grand unification scale M_GUT, as can occur in mirage mediation and other models. In addition to M_in, such `sub-GUT' models have the 4 parameters of the CMSSM, namely a common gaugino mass m_{1/2}, a common soft supersymmetry-breaking scalar mass m_0, a common trilinear mixing parameter A and the ratio of MSSM Higgs vevs tan β , assuming that the Higgs mixing parameter μ > 0. We take into account constraints on strongly- and electroweakly-interacting sparticles from ˜ 36/fb of LHC data at 13 TeV and the LUX and 2017 PICO, XENON1T and PandaX-II searches for dark matter scattering, in addition to the previous LHC and dark matter constraints as well as full sets of flavour and electroweak constraints. We find a preference for M_in˜ 10^5 to 10^9 GeV, with M_in˜ M_GUT disfavoured by Δ χ ^2 ˜ 3 due to the BR(B_{s, d} → μ ^+μ ^-) constraint. The lower limits on strongly-interacting sparticles are largely determined by LHC searches, and similar to those in the CMSSM. We find a preference for the LSP to be a Bino or Higgsino with m_{\\tilde{χ }^01} ˜ 1 TeV, with annihilation via heavy Higgs bosons H / A and stop coannihilation, or chargino coannihilation, bringing the cold dark matter density into the cosmological range. We find that spin-independent dark matter scattering is likely to be within reach of the planned LUX-Zeplin and XENONnT experiments. We probe the impact of the (g-2)_μ constraint, finding similar results whether or not it is included.
Flooded Dark Matter and S level rise

NASA Astrophysics Data System (ADS)

Randall, Lisa; Scholtz, Jakub; Unwin, James

2016-03-01

Most dark matter models set the dark matter relic density by some interaction with Standard Model particles. Such models generally assume the existence of Standard Model particles early on, with the dark matter relic density a later consequence of those interactions. Perhaps a more compelling assumption is that dark matter is not part of the Standard Model sector and a population of dark matter too is generated at the end of inflation. This democratic assumption about initial conditions does not necessarily provide a natural value for the dark matter relic density, and furthermore superficially leads to too much entropy in the dark sector relative to ordinary matter. We address the latter issue by the late decay of heavy particles produced at early times, thereby associating the dark matter relic density with the lifetime of a long-lived state. This paper investigates what it would take for this scenario to be compatible with observations in what we call Flooded Dark Matter (FDM) models and discusses several interesting consequences. One is that dark matter can be very light and furthermore, light dark matter is in some sense the most natural scenario in FDM as it is compatible with larger couplings of the decaying particle. A related consequence is that the decay of the field with the smallest coupling and hence the longest lifetime dominates the entropy and possibly the matter content of the Universe, a principle we refer to as "Maximum Baroqueness". We also demonstrate that the dark sector should be colder than the ordinary sector, relaxing the most stringent free-streaming constraints on light dark matter candidates. We will discuss the potential implications for the core-cusp problem in a follow-up paper. The FDM framework will furthermore have interesting baryogenesis implications. One possibility is that dark matter is like the baryon asymmetry and both are simultaneously diluted by a late entropy dump. Alternatively, FDM is compatible with an elegant non-thermal leptogenesis implementation in which decays of a heavy right-handed neutrino lead to late time reheating of the Standard Model degrees of freedom and provide suitable conditions for creation of a lepton asymmetry.
Correlation Analysis between Spin, Velocity Shear, and Vorticity of Baryonic and Dark Matter Halos

NASA Astrophysics Data System (ADS)

Liu, Li-li

2017-04-01

Based on the cosmological hydrodynamic simulations, we investigate the correlations between the spin, velocity shear and vorticity in dark matter halos, as well as the relationship between the baryonic matter and the dark matter. We find that (1) the difference between the vorticity of baryonic matter and that of dark matter is evident on the scales of < 0.2 h-1 Mpc; (2) the vorticity of baryonic matter exhibits a stronger correlation with the tensor of velocity shear than the vorticity of dark matter does; and (3) the spinning direction of small-mass dark matter halos tends to be parallel to the direction of their host filaments, while the spinning direction of massive dark matter halos tends to be perpendicular to the direction of their host filaments, and the intensity of this kind correlation depends on the size of simulation box, and the simulation accuracy. These factors may cause the relationship between the the spins of dark matter halos and those of galaxies to be complicated, and affect the correlation between the galaxy spins and the nearby large-scale structures.
Concentrated dark matter: Enhanced small-scale structure from codecaying dark matter

NASA Astrophysics Data System (ADS)

Dror, Jeff A.; Kuflik, Eric; Melcher, Brandon; Watson, Scott

2018-03-01

We study the cosmological consequences of codecaying dark matter—a recently proposed mechanism for depleting the density of dark matter through the decay of nearly degenerate particles. A generic prediction of this framework is an early dark matter dominated phase in the history of the Universe, that results in the enhanced growth of dark matter perturbations on small scales. We compute the duration of the early matter dominated phase and show that the perturbations are robust against washout from free streaming. The enhanced small-scale structure is expected to survive today in the form of compact microhalos and can lead to significant boost factors for indirect-detection experiments, such as FERMI, where dark matter would appear as point sources.
Probes for dark matter physics

NASA Astrophysics Data System (ADS)

Khlopov, Maxim Yu.

The existence of cosmological dark matter is in the bedrock of the modern cosmology. The dark matter is assumed to be nonbaryonic and consists of new stable particles. Weakly Interacting Massive Particle (WIMP) miracle appeals to search for neutral stable weakly interacting particles in underground experiments by their nuclear recoil and at colliders by missing energy and momentum, which they carry out. However, the lack of WIMP effects in their direct underground searches and at colliders can appeal to other forms of dark matter candidates. These candidates may be weakly interacting slim particles, superweakly interacting particles, or composite dark matter, in which new particles are bound. Their existence should lead to cosmological effects that can find probes in the astrophysical data. However, if composite dark matter contains stable electrically charged leptons and quarks bound by ordinary Coulomb interaction in elusive dark atoms, these charged constituents of dark atoms can be the subject of direct experimental test at the colliders. The models, predicting stable particles with charge ‑ 2 without stable particles with charges + 1 and ‑ 1 can avoid severe constraints on anomalous isotopes of light elements and provide solution for the puzzles of dark matter searches. In such models, the excessive ‑ 2 charged particles are bound with primordial helium in O-helium atoms, maintaining specific nuclear-interacting form of the dark matter. The successful development of composite dark matter scenarios appeals for experimental search for doubly charged constituents of dark atoms, making experimental search for exotic stable double charged particles experimentum crucis for dark atoms of composite dark matter.
Warm dark matter effects in a spherical collapse model with shear and angular momentum

NASA Astrophysics Data System (ADS)

Marciu, Mihai

2016-03-01

This paper investigates the nonlinear structure formation in a spherical top-hat collapse model based on the pseudo-Newtonian approximation. The system is composed of warm dark matter and dark energy and the dynamical properties of the collapsing region are analyzed for various parametrizations of the dark matter equation of state which are in agreement with current observations. Concerning dark energy, observational constraints of the Chevallier-Polarski-Linder model and the Jassal-Bagla-Padmanabhan equation of state have been considered. During the collapse, the positive dark matter pressure leads to an increase of growth for dark matter and dark energy perturbations and an accelerated expansion for the spherical region. Hence, in the warm dark matter hypothesis, the structure formation is accelerated and the inconsistencies of the Λ CDM model at the galactic scales could be solved. The results obtained are applicable only to adiabatic warm dark matter physical models which are compatible with the pseudo-Newtonian approach.
The effects of baryon physics, black holes and active galactic nucleus feedback on the mass distribution in clusters of galaxies

NASA Astrophysics Data System (ADS)

Martizzi, Davide; Teyssier, Romain; Moore, Ben; Wentz, Tina

2012-06-01

The spatial distribution of matter in clusters of galaxies is mainly determined by the dominant dark matter component; however, physical processes involving baryonic matter are able to modify it significantly. We analyse a set of 500 pc resolution cosmological simulations of a cluster of galaxies with mass comparable to Virgo, performed with the AMR code RAMSES. We compare the mass density profiles of the dark, stellar and gaseous matter components of the cluster that result from different assumptions for the subgrid baryonic physics and galaxy formation processes. First, the prediction of a gravity-only N-body simulation is compared to that of a hydrodynamical simulation with standard galaxy formation recipes, and then all results are compared to a hydrodynamical simulation which includes thermal active galactic nucleus (AGN) feedback from supermassive black holes (SMBHs). We find the usual effects of overcooling and adiabatic contraction in the run with standard galaxy formation physics, but very different results are found when implementing SMBHs and AGN feedback. Star formation is strongly quenched, producing lower stellar densities throughout the cluster, and much less cold gas is available for star formation at low redshifts. At redshift z= 0 we find a flat density core of radius 10 kpc in both the dark and stellar matter density profiles. We speculate on the possible formation mechanisms able to produce such cores and we conclude that they can be produced through the coupling of different processes: (I) dynamical friction from the decay of black hole orbits during galaxy mergers; (II) AGN-driven gas outflows producing fluctuations of the gravitational potential causing the removal of collisionless matter from the central region of the cluster; (III) adiabatic expansion in response to the slow expulsion of gas from the central region of the cluster during the quiescent mode of AGN activity.
Photon and graviton mass limits

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldhaber, Alfred Scharff; Nieto, Michael Martin; Theoretical Division

2010-01-15

Efforts to place limits on deviations from canonical formulations of electromagnetism and gravity have probed length scales increasing dramatically over time. Historically, these studies have passed through three stages: (1) testing the power in the inverse-square laws of Newton and Coulomb, (2) seeking a nonzero value for the rest mass of photon or graviton, and (3) considering more degrees of freedom, allowing mass while preserving explicit gauge or general-coordinate invariance. Since the previous review the lower limit on the photon Compton wavelength has improved by four orders of magnitude, to about one astronomical unit, and rapid current progress in astronomymore » makes further advance likely. For gravity there have been vigorous debates about even the concept of graviton rest mass. Meanwhile there are striking observations of astronomical motions that do not fit Einstein gravity with visible sources. ''Cold dark matter'' (slow, invisible classical particles) fits well at large scales. ''Modified Newtonian dynamics'' provides the best phenomenology at galactic scales. Satisfying this phenomenology is a requirement if dark matter, perhaps as invisible classical fields, could be correct here too. ''Dark energy''might be explained by a graviton-mass-like effect, with associated Compton wavelength comparable to the radius of the visible universe. Significant mass limits are summarized in a table.« less
Natural implementation of neutralino dark matter

NASA Astrophysics Data System (ADS)

King, Steve F.; Roberts, Jonathan P.

2006-09-01

The prediction of neutralino dark matter is generally regarded as one of the successes of the Minimal Supersymmetric Standard Model (MSSM). However the successful regions of parameter space allowed by WMAP and collider constraints are quite restricted. We discuss fine-tuning with respect to both dark matter and Electroweak Symmetry Breaking (EWSB) and explore regions of MSSM parameter space with non-universal gaugino and third family scalar masses in which neutralino dark matter may be implemented naturally. In particular allowing non-universal gauginos opens up the bulk region that allows Bino annihilation via t-channel slepton exchange, leading to ``supernatural dark matter'' corresponding to no fine-tuning at all with respect to dark matter. By contrast we find that the recently proposed ``well tempered neutralino'' regions involve substantial fine-tuning of MSSM parameters in order to satisfy the dark matter constraints, although the fine tuning may be ameliorated if several annihilation channels act simultaneously. Although we have identified regions of ``supernatural dark matter'' in which there is no fine tuning to achieve successful dark matter, the usual MSSM fine tuning to achieve EWSB always remains.
Dark Matter Decays from Nonminimal Coupling to Gravity.

PubMed

Catà, Oscar; Ibarra, Alejandro; Ingenhütt, Sebastian

2016-07-08

We consider the standard model extended with a dark matter particle in curved spacetime, motivated by the fact that the only current evidence for dark matter is through its gravitational interactions, and we investigate the impact on the dark matter stability of terms in the Lagrangian linear in the dark matter field and proportional to the Ricci scalar. We show that this "gravity portal" induces decay even if the dark matter particle only has gravitational interactions, and that the decay branching ratios into standard model particles only depend on one free parameter: the dark matter mass. We study in detail the case of a singlet scalar as a dark matter candidate, which is assumed to be absolutely stable in flat spacetime due to a discrete Z_{2} symmetry, but which may decay in curved spacetimes due to a Z_{2}-breaking nonminimal coupling to gravity. We calculate the dark matter decay widths and we set conservative limits on the nonminimal coupling parameter from experiments. The limits are very stringent and suggest that there must exist an additional mechanism protecting the singlet scalar from decaying via this gravity portal.
Cores in Dwarf Galaxies from Fermi Repulsion

NASA Astrophysics Data System (ADS)

Randall, Lisa; Scholtz, Jakub; Unwin, James

2017-05-01

We show that Fermi repulsion can lead to cored density profiles in dwarf galaxies for sub-keV fermionic dark matter. We treat the dark matter as a quasi-degenerate self-gravitating Fermi gas and calculate its density profile assuming hydrostatic equilibrium. We find that suitable dwarf galaxy cores of size ≳130 pc can be achieved for fermion dark matter with mass in the range of 70-400 eV. While in conventional dark matter scenarios such sub-keV thermal dark matter would be excluded by free streaming bounds, the constraints are ameliorated in models with dark matter at a lower temperature than conventional thermal scenarios, such as the Flooded Dark Matter model that we have previously considered. Modifying the arguments of Tremaine and Gunn, we derive a conservative lower bound on the mass of fermionic dark matter of 70 eV and a stronger lower bound from Lymanα clouds of about 470 eV, leading to slightly smaller cores than have been observed. We comment on this result and how the tension is relaxed in dark matter scenarios with non-thermal momentum distributions.
Cosmic CARNage I: on the calibration of galaxy formation models

NASA Astrophysics Data System (ADS)

Knebe, Alexander; Pearce, Frazer R.; Gonzalez-Perez, Violeta; Thomas, Peter A.; Benson, Andrew; Asquith, Rachel; Blaizot, Jeremy; Bower, Richard; Carretero, Jorge; Castander, Francisco J.; Cattaneo, Andrea; Cora, Sofía A.; Croton, Darren J.; Cui, Weiguang; Cunnama, Daniel; Devriendt, Julien E.; Elahi, Pascal J.; Font, Andreea; Fontanot, Fabio; Gargiulo, Ignacio D.; Helly, John; Henriques, Bruno; Lee, Jaehyun; Mamon, Gary A.; Onions, Julian; Padilla, Nelson D.; Power, Chris; Pujol, Arnau; Ruiz, Andrés N.; Srisawat, Chaichalit; Stevens, Adam R. H.; Tollet, Edouard; Vega-Martínez, Cristian A.; Yi, Sukyoung K.

2018-04-01

We present a comparison of nine galaxy formation models, eight semi-analytical, and one halo occupation distribution model, run on the same underlying cold dark matter simulation (cosmological box of comoving width 125h-1 Mpc, with a dark-matter particle mass of 1.24 × 109h-1M⊙) and the same merger trees. While their free parameters have been calibrated to the same observational data sets using two approaches, they nevertheless retain some `memory' of any previous calibration that served as the starting point (especially for the manually tuned models). For the first calibration, models reproduce the observed z = 0 galaxy stellar mass function (SMF) within 3σ. The second calibration extended the observational data to include the z = 2 SMF alongside the z ˜ 0 star formation rate function, cold gas mass, and the black hole-bulge mass relation. Encapsulating the observed evolution of the SMF from z = 2 to 0 is found to be very hard within the context of the physics currently included in the models. We finally use our calibrated models to study the evolution of the stellar-to-halo mass (SHM) ratio. For all models, we find that the peak value of the SHM relation decreases with redshift. However, the trends seen for the evolution of the peak position as well as the mean scatter in the SHM relation are rather weak and strongly model dependent. Both the calibration data sets and model results are publicly available.
Dynamical dark matter: A new framework for dark-matter physics

NASA Astrophysics Data System (ADS)

Dienes, Keith R.; Thomas, Brooks

2013-05-01

Although much remains unknown about the dark matter of the universe, one property is normally considered sacrosanct: dark matter must be stable well beyond cosmological time scales. However, a new framework for dark-matter physics has recently been proposed which challenges this assumption. In the "dynamical dark matter" (DDM) framework, the dark sector consists of a vast ensemble of individual dark-matter components with differing masses, lifetimes, and cosmological abundances. Moreover, the usual requirement of stability is replaced by a delicate balancing between lifetimes and cosmological abundances across the ensemble as a whole. As a result, it is possible for the DDM ensemble to remain consistent with all experimental and observational bounds on dark matter while nevertheless giving rise to collective behaviors which transcend those normally associated with traditional dark-matter candidates. These include a new, non-trivial darkmatter equation of state as well as potentially distinctive signatures in collider and direct-detection experiments. In this review article, we provide a self-contained introduction to the DDM framework and summarize some of the work which has recently been done in this area. We also present an explicit model within the DDM framework, and outline a number of ideas for future investigation.
Comprehensive asymmetric dark matter model

NASA Astrophysics Data System (ADS)

Lonsdale, Stephen J.; Volkas, Raymond R.

2018-05-01

Asymmetric dark matter (ADM) is motivated by the similar cosmological mass densities measured for ordinary and dark matter. We present a comprehensive theory for ADM that addresses the mass density similarity, going beyond the usual ADM explanations of similar number densities. It features an explicit matter-antimatter asymmetry generation mechanism, has one fully worked out thermal history and suggestions for other possibilities, and meets all phenomenological, cosmological and astrophysical constraints. Importantly, it incorporates a deep reason for why the dark matter mass scale is related to the proton mass, a key consideration in ADM models. Our starting point is the idea of mirror matter, which offers an explanation for dark matter by duplicating the standard model with a dark sector related by a Z2 parity symmetry. However, the dark sector need not manifest as a symmetric copy of the standard model in the present day. By utilizing the mechanism of "asymmetric symmetry breaking" with two Higgs doublets in each sector, we develop a model of ADM where the mirror symmetry is spontaneously broken, leading to an electroweak scale in the dark sector that is significantly larger than that of the visible sector. The weak sensitivity of the ordinary and dark QCD confinement scales to their respective electroweak scales leads to the necessary connection between the dark matter and proton masses. The dark matter is composed of either dark neutrons or a mixture of dark neutrons and metastable dark hydrogen atoms. Lepton asymmetries are generated by the C P -violating decays of heavy Majorana neutrinos in both sectors. These are then converted by sphaleron processes to produce the observed ratio of visible to dark matter in the universe. The dynamics responsible for the kinetic decoupling of the two sectors emerges as an important issue that we only partially solve.
Large Synoptic Survey Telescope: From Science Drivers to Reference Design

DTIC Science & Technology

2008-01-01

faint time domain. The LSST design is driven by four main science themes: constraining dark energy and dark matter , taking an inventory of the Solar...Energy and Dark Matter (2) Taking an Inventory of the Solar System (3) Exploring the Transient Optical Sky (4) Mapping the Milky Way Each of these four...Constraining Dark Energy and Dark Matter Current models of cosmology require the exis- tence of both dark matter and dark energy to match observational
Detection of sub-MeV dark matter with three-dimensional Dirac materials

NASA Astrophysics Data System (ADS)

Hochberg, Yonit; Kahn, Yonatan; Lisanti, Mariangela; Zurek, Kathryn M.; Grushin, Adolfo G.; Ilan, Roni; Griffin, Sinéad M.; Liu, Zhen-Fei; Weber, Sophie F.; Neaton, Jeffrey B.

2018-01-01

We propose the use of three-dimensional Dirac materials as targets for direct detection of sub-MeV dark matter. Dirac materials are characterized by a linear dispersion for low-energy electronic excitations, with a small band gap of O (meV ) if lattice symmetries are broken. Dark matter at the keV scale carrying kinetic energy as small as a few meV can scatter and excite an electron across the gap. Alternatively, bosonic dark matter as light as a few meV can be absorbed by the electrons in the target. We develop the formalism for dark matter scattering and absorption in Dirac materials and calculate the experimental reach of these target materials. We find that Dirac materials can play a crucial role in detecting dark matter in the keV to MeV mass range that scatters with electrons via a kinetically mixed dark photon, as the dark photon does not develop an in-medium effective mass. The same target materials provide excellent sensitivity to absorption of light bosonic dark matter in the meV to hundreds of meV mass range, superior to all other existing proposals when the dark matter is a kinetically mixed dark photon.
Dark-matter particles without weak-scale masses or weak interactions.

PubMed

Feng, Jonathan L; Kumar, Jason

2008-12-05

We propose that dark matter is composed of particles that naturally have the correct thermal relic density, but have neither weak-scale masses nor weak interactions. These models emerge naturally from gauge-mediated supersymmetry breaking, where they elegantly solve the dark-matter problem. The framework accommodates single or multiple component dark matter, dark-matter masses from 10 MeV to 10 TeV, and interaction strengths from gravitational to strong. These candidates enhance many direct and indirect signals relative to weakly interacting massive particles and have qualitatively new implications for dark-matter searches and cosmological implications for colliders.
General calculation of the cross section for dark matter annihilations into two photons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garcia-Cely, Camilo; Rivera, Andres, E-mail: Camilo.Alfredo.Garcia.Cely@ulb.ac.be, E-mail: afelipe.rivera@udea.edu.co

2017-03-01

Assuming that the underlying model satisfies some general requirements such as renormalizability and CP conservation, we calculate the non-relativistic one-loop cross section for any self-conjugate dark matter particle annihilating into two photons. We accomplish this by carefully classifying all possible one-loop diagrams and, from them, reading off the dark matter interactions with the particles running in the loop. Our approach is general and leads to the same results found in the literature for popular dark matter candidates such as the neutralinos of the MSSM, minimal dark matter, inert Higgs and Kaluza-Klein dark matter.
Detecting superlight dark matter with Fermi-degenerate materials

DOE PAGES

Hochberg, Yonit; Pyle, Matt; Zhao, Yue; ...

2016-08-08

We examine in greater detail the recent proposal of using superconductors for detecting dark matter as light as the warm dark matter limit of O(keV). Detection of suc light dark matter is possible if the entire kinetic energy of the dark matter is extracted in the scattering, and if the experiment is sensitive to O(meV) energy depositions. This is the case for Fermi-degenerate materials in which the Fermi velocity exceeds the dark matter velocity dispersion in the Milky Way of ~10 –3. We focus on a concrete experimental proposal using a superconducting target with a transition edge sensor in ordermore » to detect the small energy deposits from the dark matter scatterings. Considering a wide variety of constraints, from dark matter self-interactions to the cosmic microwave background, we show that models consistent with cosmological/astrophysical and terrestrial constraints are observable with such detectors. A wider range of viable models with dark matter mass below an MeV is available if dark matter or mediator properties (such as couplings or masses) differ at BBN epoch or in stellar interiors from those in superconductors. We also show that metal targets pay a strong in-medium suppression for kinetically mixed mediators; this suppression is alleviated with insulating targets.« less
Dark Kinetic Heating of Neutron Stars and an Infrared Window on WIMPs, SIMPs, and Pure Higgsinos

NASA Astrophysics Data System (ADS)

Baryakhtar, Masha; Bramante, Joseph; Li, Shirley Weishi; Linden, Tim; Raj, Nirmal

2017-09-01

We identify a largely model-independent signature of dark matter (DM) interactions with nucleons and electrons. DM in the local galactic halo, gravitationally accelerated to over half the speed of light, scatters against and deposits kinetic energy into neutron stars, heating them to infrared blackbody temperatures. The resulting radiation could potentially be detected by the James Webb Space Telescope, the Thirty Meter Telescope, or the European Extremely Large Telescope. This mechanism also produces optical emission from neutron stars in the galactic bulge, and x-ray emission near the galactic center because dark matter is denser in these regions. For GeV-PeV mass dark matter, dark kinetic heating would initially unmask any spin-independent or spin-dependent dark matter-nucleon cross sections exceeding 2 ×10-45 cm2, with improved sensitivity after more telescope exposure. For lighter-than-GeV dark matter, cross-section sensitivity scales inversely with dark matter mass because of Pauli blocking; for heavier-than-PeV dark matter, it scales linearly with mass as a result of needing multiple scatters for capture. Future observations of dark sector-warmed neutron stars could determine whether dark matter annihilates in or only kinetically heats neutron stars. Because inelastic interstate transitions of up to a few GeV would occur in relativistic scattering against nucleons, elusive inelastic dark matter like pure Higgsinos can also be discovered.

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