Measuring the speed of dark: Detecting dark energy perturbations
Putter, Roland de; Huterer, Dragan; Linder, Eric V.
2010-05-15
The nature of dark energy can be probed not only through its equation of state but also through its microphysics, characterized by the sound speed of perturbations to the dark energy density and pressure. As the sound speed drops below the speed of light, dark energy inhomogeneities increase, affecting both cosmic microwave background and matter power spectra. We show that current data can put no significant constraints on the value of the sound speed when dark energy is purely a recent phenomenon, but can begin to show more interesting results for early dark energy models. For example, the best fit model for current data has a slight preference for dynamics [w(a){ne}-1], degrees of freedom distinct from quintessence (c{sub s{ne}}1), and early presence of dark energy [{Omega}{sub de}(a<<1){ne}0]. Future data may open a new window on dark energy by measuring its spatial as well as time variation.
Non-adiabatic perturbations in Ricci dark energy model
Karwan, Khamphee; Thitapura, Thiti E-mail: nanodsci2523@hotmail.com
2012-01-01
We show that the non-adiabatic perturbations between Ricci dark energy and matter can grow both on superhorizon and subhorizon scales, and these non-adiabatic perturbations on subhorizon scales can lead to instability in this dark energy model. The rapidly growing non-adiabatic modes on subhorizon scales always occur when the equation of state parameter of dark energy starts to drop towards -1 near the end of matter era, except that the parameter α of Ricci dark energy equals to 1/2. In the case where α = 1/2, the rapidly growing non-adiabatic modes disappear when the perturbations in dark energy and matter are adiabatic initially. However, an adiabaticity between dark energy and matter perturbations at early time implies a non-adiabaticity between matter and radiation, this can influence the ordinary Sachs-Wolfe (OSW) effect. Since the amount of Ricci dark energy is not small during matter domination, the integrated Sachs-Wolfe (ISW) effect is greatly modified by density perturbations of dark energy, leading to a wrong shape of CMB power spectrum. The instability in Ricci dark energy is difficult to be alleviated if the effects of coupling between baryon and photon on dark energy perturbations are included.
Dark energy and dark matter perturbations in singular universes
Denkiewicz, Tomasz
2015-03-01
We discuss the evolution of density perturbations of dark matter and dark energy in cosmological models which admit future singularities in a finite time. Up to now geometrical tests of the evolution of the universe do not differentiate between singular universes and ΛCDM scenario. We solve perturbation equations using the gauge invariant formalism. The analysis shows that the detailed reconstruction of the evolution of perturbations within singular cosmologies, in the dark sector, can exhibit important differences between the singular universes models and the ΛCDM cosmology. This is encouraging for further examination and gives hope for discriminating between those models with future galaxy weak lensing experiments like the Dark Energy Survey (DES) and Euclid or CMB observations like PRISM and CoRE.
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.
Perturbations of ultralight vector field dark matter
NASA Astrophysics Data System (ADS)
Cembranos, J. A. R.; Maroto, A. L.; Núñez Jareño, S. J.
2017-02-01
We study the dynamics of cosmological perturbations in models of dark matter based on ultralight coherent vector fields. Very much as for scalar field dark matter, we find two different regimes in the evolution: for modes with {k}^2≪ Hma, we have a particle-like behaviour indistinguishable from cold dark matter, whereas for modes with {k}^2≫ Hma, we get a wave-like behaviour in which the sound speed is non-vanishing and of order c s 2 ≃ k 2/ m 2 a 2. This implies that, also in these models, structure formation could be suppressed on small scales. However, unlike the scalar case, the fact that the background evolution contains a non-vanishing homogeneous vector field implies that, in general, the evolution of the three kinds of perturbations (scalar, vector and tensor) can no longer be decoupled at the linear level. More specifically, in the particle regime, the three types of perturbations are actually decoupled, whereas in the wave regime, the three vector field perturbations generate one scalar-tensor and two vector-tensor perturbations in the metric. Also in the wave regime, we find that a non-vanishing anisotropic stress is present in the perturbed energy-momentum tensor giving rise to a gravitational slip of order ( Φ - Ψ)/ Φ ˜ c s 2 . Moreover in this regime the amplitude of the tensor to scalar ratio of the scalar-tensor modes is also h/ Φ ˜ c s 2 . This implies that small-scale density perturbations are necessarily associated to the presence of gravity waves in this model. We compare their spectrum with the sensitivity of present and future gravity waves detectors.
Evolution of dark energy perturbations in scalar-tensor cosmologies
Bueno Sanchez, J. C.; Perivolaropoulos, L.
2010-05-15
We solve analytically and numerically the generalized Einstein equations in scalar-tensor cosmologies to obtain the evolution of dark energy and matter linear perturbations. We compare our results with the corresponding results for minimally coupled quintessence perturbations. We find that scalar-tensor dark energy density perturbations are amplified by a factor of about 10{sup 4} compared to minimally coupled quintessence perturbations on scales less than about 1000 h{sup -1} Mpc (sub-Hubble scales). On these scales dark energy perturbations constitute a fraction of about 10% compared to matter density perturbations. Scalar-tensor dark energy density perturbations are anticorrelated with matter linear perturbations on sub-Hubble scales. This anticorrelation of matter with negative pressure perturbations induces a mild amplification of matter perturbations by about 10% on sub-Hubble scales. The evolution of scalar field perturbations on sub-Hubble scales is scale independent and therefore corresponds to a vanishing effective speed of sound (c{sub s{Phi}=}0). We briefly discuss the observational implications of our results, which may include predictions for galaxy and cluster halo profiles that are modified compared to {Lambda}CDM. The observed properties of these profiles are known to be in some tension with the predictions of {Lambda}CDM.
How clustering dark energy affects matter perturbations
NASA Astrophysics Data System (ADS)
Mehrabi, A.; Basilakos, S.; Pace, F.
2015-09-01
The rate of structure formation in the Universe is different in homogeneous and clustered dark energy models. The degree of dark energy clustering depends on the magnitude of its effective sound speed c2_eff and for c2_eff=0 dark energy clusters in a similar fashion to dark matter while for c2_eff=1 it stays (approximately) homogeneous. In this paper we consider two distinct equations of state for the dark energy component, wd = const and w_d=w_0+w_1(z/1+z) with c2_eff as a free parameter and we try to constrain the dark energy effective sound speed using current available data including Type Ia supernovae, baryon acoustic oscillation, cosmic microwave background shift parameter (Planck and WMAP), Hubble parameter, big bang nucleosynthesis and the growth rate of structures fσ8(z). At first we derive the most general form of the equations governing dark matter and dark energy clustering under the assumption that c2_eff=const. Finally, performing an overall likelihood analysis we find that the likelihood function peaks at c2_eff=0; however, the dark energy sound speed is degenerate with respect to the cosmological parameters, namely Ωm and wd.
Roles of dark energy perturbations in dynamical dark energy models: can we ignore them?
Park, Chan-Gyung; Hwang, Jai-chan; Lee, Jae-heon; Noh, Hyerim
2009-10-09
We show the importance of properly including the perturbations of the dark energy component in the dynamical dark energy models based on a scalar field and modified gravity theories in order to meet with present and future observational precisions. Based on a simple scaling scalar field dark energy model, we show that observationally distinguishable substantial differences appear by ignoring the dark energy perturbation. By ignoring it the perturbed system of equations becomes inconsistent and deviations in (gauge-invariant) power spectra depend on the gauge choice.
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.
Observational effects of the early episodically dominating dark energy
NASA Astrophysics Data System (ADS)
Park, Chan-Gyung; Lee, Jae-heon; Hwang, Jai-chan; Noh, Hyerim
2014-10-01
We investigate the observational consequences of the early episodically dominating dark energy on the evolution of cosmological structures. For this aim, we introduce the minimally coupled scalar-field dark energy model with the Albrecht-Skordis potential, which allows a sudden ephemeral domination of a dark energy component during the radiation or early matter era. The conventional cosmological parameters in the presence of such an early dark energy are constrained with WMAP and Planck cosmic microwave background radiation data including other external data sets. It is shown that in the presence of such an early dark energy, the estimated cosmological parameters can deviate substantially from the currently known Λ cold dark matter (Λ CDM )-based parameters, with best-fit values differing by several percent for WMAP and by a percent level for Planck data. For the latter case, only a limited amount of dark energy with episodic nature is allowed since the Planck data strongly favor the Λ CDM model. Compared with the conventional dark energy model, the early dark energy dominating near the radiation-matter equality or at the early matter era results in the shorter cosmic age or the presence of tensor-type perturbation, respectively. Our analysis demonstrates that the alternative cosmological parameter estimation is allowed based on the same observations even in Einstein's gravity.
Cosmic-string-induced hot dark matter perturbations
NASA Technical Reports Server (NTRS)
Van Dalen, Anthony
1990-01-01
This paper investigates the evolution of initially relativistic matter, radiation, and baryons around cosmic string seed perturbations. A detailed analysis of the linear evolution of spherical perturbations in a universe is carried out, and this formalism is used to study the evolution of perturbations around a sphere of uniform density and fixed radius, approximating a loop of cosmic string. It was found that, on scales less than a few megaparsec, the results agree with the nonrelativistic calculation of previous authors. On greater scales, there is a deviation approaching a factor of 2-3 in the perturbation mass. It is shown that a scenario with cosmic strings, hot dark matter, and a Hubble constant greater than 75 km/sec per Mpc can generally produce structure on the observed mass scales and at the appropriate time: 1 + z = about 4 for galaxies and 1 + z = about 1.5 for Abell clusters.
Structure formation in inhomogeneous Early Dark Energy models
Batista, R.C.; Pace, F. E-mail: francesco.pace@port.ac.uk
2013-06-01
We study the impact of Early Dark Energy fluctuations in the linear and non-linear regimes of structure formation. In these models the energy density of dark energy is non-negligible at high redshifts and the fluctuations in the dark energy component can have the same order of magnitude of dark matter fluctuations. Since two basic approximations usually taken in the standard scenario of quintessence models, that both dark energy density during the matter dominated period and dark energy fluctuations on small scales are negligible, are not valid in such models, we first study approximate analytical solutions for dark matter and dark energy perturbations in the linear regime. This study is helpful to find consistent initial conditions for the system of equations and to analytically understand the effects of Early Dark Energy and its fluctuations, which are also verified numerically. In the linear regime we compute the matter growth and variation of the gravitational potential associated with the Integrated Sachs-Wolf effect, showing that these observables present important modifications due to Early Dark Energy fluctuations, though making them more similar to the ΛCDM model. We also make use of the Spherical Collapse model to study the influence of Early Dark Energy fluctuations in the nonlinear regime of structure formation, especially on δ{sub c} parameter, and their contribution to the halo mass, which we show can be of the order of 10%. We finally compute how the number density of halos is modified in comparison to the ΛCDM model and address the problem of how to correct the mass function in order to take into account the contribution of clustered dark energy. We conclude that the inhomogeneous Early Dark Energy models are more similar to the ΛCDM model than its homogeneous counterparts.
Piattella, O.F.; Martins, D.L.A.; Casarini, L. E-mail: denilsonluizm@gmail.com
2014-10-01
We consider a cosmological model of the late universe constituted by standard cold dark matter plus a dark energy component with constant equation of state w and constant effective speed of sound. By neglecting fluctuations in the dark energy component, we obtain an equation describing the evolution of sub-horizon cold dark matter perturbations through the epoch of dark matter-dark energy equality. We explore its analytic solutions and calculate an exact w-dependent correction for the dark matter growth function, logarithmic growth function and growth index parameter through the epoch considered. We test our analytic approximation with the numerical solution and find that the discrepancy is less than 1% for 0k = during the cosmic evolution up to a = 100.
Constraining dark sector perturbations II: ISW and CMB lensing tomography
NASA Astrophysics Data System (ADS)
Soergel, B.; Giannantonio, T.; Weller, J.; Battye, R. A.
2015-02-01
Any Dark Energy (DE) or Modified Gravity (MG) model that deviates from a cosmological constant requires a consistent treatment of its perturbations, which can be described in terms of an effective entropy perturbation and an anisotropic stress. We have considered a recently proposed generic parameterisation of DE/MG perturbations and compared it to data from the Planck satellite and six galaxy catalogues, including temperature-galaxy (Tg), CMB lensing-galaxy (varphi g) and galaxy-galaxy (gg) correlations. Combining these observables of structure formation with tests of the background expansion allows us to investigate the properties of DE/MG both at the background and the perturbative level. Our constraints on DE/MG are mostly in agreement with the cosmological constant paradigm, while we also find that the constraint on the equation of state w (assumed to be constant) depends on the model assumed for the perturbation evolution. We obtain w=-0.92+0.20-0.16 (95% CL; CMB+gg+Tg) in the entropy perturbation scenario; in the anisotropic stress case the result is w=-0.86+0.17-0.16. Including the lensing correlations shifts the results towards higher values of w. If we include a prior on the expansion history from recent Baryon Acoustic Oscillations (BAO) measurements, we find that the constraints tighten closely around w=-1, making it impossible to measure any DE/MG perturbation evolution parameters. If, however, upcoming observations from surveys like DES, Euclid or LSST show indications for a deviation from a cosmological constant, our formalism will be a useful tool towards model selection in the dark sector.
Scalar perturbations in cosmological models with dark energy-dark matter interaction
Eingorn, Maxim; Kiefer, Claus E-mail: kiefer@thp.uni-koeln.de
2015-07-01
Scalar cosmological perturbations are investigated in the framework of a model with interacting dark energy and dark matter. In addition to these constituents, the inhomogeneous Universe is supposed to be filled with the standard noninteracting constituents corresponding to the conventional ΛCDM model. The interaction term is chosen in the form of a linear combination of dark sector energy densities with evolving coefficients. The methods of discrete cosmology are applied, and strong theoretical constraints on the parameters of the model are derived. A brief comparison with observational data is performed.
Semi-dynamical perturbations of unified dark energy
Lombriser, Lucas; Taylor, Andy E-mail: ant@roe.ac.uk
2015-11-01
Linear cosmological perturbations of a large class of modified gravity and dark energy models can be unified in the effective field theory of cosmic acceleration, encompassing Horndeski scalar-tensor theories and beyond. The fully available model space inherent to this formalism cannot be constrained by measurements in the quasistatic small-scale regime alone. To facilitate the analysis of modifications from the concordance model beyond this limit, we introduce a semi-dynamical treatment extrapolated from the evolution of perturbations at a pivot scale of choice. At small scales, and for Horndeski theories, the resulting modifications recover a quasistatic approximation but account for corrections to it near the Hubble scale. For models beyond Horndeski gravity, we find that the velocity field and time derivative of the spatial metric potential can generally not be neglected, even in the small-scale limit. We test the semi-dynamical approximation against the linear perturbations of a range of dark energy and modified gravity models, finding good agreement between the two.
Can We Hope To Detect Dark Energy Perturbations?
NASA Astrophysics Data System (ADS)
Bean, R.; Doré, O.
2005-08-01
We review the implications of having a non-trivial matter component in the Universe and the potential for detecting such a component through the matter power spectrum and ISW effect. We adopt a phenomenological approach and consider the mysterious dark energy to be a cosmic fluid. It is thus fully characterized, up to linear order, by its equation of state and its speed of sound. Whereas the equation of state has been widely studied in the literature, less interest has been devoted to the speed of sound. Its observational consequences come predominantly from very large-scale modes of dark matter perturbations (k < 0.01 h Mpc-1). Because these modes have hardly been probed so far by large scale galaxy surveys, we investigate whether joint constraints can be placed on those two quantities using the recent CMB fluctuations measurements by WMAP and the recently measured CMB large-scale structure cross-correlation.
Dark matter perturbations and viscosity: A causal approach
NASA Astrophysics Data System (ADS)
Acquaviva, Giovanni; John, Anslyn; Pénin, Aurélie
2016-08-01
The inclusion of dissipative effects in cosmic fluids modifies their clustering properties and could have observable effects on the formation of large-scale structures. We analyze the evolution of density perturbations of cold dark matter endowed with causal bulk viscosity. The perturbative analysis is carried out in the Newtonian approximation and the bulk viscosity is described by the causal Israel-Stewart (IS) theory. In contrast to the noncausal Eckart theory, we obtain a third-order evolution equation for the density contrast that depends on three free parameters. For certain parameter values, the density contrast and growth factor in IS mimic their behavior in Λ CDM when z ≥1 . Interestingly, and contrary to intuition, certain sets of parameters lead to an increase of the clustering.
Dark and singular optical solitons perturbation with fractional temporal evolution
NASA Astrophysics Data System (ADS)
Younis, Muhammad; ur Rehman, Hamood; Rizvi, Syed Tahir Raza; Mahmood, Syed Amer
2017-04-01
The article studies the dynamics of dark, singular, combined optical solitons and many other periodic solutions to fractional temporal perturbed nonlinear Schrödinger equation in nonlinear optics. The fractional extended Fan sub-equation method is first time used for any fractional temporal nonlinear Schrödinger equation. The solutions are of qualitatively different nature, depending on the five parameters. The constraint conditions, for the existence of the solitons, are also listed. Moreover a couple of other solutions known as combined soliton and combined periodic solution, fall out as a by product in limiting cases.
Linear perturbation constraints on multi-coupled dark energy
NASA Astrophysics Data System (ADS)
Piloyan, Arpine; Marra, Valerio; Baldi, Marco; Amendola, Luca
2014-02-01
The Multi-coupled Dark Energy (McDE) scenario has been recently proposed as a specific example of a cosmological model characterized by a non-standard physics of the dark sector of the universe that nevertheless gives an expansion history which does not significantly differ from the one of the standard ΛCDM model. Thanks to a dynamical screening mechanism, in fact, the interaction between the Dark Energy field and the Dark Matter sector is effectively suppressed at the background level during matter domination. As a consequence, background observables cannot discriminate a McDE cosmology from ΛCDM for a wide range of model parameters. On the other hand, linear perturbations are expected to provide tighter bounds due to the existence of attractive and repulsive fifth-forces associated with the dark interactions. In this work, we present the first constraints on the McDE scenario obtained by comparing the predicted evolution of linear density perturbations with a large compilation of recent data sets for the growth rate fσ8, including 6dFGS, LRG, BOSS, WiggleZ and VIPERS. Confirming qualitative expectations, growth rate data provide much tighter bounds on the model parameters as compared to the extremely loose bounds that can be obtained when only the background expansion history is considered. In particular, the 95% confidence level on the coupling strength |β| is reduced from |β| <= 83 (background constraints only) to |β| <= 0.88 (background and linear perturbation constraints). We also investigate how these constraints further improve when using data from future wide-field surveys such as supernova data from LSST and growth rate data from Euclid-type missions. In this case the 95% confidence level on the coupling further reduce to |β| <= 0.85. Such constraints are in any case still consistent with a scalar fifth-force of gravitational strength, and we foresee that tighter bounds might be possibly obtained from the investigation of nonlinear structure
Linear perturbation constraints on multi-coupled dark energy
Piloyan, Arpine; Marra, Valerio; Amendola, Luca; Baldi, Marco E-mail: valerio.marra@me.com E-mail: l.amendola@thphys.uni-heidelberg.de
2014-02-01
The Multi-coupled Dark Energy (McDE) scenario has been recently proposed as a specific example of a cosmological model characterized by a non-standard physics of the dark sector of the universe that nevertheless gives an expansion history which does not significantly differ from the one of the standard ΛCDM model. Thanks to a dynamical screening mechanism, in fact, the interaction between the Dark Energy field and the Dark Matter sector is effectively suppressed at the background level during matter domination. As a consequence, background observables cannot discriminate a McDE cosmology from ΛCDM for a wide range of model parameters. On the other hand, linear perturbations are expected to provide tighter bounds due to the existence of attractive and repulsive fifth-forces associated with the dark interactions. In this work, we present the first constraints on the McDE scenario obtained by comparing the predicted evolution of linear density perturbations with a large compilation of recent data sets for the growth rate fσ{sub 8}, including 6dFGS, LRG, BOSS, WiggleZ and VIPERS. Confirming qualitative expectations, growth rate data provide much tighter bounds on the model parameters as compared to the extremely loose bounds that can be obtained when only the background expansion history is considered. In particular, the 95% confidence level on the coupling strength |β| is reduced from |β| ≤ 83 (background constraints only) to |β| ≤ 0.88 (background and linear perturbation constraints). We also investigate how these constraints further improve when using data from future wide-field surveys such as supernova data from LSST and growth rate data from Euclid-type missions. In this case the 95% confidence level on the coupling further reduce to |β| ≤ 0.85. Such constraints are in any case still consistent with a scalar fifth-force of gravitational strength, and we foresee that tighter bounds might be possibly obtained from the investigation of nonlinear
Constraining dark sector perturbations I: cosmic shear and CMB lensing
Battye, Richard A.; Moss, Adam; Pearson, Jonathan A. E-mail: adam.moss@nottingham.ac.uk
2015-04-01
We present current and future constraints on equations of state for dark sector perturbations. The equations of state considered are those corresponding to a generalized scalar field model and time-diffeomorphism invariant L(g) theories that are equivalent to models of a relativistic elastic medium and also Lorentz violating massive gravity. We develop a theoretical understanding of the observable impact of these models. In order to constrain these models we use CMB temperature data from Planck, BAO measurements, CMB lensing data from Planck and the South Pole Telescope, and weak galaxy lensing data from CFHTLenS. We find non-trivial exclusions on the range of parameters, although the data remains compatible with w=−1. We gauge how future experiments will help to constrain the parameters. This is done via a likelihood analysis for CMB experiments such as CoRE and PRISM, and tomographic galaxy weak lensing surveys, focussing in on the potential discriminatory power of Euclid on mildly non-linear scales.
Early-matter-like dark energy and the cosmic microwave background
Aurich, R.; Lustig, S. E-mail: sven.lustig@uni-ulm.de
2016-01-01
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 phenomenological 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.
Effective action approach to cosmological perturbations in dark energy and modified gravity
Battye, Richard A.; Pearson, Jonathan A. E-mail: jp@jb.man.ac.uk
2012-07-01
In light of upcoming observations modelling perturbations in dark energy and modified gravity models has become an important topic of research. We develop an effective action to construct the components of the perturbed dark energy momentum tensor which appears in the perturbed generalized gravitational field equations, δG{sup μν} = 8πGδT{sup μν}+δU{sup μν} for linearized perturbations. Our method does not require knowledge of the Lagrangian density of the dark sector to be provided, only its field content. The method is based on the fact that it is only necessary to specify the perturbed Lagrangian to quadratic order and couples this with the assumption of global statistical isotropy of spatial sections to show that the model can be specified completely in terms of a finite number of background dependent functions. We present our formalism in a coordinate independent fashion and provide explicit formulae for the perturbed conservation equation and the components of δU{sup μ}{sub ν} for two explicit generic examples: (i) the dark sector does not contain extra fields, L = L(g{sub μν}) and (ii) the dark sector contains a scalar field and its first derivative L = L(g{sub μν},φ,∇{sub μ}φ). We discuss how the formalism can be applied to modified gravity models containing derivatives of the metric, curvature tensors, higher derivatives of the scalar fields and vector fields.
Cosmological perturbations during the Bose-Einstein condensation of dark matter
Freitas, R.C.; Gonçalves, S.V.B. E-mail: sergio.vitorino@pq.cnpq.br
2013-04-01
In the present work, we analyze the evolution of the scalar and tensorial perturbations and the quantities relevant for the physical description of the Universe, as the density contrast of the scalar perturbations and the gravitational waves energy density during the Bose-Einstein condensation of dark matter. The behavior of these parameters during the Bose-Einstein phase transition of dark matter is analyzed in details. To study the cosmological dynamics and evolution of scalar and tensorial perturbations in a Universe with and without cosmological constant we use both analytical and numerical methods. The Bose-Einstein phase transition modifies the evolution of gravitational waves of cosmological origin, as well as the process of large-scale structure formation.
NASA Astrophysics Data System (ADS)
Sun, Cheng-Yi; Song, Yu; Yue, Rui-Hong
2013-02-01
It was found that the model with interaction between cold dark matter (CDM) and dark energy (DE) proportional to the energy density of CDM ρ m and constant equation of state of DE w d suffered from instabilities of the density perturbations on the super-Hubble scales. Here we suggest a new covariant model for the energy-momentum transfer between CDM and DE. Then using the covariant model, we analyze the evolution of density perturbations on the super-Hubble scale. We find that the instabilities can be avoided in the model with constant w d and interaction proportional to ρ m . Furthermore, we analyze the dominant non-adiabatic mode in the radiation era and find that the mode grows regularly.
Early plant embryogenesis-dark ages or dark matter?
Bayer, Martin; Slane, Daniel; Jürgens, Gerd
2017-02-01
In nearly all flowering plants, the basic body plan is laid down during embryogenesis. In Arabidopsis, the crucial cell types are established extremely early as reflected in the stereotypic sequence of oriented cell divisions in the developing young embryo. Research into early embryogenesis was especially focused on the role of the infamous tryptophan derivative auxin in establishing embryo polarity and generating the main body axis. However, it is becoming obvious that the mere link to auxin does not provide any mechanistic understanding of early embryo patterning. Taking recent research into account, we discuss mechanisms underlying early embryonic patterning from an evolutionary perspective.
Probing for Dark Energy Perturbations using the CMB and Large Scale Structure?
NASA Astrophysics Data System (ADS)
Bean, Rachel; Doré, Olivier
2004-12-01
We review the implications of having a non-trivial matter component in the universe and the potential for detecting such a component through the matter power spectrum and ISW effect. We adopt a phenomenological approach and consider the mysterious dark energy to be a cosmic fluid. It is thus fully characterized, up to linear order, by its equation of state and its speed of sound. Whereas the equation of state has been widely studied in the literature, less interest has been devoted to the speed of sound. Its observational consequences come predominantly from very large scale modes of dark matter perturbations (k < 0.01hMpc-1). Since these modes have hardly been probed so far by large scale galaxy surveys, we investigate whether joint constraints that can be placed on those two quantities using the recent CMB fluctuations measurements by WMAP as well as the recently measured CMB large scale structure cross-correlation.
NASA Astrophysics Data System (ADS)
Bean, Rachel; Doré, Olivier
2004-04-01
We review the implications of having a nontrivial matter component in the Universe and the potential for detecting such a component through the matter power spectrum and integrated Sachs-Wolfe effect. We adopt a phenomenological approach and consider the mysterious dark energy to be a cosmic fluid. It is thus fully characterized, up to linear order, by its equation of state and its speed of sound. Whereas the equation of state has been widely studied in the literature, less interest has been devoted to the speed of sound. Its observational consequences come predominantly from very large scale modes of dark matter perturbations (k<0.01h Mpc-1). Since these modes have hardly been probed so far by large scale galaxy surveys, we investigate whether joint constraints can be placed on those two quantities using the recent cosmic microwave background (CMB) fluctuations measurements by the Wilkinson Microwave Anisotropy Probe as well as the recently measured CMB large scale structure cross correlation. We find only a tentative 1 sigma detection of the speed of sound, from CMB alone, c2s<0.04 at this low significance level. Furthermore, the current uncertainties in bias in the matter power spectrum preclude any constraints being placed using the cross correlation of CMB with the NRAO VLA Sky Survey radio survey.
Nicolaou, Costa; Lau, Wah Tung; Gad, Raanan; Akhavan, Hooman; Schilling, Ryan; Levi, Ofer
2013-12-16
We demonstrate for the first time a 300nm thick, 300μm × 300μm 2D dielectric photonic crystal slab membrane with a quality factor of 10,600 by coupling light to slightly perturbed dark modes through alternating nano-hole sizes. The newly created fundamental guided resonances greatly reduce nano-fabrication accuracy requirements. Moreover, we created a new layer architecture resulting in electric field enhancement at the interface between the slab and sensing regions, and spectral sensitivity of >800 nm/RIU, that is, >0.8 of the single-mode theoretical upper limit of spectral sensitivity.
The sensitivity of BAO dark energy constraints to general isocurvature perturbations
Kasanda, S. Muya; Zunckel, C.; Moodley, K.; Bassett, B.A.; Okouma, P. E-mail: caroline.zunckel@gmail.com E-mail: bruce.a.bassett@gmail.com
2012-07-01
Baryon Acoustic Oscillation (BAO) surveys will be a leading method for addressing the dark energy challenge in the next decade. We explore in detail the effect of allowing for small amplitude admixtures of general isocurvature perturbations in addition to the dominant adiabatic mode. We find that non-adiabatic initial conditions leave the sound speed unchanged but instead excite different harmonics. These harmonics couple differently to Silk damping, altering the form and evolution of acoustic waves in the baryon-photon fluid prior to decoupling. This modifies not only the scale on which the sound waves imprint onto the baryon distribution, which is used as the standard ruler in BAO surveys, but also the shape, width and height of the BAO peak. We discuss these effects in detail and show how more general initial conditions impact our interpretation of cosmological data in dark energy studies. We find that the inclusion of these additional isocurvature modes leads to a decrease in the Dark Energy Task Force figure of merit (FoM) by 46% i.e., FoM{sub ISO} = 0.54 × FoM{sub AD} and 53% for the BOSS and ADEPT experiments respectively when considered in conjunction with PLANK data. We also show that the incorrect assumption of adiabaticity has the potential to bias our estimates of the dark energy parameters by 2.7σ (2.2σ) for a single correlated isocurvature mode (CDM isocurvature), and up to 4.9σ (5.7σ) for three correlated isocurvature modes in the case of the BOSS (ADEPT) experiment. We find that the use of the large scale structure data in conjunction with CMB data improves our ability to measure the contributions of different modes to the initial conditions by as much as 95% for certain modes in the fully correlated case.
Li, Jun; Yang, Rongjia; Chen, Bohai E-mail: yangrj08@gmail.com
2014-12-01
We apply the Statefinder hierarchy and the growth rate of matter perturbations to discriminate modified Chaplygin gas (MCG), generalized Chaplygin gas (GCG), superfluid Chaplygin gas (SCG), purely kinetic k-essence (PKK), and ΛCDM model. We plot the evolutional trajectories of these models in the Statefinder plane and in the composite diagnostic plane. We find that GCG, MCG, SCG, PKK, and ΛCDM can be distinguished well from each other at the present epoch by using the composite diagnostic (ε(z), S{sup (1)}{sub 5}). Using other combinations, such as (S{sup (1)}{sub 3}, S{sup (1)}{sub 4}), (S{sup (1)}{sub 3}, S{sub 5}), (ε(z), S{sup (1)}{sub 3}), and (ε(z), S{sub 4}), some of these five dark energy models cannot be distinguished.
Vlah, Zvonimir; Seljak, Uroš; Baldauf, Tobias; McDonald, Patrick; Okumura, Teppei E-mail: seljak@physik.uzh.ch E-mail: teppei@ewha.ac.kr
2012-11-01
We develop a perturbative approach to redshift space distortions (RSD) using the phase space distribution function approach and apply it to the dark matter redshift space power spectrum and its moments. RSD can be written as a sum over density weighted velocity moments correlators, with the lowest order being density, momentum density and stress energy density. We use standard and extended perturbation theory (PT) to determine their auto and cross correlators, comparing them to N-body simulations. We show which of the terms can be modeled well with the standard PT and which need additional terms that include higher order corrections which cannot be modeled in PT. Most of these additional terms are related to the small scale velocity dispersion effects, the so called finger of god (FoG) effects, which affect some, but not all, of the terms in this expansion, and which can be approximately modeled using a simple physically motivated ansatz such as the halo model. We point out that there are several velocity dispersions that enter into the detailed RSD analysis with very different amplitudes, which can be approximately predicted by the halo model. In contrast to previous models our approach systematically includes all of the terms at a given order in PT and provides a physical interpretation for the small scale dispersion values. We investigate RSD power spectrum as a function of μ, the cosine of the angle between the Fourier mode and line of sight, focusing on the lowest order powers of μ and multipole moments which dominate the observable RSD power spectrum. Overall we find considerable success in modeling many, but not all, of the terms in this expansion. This is similar to the situation in real space, but predicting power spectrum in redshift space is more difficult because of the explicit influence of small scale dispersion type effects in RSD, which extend to very large scales.
Phenomenology of dark energy: general features of large-scale perturbations
Pèrenon, Louis; Piazza, Federico; Marinoni, Christian; Hui, Lam E-mail: federico.piazza@cpt.univ-mrs.fr E-mail: lh399@columbia.edu
2015-11-01
We present a systematic exploration of dark energy and modified gravity models containing a single scalar field non-minimally coupled to the metric. Even though the parameter space is large, by exploiting an effective field theory (EFT) formulation and by imposing simple physical constraints such as stability conditions and (sub-)luminal propagation of perturbations, we arrive at a number of generic predictions. (1) The linear growth rate of matter density fluctuations is generally suppressed compared to ΛCDM at intermediate redshifts (0.5 ∼< z ∼< 1), despite the introduction of an attractive long-range scalar force. This is due to the fact that, in self-accelerating models, the background gravitational coupling weakens at intermediate redshifts, over-compensating the effect of the attractive scalar force. (2) At higher redshifts, the opposite happens; we identify a period of super-growth when the linear growth rate is larger than that predicted by ΛCDM. (3) The gravitational slip parameter η—the ratio of the space part of the metric perturbation to the time part—is bounded from above. For Brans-Dicke-type theories η is at most unity. For more general theories, η can exceed unity at intermediate redshifts, but not more than about 1.5 if, at the same time, the linear growth rate is to be compatible with current observational constraints. We caution against phenomenological parametrization of data that do not correspond to predictions from viable physical theories. We advocate the EFT approach as a way to constrain new physics from future large-scale-structure data.
Phenomenology of dark energy: general features of large-scale perturbations
NASA Astrophysics Data System (ADS)
Pèrenon, Louis; Piazza, Federico; Marinoni, Christian; Hui, Lam
2015-11-01
We present a systematic exploration of dark energy and modified gravity models containing a single scalar field non-minimally coupled to the metric. Even though the parameter space is large, by exploiting an effective field theory (EFT) formulation and by imposing simple physical constraints such as stability conditions and (sub-)luminal propagation of perturbations, we arrive at a number of generic predictions. (1) The linear growth rate of matter density fluctuations is generally suppressed compared to ΛCDM at intermediate redshifts (0.5 lesssim z lesssim 1), despite the introduction of an attractive long-range scalar force. This is due to the fact that, in self-accelerating models, the background gravitational coupling weakens at intermediate redshifts, over-compensating the effect of the attractive scalar force. (2) At higher redshifts, the opposite happens; we identify a period of super-growth when the linear growth rate is larger than that predicted by ΛCDM. (3) The gravitational slip parameter η—the ratio of the space part of the metric perturbation to the time part—is bounded from above. For Brans-Dicke-type theories η is at most unity. For more general theories, η can exceed unity at intermediate redshifts, but not more than about 1.5 if, at the same time, the linear growth rate is to be compatible with current observational constraints. We caution against phenomenological parametrization of data that do not correspond to predictions from viable physical theories. We advocate the EFT approach as a way to constrain new physics from future large-scale-structure data.
Vlah, Zvonimir; Seljak, Uroš; Okumura, Teppei; Desjacques, Vincent E-mail: seljak@physik.uzh.ch E-mail: Vincent.Desjacques@unige.ch
2013-10-01
Numerical simulations show that redshift space distortions (RSD) introduce strong scale dependence in the power spectra of halos, with ten percent deviations relative to linear theory predictions even on relatively large scales (k < 0.1h/Mpc) and even in the absence of satellites (which induce Fingers-of-God, FoG, effects). If unmodeled these effects prevent one from extracting cosmological information from RSD surveys. In this paper we use Eulerian perturbation theory (PT) and Eulerian halo biasing model and apply it to the distribution function approach to RSD, in which RSD is decomposed into several correlators of density weighted velocity moments. We model each of these correlators using PT and compare the results to simulations over a wide range of halo masses and redshifts. We find that with an introduction of a physically motivated halo biasing, and using dark matter power spectra from simulations, we can reproduce the simulation results at a percent level on scales up to k ∼ 0.15h/Mpc at z = 0, without the need to have free FoG parameters in the model.
Aoyama, Shohei; Sekiguchi, Toyokazu; Sugiyama, Naoshi; Ichiki, Kiyotomo E-mail: toyokazu.sekiguchi@nagoya-u.jp E-mail: naoshi@nagoya-u.jp
2014-07-01
Decaying dark matter (DDM) is a candidate which can solve the discrepancies between predictions of the concordance ΛCDM model and observations at small scales such as the number counts of companion galaxies of the Milky Way and the density profile at the center of galaxies. Previous studies are limited to the cases where the decay particles are massless and/or have almost degenerate masses with that of mother particles. Here we expand the DDM models so that one can consider the DDM with arbitrary lifetime and the decay products with arbitrary masses. We calculate the time evolutions of perturbed phase-space distribution functions of decay products for the first time and study effects of DDM on the temperature anisotropy in the cosmic microwave background and the matter power spectrum at present. From a recent observational estimate of σ{sub 8}, we derive constraints on the lifetime of DDM and the mass ratio between the decay products and DDM. We also discuss implications of the DDM model for the discrepancy in the measurements of σ{sub 8} recently claimed by the Planck satellite collaboration.
Perturbation of a planetary orbit by the Lambda-term (dark energy) in Einstein equations
NASA Astrophysics Data System (ADS)
Dumin, Yurii
The problem of cosmological influences at small (e.g. interplanetary) scales is discussed for a few decades, starting from the early 1930's, but still remains unsolved definitively by now [1]. This subject became especially topical in the context of the dark-energy-dominated cosmology, because the commonly-used arguments against the local Hubble expansion (such as Einstein-Straus theorem [2]) are inapplicable when the most contribution to the energy density of the Universe comes from the perfectly-uniform dark energy (Lambda-term). Moreover, there are some empirical evidences in favor of the local cosmological influences. For example, inclusion of the local Hubble expansion into dynamics of the Earth-Moon system enables us to resolve a long-standing discrepancy in the rates of secular increase of the lunar semi-major axis (a) mea-sured by the lunar laser ranging and (b) derived from the astrometric observations of the Earth's rotation deceleration [3, 4]. The aim of the present report is to provide a detailed mathematical treatment of the respective two-body problem in the framework of General Relativity, which is based on the Kottler metric reduced to the Robertson-Walker cosmological asymptotics, as outlined in our earlier work [5]. References: 1. W.B. Bonnor. Gen. Rel. Grav., v.32, p.1005 (2000). 2. A. Einstein and E.G. Straus. Rev. Mod. Phys., v.17, p.120 (1945). 3. Yu.V. Dumin. Adv. Space Res., v.31, p.2461 (2003). 4. Yu.V. Dumin. In Proc. 11th Marcel Grossmann Meeting on General Relativity, World Sci., Singapore, p.1752 (2008). 5. Yu.V. Dumin. Phys. Rev. Lett., v.98, p.059001 (2007).
Dark Matter Benchmark Models for Early LHC Run-2 Searches. Report of the ATLAS/CMS Dark Matter Forum
Abercrombie, Daniel
2015-07-06
One of the guiding principles of this report is to channel the efforts of the ATLAS and CMS collaborations towards a minimal basis of dark matter models that should influence the design of the early Run-2 searches. At the same time, a thorough survey of realistic collider signals of Dark Matter is a crucial input to the overall design of the search program.
Dent, James B.; Dutta, Sourish; Weiler, Thomas J.
2009-01-15
The effect of quintessence perturbations on the integrated Sachs-Wolfe (ISW) effect is studied for a mixed dynamical scalar field dark energy (DDE) and pressureless perfect fluid dark matter. A new and general methodology is developed to track the growth of the perturbations, which uses only the equation of state (EoS) parameter w{sub DDE}(z){identical_to}p{sub DDE}/{rho}{sub DDE} of the scalar field DDE, and the initial values of the relative entropy perturbation (between the matter and DDE) and the intrinsic entropy perturbation of the scalar field DDE as inputs. We also derive a relation between the rest-frame sound speed c-circumflex{sub s,DDE}{sup 2} of an arbitrary scalar field DDE component and its EoS w{sub DDE}(z). We show that the ISW signal differs from that expected in a {lambda}CDM cosmology by as much as +20% to -80% for parametrizations of w{sub DDE} consistent with SNIa data, and about {+-}20% for parametrizations of w{sub DDE} consistent with SNIa+CMB+BAO data, at 95% confidence. Our results indicate that, at least in principle, the ISW effect can be used to phenomenologically distinguish a cosmological constant from DDE.
NASA Astrophysics Data System (ADS)
Basilakos, Spyros; Nesseris, Savvas
2016-12-01
The growth index of matter fluctuations is computed for ten distinct accelerating cosmological models and confronted by the latest growth-rate data via a two-step process. First, we implement a joint statistical analysis in order to place constraints on the free parameters of all models using solely background data. Second, using the observed growth rate of clustering from various galaxy surveys we test the performance of the current cosmological models at the perturbation level while either marginalizing over σ8 or having it as a free parameter. As a result, we find that at a statistical level, i.e., after considering the best-fit χ2 or the value of the Akaike information criterion, most models are in very good agreement with the growth-rate data and are practically indistinguishable from Λ CDM . However, when we also consider the internal consistency of the models by comparing the theoretically predicted values of (γ0,γ1), i.e., the value of the growth index γ (z ) and its derivative today, with the best-fit ones, we find that the predictions of three out of ten dark energy models are in mild tension with the best-fit ones when σ8 is marginalized over. When σ8 is free we find that most models are not only in mild tension, but also predict low values for σ8. This could be attributed to either a systematic problem with the growth-rate data or the emergence of new physics at low redshifts, with the latter possibly being related to the well-known issue of the lack of power at small scales. Finally, by utilizing mock data based on an large synoptic survey telescope-like survey we show that with future surveys and by using the growth index parametrization, it will be possible to resolve the issue of the low σ8 but also the tension between the fitted and theoretically predicted values of (γ0,γ1).
Statistics of magnification perturbations by substructure in the cold dark matter cosmological model
Rozo, Eduardo; Zentner, Andrew R.; Bertone, Gianfranco; Chen, Jacqueline; /KICP, Chicago /Chicago U., Astron. Astrophys. Ctr.
2005-06-01
We study the statistical properties of magnification perturbations by substructures in strong lensed systems using linear perturbation theory and an analytical substructure model including tidal truncation and a continuous substructure mass spectrum. We demonstrate that magnification perturbations are dominated by perturbers found within a tidal radius of an image, and that sizable magnification perturbations may arise from small, coherent contributions from several substructures within the lens halo. We find that the root-mean-square (rms) fluctuation of the magnification perturbation is {approx}10% to {approx}20% and both the average and rms perturbations are sensitive to the mass spectrum and density profile of the perturbers. Interestingly,we find that relative to a smooth model of the same mass, the average magnification in clumpy models is lower (higher) than that in smooth models for positive (negative) parity images. This is opposite from what is observed if one assumes that the image magnification predicted by the best-fit smooth model of a lens is a good proxy for what the observed magnification would have been if substructures were absent. While it is possible for this discrepancy to be resolved via nonlinear perturbers, we argue that a more likely explanation is that the assumption that the best-fit lens model is a good proxy for the magnification in the absence of substructure is not correct. We conclude that a better theoretical understanding of the predicted statistical properties of magnification perturbations by CDM substructure is needed in order to affirm that CDM substructures have been unambiguously detected.
Gavela, M.B.; Hernández, D.; Honorez, L. Lopez; Mena, O.; Rigolin, S. E-mail: d.hernandez@uam.es E-mail: omena@ific.uv.es
2009-07-01
The two dark sectors of the universe—dark matter and dark energy—may interact with each other. Background and linear density perturbation evolution equations are developed for a generic coupling. We then establish the general conditions necessary to obtain models free from non-adiabatic instabilities. As an application, we consider a viable universe in which the interaction strength is proportional to the dark energy density. The scenario does not exhibit ''phantom crossing'' and is free from instabilities, including early ones. A sizeable interaction strength is compatible with combined WMAP, HST, SN, LSS and H(z) data. Neutrino mass and/or cosmic curvature are allowed to be larger than in non-interacting models. Our analysis sheds light as well on unstable scenarios previously proposed.
A Study of Early/Slow VLF Perturbations Observed at Agra, India
NASA Astrophysics Data System (ADS)
Pandey, Uma; Singh, Ashutosh K.; Singh, Om P.; Singh, Birbal; Saraswat, Vibhav K.
2016-06-01
We present here the results of sub-ionospheric VLF perturbations observed on NWC (19.8 kHz) transmitter signal propagating in the Earth-ionosphere waveguide, monitored at our low latitude station Agra. During the period of observation (June-December 2011), we found 89 cases of VLF perturbation, while only 73 cases showing early character associated with strong lightning discharges. Out of 73 events, 64 ( 84%) of the early VLF perturbations are found to be early/slow in nature; the remaining 9 events are early/fast. The onset duration of these early/slow VLF perturbations is up to 5 s. A total of 54 observed early events show amplitude change lying between ± 3.0 dB, and phase change ± 12 degree, respectively, and found to occur mainly during nighttime. One of the interesting results we found is that the events with larger recovery time lie far away from the VLF propagation path, while events with smaller duration of recovery are within the ± 50-100 km of signal path. The World Wide Lightning Location Network (WWLLN) data is analysed to find the location of causative lightning and temporal variation. The lightning discharge and associated processes that lead to early VLF events are discussed.
Gómez-Valent, Adrià; Karimkhani, Elahe; Solà, Joan E-mail: e.karimkhani91@basu.ac.ir
2015-12-01
We determine the Hubble expansion and the general cosmic perturbation equations for a general system consisting of self-conserved matter, ρ{sub m}, and self-conserved dark energy (DE), ρ{sub D}. While at the background level the two components are non-interacting, they do interact at the perturbations level. We show that the coupled system of matter and DE perturbations can be transformed into a single, third order, matter perturbation equation, which reduces to the (derivative of the) standard one in the case that the DE is just a cosmological constant. As a nontrivial application we analyze a class of dynamical models whose DE density ρ{sub D}(H) consists of a constant term, C{sub 0}, and a series of powers of the Hubble rate. These models were previously analyzed from the point of view of dynamical vacuum models, but here we treat them as self-conserved DE models with a dynamical equation of state. We fit them to the wealth of expansion history and linear structure formation data and compare their fit quality with that of the concordance ΛCDM model. Those with C{sub 0}=0 include the so-called ''entropic-force'' and ''QCD-ghost'' DE models, as well as the pure linear model ρ{sub D}∼H, all of which appear strongly disfavored. The models with C{sub 0}≠0 , in contrast, emerge as promising dynamical DE candidates whose phenomenological performance is highly competitive with the rigid Λ-term inherent to the ΛCDM.
Axion as a cold dark matter candidate: analysis to third order perturbation for classical axion
Noh, Hyerim; Hwang, Jai-chan; Park, Chan-Gyung E-mail: jchan@knu.ac.kr
2015-12-01
We investigate aspects of axion as a coherently oscillating massive classical scalar field by analyzing third order perturbations in Einstein's gravity in the axion-comoving gauge. The axion fluid has its characteristic pressure term leading to an axion Jeans scale which is cosmologically negligible for a canonical axion mass. Our classically derived axion pressure term in Einstein's gravity is identical to the one derived in the non-relativistic quantum mechanical context in the literature. We present the general relativistic continuity and Euler equations for an axion fluid valid up to third order perturbation. Equations for axion are exactly the same as that of a zero-pressure fluid in Einstein's gravity except for an axion pressure term in the Euler equation. Our analysis includes the cosmological constant.
On the reach of perturbative methods for dark matter density fields
Baldauf, Tobias; Zaldarriaga, Matias; Schaan, Emmanuel E-mail: eschaan@astro.princeton.edu
2016-03-01
We study the mapping from Lagrangian to Eulerian space in the context of the Effective Field Theory (EFT) of Large Scale Structure. We compute Lagrangian displacements with Lagrangian Perturbation Theory (LPT) and perform the full non-perturbative transformation from displacement to density. When expanded up to a given order, this transformation reproduces the standard Eulerian Perturbation Theory (SPT) at the same order. However, the full transformation from displacement to density also includes higher order terms. These terms explicitly resum long wavelength motions, thus making the resulting density field better correlated with the true non-linear density field. As a result, the regime of validity of this approach is expected to extend that of the Eulerian EFT, and match that of the IR-resummed Eulerian EFT. This approach thus effectively enables a test of the IR-resummed EFT at the field level. We estimate the size of stochastic, non-perturbative contributions to the matter density power spectrum. We find that in our highest order calculation, at redshift z = 0 the power spectrum of the density field is reproduced with an accuracy of 1% (10%) up to k = 0.25 hMpc{sup −1} (k = 0.46 hMpc{sup −1}). We believe that the dominant source of the remaining error is the stochastic contribution. Unfortunately, on these scales the stochastic term does not yet scale as k{sup 4} as it does in the very low k regime. Thus, modeling this contribution might be challenging.
On the reach of perturbative descriptions for dark matter displacement fields
Baldauf, Tobias; Zaldarriaga, Matias; Schaan, Emmanuel E-mail: eschaan@astro.princeton.edu
2016-03-01
We study Lagrangian Perturbation Theory (LPT) and its regularization in the Effective Field Theory (EFT) approach. We evaluate the LPT displacement with the same phases as a corresponding N-body simulation, which allows us to compare perturbation theory to the non-linear simulation with significantly reduced cosmic variance, and provides a more stringent test than simply comparing power spectra. We reliably detect a non-vanishing leading order EFT coefficient and a stochastic displacement term, uncorrelated with the LPT terms. This stochastic term is expected in the EFT framework, and, to the best of our understanding, is not an artifact of numerical errors or transients in our simulations. This term constitutes a limit to the accuracy of perturbative descriptions of the displacement field and its phases, corresponding to a 1% error on the non-linear power spectrum at k = 0.2 h{sup −1}Mpc at z = 0. Predicting the displacement power spectrum to higher accuracy or larger wavenumbers thus requires a model for the stochastic displacement.
NASA Astrophysics Data System (ADS)
Ruhl, M.; Hesselbo, S. P.; Hinnov, L.; Jenkyns, H. C.; Storm, M.; Xu, W.; Riding, J. B.; Ullmann, C. V.
2015-12-01
The Early Jurassic (201.3 to 174.1 Ma) is bracketed by the end-Triassic mass extinction and global warming event, and the Toarcian-Aalenian shift to (global) icehouse conditions (McElwain et al., 1999; Hesselbo et al., 2002; Ruhl et al., 2011; Korte et al., in review). It is further marked by the early Toarcian Oceanic Anoxic Event (T-OAE), with possibly the largest exogenic carbon cycle perturbation of the Mesozoic and related perturbations in global geochemical cycles, climate and the environment, which are linked to large igneous province emplacement in the Karoo-Ferrar region (Jenkyns, 2010; Burgess et al., 2015). Furthermore, Early Jurassic continental rifting and the break-up of Pangaea and subsequent Early Jurassic opening of the Hispanic Corridor and Viking Strait respectively linked the equatorial Tethys Ocean to Eastern Panthalassa and the high-latitude Arctic Boreal realm. This initiated changes in (global) ocean currents and Earth's heat distribution and ultimately was followed by the opening of the proto-North Atlantic (Porter et al., 2013; Korte et al., in review). Here, we present high-resolution (sub-precession scale) elemental concentration data from the Mochras borehole (UK), which represents ~1300m of possibly the most complete and expanded lower Jurassic hemi-pelagic marine sedimentary archive known. We construct a floating ~9 Myr astronomical time-scale for the complete Early Jurassic Pliensbachian stage and biozones. Combined with radiometric and astrochronological constraints on early Jurassic stage boundaries, we construct a new Early Jurassic Time-Scale. With this we assess the duration and rate of change of early Jurassic global carbon cycle and climatic perturbations and we asses fundamental changes in the nature and expression of Early Jurassic long (100 - 1000 kyr) eccentricity cycles.
Early Galaxy Formation in Warm Dark Matter Cosmologies
NASA Astrophysics Data System (ADS)
Dayal, Pratika; Mesinger, Andrei; Pacucci, Fabio
2015-06-01
We present a framework for high-redshift (z≳ 7) galaxy formation that traces their dark matter (DM) and baryonic assembly in four cosmologies: cold dark matter (CDM) and warm dark matter (WDM) with particle masses of {{m}x} = 1.5, 3, and 5 keV. We use the same astrophysical parameters regulating star formation and feedback, chosen to match current observations of the evolving ultraviolet luminosity function (UV LF). We find that the assembly of observable (with current and upcoming instruments) galaxies in CDM and {{m}x}≥slant 3 keV WDM results in similar halo mass-to-light ratios (M/L), stellar mass densities (SMDs), and UV LFs. However, the suppression of small-scale structure leads to a notably delayed and subsequently more rapid stellar assembly in the 1.5 keV WDM model. Thus, galaxy assembly in {{m}x}≲ 2 keV WDM cosmologies is characterized by (1) a dearth of small-mass halos hosting faint galaxies and (2) a younger, more UV-bright stellar population, for a given stellar mass. The higher M/L (effect 2) partially compensates for the dearth of small-mass halos (effect 1), making the resulting UV LFs closer to CDM than expected from simple estimates of halo abundances. We find that the redshift evolution of the SMD is a powerful probe of the nature of DM. Integrating down to a limit of {{M}UV}=-16.5 for the James Webb Space Telescope (JWST), the SMD evolves as log (SMD) \\propto -0.63(1+z) in {{m}x}=1.5 keV WDM, as compared to log (SMD) \\propto -0.44(1+z) in CDM. Thus, high-redshift stellar assembly provides a powerful test bed for WDM models, accessible with the upcoming JWST.
Dark energy at early times, the Hubble parameter, and the string axiverse
NASA Astrophysics Data System (ADS)
Karwal, Tanvi; Kamionkowski, Marc
2016-11-01
Precise measurements of the cosmic microwave background (CMB) power spectrum are in excellent agreement with the predictions of the standard Λ CDM cosmological model. However, there is some tension between the value of the Hubble parameter H0 inferred from the CMB and that inferred from observations of the Universe at lower redshifts, and the unusually small value of the dark-energy density is a puzzling ingredient of the model. In this paper, we explore a scenario with a new exotic energy density that behaves like a cosmological constant at early times and then decays quickly at some critical redshift zc. An exotic energy density like this is motivated by some string-axiverse-inspired scenarios for dark energy. By increasing the expansion rate at early times, the very precisely determined angular scale of the sound horizon at decoupling can be preserved with a larger Hubble constant. We find, however, that the Planck temperature power spectrum tightly constrains the magnitude of the early dark-energy density and thus any shift in the Hubble constant obtained from the CMB. If the reionization optical depth is required to be smaller than the Planck 2016 2 σ upper bound τ ≲0.0774 , then early dark energy allows a Hubble-parameter shift of at most 1.6 km s-1 Mpc-1 (at zc≃1585 ), too small to fully alleviate the Hubble-parameter tension. Only if τ is increased by more than 5 σ can the CMB Hubble parameter be brought into agreement with that from local measurements. In the process, we derive strong constraints to the contribution of early dark energy at the time of recombination—it can never exceed ˜2 % of the radiation/matter density for 10 ≲zc≲1 05 .
NASA Astrophysics Data System (ADS)
Grin, Daniel; Hanson, Duncan; Holder, Gilbert P.; Doré, Olivier; Kamionkowski, Marc
2014-01-01
Primordial isocurvature fluctuations between photons and either neutrinos or nonrelativistic species such as baryons or dark matter are known to be subdominant to adiabatic fluctuations. Perturbations in the relative densities of baryons and dark matter (known as compensated isocurvature perturbations or CIPs), however, are surprisingly poorly constrained. CIPs leave no imprint in the cosmic microwave background (CMB) on observable scales, at least at linear order in their amplitude and zeroth order in the amplitude of adiabatic perturbations. It is thus not yet empirically known if baryons trace dark matter at the surface of last scattering. If CIPs exist, they would spatially modulate the Silk damping scale and acoustic horizon, causing distinct fluctuations in the CMB temperature/polarization power spectra across the sky: this effect is first order in both the CIP and adiabatic mode amplitudes. Here, temperature data from the Wilkinson Microwave Anisotropy Probe (WMAP) are used to conduct the first CMB-based observational search for CIPs, using off-diagonal correlations and the CMB trispectrum. Reconstruction noise from weak lensing and point sources is shown to be negligible for this data set. No evidence for CIPs is observed, and a 95% confidence upper limit of 1.1×10-2 is imposed to the amplitude of a scale-invariant CIP power spectrum. This limit agrees with CIP sensitivity forecasts for WMAP and is competitive with smaller-scale constraints from measurements of the baryon fraction in galaxy clusters. It is shown that the root-mean-squared CIP amplitude on 5-100° scales is smaller than ˜0.07-0.17 (depending on the scale) at the 95% confidence level. Temperature data from the Planck satellite will provide an even more sensitive probe for the existence of CIPs, as will the upcoming ACTPol and SPTPol experiments on smaller angular scales.
Tilden, A R; Becker, M A; Amma, L L; Arciniega, J; McGaw, A K
1997-03-01
Melatonin was measured in a species of aerobic photosynthetic bacteria, Erythrobacter longus, grown in either constant light or constant dark. A radioimmunoassay was used to quantify melatonin levels and thin-layer chromatography to confirm the identity of melatonin immunoactivity. Melatonin levels were significantly higher (nearly 2.3-fold) in the dark-grown than in the light-grown samples. Also, the homogenates of the dark-grown bacteria retained melatonin-producing enzymatic activity, whereas the light-grown homogenates did not; melatonin levels extracted from the dark-grown homogenates increased with increasing extraction time, reaching as high as 29.2 ng.mg-1 protein at 120 min. Removal of membrane fragments from homogenates did not influence melatonin levels in light-grown homogenate, but this procedure increased melatonin levels in dark-grown homogenate, indicating that at least some of the enzymes in the pathway of melatonin production are not membrane-bound. This study is the second to demonstrate the presence of melatonin at the prokaryotic level, supporting the evidence that melatonin appeared very early in evolution. Its function in prokaryotes has not been determined, but may relate to its antioxidative actions.
Gaugessence: a dark energy model with early time radiation-like equation of state
NASA Astrophysics Data System (ADS)
Mehrabi, Ahmad; Maleknejad, Azade; Kamali, Vahid
2017-03-01
In this work, we study a new quintessence model associated with non-Abelian gauge fields, minimally coupled to Einstein gravity. This gauge theory has been recently introduced and studied as an inflationary model, called gauge-flation. Here, however, we are interested in the late time cosmology of the model in the presence of matter and radiation to explain the present time accelerating Universe. During the radiation and matter eras, the gauge field tracks radiation and basically acts like a dark radiation sector. As we approach lower redshifts, the dark component takes the form of a dark energy source which eventually becomes the dominate part of the energy budget of the Universe. Due to the tracking feature of our model, solutions with different initial values are attracted to a common trajectory. The existence of early dark radiation is a robust prediction of our model which contributes to the effective number of relativistic species, N_{eff} and has its own interesting observational features.
Cooper, Emily A.; Norcia, Anthony M.
2015-01-01
The nervous system has evolved in an environment with structure and predictability. One of the ubiquitous principles of sensory systems is the creation of circuits that capitalize on this predictability. Previous work has identified predictable non-uniformities in the distributions of basic visual features in natural images that are relevant to the encoding tasks of the visual system. Here, we report that the well-established statistical distributions of visual features -- such as visual contrast, spatial scale, and depth -- differ between bright and dark image components. Following this analysis, we go on to trace how these differences in natural images translate into different patterns of cortical input that arise from the separate bright (ON) and dark (OFF) pathways originating in the retina. We use models of these early visual pathways to transform natural images into statistical patterns of cortical input. The models include the receptive fields and non-linear response properties of the magnocellular (M) and parvocellular (P) pathways, with their ON and OFF pathway divisions. The results indicate that there are regularities in visual cortical input beyond those that have previously been appreciated from the direct analysis of natural images. In particular, several dark/bright asymmetries provide a potential account for recently discovered asymmetries in how the brain processes visual features, such as violations of classic energy-type models. On the basis of our analysis, we expect that the dark/bright dichotomy in natural images plays a key role in the generation of both cortical and perceptual asymmetries. PMID:26020624
Early life stress perturbs the maturation of microglia in the developing hippocampus.
Delpech, Jean-Christophe; Wei, Lan; Hao, Jin; Yu, Xiaoqing; Madore, Charlotte; Butovsky, Oleg; Kaffman, Arie
2016-10-01
Children exposed to abuse or neglect show abnormal hippocampal development and similar findings have been reported in rodent models. Using brief daily separation (BDS), a mouse model of early life stress, we previously showed that exposure to BDS impairs hippocampal function in adulthood and perturbs synaptic maturation, synaptic pruning, axonal growth and myelination in the developing hippocampus. Given that microglia are involved in these developmental processes, we tested whether BDS impairs microglial activity in the hippocampus of 14 (during BDS) and 28-day old mice (one week after BDS). We found that BDS increased the density and altered the morphology of microglia in the hippocampus of 14-day old pups, effects that were no longer present on postnatal day (PND) 28. Despite the normal cell number and morphology seen at PND28, the molecular signature of hippocampal microglia, assessed using the NanoString immune panel, was altered at both ages. We showed that during normal hippocampal development, microglia undergo significant changes between PND14 and PND28, including reduced cell density, decreased ex vivo phagocytic activity, and an increase in the expression of genes involved in inflammation and cell migration. However, microglia harvested from the hippocampus of 28-day old BDS mice showed an increase in phagocytic activity and reduced expression of genes that normally increase across development. Promoter analysis indicated that alteration in the transcriptional activity of PU.1, Creb1, Sp1, and RelA accounted for most of the transcriptional changes seen during normal microglia development and for most of the BDS-induced changes at PND14 and PND28. These findings are the first to demonstrate that early life stress dysregulates microglial function in the developing hippocampus and to identify key transcription factors that are likely to mediate these changes.
Early life stress perturbs the maturation of microglia in the developing hippocampus
Delpech, Jean-Christophe; Wei, Lan; Hao, Jin; Yu, Xiaoqing; Madore, Charlotte; Butovsky, Oleg; Kaffman, Arie
2016-01-01
Children exposed to abuse or neglect show abnormal hippocampal development and similar findings have been reported in rodent models. Using brief daily separation (BDS), a mouse model of early life stress, we previously showed that exposure to BDS impairs hippocampal function in adulthood and perturbs synaptic maturation, synaptic pruning, axonal growth and myelination in the developing hippocampus. Given that microglia are involved in these developmental processes, we tested whether BDS impairs microglial activity in the hippocampus of 14 (during BDS) and 28-day old mice (one week after BDS). We found that BDS increased the density and altered the morphology of microglia in the hippocampus of 14-day old pups, effects that were no longer present on postnatal day (PND) 28. Despite the normal cell number and morphology seen at PND28, the molecular signature of hippocampal microglia, assessed using the NanoString immune panel, was altered at both ages. We showed that during normal hippocampal development, microglia undergo significant changes between PND14 and PND28, including reduced cell density, decreased ex vivo phagocytic activity, and an increase in the expression of genes involved in inflammation and cell migration. However, microglia harvested from the hippocampus of 28-day old BDS mice showed an increase in phagocytic activity and reduced expression of genes that normally increase across development. Promoter analysis indicated that alteration in the transcriptional activity of PU.1, Creb1, Sp1, and RelA accounted for most of the transcriptional changes seen during normal microglia development and for most of the BDS-induced changes at PND14 and PND28. These findings are the first to demonstrate that early life stress dysregulates microglial function in the developing hippocampus and to identify key transcription factors that are likely to mediate these changes. PMID:27301858
Superheavy thermal dark matter and primordial asymmetries
NASA Astrophysics Data System (ADS)
Bramante, Joseph; Unwin, James
2017-02-01
The early universe could feature multiple reheating events, leading to jumps in the visible sector entropy density that dilute both particle asymmetries and the number density of frozen-out states. In fact, late time entropy jumps are usually required in models of Affleck-Dine baryogenesis, which typically produces an initial particle-antiparticle asymmetry that is much too large. An important consequence of late time dilution, is that a smaller dark matter annihilation cross section is needed to obtain the observed dark matter relic density. For cosmologies with high scale baryogenesis, followed by radiation-dominated dark matter freeze-out, we show that the perturbative unitarity mass bound on thermal relic dark matter is relaxed to 1010 GeV. We proceed to study superheavy asym-metric dark matter models, made possible by a sizable entropy injection after dark matter freeze-out, and identify how the Affleck-Dine mechanism would generate the baryon and dark asymmetries.
Dark matter inside early-type galaxies as function of mass and redshift
NASA Astrophysics Data System (ADS)
Nigoche-Netro, A.; Ramos-Larios, G.; Lagos, P.; Ruelas-Mayorga, A.; de la Fuente, E.; Kemp, S. N.; Navarro, S. G.; Corral, L. J.; Hidalgo-Gámez, A. M.
2016-10-01
We study the behaviour of the dynamical and stellar mass inside the effective radius (re) of early-type galaxies (ETGs). We use several samples of ETGs - ranging from 19 000 to 98 000 objects - from the ninth data release of the Sloan Digital Sky Survey. We consider Newtonian dynamics, different light profiles and different initial mass functions (IMF) to calculate the dynamical and stellar mass. We assume that any difference between these two masses is due to dark matter and/or a non-universal IMF. The main results for galaxies in the redshift range 0.0024 < z < 0.3500 and in the dynamical mass range 9.5 < log(M) < 12.5 are: (i) a significant part of the intrinsic dispersion of the distribution of dynamical versus stellar mass is due to redshift; (ii) the difference between dynamical and stellar mass increases as a function of dynamical mass and decreases as a function of redshift; (iii) the difference between dynamical and stellar mass goes from approximately 0 to 70 per cent of the dynamical mass depending on mass and redshift; (iv) these differences could be due to dark matter or a non-universal IMF or a combination of both; (v) the amount of dark matter inside ETGs would be equal to or less than the difference between dynamical and stellar mass depending on the impact of the IMF on the stellar mass estimation; (vi) the previous results go in the same direction of some results of the Fundamental Plane (FP) found in the literature in the sense that they could be interpreted as an increase of dark matter along the FP and a dependence of the FP on redshift.
The density of dark matter haloes of early-type galaxies in low-density environments
NASA Astrophysics Data System (ADS)
Corsini, E. M.; Wegner, G. A.; Thomas, J.; Saglia, R. P.; Bender, R.
2017-04-01
New photometric and long-slit spectroscopic observations are presented for NGC 7113, PGC 1852, and PGC 67207 which are three bright galaxies residing in low-density environments. The surface-brightness distribution is analysed from the KS-band images taken with adaptive optics at the Gemini North Telescope and the ugriz-band images from the Sloan Digital Sky Survey while the line-of-sight stellar velocity distribution and line-strength Lick indices inside the effective radius are measured along several position angles. The age, metallicity, and α-element abundance of the galaxies are estimated from single stellar-population models. In spite of the available morphological classification, images show that PGC 1852 is a barred spiral which we do not further consider for mass modelling. The structural parameters of the two early-type galaxies NGC 7113 and PGC 67207 are obtained from a two-dimensional photometric decomposition and the mass-to-light ratio of all the (luminous and dark) mass that follows the light is derived from orbit-based axisymmetric dynamical modelling together with the mass density of the dark matter halo. The dynamically derived mass that follows the light is about a factor of 2 larger than the stellar mass derived using stellar-population models with Kroupa initial mass function. Both galaxies have a lower content of halo dark matter with respect to early-type galaxies in high-density environments and in agreement with the predictions of semi-analytical models of galaxy formation.
NASA Astrophysics Data System (ADS)
Samurović, S.
2014-10-01
Context. The departures from Newtonian dynamics based on the mass-follows-light approach discovered in the outer parts of some early-type galaxies imply the existence of dark matter and/or necessary modifications to the Newtonian approach. We study dynamical models of a sample of ten early-type galaxies in both Newtonian and MOND approaches. Aims: The measurements of the radial velocities of the globular clusters in ten massive early-type galaxies are used to test the predictions of dynamical models with and without dark matter assuming Newtonian and MOND approaches out to several effective radii. Methods: The globular clusters taken from the SLUGGS database are used as tracers of the gravitational potential of the galaxies in a sample. We solve the Jeans equation for both the Newtonian (mass-follows-light and dark matter models) and the MOND approaches by assuming spherical symmetry and compare the resulting mass-to-light ratios with stellar population synthesis models. For both approaches, we apply various assumptions on velocity anisotropy. Results: We find that the Newtonian mass-follows-light models without a significant amount of dark matter can provide successful fits for only one galaxy (NGC 2768), and for the remaining nine early-type galaxies, various amounts of dark matter are required in the outer parts beyond 2 - 3Re. With MOND models, we find that four early-type galaxies could be fit without dark matter and that the remaining six galaxies require an additional dark component to successfully fit the line-of-sight observed velocity dispersions; the galaxy NGC 4486 (M 87) is the only galaxy for which dark matter is required in the inner regions, and MOND cannot fit the data without additional dark matter. In the inner region, the galaxy NGC 4365 requires higher mass-to-light ratios than the stellar values from population synthesis, but a reasonable mass-to-light ratio can be reached for MOND assuming slightly tangential orbits. The ten galaxies can be
NASA Astrophysics Data System (ADS)
Caprini, Chiara; Tamanini, Nicola
2016-10-01
We perform a forecast analysis of the capability of the eLISA space-based interferometer to constrain models of early and interacting dark energy using gravitational wave standard sirens. We employ simulated catalogues of standard sirens given by merging massive black hole binaries visible by eLISA, with an electromagnetic counterpart detectable by future telescopes. We consider three-arms mission designs with arm length of 1, 2 and 5 million km, 5 years of mission duration and the best-level low frequency noise as recently tested by the LISA Pathfinder. Standard sirens with eLISA give access to an intermediate range of redshift 1 lesssim z lesssim 8, and can therefore provide competitive constraints on models where the onset of the deviation from ΛCDM (i.e. the epoch when early dark energy starts to be non-negligible, or when the interaction with dark matter begins) occurs relatively late, at z lesssim 6. If instead early or interacting dark energy is relevant already in the pre-recombination era, current cosmological probes (especially the cosmic microwave background) are more efficient than eLISA in constraining these models, except possibly in the interacting dark energy model if the energy exchange is proportional to the energy density of dark energy.
Early Cretaceous CO2 Pulses: Trigger of Carbon Cycle Perturbations and of Biocalcification Crises
NASA Astrophysics Data System (ADS)
Weissert, H.; Wissler, L.; Hennig, S.
2003-04-01
The Early Cretaceous C-isotope curve is marked by several positive carbon isotope anomalies with an amplitude of 2-3 ppm and lasting up to millions of years. The two most prominent of these excursions are of Late Valanginian and Aptian age. Isotopic mass balance models suggest that positive carbon isotope excursions reflect altered partitioning of carbon between the oxidized and reduced carbon sinks and that these changes occurred in response to elevated atmospheric CO_2 levels and coupled climate change. Both carbon isotope anomalies coincide with episodes of increased volcanic activity, which is regarded as the source of excess atmospheric carbon dioxide. The Aptian carbon isotope anomaly is preceded by a short-lived negative carbon isotope pulse of up to 2 ppm amplitude while a comparable pulse is not recognized at the base of the Valanginian carbon isotope excursion. This C- isotope event may record a climate-induced destabilisation of sedimentary gas hydrates and the sudden release of methane to oceans and atmosphere. Both, the Aptian and the Valanginian carbon isotope excursions are accompanied by biocalcification crises on carbonate platforms and in pelagic environments. The Valanginian carbonate platform drowning, the nannoconid crisis and the disappearance of calpionellids coincide with the beginning of the positive carbon isotope anomaly. The Aptian biocalcification crises on platforms and in pelagic environments started before the negative carbon isotope spike. Both crises in biocalcification may have been triggered by p CO_2-induced changes in surface water chemistry and/or by sudden changes in temperatures and/or by changes in nutrient levels. Available paleoclimate data and the bulk oxygen isotope records show no evidence for major low latitude ocean paleotemperature changes at the base of the Valanginian isotope anomaly. Partial choking of carbonate production during the Aptian occurred at a time of decreasing oxygen isotope values in pelagic bulk
Copper and thermal perturbations on the early life processes of the hard coral Platygyra acuta
NASA Astrophysics Data System (ADS)
Kwok, C. K.; Lam, K. Y.; Leung, S. M.; Chui, A. P. Y.; Ang, P. O.
2016-09-01
Anthropogenic pollutants and climate change are major threats to coral reefs today. Yet interactions between chemical and thermal perturbations have not been fully explored in reef studies. Here, we present the single and combined effects of copper (Cu) with thermal stress on five early life-history stages/processes (fertilization, larval mortality, swimming ability, metamorphosis and growth of juvenile recruits) of the massive coral Platygyra acuta in Hong Kong. In the first four experiments, coral gametes and larvae were exposed to different Cu doses (0-200 μg L-1, apart from the fertilization assay in which 0-1000 μg L-1 was used) and temperature treatments (ambient and ambient +2 or +3 °C as a thermal stress treatment) following a factorial experimental design. Exposure time was 5 h for the fertilization assay and 48 h for the other experiments. The last experiment on growth of coral recruits was conducted over 56 d with 0-80 μg L-1 Cu used. Cu significantly reduced percent fertilization success, percentage of active swimming larvae and larval survivorship (EC50s, the half maximal effective concentrations, for percent fertilization success and percentage of active swimming larvae were 92-145 and 45-47 μg L-1 respectively. While LC50, the lethal concentration that kills 50% of the population, was 101-110 μg L-1), while growth of coral recruits was not affected at 80 μg L-1 Cu for 56 d. No settling cues were used in the settlement experiment. In their absence, percent metamorphosis increased with Cu doses, in sharp contrast to earlier findings. Settlement and metamorphosis may thus be strategies for coral larvae to escape from Cu toxicity. Thermal treatment did not significantly affect any experimental end points. This is likely because the thermal regimes used in the experiments were within the range experienced by local corals. The high variability in Cu toxicities indicates differential susceptibilities of the various life-history stages/processes of P
Dilaton dominance in the early universe dilutes dark matter relic abundances
Lahanas, A. B.
2011-05-15
The role of the dilaton field and its coupling to matter may result in a dilution of dark matter (DM) relic densities. This is to be contrasted with quintessence scenarios in which relic densities are augmented, due to modification of the expansion rate, since the Universe is not radiation dominated at DM decoupling. The dilaton field, besides this, affects relic densities through its coupling to dust which tends to decrease relic abundances. Thus two separate mechanisms compete with each other resulting, in general, in a decrease of the relic density. This feature may be welcomed and can help the situation if direct dark matter experiments point towards small neutralino-nucleon cross sections, implying small neutralino annihilation rates and hence large relic densities, at least in the popular supersymmetric scenarios. In the presence of a diluting mechanism, both experimental constraints can be met. The role of the dilaton for this mechanism has been studied in the context of the noncritical string theory but in this work we follow a rather general approach assuming that the dilaton dominates only at early eras long before big bang nucleosynthesis.
Globular clusters, satellite galaxies and stellar haloes from early dark matter peaks
NASA Astrophysics Data System (ADS)
Moore, Ben; Diemand, Juerg; Madau, Piero; Zemp, Marcel; Stadel, Joachim
2006-05-01
The Milky Way contains several distinct old stellar components that provide a fossil record of its formation. We can understand their spatial distribution and kinematics in a hierarchical formation scenario by associating the protogalactic fragments envisaged by Searle & Zinn (1978) with the rare peaks able to cool gas in the cold dark matter density field collapsing at redshift z > 10. We use hierarchical structure formation simulations to explore the kinematics and spatial distribution of these early star-forming structures in galaxy haloes today. Most of the protogalaxies rapidly merge, their stellar contents and dark matter becoming smoothly distributed and forming the inner Galactic halo. The metal-poor globular clusters and old halo stars become tracers of this early evolutionary phase, centrally biased and naturally reproducing the observed steep fall off with radius. The most outlying peaks fall in late and survive to the present day as satellite galaxies. The observed radial velocity dispersion profile and the local radial velocity anisotropy of Milky Way halo stars are successfully reproduced in this model. If this epoch of structure formation coincides with a suppression of further cooling into lower sigma peaks then we can reproduce the rarity, kinematics and spatial distribution of satellite galaxies as suggested by Bullock, Kravtsov & Weinberg (2000). Reionization at z= 12 +/- 2 provides a natural solution to the missing satellites problem. Measuring the distribution of globular clusters and halo light on scales from galaxies to clusters could be used to constrain global versus local reionization models. If reionization occurs contemporary, our model predicts a constant frequency of blue globulars relative to the host halo mass, except for dwarf galaxies where the average relative frequencies become smaller.
ERIC Educational Resources Information Center
Bown, Kathryn; Sumsion, Jennifer; Press, Frances
2011-01-01
The article reports on a study investigating influences on Australian politicians' decision making for early childhood education and care (ECEC) policy. The astronomical concept of dark matter is utilised as a metaphor for considering normalising, and therefore frequently difficult to detect and disrupt, influences implicated in politicians'…
Kinematic properties and dark matter fraction of Virgo dwarf early-type galaxies
NASA Astrophysics Data System (ADS)
Toloba, E.; Boselli, A.; Peletier, R.; Gorgas, J.
2015-03-01
What happens to dwarf galaxies as they enter the cluster potential well is one of the main unknowns in studies of galaxy evolution. Several evidence suggests that late-type galaxies enter the cluster and are transformed to dwarf early-type galaxies (dEs). We study the Virgo cluster to understand which mechanisms are involved in this transformation. We find that the dEs in the outer parts of Virgo have rotation curves with shapes and amplitudes similar to late-type galaxies of the same luminosity (Fig. 1). These dEs are rotationally supported, have disky isophotes, and younger ages than those dEs in the center of Virgo, which are pressure supported, often have boxy isophotes and are older (Fig. 1). Ram pressure stripping, thus, explains the properties of the dEs located in the outskirts of Virgo. However, the dEs in the central cluster regions, which have lost their angular momentum, must have suffered a more violent transformation. A combination of ram pressure stripping and harassment is not enough to remove the rotation and the spiral/disky structures of these galaxies. We find that on the the Faber-Jackson and the Fundamental Plane relations dEs deviate from the trends of massive elliptical galaxies towards the position of dark matter dominated systems such as the dwarf spheroidal satellites of the Milky Way and M31. Both, rotationally and pressure supported dEs, however, populate the same region in these diagrams. This indicates that dEs have a non-negligible dark matter fraction within their half light radius.
NASA Astrophysics Data System (ADS)
Sonnenfeld, A.; Treu, T.; Gavazzi, R.; Marshall, P. J.; Auger, M. W.; Suyu, S. H.; Koopmans, L. V. E.; Bolton, A. S.
2012-06-01
Stars and dark matter account for most of the mass of early-type galaxies, but uncertainties in the stellar population and the dark matter profile make it challenging to distinguish between the two components. Nevertheless, precise observations of stellar and dark matter are extremely valuable for testing the many models of structure formation and evolution. We present a measurement of the stellar mass and inner slope of the dark matter halo of a massive early-type galaxy at z = 0.222. The galaxy is the foreground deflector of the double Einstein ring gravitational lens system SDSSJ0946+1006, also known as the "Jackpot." By combining the tools of lensing and dynamics we first constrain the mean slope of the total mass density profile (\\rho _{tot}\\propto r^{-\\gamma ^{\\prime }}) within the radius of the outer ring to be γ' = 1.98 ± 0.02 ± 0.01. Then we obtain a bulge-halo decomposition, assuming a power-law form for the dark matter halo. Our analysis yields γDM = 1.7 ± 0.2 for the inner slope of the dark matter profile, in agreement with theoretical findings on the distribution of dark matter in ellipticals, and a stellar mass from lensing and dynamics M LD * = 5.5-1.3 +0.4 × 1011 M ⊙. By comparing this measurement with stellar masses inferred from stellar population synthesis fitting we find that a Salpeter initial mass function (IMF) provides a good description of the stellar population of the lens while the probability of the IMF being heavier than Chabrier is 95%. Our data suggest that growth by accretion of small systems from a compact red nugget is a plausible formation scenario for this object.
Carbon recombination line observations of the sharpless 140 region. [of early stars in dark clouds
NASA Technical Reports Server (NTRS)
Knapp, G. R.; Brown, R. L.; Kuiper, T. B. H.; Kakar, R. K.
1976-01-01
Carbon recombination-line emission has been detected at two frequencies from a dark cloud contiguous with the small H II region Sharpless 140. The observations show the dark cloud to be of unusually low temperature and to have a markedly inhomogeneous density distribution, with localized region of high density surrounding one or more embedded stars. The carbon is probably ionized by photons from both the exciting star of S140 and the embedded stars. The dark cloud and S140 apparently represent two stages of star formation which have occurred over a period of at least 500,000 years in adjacent regions of the same dark cloud.
Sayal, Rupinder; Dresch, Jacqueline M; Pushel, Irina; Taylor, Benjamin R; Arnosti, David N
2016-01-01
Enhancers constitute one of the major components of regulatory machinery of metazoans. Although several genome-wide studies have focused on finding and locating enhancers in the genomes, the fundamental principles governing their internal architecture and cis-regulatory grammar remain elusive. Here, we describe an extensive, quantitative perturbation analysis targeting the dorsal-ventral patterning gene regulatory network (GRN) controlled by Drosophila NF-κB homolog Dorsal. To understand transcription factor interactions on enhancers, we employed an ensemble of mathematical models, testing effects of cooperativity, repression, and factor potency. Models trained on the dataset correctly predict activity of evolutionarily divergent regulatory regions, providing insights into spatial relationships between repressor and activator binding sites. Importantly, the collective predictions of sets of models were effective at novel enhancer identification and characterization. Our study demonstrates how experimental dataset and modeling can be effectively combined to provide quantitative insights into cis-regulatory information on a genome-wide scale. DOI: http://dx.doi.org/10.7554/eLife.08445.001 PMID:27152947
Artificial selection on egg size perturbs early pattern formation in Drosophila melanogaster.
Miles, Cecelia M; Lott, Susan E; Hendriks, Cris L Luengo; Ludwig, Michael Z; Manu; Williams, Calvin L; Kreitman, Martin
2011-01-01
Pattern formation in Drosophila embryogenesis has been widely investigated as a developmental and evolutionary model of robustness. To ask whether genetic variation for pattern formation is suppressed in this system, artificial selection for divergent egg size was used to challenge the scaling of even-skipped (eve) pattern formation in mitotic cycle 14 (stage 5) embryos of Drosophila melanogaster. Three-dimensional confocal imaging revealed shifts in the allometry of eve pair-rule stripes along both anterior–posterior (A–P) and dorsoventral (D–V) axes as a correlated response to egg size selection, indicating the availability of genetic variation for this buffered trait. Environmental perturbation was not required for the manifestation of this variation. The number of nuclei at the cellular blastoderm stage also changed in response to selection, with large-egg selected lines having more than 1000 additional nuclei relative to small-egg lines. This increase in nuclear number in larger eggs does not scale with egg size, however, as nuclear density is inversely correlated with egg length. Nuclear density varies along the A–P axis but does not correlate with the shift in eve stripe allometry between the selection treatments. Despite its macroevolutionary conservation, both eve stripe patterning and blastoderm cell number vary genetically both within and between closely related species.
Ten scenarios from early radiation to late time acceleration with a minimally coupled dark energy
Fay, Stéphane
2013-09-01
We consider General Relativity with matter, radiation and a minimally coupled dark energy defined by an equation of state w. Using dynamical system method, we find the equilibrium points of such a theory assuming an expanding Universe and a positive dark energy density. Two of these points correspond to classical radiation and matter dominated epochs for the Universe. For the other points, dark energy mimics matter, radiation or accelerates Universe expansion. We then look for possible sequences of epochs describing a Universe starting with some radiation dominated epoch(s) (mimicked or not by dark energy), then matter dominated epoch(s) (mimicked or not by dark energy) and ending with an accelerated expansion. We find ten sequences able to follow this Universe history without singular behaviour of w at some saddle points. Most of them are new in dark energy literature. To get more than these ten sequences, w has to be singular at some specific saddle equilibrium points. This is an unusual mathematical property of the equation of state in dark energy literature, whose physical consequences tend to be discarded by observations. This thus distinguishes the ten above sequences from an infinity of ways to describe Universe expansion.
Belloso, Alicia Bueno; García-Bellido, Juan; Sapone, Domenico E-mail: juan.garciabellido@uam.es
2011-10-01
We provide exact solutions to the cosmological matter perturbation equation in a homogeneous FLRW universe with a vacuum energy that can be parametrized by a constant equation of state parameter w and a very accurate approximation for the Ansatz w(a) = w{sub 0}+w{sub a}(1−a). We compute the growth index γ = log f(a)/log Ω{sub m}(a), and its redshift dependence, using the exact and approximate solutions in terms of Legendre polynomials and show that it can be parametrized as γ(a) = γ{sub 0}+γ{sub a}(1−a) in most cases. We then compare four different types of dark energy (DE) models: wΛCDM, DGP, f(R) and a LTB-large-void model, which have very different behaviors at z∼>1. This allows us to study the possibility to differentiate between different DE alternatives using wide and deep surveys like Euclid, which will measure both photometric and spectroscopic redshifts for several hundreds of millions of galaxies up to redshift z ≅ 2. We do a Fisher matrix analysis for the prospects of differentiating among the different DE models in terms of the growth index, taken as a given function of redshift or with a principal component analysis, with a value for each redshift bin for a Euclid-like survey. We use as observables the complete and marginalized power spectrum of galaxies P(k) and the Weak Lensing (WL) power spectrum. We find that, using P(k), one can reach (2%, 5%) errors in (w{sub 0},w{sub a}), and (4%, 12%) errors in (γ{sub 0},γ{sub a}), while using WL we get errors at least twice as large. These estimates allow us to differentiate easily between DGP, f(R) models and ΛCDM, while it would be more difficult to distinguish the latter from a variable equation of state parameter or LTB models using only the growth index.
Evolution of density and velocity profiles of dark matter and dark energy in spherical voids
NASA Astrophysics Data System (ADS)
Novosyadlyj, Bohdan; Tsizh, Maksym; Kulinich, Yurij
2017-02-01
We analyse the evolution of cosmological perturbations which leads to the formation of large isolated voids in the Universe. We assume that initial perturbations are spherical and all components of the Universe (radiation, matter and dark energy) are continuous media with ideal fluid energy-momentum tensors, which interact only gravitationally. Equations of the evolution of perturbations for every component in the comoving to cosmological background reference frame are obtained from equations of energy and momentum conservation and Einstein's ones and are integrated numerically. Initial conditions are set at the early stage of evolution in the radiation-dominated epoch, when the scale of perturbation is much larger than the particle horizon. Results show how the profiles of density and velocity of matter and dark energy are formed and how they depend on parameters of dark energy and initial conditions. In particular, it is shown that final matter density and velocity amplitudes change within range ˜4-7 per cent when the value of equation-of-state parameter of dark energy w vary in the range from -0.8 to -1.2, and change within ˜1 per cent only when the value of effective sound speed of dark energy vary over all allowable range of its values.
Cosmological magnetic field: a fossil of density perturbations in the early universe.
Ichiki, Kiyotomo; Takahashi, Keitaro; Ohno, Hiroshi; Hanayama, Hidekazu; Sugiyama, Naoshi
2006-02-10
The origin of the substantial magnetic fields that are found in galaxies and on even larger scales, such as in clusters of galaxies, is yet unclear. If the second-order couplings between photons and electrons are considered, then cosmological density fluctuations, which explain the large-scale structure of the universe, can also produce magnetic fields on cosmological scales before the epoch of recombination. By evaluating the power spectrum of these cosmological magnetic fields on a range of scales, we show here that magnetic fields of 10(-18.1) gauss are generated at a 1-megaparsec scale and can be even stronger at smaller scales (10(-14.1) gauss at 10 kiloparsecs). These fields are large enough to seed magnetic fields in galaxies and may therefore have affected primordial star formation in the early universe.
Perturbations for transient acceleration
Vargas, Cristofher Zuñiga; Zimdahl, Winfried; Hipólito-Ricaldi, Wiliam S. E-mail: hipolito@ceunes.ufes.br
2012-04-01
According to the standard ΛCDM model, the accelerated expansion of the Universe will go on forever. Motivated by recent observational results, we explore the possibility of a finite phase of acceleration which asymptotically approaches another period of decelerated expansion. Extending an earlier study on a corresponding homogeneous and isotropic dynamics, in which interactions between dark matter and dark energy are crucial, the present paper also investigates the dynamics of the matter perturbations both on the Newtonian and General Relativistic (GR) levels and quantifies the potential relevance of perturbations of the dark-energy component. In the background, the model is tested against the Supernova type Ia (SNIa) data of the Constitution set and on the perturbative level against growth rate data, among them those of the WiggleZ survey, and the data of the 2dFGRS project. Our results indicate that a transient phase of accelerated expansion is not excluded by current observations.
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.
Yamazaki, Makoto; Miyake, Manami; Sato, Hiroko; Masutomi, Naoya; Tsutsui, Naohisa; Adam, Klaus-Peter; Alexander, Danny C.; Lawton, Kay A.; Milburn, Michael V.; Ryals, John A.; Wulff, Jacob E.; Guo, Lining
2013-04-01
Drug-induced liver injury (DILI) is a significant consideration for drug development. Current preclinical DILI assessment relying on histopathology and clinical chemistry has limitations in sensitivity and discordance with human. To gain insights on DILI pathogenesis and identify potential biomarkers for improved DILI detection, we performed untargeted metabolomic analyses on rats treated with thirteen known hepatotoxins causing various types of DILI: necrosis (acetaminophen, bendazac, cyclosporine A, carbon tetrachloride, ethionine), cholestasis (methapyrilene and naphthylisothiocyanate), steatosis (tetracycline and ticlopidine), and idiosyncratic (carbamazepine, chlorzoxasone, flutamide, and nimesulide) at two doses and two time points. Statistical analysis and pathway mapping of the nearly 1900 metabolites profiled in the plasma, urine, and liver revealed diverse time and dose dependent metabolic cascades leading to DILI by the hepatotoxins. The most consistent change induced by the hepatotoxins, detectable even at the early time point/low dose, was the significant elevations of a panel of bile acids in the plasma and urine, suggesting that DILI impaired hepatic bile acid uptake from the circulation. Furthermore, bile acid amidation in the hepatocytes was altered depending on the severity of the hepatotoxin-induced oxidative stress. The alteration of the bile acids was most evident by the necrosis and cholestasis hepatotoxins, with more subtle effects by the steatosis and idiosyncratic hepatotoxins. Taking together, our data suggest that the perturbation of bile acid homeostasis is an early event of DILI. Upon further validation, selected bile acids in the circulation could be potentially used as sensitive and early DILI preclinical biomarkers. - Highlights: ► We used metabolomics to gain insights on drug induced liver injury (DILI) in rats. ► We profiled rats treated with thirteen hepatotoxins at two doses and two time points. ► The toxins decreased the
Early-Life Stress Perturbs Key Cellular Programs in the Developing Mouse Hippocampus.
Wei, Lan; Hao, Jin; Lacher, Richard K; Abbott, Thomas; Chung, Lisa; Colangelo, Christopher M; Kaffman, Arie
2015-01-01
Conflicting reports are available with regard to the effects of childhood abuse and neglect on hippocampal function in children. While earlier imaging studies and some animal work have suggested that the effects of early-life stress (ELS) manifest only in adulthood, more recent studies have documented impaired hippocampal function in maltreated children and adolescents. Additional work using animal modes is needed to clarify the effects of ELS on hippocampal development. In this regard, genomic, proteomic, and molecular tools uniquely available in the mouse make it a particularly attractive model system to study this issue. However, very little work has been done so far to characterize the effects of ELS on hippocampal development in the mouse. To address this issue, we examined the effects of brief daily separation (BDS), a mouse model of ELS that impairs hippocampal-dependent memory in adulthood, on hippocampal development in 28-day-old juvenile mice. This age was chosen because it corresponds to the developmental period in which human imaging studies have revealed abnormal hippocampal development in maltreated children. Exposure to BDS caused a significant decrease in the total protein content of synaptosomes harvested from the hippocampus of 28-day-old male and female mice, suggesting that BDS impairs normal synaptic development in the juvenile hippocampus. Using a novel liquid chromatography multiple reaction monitoring mass spectrometry (LC-MRM) assay, we found decreased expression of many synaptic proteins, as well as proteins involved in axonal growth, myelination, and mitochondrial activity. Golgi staining in 28-day-old BDS mice showed an increase in the number of immature and abnormally shaped spines and a decrease in the number of mature spines in CA1 neurons, consistent with defects in synaptic maturation and synaptic pruning at this age. In 14-day-old pups, BDS deceased the expression of proteins involved in axonal growth and myelination, but did not
Sapone, Domenico; Kunz, Martin
2009-10-15
Dark energy perturbations are normally either neglected or else included in a purely numerical way, obscuring their dependence on underlying parameters like the equation of state or the sound speed. However, while many different explanations for the dark energy can have the same equation of state, they usually differ in their perturbations so that these provide a fingerprint for distinguishing between different models with the same equation of state. In this paper we derive simple yet accurate approximations that are able to characterize a specific class of models (encompassing most scalar-field models) which is often generically called 'dark energy'. We then use the approximate solutions to look at the impact of the dark energy perturbations on the dark matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background radiation.
Constraints on the very early universe from thermal WIMP dark matter
Drees, Manuel; Kakizaki, Mitsuru; Iminniyaz, Hoernisa
2007-11-15
We investigate the relic density n{sub {chi}} of nonrelativistic long-lived or stable particles {chi} in nonstandard cosmological scenarios. We calculate the relic abundance starting from arbitrary initial temperatures of the radiation-dominated epoch, and derive the lower bound on the initial temperature T{sub 0}{>=}m{sub {chi}}/23, assuming that thermally produced {chi} particles account for the dark matter energy density in the Universe; this bound holds for all {chi} annihilation cross sections. We also investigate cosmological scenarios with modified expansion rate. Even in this case an approximate formula similar to the standard one is capable of predicting the final relic abundance correctly. Choosing the {chi} annihilation cross section such that the observed cold dark matter abundance is reproduced in standard cosmology, we constrain possible modifications of the expansion rate at T{approx}m{sub {chi}}/20, well before big bang nucleosynthesis.
Detecting early stage pressure ulcer on dark skin using multispectral imager
NASA Astrophysics Data System (ADS)
Yi, Dingrong; Kong, Linghua; Sprigle, Stephen; Wang, Fengtao; Wang, Chao; Liu, Fuhan; Adibi, Ali; Tummala, Rao
2010-02-01
We are developing a handheld multispectral imaging device to non-invasively inspect stage I pressure ulcers in dark pigmented skins without the need of touching the patient's skin. This paper reports some preliminary test results of using a proof-of-concept prototype. It also talks about the innovation's impact to traditional multispectral imaging technologies and the fields that will potentially benefit from it.
Earth-mass dark-matter haloes as the first structures in the early Universe.
Diemand, J; Moore, B; Stadel, J
2005-01-27
The Universe was nearly smooth and homogeneous before a redshift of z = 100, about 20 million years after the Big Bang. After this epoch, the tiny fluctuations imprinted upon the matter distribution during the initial expansion began to collapse because of gravity. The properties of these fluctuations depend on the unknown nature of dark matter, the determination of which is one of the biggest challenges in present-day science. Here we report supercomputer simulations of the concordance cosmological model, which assumes neutralino dark matter (at present the preferred candidate), and find that the first objects to form are numerous Earth-mass dark-matter haloes about as large as the Solar System. They are stable against gravitational disruption, even within the central regions of the Milky Way. We expect over 10(15) to survive within the Galactic halo, with one passing through the Solar System every few thousand years. The nearest structures should be among the brightest sources of gamma-rays (from particle-particle annihilation).
Flex, Elisabetta; Niceta, Marcello; Cecchetti, Serena; Thiffault, Isabelle; Au, Margaret G; Capuano, Alessandro; Piermarini, Emanuela; Ivanova, Anna A; Francis, Joshua W; Chillemi, Giovanni; Chandramouli, Balasubramanian; Carpentieri, Giovanna; Haaxma, Charlotte A; Ciolfi, Andrea; Pizzi, Simone; Douglas, Ganka V; Levine, Kara; Sferra, Antonella; Dentici, Maria Lisa; Pfundt, Rolph R; Le Pichon, Jean-Baptiste; Farrow, Emily; Baas, Frank; Piemonte, Fiorella; Dallapiccola, Bruno; Graham, John M; Saunders, Carol J; Bertini, Enrico; Kahn, Richard A; Koolen, David A; Tartaglia, Marco
2016-10-06
Microtubules are dynamic cytoskeletal elements coordinating and supporting a variety of neuronal processes, including cell division, migration, polarity, intracellular trafficking, and signal transduction. Mutations in genes encoding tubulins and microtubule-associated proteins are known to cause neurodevelopmental and neurodegenerative disorders. Growing evidence suggests that altered microtubule dynamics may also underlie or contribute to neurodevelopmental disorders and neurodegeneration. We report that biallelic mutations in TBCD, encoding one of the five co-chaperones required for assembly and disassembly of the αβ-tubulin heterodimer, the structural unit of microtubules, cause a disease with neurodevelopmental and neurodegenerative features characterized by early-onset cortical atrophy, secondary hypomyelination, microcephaly, thin corpus callosum, developmental delay, intellectual disability, seizures, optic atrophy, and spastic quadriplegia. Molecular dynamics simulations predicted long-range and/or local structural perturbations associated with the disease-causing mutations. Biochemical analyses documented variably reduced levels of TBCD, indicating relative instability of mutant proteins, and defective β-tubulin binding in a subset of the tested mutants. Reduced or defective TBCD function resulted in decreased soluble α/β-tubulin levels and accelerated microtubule polymerization in fibroblasts from affected subjects, demonstrating an overall shift toward a more rapidly growing and stable microtubule population. These cells displayed an aberrant mitotic spindle with disorganized, tangle-shaped microtubules and reduced aster formation, which however did not alter appreciably the rate of cell proliferation. Our findings establish that defective TBCD function underlies a recognizable encephalopathy and drives accelerated microtubule polymerization and enhanced microtubule stability, underscoring an additional cause of altered microtubule dynamics with
Formation of the spherical voids in the models of the universe with dark energy
NASA Astrophysics Data System (ADS)
Tsizh, M.; Novosyadlyj, B.
2016-06-01
We analyze evolution of cosmological perturbations which lead to the formation of large voids in the distribution of galaxies. We suppose that perturbations are spherical and main energetic components – radiation, matter and dark energy – are continuous media with ideal fluid energy-momentum tensors, which interact only gravitationally. Equations of the evolution of perturbations in the comoving to cosmological background reference frame for every component are obtained from equations of conservation and Einstein's ones and are integrated by modified Euler method with setting the initial conditions at the early stage of evolution in radiation-dominated epoch, when the scale of perturbation is mush larger than particle horizon. Obtained results illustrate dynamics of dark energy in the void region and its dependence on parameter of effective speed of sound of dark energy.
Early Childhood Inclusion: A Silver Lining in the Dark Clouds for African Immigrant Children?
ERIC Educational Resources Information Center
Agbenyega, Joseph; Peers, Chris
2010-01-01
This article presents preliminary findings of an ongoing study that attempts to gauge the level of access to and support for early childhood education and care programs for sub Saharan African immigrant families living in Melbourne Australia. Using the Australian Early Years Learning Framework as a guide, we explored 30 parents' perception of…
NASA Astrophysics Data System (ADS)
Dodelson, Scott; Huterer, Dragan
2015-03-01
Maps of the Universe when it was 400,000 years old from observations of the cosmic microwave background and over the last ten billion years from galaxy surveys point to a compelling cosmological model. This model requires a very early epoch of accelerated expansion, inflation, during which the seeds of structure were planted via quantum mechanical fluctuations. These seeds began to grow via gravitational instability during the epoch in which dark matter dominated the energy density of the universe, transforming small perturbations laid down during inflation into nonlinear structures such as million light-year sized clusters, galaxies, stars, planets, and people. Over the past few billion years, we have entered a new phase, during which the expansion of the Universe is accelerating presumably driven by yet another substance, dark energy.
The formation and evolution of dark matter halos early in cosmic history
NASA Astrophysics Data System (ADS)
Ernest, Alllan David; Collins, Matthew P.
2015-08-01
Observational evidence points to the formation of super-massive black holes, heavy elements and halo structure much earlier in cosmic history than expected [1], and this is challenging for Lambda Cold Dark Matter (LCDM) theory. However, if photon scattering cross sections were less than expected it becomes possible for halos to form at earlier times and relax the tensions that exist with LCDM theory. This may indeed be the case: it has recently been shown [2,3] that photon-particle scattering cross sections vary significantly with the eigenspectral distribution of the scattering particle in deep gravity wells, an effect that depends on the degree of localization of the particle wavefunction and the proximity of the halo to thermal equilibrium. Cross sections tend to be lower the larger and deeper the gravitational well. This purely quantum effect means that accepted cross sections, as measured on Earth and used to determine the rate and timing of halo formation, may not be applicable to deep gravity wells, not only at the present epoch but throughout cosmic history.By combining reduced photon scattering cross sections with Carr’s primordial black hole mass spectrum formulation[4] calculated at the last phase transition (t = 1 s), it is possible to provide a scenario of halo formation that enables galaxies and halos to form much earlier in cosmic history, yet maintain consistency with cosmic microwave background observations and primordial nucleosynthesis. In addition this scenario provides a unified model relating globular clusters, dwarf spheroidal galaxies and bulges, enables an understanding of the black hole-bulge/black hole-dark halo relations, and enables prediction of dark to visible matter, based on the physical parameters of a halo. This scenario will be presented and discussed.[1] Xue-Bing Wu et al, 2015, Nature, 518,512-515 doi: 10.1038/nature14241[2] Ernest A. D., 2009, J. Phys. A: Math. Theor. 42 115207, 115208[3] Ernest A. D, 2012, in Advances in
NASA Astrophysics Data System (ADS)
Remus, Rhea-Silvia; Dolag, Klaus; Naab, Thorsten; Burkert, Andreas; Hirschmann, Michaela; Hoffmann, Tadziu L.; Johansson, Peter H.
2017-01-01
We present evidence from cosmological hydrodynamical simulations for a co-evolution of the slope of the total (dark and stellar) mass density profile, γtot, and the dark matter fraction within the half-mass radius, fDM, in early-type galaxies. The relation can be described as γtot = A fDM + B for all systems at all redshifts. The trend is set by the decreasing importance of gas dissipation towards lower redshifts and for more massive systems. Early-type galaxies are smaller, more concentrated, have lower fDM and steeper γtot at high redshifts and at lower masses for a given redshift; fDM and γtot are good indicators for growth by `dry' merging. The values for A and B change distinctively for different feedback models, and this relation can be used as a test for such models. A similar correlation exists between γtot and the stellar mass surface density Σ*. A model with weak stellar feedback and feedback from black holes is in best agreement with observations. All simulations, independent of the assumed feedback model, predict steeper γtot and lower fDM at higher redshifts. While the latter is in agreement with the observed trends, the former is in conflict with lensing observations, which indicate constant or decreasing γtot. This discrepancy is shown to be artificial: the observed trends can be reproduced from the simulations using observational methodology to calculate the total density slopes.
Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.; ...
2015-02-17
Here, we investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We also perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. Furthermore, we found that the dark matter mass projected within the innermore » 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M * = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.« less
Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.; Suyu, Sherry H.; Gavazzi, Raphaël; Auger, Matthew W.; Nipoti, Carlo
2015-02-20
We investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. We find that the dark matter mass projected within the inner 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M {sub *} = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.
Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.; Suyu, Sherry H.; Gavazzi, Raphaël; Auger, Matthew W.; Nipoti, Carlo
2015-02-17
Here, we investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We also perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. Furthermore, we found that the dark matter mass projected within the inner 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M * = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.
NASA Astrophysics Data System (ADS)
Sonnenfeld, Alessandro; Treu, Tommaso; Marshall, Philip J.; Suyu, Sherry H.; Gavazzi, Raphaël; Auger, Matthew W.; Nipoti, Carlo
2015-02-01
We investigate the cosmic evolution of the internal structure of massive early-type galaxies over half of the age of the universe. We perform a joint lensing and stellar dynamics analysis of a sample of 81 strong lenses from the Strong Lensing Legacy Survey and Sloan ACS Lens Survey and combine the results with a hierarchical Bayesian inference method to measure the distribution of dark matter mass and stellar initial mass function (IMF) across the population of massive early-type galaxies. Lensing selection effects are taken into account. We find that the dark matter mass projected within the inner 5 kpc increases for increasing redshift, decreases for increasing stellar mass density, but is roughly constant along the evolutionary tracks of early-type galaxies. The average dark matter slope is consistent with that of a Navarro-Frenk-White profile, but is not well constrained. The stellar IMF normalization is close to a Salpeter IMF at log M * = 11.5 and scales strongly with increasing stellar mass. No dependence of the IMF on redshift or stellar mass density is detected. The anti-correlation between dark matter mass and stellar mass density supports the idea of mergers being more frequent in more massive dark matter halos.
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.
Advances in Early Memory Development Research: Insights about the Dark Side of the Moon
ERIC Educational Resources Information Center
Courage, Mary L.; Howe, Mark L.
2004-01-01
Over the past three decades impressive progress has been made in documenting the development of encoding, storage, and retrieval processes in preverbal infants and children. This literature includes an extensive and diverse database as well as theoretical conjecture about the underlying processes that drive early memory development. A selective…
NASA Astrophysics Data System (ADS)
D'Onofrio, Roberta; Luciani, Valeria; Fornaciari, Eliana; Giusberti, Luca; Boscolo Galazzo, Flavia; Dallanave, Edoardo; Westerhold, Thomas; Sprovieri, Mario; Telch, Sonia
2016-09-01
Several early Eocene hyperthermals have been recently investigated and characterized in terms of temperature anomalies and oceanographic changes. The effects of these climatic perturbations on biotic communities are much less constrained. Here we present new records from the Terche section (northeastern Italy) that, for the first time, integrates data on planktic foraminifera and calcareous nannofossils across three post-Paleocene-Eocene Thermal Maximum negative carbon isotope excursions (CIEs). The biomagnetostratigraphic framework generated at Terche allows us to confidently relate such CIEs to the Eocene Thermal Maximum 2 (ETM2), H2, and I1 events. Each of these events coincides with lithological anomalies characterized by significantly lower calcium carbonate content (marly units, MUs). We interpret these MUs as mainly linked to an effect of increased terrigenous dilution, as dissolution proxies do not display significant variations. Calcareous plankton assemblages change significantly across these events and radiolarians increase. Observed changes suggest that transient warming and environmental perturbations, though more intense during ETM2, occurred during each of the three investigated perturbations. Variations among calcareous plankton suggest increase in surface-water eutrophication with respect to the pre-event conditions, coupled with a weakening of the upper water-column thermal stratification. Higher nutrient discharge was related to intensification of the hydrological cycle as a consequence of the warmer climate. These conditions persisted during the early CIE recovery, implying slower recovery rates for the environment and biota than for the carbon cycle.
NASA Astrophysics Data System (ADS)
Bai, Yang; Schwaller, Pedro
2014-03-01
Most of the mass of ordinary matter has its origin from quantum chromodynamics (QCD). A similar strong dynamics, dark QCD, could exist to explain the mass origin of dark matter. Using infrared fixed points of the two gauge couplings, we provide a dynamical mechanism that relates the dark QCD confinement scale to our QCD scale, and hence provides an explanation for comparable dark baryon and proton masses. Together with a mechanism that generates equal amounts of dark baryon and ordinary baryon asymmetries in the early Universe, the similarity of dark matter and ordinary matter energy densities can be naturally explained. For a large class of gauge group representations, the particles charged under both QCD and dark QCD, necessary ingredients for generating the infrared fixed points, are found to have masses at 1-2 TeV, which sets the scale for dark matter direct detection and novel collider signatures involving visible and dark jets.
Long-lived light mediator to dark matter and primordial small scale spectrum
Zhang, Yue
2015-05-06
We calculate the early universe evolution of perturbations in the dark matter energy density in the context of simple dark sector models containing a GeV scale light mediator. We consider the case that the mediator is long-lived, with lifetime up to a second, and before decaying it temporarily dominates the energy density of the universe. We show that for primordial perturbations that enter the horizon around this period, the interplay between linear growth during matter domination and collisional damping can generically lead to a sharp peak in the spectrum of dark matter density perturbation. As a result, the population of the smallest DM halos gets enhanced. Possible implications of this scenario are discussed.
Long-lived light mediator to dark matter and primordial small scale spectrum
Zhang, Yue
2015-05-01
We calculate the early universe evolution of perturbations in the dark matter energy density in the context of simple dark sector models containing a GeV scale light mediator. We consider the case that the mediator is long-lived, with lifetime up to a second, and before decaying it temporarily dominates the energy density of the universe. We show that for primordial perturbations that enter the horizon around this period, the interplay between linear growth during matter domination and collisional damping can generically lead to a sharp peak in the spectrum of dark matter density perturbation. As a result, the population of the smallest DM halos gets enhanced. Possible implications of this scenario are discussed.
Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica
2016-06-01
Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures ∼10 000 K) objects. We follow the evolution of dark stars from their inception at ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses >[Formula: see text] and luminosities >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.
NASA Astrophysics Data System (ADS)
Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica
2016-06-01
Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (˜10 AU) and cool (surface temperatures ˜10 000 K) objects. We follow the evolution of dark stars from their inception at ˜1{{M}⊙} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses >{{10}6}{{M}⊙} and luminosities >{{10}10}{{L}⊙} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.
NASA Astrophysics Data System (ADS)
Sanders, Robert H.
2014-02-01
1. Introduction; 2. Early history of the dark matter hypothesis; 3. The stability of disk galaxies: the dark halo solutions; 4. Direct evidence: extended rotation curves of spiral galaxies; 5. The maximum disk: light traces mass; 6. Cosmology and the birth of astroparticle physics; 7. Clusters revisited: missing mass found; 8. CDM confronts galaxy rotation curves; 9. The new cosmology: dark matter is not enough; 10. An alternative to dark matter: Modified Newtonian Dynamics; 11. Seeing dark matter: the theory and practice of detection; 12. Reflections: a personal point of view; Appendix; References; Index.
Dark energy and dark matter from an additional adiabatic fluid
NASA Astrophysics Data System (ADS)
Dunsby, Peter K. S.; Luongo, Orlando; Reverberi, Lorenzo
2016-10-01
The dark sector is described by an additional barotropic fluid which evolves adiabatically during the Universe's history and whose adiabatic exponent γ is derived from the standard definitions of specific heats. Although in general γ is a function of the redshift, the Hubble parameter and its derivatives, we find that our assumptions lead necessarily to solutions with γ =constant in a Friedmann-Lemaître-Robertson-Walker universe. The adiabatic fluid acts effectively as the sum of two distinct components, one evolving like nonrelativistic matter and the other depending on the value of the adiabatic index. This makes the model particularly interesting as a way of simultaneously explaining the nature of both dark energy and dark matter, at least at the level of the background cosmology. The Λ CDM model is included in this family of theories when γ =0 . We fit our model to supernovae Ia, H (z ) and baryonic acoustic oscillation data, discussing the model selection criteria. The implications for the early Universe and the growth of small perturbations in this model are also discussed.
Nonthermal dark matter models and signals
NASA Astrophysics Data System (ADS)
Okada, Hiroshi; Orikasa, Yuta; Toma, Takashi
2016-03-01
Many experiments exploring weakly interacting massive particles (WIMPs) such as direct, indirect and collider searches have been carried out until now. However, a clear signal of a WIMP has not been found yet and it makes us to suspect that WIMPs are questionable as a dark matter candidate. Taking into account this situation, we propose two models in which dark matter relic density is produced by decay of a metastable particle. In the first model, the metastable particle is a feebly interacting massive particle, which is the so-called FIMP, produced by freeze-in mechanism in the early universe. In the second model, the decaying particle is thermally produced the same as the usual WIMP. However decay of the particle into dark matter is led by a higher dimensional operator. As a phenomenologically interesting feature of nonthermal dark matter discussed in this paper, a strong sharp gamma-ray emission as an indirect detection signal occurs due to internal bremsstrahlung, although some parameter space has already been ruled out by this process. Moreover combining other experimental and theoretical constraints such as dark matter relic density, big bang nucleosynthesis, collider, gamma-rays and perturbativity of couplings, we discuss the two nonthermal DM models.
NASA Astrophysics Data System (ADS)
Beckwith, A. W.
2015-07-01
We find that having the scale factor close to zero due to a given magnetic field value in an early universe magnetic field affects how we would interpret Mukhanov's chapter on “self reproduction” of the universe in in his reference. The stronger an early-universe magnetic field is, the greater the likelihood of production of about 20 new domains of size 1/H, with H the early-universe Hubble constant, per Planck time interval in evolution. We form DM from considerations as to a minimum time step, and then generate DM via axions. Through Ng's quantum infinite statistics, we compare a DM count, giving entropy. The remainder of the document is in terms of DE as well as comparing entropy in galaxies versus entropy in the universe, through a lens of Mistra's quantum theory of the big bang.
New Efforts to Identify Dark Matter
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2016-09-01
among them.In the early universe, small density perturbations on sub-galactic scales produce dwarf galaxies in the lambda-CDM model. But in the warm dark matter model, the longer free streaming length of the dark matter particles smooth out some of those small perturbations. This results in the formation of fewer dwarf galaxies which fits better with our current observations.Limits on Warm Dark MatterSo how can we test this alternative model? The maximum number density of dark-matter halos predicted by the warm dark matter model at a given redshift depends on the mass of the candidate dark matter particle: a larger particle mass means that more halos form. We therefore can set lower limits on the mass of dark matter particles in a two-step process:Calculate the maximum number density of dark matter halos predicted by models, andCompare this to the measured abundance of the faintest galaxies at a given redshift.Another way of looking at it: for different values of the dark matter particle mass mX, this shows the maximum number density of dark matter halos predicted at z = 6. The shaded areas represent the observed number density of faint galaxies at different confidence levels. [Menci et al. 2016]Recently, unprecedented new Hubble observations of ultra-faint, lensed galaxies in the Hubble Frontier Fields at z~6 have allowed for the discovery of more faint galaxies at this redshift than ever before. Now, a team of scientists led by Nicola Menci (INAF Rome) have used these observations to set a new limit on the lowest mass that candidate dark matter particles can have.Menci and collaborators find that these new observations constrain the particle masses to be above 2.9 keV at the 1 confidence level. These constitute the tightest constraints on the mass of candidate warm dark matter particles derived to date, and they even allow us to rule out some production mechanisms for theorized particles.Extending this analysis to other clusters with deep observations will only
The dark matter annihilation boost from low-temperature reheating
NASA Astrophysics Data System (ADS)
Erickcek, Adrienne L.
2015-11-01
The evolution of the Universe between inflation and the onset of big bang nucleosynthesis is difficult to probe and largely unconstrained. This ignorance profoundly limits our understanding of dark matter: we cannot calculate its thermal relic abundance without knowing when the Universe became radiation dominated. Fortunately, small-scale density perturbations provide a probe of the early Universe that could break this degeneracy. If dark matter is a thermal relic, density perturbations that enter the horizon during an early matter-dominated era grow linearly with the scale factor prior to reheating. The resulting abundance of substructure boosts the annihilation rate by several orders of magnitude, which can compensate for the smaller annihilation cross sections that are required to generate the observed dark matter density in these scenarios. In particular, thermal relics with masses less than a TeV that thermally and kinetically decouple prior to reheating may already be ruled out by Fermi-LAT observations of dwarf spheroidal galaxies. Although these constraints are subject to uncertainties regarding the internal structure of the microhalos that form from the enhanced perturbations, they open up the possibility of using gamma-ray observations to learn about the reheating of the Universe.
Structure formation with scalar field dark matter: the field approach
Magaña, Juan; Sánchez-Salcedo, F.J.; Matos, Tonatiuh; Suárez, Abril E-mail: tmatos@fis.cinvestav.mx E-mail: jsanchez@astro.unam.mx
2012-10-01
We study the formation of structure in the Universe assuming that dark matter can be described by a scalar field Φ-tilde with a potential V(Φ) = −m{sup 2}Φ-tilde {sup 2}/2+λΦ-tilde {sup 4}/4. We derive the evolution equations of the scalar field in the linear regime of perturbations. We investigate the symmetry breaking and possibly a phase transition of this scalar field in the early Universe. At low temperatures, the scalar perturbations have an oscillating growing mode and therefore, this kind of dark matter could lead to the formation of gravitational structures. In order to study the nonlinear regime, we use the spherical collapse model and show that, in the quadratic potential limit, this kind of dark matter can form virialized structures. The main difference with the traditional Cold Dark Matter paradigm is that the formation of structure in the scalar field model can occur at earlier times. Thus, if the dark matter behaves as a scalar field, large galaxies are expected to be formed already at high redshifts.
Reincke, Samuel A. J.; Hanganu-Opatz, Ileana L.
2017-01-01
Early life exposure to stressful situations impairs cognitive performance of adults and contributes to the etiology of several psychiatric disorders. Most of affected cognitive abilities rely on coupling by synchrony within complex neuronal networks, including prefrontal cortex (PFC), hippocampus (HP), and perirhinal cortex (PRH). Yet it remains poorly understood how early life stress (ELS) induces dysfunction within these networks during the course of development. Here we used intermittent maternal separation during the first 2 postnatal weeks to mimic ELS and monitored the recognition memory and functional coupling within prefrontal-hippocampal-perirhinal circuits in juvenile rats. While maternally-separated female rats showed largely normal behavior, male rats experiencing this form of ELS had poorer location and recency recognition memory. Simultaneous multi-site extracellular recordings of network oscillations and neuronal spiking from PFC, HP, and PRH in vivo revealed corresponding decrease of oscillatory activity in theta and beta frequency bands in the PFC of male but not female rats experiencing maternal separation. This deficit was accompanied by weaker cross-frequency coupling within juvenile prefrontal-hippocampal networks. These results indicate that already at juvenile age ELS mimicked by maternal separation induces sex-specific deficits in recognition memory that might have as underlying mechanism a disturbed communication between PFC and HP. PMID:28169319
Reincke, Samuel A J; Hanganu-Opatz, Ileana L
2017-02-07
Early life exposure to stressful situations impairs cognitive performance of adults and contributes to the etiology of several psychiatric disorders. Most of affected cognitive abilities rely on coupling by synchrony within complex neuronal networks, including prefrontal cortex (PFC), hippocampus (HP), and perirhinal cortex (PRH). Yet it remains poorly understood how early life stress (ELS) induces dysfunction within these networks during the course of development. Here we used intermittent maternal separation during the first 2 postnatal weeks to mimic ELS and monitored the recognition memory and functional coupling within prefrontal-hippocampal-perirhinal circuits in juvenile rats. While maternally-separated female rats showed largely normal behavior, male rats experiencing this form of ELS had poorer location and recency recognition memory. Simultaneous multi-site extracellular recordings of network oscillations and neuronal spiking from PFC, HP, and PRH in vivo revealed corresponding decrease of oscillatory activity in theta and beta frequency bands in the PFC of male but not female rats experiencing maternal separation. This deficit was accompanied by weaker cross-frequency coupling within juvenile prefrontal-hippocampal networks. These results indicate that already at juvenile age ELS mimicked by maternal separation induces sex-specific deficits in recognition memory that might have as underlying mechanism a disturbed communication between PFC and HP.
NASA Astrophysics Data System (ADS)
Percival, Lawrence; Cohen, Anthony; Davies, Marc; Dickson, Alexander; Jenkyns, Hugh; Hesselbo, Stephen; Mather, Tamsin; Xu, Weimu; Storm, Marisa
2016-04-01
The Mesozoic Era marked a time of greenhouse conditions on Earth, punctuated by a number of abrupt perturbations to the carbon cycle, such as Ocean Anoxic Events (OAEs). OAEs are typically marked in the stratigraphic record by the appearance of organic-rich shales, and excursions in carbon-isotope ratios registered in carbonates and organic matter. A range of geochemical evidence indicates changes to global temperatures, typically featuring abrupt warming possibly caused by CO2 emissions resulting from Large Igneous Province (LIP) volcanism. A warmer atmosphere is thought to have led to changes in the global hydrological cycle, which would likely have enhanced global weathering rates. The Toarcian OAE (T-OAE) is inferred, from osmium isotope ratios in organic-rich mudrocks from Yorkshire and western North America, to have been a time of such increased weathering rates. However, it is likely that the sediments at these locations were deposited in relatively hydrographically restricted environments, potentially more susceptible to the influence of local input; consequently, they may not offer the best representation of the global seawater Os-isotope composition at that time. In this study, we have measured the osmium isotope composition of siciliclastic mudrocks in a core from the Mochras borehole (Llanbedr Farm, Cardigan Bay Basin, Wales), which constitutes a sedimentary record for a fully open-marine seaway that connected Tethys to the Boreal ocean during the Toarcian. We analysed samples from strata including both the T-OAE and preceding Pliensbachian-Toarcian boundary (Pl-To), both of which record multiple geochemical excursions and records of elevated extinction amongst benthic fauna. We find that the latest Pliensbachian records seawater 187Os/188Os of ~0.35-0.4, rising to ~0.5 at the Pl-To boundary, before a further rise to ~0.7 during the T-OAE. We conclude that such increases in radiogenic Os flux to the ocean system resulted from enhanced continental
NASA Astrophysics Data System (ADS)
Bodin, Stéphane; Krencker, Francois-Nicolas; Kothe, Tim; Hoffmann, René; Mattioli, Emanuela; Heimhofer, Ulrich; Kabiri, Lahcen
2016-04-01
Preceding the early Toarcian Oceanic Anoxic Event by ∼1 Myr, the Pliensbachian-Toarcian boundary event is in many aspects as severe and disturbing for the environment as its better-studied successor. Both events are associated with rapid and pronounced global warming, major faunal and floral turnover, increased hydrological cycling and dramatic collapses of carbonate production. To better characterize the Pliensbachian-Toarcian boundary event, a high-resolution, paired carbonate and organic matter carbon isotope survey of three sections from the Central High Atlas Basin of Morocco has been undertaken. A pronounced negative shift in the carbonate carbon-isotope record, not paralleled by a similar excursion in the organic carbon, can be linked to the collapse of the neritic carbonate factory in the earliest Toarcian. These results show that, contrary to the Toarcian Oceanic Anoxic Event, a rapid and massive injection of 13C-depleted carbon into the atmosphere is not responsible for the environmental perturbations observed during the Pliensbachian-Toarcian boundary event. However, input of isotopically non-depleted carbon such as mantle source CO2 into the atmosphere as a potential cause for the Pliensbachian-Toarcian boundary event cannot be excluded. This would most probably be sourced from an early pulse of the Karoo-Ferrar Large Igneous Province.
Chen, Jiangfei; Huang, Changjiang; Truong, Lisa; La Du, Jane; Tilton, Susan C.; Waters, Katrina M.; Lin, Kuanfei; Tanguay, Robert L; Dong, Qiaoxiang
2012-01-01
Trimethyltin chloride (TMT) is an organotin contaminant, widely detected in aqueous environments, posing potential human and environmental risks. In this study, we utilized the zebrafish model to investigate the impact of transient TMT exposure on developmental progression, angiogenesis, and cardiovascular development. Embryos were waterborne exposed to a wide TMT concentration range from 8 to 96 hours post fertilization (hpf). The TMT concentration that led to mortality in 50% of the embryos (LC50) at 96 hpf was 8.2 μM; malformations in 50% of the embryos (EC50) was 2.8 μM. The predominant response observed in surviving embryos was pericardial edema. Additionally, using the Tg (fli1a: EGFP) y1 transgenic zebrafish line to non-invasively monitor vascular development, TMT exposure led to distinct disarrangements in the vascular system. The most susceptible developmental stage to TMT exposure was between 48–72 hpf. High density whole genome microarrays were used to identify the early transcriptional changes following TMT exposure from 48 to 60 hpf or 72 hpf. In total, 459 transcripts were differentially expressed at least 2-fold (P < 0.05) by TMT compared to control. Using Ingenuity Pathway Analysis (IPA) tools, it was revealed that the transcripts misregulated by TMT exposure were clustered in numerous categories including metabolic and cardiovascular disease, cellular function, cell death, molecular transport, and physiological development. In situ localization of highly elevated transcripts revealed intense staining of ADP-ribosylation factors arf3 and arf5 in the head, trunk, and tail regions. When arf5 expression was blocked by morpholinos, the zebrafish did not display the prototypical TMT-induced vascular deficits, indicating that the induction of arf5 was necessary for TMT-induced vascular toxicity. PMID:23000284
NASA Astrophysics Data System (ADS)
Luciani, Valeria; Dickens, Gerald R.; Backman, Jan; Fornaciari, Eliana; Giusberti, Luca; Agnini, Claudia; D'Onofrio, Roberta
2016-04-01
A marked switch in the abundance of the planktic foraminiferal genera Morozovella and Acarinina occurred at low-latitude sites near the start of the Early Eocene Climatic Optimum (EECO), a multi-million-year interval when Earth surface temperatures reached their Cenozoic maximum. Stable carbon and oxygen isotope data of bulk sediment are presented from across the EECO at two locations: Possagno in northeast Italy and Deep Sea Drilling Project (DSDP) Site 577 in the northwest Pacific. Relative abundances of planktic foraminifera are presented from these two locations, as well as from Ocean Drilling Program (ODP) Site 1051 in the northwest Atlantic. All three sections have good stratigraphic markers, and the δ13C records at each section can be correlated amongst each other and to δ13C records at other locations across the globe. These records show that a series of negative carbon isotope excursions (CIEs) occurred before, during and across the EECO, which is defined here as the interval between the J event and the base of Discoaster sublodoensis. Significant though ephemeral modifications in planktic foraminiferal assemblages coincide with some of the short-term CIEs, which were marked by increases in the relative abundance of Acarinina, similar to what happened across established hyperthermal events in Tethyan settings prior to the EECO. Most crucially, a temporal link exists between the onset of the EECO, carbon cycle changes during this time and the decline in Morozovella. Possible causes are manifold and may include temperature effects on photosymbiont-bearing planktic foraminifera and changes in ocean chemistry.
Causal compensated perturbations in cosmology
NASA Technical Reports Server (NTRS)
Veeraraghavan, Shoba; Stebbins, Albert
1990-01-01
A theoretical framework is developed to calculate linear perturbations in the gravitational and matter fields which arise causally in response to the presence of stiff matter sources in a FRW cosmology. It is shown that, in order to satisfy energy and momentum conservation, the gravitational fields of the source must be compensated by perturbations in the matter and gravitational fields, and the role of such compensation in containing the initial inhomogeneities in their subsequent evolution is discussed. A complete formal solution is derived in terms of Green functions for the perturbations produced by an arbitrary source in a flat universe containing cold dark matter. Approximate Green function solutions are derived for the late-time density perturbations and late-time gravitational waves in a universe containing a radiation fluid. A cosmological energy-momentum pseudotensor is defined to clarify the nature of energy and momentum conservation in the expanding universe.
NASA Astrophysics Data System (ADS)
McGuire, C.; Fuller, G. A.; Peretto, N.; Zhang, Q.; Traficante, A.; Avison, A.; Jimenez-Serra, I.
2016-10-01
Context. Investigations into the substructure of massive star forming regions are essential for understanding the observed relationships between core mass distributions and mass distributions in stellar clusters, differentiating between proposed mechanisms of massive star formation. Aims: We study the substructure in the two largest fragments (i.e. cores) MM1 and MM2, in the infrared dark cloud complex SDC13. As MM1 appears to be in a later stage of evolution than MM2, comparing their substructure provides an insight in to the early evolution of massive clumps. Methods: We report the results of high resolution SMA dust continuum observations towards MM1 and MM2. Combining these data with Herschel observations, we carry out RADMC-3D radiative transfer modelling to characterise the observed substructure. Results: SMA continuum data indicates 4 sub-fragments in the SDC13 region. The nature of the second brightest sub-fragment (B) is uncertain as it does not appear as prominent at the lower MAMBO resolution or at radio wavelengths. Statistical analysis indicates that it is unlikely to be a background source, an AGB star, or the free-free emission of a HII region. It is plausible that B is a runaway object ejected from MM1. MM1, which is actively forming stars, consists of two sub-fragments A and C. This is confirmed by 70 μmHerschel data. While MM1 and MM2 appear quite similar in previous low resolution observations, at high resolution, the sub-fragment at the centre of MM2 (D) is much fainter than sub-fragment at the centre of MM1 (A). RADMC-3D models of MM1 and MM2 are able to reproduce these results, modelling MM2 with a steeper density profile and higher mass than is required for MM1. The relatively steep density profile of MM2 depends on a significant temperature decrease in its centre, justified by the lack of star formation in MM2. A final stellar population for MM1 was extrapolated, indicating a star formation efficiency typical of regions of core and cluster
Dark matter from dark energy in q-theory
NASA Astrophysics Data System (ADS)
Klinkhamer, F. R.; Volovik, G. E.
2017-01-01
A constant (spacetime-independent) q-field may play a crucial role for the cancellation of Planck-scale contributions to the gravitating vacuum energy density. We now show that a small spacetime-dependent perturbation of the equilibrium q-field behaves gravitationally as a pressureless perfect fluid. This makes the fluctuating part of the q-field a candidate for the inferred dark-matter component of the present universe. For a Planck-scale oscillation frequency of the q-field perturbation, the implication would be that direct searches for dark-matter particles would remain unsuccessful in the foreseeable future.
Nearly Supersymmetric Dark Atoms
Behbahani, Siavosh R.; Jankowiak, Martin; Rube, Tomas; Wacker, Jay G.; /SLAC /Stanford U., ITP
2011-08-12
Theories of dark matter that support bound states are an intriguing possibility for the identity of the missing mass of the Universe. This article proposes a class of models of supersymmetric composite dark matter where the interactions with the Standard Model communicate supersymmetry breaking to the dark sector. In these models supersymmetry breaking can be treated as a perturbation on the spectrum of bound states. Using a general formalism, the spectrum with leading supersymmetry effects is computed without specifying the details of the binding dynamics. The interactions of the composite states with the Standard Model are computed and several benchmark models are described. General features of non-relativistic supersymmetric bound states are emphasized.
Nearly Supersymmetric Dark Atoms
Behbahani, Siavosh R.; Jankowiak, Martin; Rube, Tomas; ...
2011-01-01
Theories of dark matter that support bound states are an intriguing possibility for the identity of the missing mass of the Universe. This article proposes a class of models of supersymmetric composite dark matter where the interactions with the Standard Model communicate supersymmetry breaking to the dark sector. In these models, supersymmetry breaking can be treated as a perturbation on the spectrum of bound states. Using a general formalism, the spectrum with leading supersymmetry effects is computed without specifying the details of the binding dynamics. The interactions of the composite states with the Standard Model are computed, and several benchmarkmore » models are described. General features of nonrelativistic supersymmetric bound states are emphasized.« less
Castillo-Padilla, Diana V; Funke, Klaus
2016-01-01
Early cortical critical period resembles a state of enhanced neuronal plasticity enabling the establishment of specific neuronal connections during first sensory experience. Visual performance with regard to pattern discrimination is impaired if the cortex is deprived from visual input during the critical period. We wondered how unspecific activation of the visual cortex before closure of the critical period using repetitive transcranial magnetic stimulation (rTMS) could affect the critical period and the visual performance of the experimental animals. Would it cause premature closure of the plastic state and thus worsen experience-dependent visual performance, or would it be able to preserve plasticity? Effects of intermittent theta-burst stimulation (iTBS) were compared with those of an enriched environment (EE) during dark-rearing (DR) from birth. Rats dark-reared in a standard cage showed poor improvement in a visual pattern discrimination task, while rats housed in EE or treated with iTBS showed a performance indistinguishable from rats reared in normal light/dark cycle. The behavioral effects were accompanied by correlated changes in the expression of brain-derived neurotrophic factor (BDNF) and atypical PKC (PKCζ/PKMζ), two factors controlling stabilization of synaptic potentiation. It appears that not only nonvisual sensory activity and exercise but also cortical activation induced by rTMS has the potential to alleviate the effects of DR on cortical development, most likely due to stimulation of BDNF synthesis and release. As we showed previously, iTBS reduced the expression of parvalbumin in inhibitory cortical interneurons, indicating that modulation of the activity of fast-spiking interneurons contributes to the observed effects of iTBS.
NASA Technical Reports Server (NTRS)
Orton, G.; Fletcher, L.; Yanamandra-Fisher, P.; Sanchez-Lavega, A.; Perez-Hoyos, S.; Baines, K.; de Pater, I.; Wong, M.; Goetz, R.; Valkov, S.; Greco, J.; Edwards, M.; Rogers, J.
2011-01-01
On 2010 November 9, a perturbation appeared in Jupiter's South Equatorial Belt (SEB), which began a classical "revival" of the SEB, returning the entire axisymmetric region to its normal dark color from its anomalous, light, "faded" state. The early revival is marked by strong upwelling gas at the outbreak location, to the west of which appear alternating clear and cloudy regions. Clear regions are correlated with dark clouds near the outbreak and in a southern retrograding branch but less so in a northern prograding branch. A 5-micrometer image from 2010 March 1 shows much of the SEB closer to a pre-faded state.
Joseph Silk
2016-07-12
One of the greatest mysteries in the cosmos is that it is mostly dark.Â Astronomers and particle physicists today are seeking to unravel the nature of this mysterious, but pervasive dark matter which has profoundly influenced the formation of structure in the universe. Â I will describe the complex interplay between galaxy formation and dark matter detectability and review recent attempts to measure particle dark matter by direct and indirect means.
Tomozeiu, Mihai; Mayer, Lucio; Quinn, Thomas
2016-02-20
We present the first simulations of tidal stirring of dwarf galaxies in the Local Group carried out in a fully cosmological context. We use the ErisDARK cosmological simulation of a Milky Way (MW)-sized galaxy to identify some of the most massive subhalos (M{sub vir} > 10{sup 8} M{sub ⊙}) that fall into the main host before z = 2. Subhalos are replaced before infall with extremely high-resolution models of dwarf galaxies comprising a faint stellar disk embedded in a dark matter halo. The set of models contains cuspy halos as well as halos with “cored” profiles (with the cusp coefficient γ = 0.6) consistent with recent results of hydrodynamical simulations of dwarf galaxy formation. The simulations are then run to z = 0 with as many as 54 million particles and resolutions as small as ∼4 pc using the new parallel N-body code ChaNGa. The stellar components of all satellites are significantly affected by tidal stirring, losing stellar mass, and undergoing a morphological transformation toward a pressure supported spheroidal system. However, while some remnants with cuspy halos maintain significant rotational flattening and disk-like features, all the shallow halo models achieve v{sub rot}/σ{sub ⋆} < 0.5 and round shapes typical of dSph satellites of the MW and M31. Mass loss is also enhanced in the latter, and remnants can reach luminosities and velocity dispersions as low as those of ultra-faint dwarfs.
Status and Early Results from the Axion Dark Matter eXperiment - High Frequency (ADMX-HF)
NASA Astrophysics Data System (ADS)
Lewis, Samantha; ADMX-HF Collaboration
2016-03-01
The axion was originally proposed as a solution to the Strong-CP problem of the Standard Model. A sufficiently light axion (1 - 1000 μ eV) also represents an excellent cold dark matter candidate. Such axions may be detected by their resonant conversion to photons in a high- Q microwave cavity permeated by a strong magnetic field. Previous experiments have probed the first decade in mass using this method. ADMX-HF was designed and built as an innovation test-bed and a data pathfinder for the second decade in mass range. The experiment, initially configured with a 9-tesla magnet, dilution refrigerator, 2-liter tunable copper cavity, and a Josephson Parametric Amplifier, is now operational with a system noise temperature approximately twice the Standard Quantum Limit. Preliminary data in the 25 μ eV range (on the order of 6 GHz in resonant frequency) will be presented, as well as an overview of ongoing R&D on new cavity and amplifier technologies that will be validated in situ within the next few years. This work was supported by the NSF, under Grants PHY-1067242 and PHY-1306729, the US DOE under Contract DE-AC52-07NA27344, and an award from the Heising-Simons Foundation.
ERIC Educational Resources Information Center
George Washington Univ., Washington, DC. Inst. for Educational Leadership.
"Options in Education" is a radio news program which focuses on issues and developments in education. This transcript contains discussions of Jonathon Kozol's book "The Night Is Dark and I Am Far from Home," the voucher system in education, and California's early education plan and "Reform for Intermediate and Secondary…
Davoudiasl, Hooman; Hooper, Dan; McDermott, Samuel D
2016-01-22
We describe a general scenario, dubbed "inflatable dark matter," in which the density of dark matter particles can be reduced through a short period of late-time inflation in the early Universe. The overproduction of dark matter that is predicted within many, otherwise, well-motivated models of new physics can be elegantly remedied within this context. Thermal relics that would, otherwise, be disfavored can easily be accommodated within this class of scenarios, including dark matter candidates that are very heavy or very light. Furthermore, the nonthermal abundance of grand unified theory or Planck scale axions can be brought to acceptable levels without invoking anthropic tuning of initial conditions. A period of late-time inflation could have occurred over a wide range of scales from ∼MeV to the weak scale or above, and could have been triggered by physics within a hidden sector, with small but not necessarily negligible couplings to the standard model.
NASA Astrophysics Data System (ADS)
Davoudiasl, Hooman; Hooper, Dan; McDermott, Samuel D.
2016-01-01
We describe a general scenario, dubbed "inflatable dark matter," in which the density of dark matter particles can be reduced through a short period of late-time inflation in the early Universe. The overproduction of dark matter that is predicted within many, otherwise, well-motivated models of new physics can be elegantly remedied within this context. Thermal relics that would, otherwise, be disfavored can easily be accommodated within this class of scenarios, including dark matter candidates that are very heavy or very light. Furthermore, the nonthermal abundance of grand unified theory or Planck scale axions can be brought to acceptable levels without invoking anthropic tuning of initial conditions. A period of late-time inflation could have occurred over a wide range of scales from ˜MeV to the weak scale or above, and could have been triggered by physics within a hidden sector, with small but not necessarily negligible couplings to the standard model.
Asymmetric Dark Matter and Dark Radiation
Blennow, Mattias; Martinez, Enrique Fernandez; Mena, Olga; Redondo, Javier; Serra, Paolo E-mail: enfmarti@cern.ch E-mail: redondo@mppmu.mpg.de
2012-07-01
Asymmetric Dark Matter (ADM) models invoke a particle-antiparticle asymmetry, similar to the one observed in the Baryon sector, to account for the Dark Matter (DM) abundance. Both asymmetries are usually generated by the same mechanism and generally related, thus predicting DM masses around 5 GeV in order to obtain the correct density. The main challenge for successful models is to ensure efficient annihilation of the thermally produced symmetric component of such a light DM candidate without violating constraints from collider or direct searches. A common way to overcome this involves a light mediator, into which DM can efficiently annihilate and which subsequently decays into Standard Model particles. Here we explore the scenario where the light mediator decays instead into lighter degrees of freedom in the dark sector that act as radiation in the early Universe. While this assumption makes indirect DM searches challenging, it leads to signals of extra radiation at BBN and CMB. Under certain conditions, precise measurements of the number of relativistic species, such as those expected from the Planck satellite, can provide information on the structure of the dark sector. We also discuss the constraints of the interactions between DM and Dark Radiation from their imprint in the matter power spectrum.
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.
NASA Astrophysics Data System (ADS)
Bahcall, Neta A.
2015-10-01
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.
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
Vachaspati, Tanmay
2009-09-15
Recent astrophysical observations have motivated novel theoretical models of the dark matter sector. A class of such models predicts the existence of GeV scale cosmic strings that communicate with the standard model sector by Aharonov-Bohm interactions with electrically charged particles. We discuss the cosmology of these 'dark strings' and investigate possible observational signatures. More elaborate dark sector models are argued to contain hybrid topological defects that may also have observational signatures.
Bashir, A.; Cotti, U.; De Leon, C. L.; Raya, A; Villasenor, L.
2008-07-02
One of the biggest scientific mysteries of our time resides in the identification of the particles that constitute a large fraction of the mass of our Universe, generically known as dark matter. We review the observations and the experimental data that imply the existence of dark matter. We briefly discuss the properties of the two best dark-matter candidate particles and the experimental techniques presently used to try to discover them. Finally, we mention a proposed project that has recently emerged within the Mexican community to look for dark matter.
Bringing isolated dark matter out of isolation: Late-time reheating and indirect detection
NASA Astrophysics Data System (ADS)
Erickcek, Adrienne L.; Sinha, Kuver; Watson, Scott
2016-09-01
In standard cosmology, the growth of structure becomes significant following matter-radiation equality. In nonthermal histories, where an effectively matter-dominated phase occurs due to scalar oscillations prior to big bang nucleosynthesis, a new scale at smaller wavelengths appears in the matter power spectrum. Density perturbations that enter the horizon during the early matter-dominated era (EMDE) grow linearly with the scale factor prior to the onset of radiation domination, which leads to enhanced inhomogeneity on small scales if dark matter (DM) thermally and kinetically decouples during the EMDE. The microhalos that form from these enhanced perturbations significantly boost the self-annihilation rate for dark matter. This has important implications for indirect detection experiments: the larger annihilation rate may result in observable signals from dark matter candidates that are usually deemed untestable. As a proof of principle, we consider binos in heavy supersymmetry with an intermediate extended Higgs sector and all other superpartners decoupled. We find that these isolated binos, which lie under the neutrino floor, can account for the dark matter relic density and decouple from the standard model early enough to preserve the enhanced small-scale inhomogeneity generated during the EMDE. If early forming microhalos survive as subhalos within larger microhalos, the resulting boost to the annihilation rate for bino dark matter near the pseudoscalar resonance exceeds the upper limit established by Fermi-LAT's observations of dwarf spheroidal galaxies. These DM candidates motivate the N -body simulations required to eliminate uncertainties in the microhalos' internal structure by exemplifying how an EMDE can enable Fermi-LAT to probe isolated dark matter.
Dark matter and dark radiation
Ackerman, Lotty; Buckley, Matthew R.; Carroll, Sean M.; Kamionkowski, Marc
2009-01-15
We explore the feasibility and astrophysical consequences of a new long-range U(1) gauge field ('dark electromagnetism') that couples only to dark matter, not to the standard model. The dark matter consists of an equal number of positive and negative charges under the new force, but annihilations are suppressed if the dark-matter mass is sufficiently high and the dark fine-structure constant {alpha}-circumflex is sufficiently small. The correct relic abundance can be obtained if the dark matter also couples to the conventional weak interactions, and we verify that this is consistent with particle-physics constraints. The primary limit on {alpha}-circumflex comes from the demand that the dark matter be effectively collisionless in galactic dynamics, which implies {alpha}-circumflex < or approx. 10{sup -3} for TeV-scale dark matter. These values are easily compatible with constraints from structure formation and primordial nucleosynthesis. We raise the prospect of interesting new plasma effects in dark-matter dynamics, which remain to be explored.
Unified dark energy-dark matter model with inverse quintessence
Ansoldi, Stefano; Guendelman, Eduardo I. E-mail: guendel@bgu.ac.il
2013-05-01
We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-canonical kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the dark energy vanishes in the early universe and then grows with time. This constitutes an ''inverse quintessence scenario'', where the universe starts from a zero vacuum energy density state, instead of approaching it in the future.
Dark matter: Theoretical perspectives
Turner, M.S. Fermi National Accelerator Lab., Batavia, IL )
1993-06-01
The author both reviews and makes the case for the current theoretical prejudice: a flat Universe whose dominant constituent is nonbaryonic dark matter, emphasizing that this is still a prejudice and not yet fact. The theoretical motivation for nonbaryonic dark matter is discussed in the context of current elementary-particle theory, stressing that (i) there are no dark-matter candidates within the [open quotes]standard model[close quotes] of particle physics, (ii) there are several compelling candidates within attractive extensions of the standard model of particle physics, and (iii) the motivation for these compelling candidates comes first and foremost from particle physics. The dark-matter problem is now a pressing issue in both cosmology and particle physics, and the detection of particle dark matter would provide evidence for [open quotes]new physics.[close quotes] The compelling candidates are a very light axion (10[sup [minus]6]--10[sup [minus]4] eV), a light neutrino (20--90 eV), and a heavy neutralino (10 GeV--2 TeV). The production of these particles in the early Universe and the prospects for their detection are also discussed. The author briefly mentions more exotic possibilities for the dark matter, including a nonzero cosmological constant, superheavy magnetic monopoles, and decaying neutrinos. 119 refs.
Dark matter: theoretical perspectives.
Turner, M S
1993-01-01
I both review and make the case for the current theoretical prejudice: a flat Universe whose dominant constituent is nonbaryonic dark matter, emphasizing that this is still a prejudice and not yet fact. The theoretical motivation for nonbaryonic dark matter is discussed in the context of current elementary-particle theory, stressing that (i) there are no dark-matter candidates within the "standard model" of particle physics, (ii) there are several compelling candidates within attractive extensions of the standard model of particle physics, and (iii) the motivation for these compelling candidates comes first and foremost from particle physics. The dark-matter problem is now a pressing issue in both cosmology and particle physics, and the detection of particle dark matter would provide evidence for "new physics." The compelling candidates are a very light axion (10(-6)-10(-4) eV), a light neutrino (20-90 eV), and a heavy neutralino (10 GeV-2 TeV). The production of these particles in the early Universe and the prospects for their detection are also discussed. I briefly mention more exotic possibilities for the dark matter, including a nonzero cosmological constant, superheavy magnetic monopoles, and decaying neutrinos. PMID:11607395
Dark matter: Theoretical perspectives
Turner, M.S. |
1993-01-01
I both review and make the case for the current theoretical prejudice: a flat Universe whose dominant constituent is nonbaryonic dark matter, emphasizing that this is still a prejudice and not yet fact. The theoretical motivation for nonbaryonic dark matter is discussed in the context of current elementary-particle theory, stressing that: (1) there are no dark matter candidates within the standard model of particle physics; (2) there are several compelling candidates within attractive extensions of the standard model of particle physics; and (3) the motivation for these compelling candidates comes first and foremost from particle physics. The dark-matter problem is now a pressing issue in both cosmology and particle physics, and the detection of particle dark matter would provide evidence for ``new physics.`` The compelling candidates are: a very light axion ( 10{sup {minus}6} eV--10{sup {minus}4} eV); a light neutrino (20 eV--90 eV); and a heavy neutralino (10 GeV--2 TeV). The production of these particles in the early Universe and the prospects for their detection are also discussed. I briefly mention more exotic possibilities for the dark matter, including a nonzero cosmological constant, superheavy magnetic monopoles, and decaying neutrinos.
Dark matter: Theoretical perspectives
Turner, M.S. . Enrico Fermi Inst. Fermi National Accelerator Lab., Batavia, IL )
1993-01-01
I both review and make the case for the current theoretical prejudice: a flat Universe whose dominant constituent is nonbaryonic dark matter, emphasizing that this is still a prejudice and not yet fact. The theoretical motivation for nonbaryonic dark matter is discussed in the context of current elementary-particle theory, stressing that: (1) there are no dark matter candidates within the standard model of particle physics; (2) there are several compelling candidates within attractive extensions of the standard model of particle physics; and (3) the motivation for these compelling candidates comes first and foremost from particle physics. The dark-matter problem is now a pressing issue in both cosmology and particle physics, and the detection of particle dark matter would provide evidence for new physics.'' The compelling candidates are: a very light axion ( 10[sup [minus]6] eV--10[sup [minus]4] eV); a light neutrino (20 eV--90 eV); and a heavy neutralino (10 GeV--2 TeV). The production of these particles in the early Universe and the prospects for their detection are also discussed. I briefly mention more exotic possibilities for the dark matter, including a nonzero cosmological constant, superheavy magnetic monopoles, and decaying neutrinos.
Fingerprinting dark energy. III. Distinctive marks of viscosity
NASA Astrophysics Data System (ADS)
Sapone, Domenico; Majerotto, Elisabetta
2012-06-01
The characterization of dark energy is one of the primary goals in cosmology especially now that many new experiments are being planned with the aim of reaching a high sensitivity on cosmological parameters. It is known that if we move away from the simple cosmological constant model then we need to consider perturbations in the dark energy fluid. This means that dark energy has two extra degrees of freedom: the sound speed cs2 and the anisotropic stress σ. If dark energy is inhomogenous at the scales of interest then the gravitational potentials are modified and the evolution of the dark matter perturbations is also directly affected. In this paper we add an anisotropic component to the dark energy perturbations. Following the idea introduced in D. Sapone and M. Kunz, Phys. Rev. DPRVDAQ1550-7998 80, 083519 (2009)10.1103/PhysRevD.80.083519, we solve analytically the equations of perturbations in the dark sector, finding simple and accurate approximated solutions. We also find that the evolution of the density perturbations is governed by an effective sound speed that depends on both the sound speed and the anisotropic stress parameter. We then use these solutions to look at the impact of the dark energy perturbations on the matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background.
Bouncing Cosmologies with Dark Matter and Dark Energy
NASA Astrophysics Data System (ADS)
Cai, Yi-Fu; Marcianò, Antonino; Wang, Dong-Gang; Wilson-Ewing, Edward
2017-01-01
We review matter bounce scenarios where the matter content is dark matter and dark energy. These cosmologies predict a nearly scale-invariant power spectrum with a slightly red tilt for scalar perturbations and a small tensor-to-scalar ratio. Importantly, these models predict a positive running of the scalar index, contrary to the predictions of the simplest inflationary and ekpyrotic models, and hence could potentially be falsified by future observations. We also review how bouncing cosmological space-times can arise in theories where either the Einstein equations are modified or where matter fields that violate the null energy condition are included.
Dark chocolate exacerbates acne.
Vongraviopap, Saivaree; Asawanonda, Pravit
2016-05-01
The effects of chocolate on acne exacerbations have recently been reevaluated. For so many years, it was thought that it had no role in worsening acne. To investigate whether 99% dark chocolate, when consumed in regular daily amounts, would cause acne to worsen in acne-prone male subjects, twenty-five acne prone male subjects were asked to consume 25 g of 99% dark chocolate daily for 4 weeks. Assessments which included Leeds revised acne scores as well as lesion counts took place weekly. Food frequency questionnaire was used, and daily activities were recorded. Statistically significant changes of acne scores and numbers of comedones and inflammatory papules were detected as early as 2 weeks into the study. At 4 weeks, the changes remained statistically significant compared to baseline. Dark chocolate when consumed in normal amounts for 4 weeks can exacerbate acne in male subjects with acne-prone skin.
NASA Astrophysics Data System (ADS)
Froggatt, C. D.; Nielsen, H. B.
2015-04-01
It is suggested that the Tunguska event in June 1908 was due to a cm-large ball of a condensate of bound states of 6 top and 6 antitop quarks containing highly compressed ordinary matter. Such balls are supposed to make up the dark matter as we earlier proposed. The expected rate of impact of this kind of dark matter ball with the earth seems to crudely match a time scale of 200 years between the impacts. The main explosion of the Tunguska event is explained in our picture as material coming out from deep within the earth, where it has been heated and compressed by the ball penetrating to a depth of several thousand km. Thus the effect has some similarity with volcanic activity as suggested by Kundt. We discuss the possible identification of kimberlite pipes with earlier Tunguska-like events. A discussion of how the dark matter balls may have formed in the early universe is also given.
NASA Technical Reports Server (NTRS)
Turner, Michael S.
1989-01-01
The types of particles which may provide the nonluminous mass required by big-bang cosmological models are listed and briefly characterized. The observational evidence for the existence of dark matter (outweighing the luminous component by at least a factor of 10) is reviewed; the theoretical arguments favoring mainly nonbaryonic dark matter are summarized; and particular attention is given to weakly interacting massive particles (WIMPs) remaining as relics from the early universe. The WIMPs are classified as thermal relics (heavy stable neutrinos and lighter neutralinos), asymmetric relics (including baryons), nonthermal relics (superheavy magnetic monopoles, axions, and soliton stars), and truly exotic relics (relativistic debris or vacuum energy). Explanations for the current apparent baryon/exotica ratio of about 0.1 in different theoretical scenarios are considered, and the problems of experimental and/or observational dark-matter detection are examined.
ERIC Educational Resources Information Center
Lincoln, Don
2013-01-01
It's a dark, dark universe out there, and I don't mean because the night sky is black. After all, once you leave the shadow of the Earth and get out into space, you're surrounded by countless lights glittering everywhere you look. But for all of Sagan's billions and billions of stars and galaxies, it's a jaw-dropping fact that the ordinary kind of…
Quantum Yang-Mills Dark Energy
NASA Astrophysics Data System (ADS)
Pasechnik, Roman
2016-02-01
In this short review, I discuss basic qualitative characteristics of quantum non-Abelian gauge dynamics in the non-stationary background of the expanding Universe in the framework of the standard Einstein--Yang--Mills formulation. A brief outlook of existing studies of cosmological Yang--Mills fields and their properties will be given. Quantum effects have a profound impact on the gauge field-driven cosmological evolution. In particular, a dynamical formation of the spatially-homogeneous and isotropic gauge field condensate may be responsible for both early and late-time acceleration, as well as for dynamical compensation of non-perturbative quantum vacua contributions to the ground state of the Universe. The main properties of such a condensate in the effective QCD theory at the flat Friedmann--Lema\\'itre--Robertson--Walker (FLRW) background will be discussed within and beyond perturbation theory. Finally, a phenomenologically consistent dark energy can be induced dynamically as a remnant of the QCD vacua compensation arising from leading-order graviton-mediated corrections to the QCD ground state.
Greives, Timothy J; Fudickar, Adam M; Atwell, Jonathan W; Meddle, Simone L; Ketterson, Ellen D
2016-09-15
To optimally time reproduction, animals must coordinate changes in the hypothalamo-pituitary-gonadal (HPG) axis. The extent of intra-species variation in seasonal timing of reproductive function is considerable, both within and among populations. Dark-eyed junco (Junco hyemalis) populations are known to differ in their reproductive timing response to cues experienced in the same habitat in late winter/early spring. Specifically in juncos cohabitating on shared wintering grounds, residents initiate breeding and reproductive activity but migrants delay reproductive development and prepare to migrate before breeding. Here, we test the hypothesis that the pituitary gland acts as a 'control point' to modulate differential HPG axis activity across populations. We sampled free-living resident and migrant juncos on their shared over-wintering grounds in March, thus all individuals were experiencing the same environmental cues, including photoperiod. We predicted that during this critical time of transition, residents would more readily respond to repeated gonadotropin releasing hormone (GnRH) stimulation with increases in luteinizing hormone (LH), in contrast to migrants, which should delay full reproductive activity. Our data indicate that migrant females, while still on the overwintering grounds, have a reduced LH response to repeated GnRH injections compared to resident females. Male migrant and resident birds did not differ in their responsiveness to repeated GnRH. Our results suggest a sex difference in the costs of mistimed activation of the HPG axis, with female migrants being less responsive than residents females and males to repeated stimulation. Further, our data implicate a key role for the pituitary in regulating appropriate reproductive timing responses.
NASA Astrophysics Data System (ADS)
Ragan, Sarah E.; Henning, Thomas; Beuther, Henrik
2013-11-01
Infrared-dark clouds (IRDCs) harbor the early phases of cluster and high-mass star formation and are comprised of cold (~20 K), dense (n > 104 cm-3) gas. The spectral energy distribution (SED) of IRDCs is dominated by the far-infrared and millimeter wavelength regime, and our initial Herschel study examined IRDCs at the peak of the SED with high angular resolution. Here we present a follow-up study using the SABOCA instrument on APEX which delivers 7.8″ angular resolution at 350 μm, matching the resolution we achieved with Herschel/PACS, and allowing us to characterize substructure on ~0.1 pc scales. Our sample of 11 nearby IRDCs are a mix of filamentary and clumpy morphologies, and the filamentary clouds show significant hierarchical structure, while the clumpy IRDCs exhibit little hierarchical structure. All IRDCs, regardless of morphology, have about 14% of their total mass in small scale core-like structures which roughly follow a trend of constant volume density over all size scales. Out of the 89 protostellar cores we identified in this sample with Herschel, we recover 40 of the brightest and re-fit their SEDs and find their properties agree fairly well with our previous estimates (⟨ T ⟩ ~ 19 K). We detect a new population of "cold cores" which have no 70 μm counterpart, but are 100 and 160 μm-bright, with colder temperatures (⟨ T ⟩ ~ 16 K). This latter population, along with SABOCA-only detections, are predominantly low-mass objects, but their evolutionary diagnostics are consistent with the earliest starless or prestellar phase of cores in IRDCs. Based on observations carried out with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between Max Planck Institut für Radioastronomie (MPIfR), Onsala Space Observatory (OSO), and the European Southern Observatory (ESO).Appendices are available in electronic form at http://www.aanda.org
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.
Light dark photon and fermionic dark radiation for the Hubble constant and the structure formation
NASA Astrophysics Data System (ADS)
Ko, P.; Tang, Yong
2016-11-01
Motivated by the tensions in the Hubble constant H0 and the structure growth σ8 between Planck results and other low redshift measurements, we discuss some cosmological effects of a dark sector model in which dark matter (DM) interacts with fermionic dark radiation (DR) through a light gauge boson (dark photon). Such kind of models are very generic in particle physics with a dark sector with dark gauge symmetries. The effective number of neutrinos is increased by δNeff ∼ 0.5 due to light dark photon and fermionic DR, thereby resolving the conflicts in H0. The elastic scattering between DM and DR induces suppression for DM's density perturbation, but without acoustic oscillations. For weakly-interacting DM around 100 GeV, the new gauge coupling should be ∼10-4 to have sizable effect on matter power spectrum in order to relax the tension in σ8.
Consistent perturbations in an imperfect fluid
Sawicki, Ignacy; Amendola, Luca; Saltas, Ippocratis D.; Kunz, Martin E-mail: i.saltas@sussex.ac.uk E-mail: martin.kunz@unige.ch
2013-01-01
We present a new prescription for analysing cosmological perturbations in a more-general class of scalar-field dark-energy models where the energy-momentum tensor has an imperfect-fluid form. This class includes Brans-Dicke models, f(R) gravity, theories with kinetic gravity braiding and generalised galileons. We employ the intuitive language of fluids, allowing us to explicitly maintain a dependence on physical and potentially measurable properties. We demonstrate that hydrodynamics is not always a valid description for describing cosmological perturbations in general scalar-field theories and present a consistent alternative that nonetheless utilises the fluid language. We apply this approach explicitly to a worked example: k-essence non-minimally coupled to gravity. This is the simplest case which captures the essential new features of these imperfect-fluid models. We demonstrate the generic existence of a new scale separating regimes where the fluid is perfect and imperfect. We obtain the equations for the evolution of dark-energy density perturbations in both these regimes. The model also features two other known scales: the Compton scale related to the breaking of shift symmetry and the Jeans scale which we show is determined by the speed of propagation of small scalar-field perturbations, i.e. causality, as opposed to the frequently used definition of the ratio of the pressure and energy-density perturbations.
Hipolito-Ricaldi, W. S.; Velten, H. E. S.; Zimdahl, W.
2010-09-15
We investigate the cosmological perturbation dynamics for a universe consisting of pressureless baryonic matter and a viscous fluid, the latter representing a unified model of the dark sector. In the homogeneous and isotropic background the total energy density of this mixture behaves as a generalized Chaplygin gas. The perturbations of this energy density are intrinsically nonadiabatic and source relative entropy perturbations. The resulting baryonic matter power spectrum is shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also Hubble-function and supernovae Ia data, shows that, different from other studies, there exists a maximum in the probability distribution for a negative present value q{sub 0{approx_equal}}-0.53 of the deceleration parameter. Moreover, while previous descriptions on the basis of generalized Chaplygin-gas models were incompatible with the matter power-spectrum data since they required a much too large amount of pressureless matter, the unified model presented here favors a matter content that is of the order of the baryonic matter abundance suggested by big-bang nucleosynthesis.
Cosmological anisotropy from non-comoving dark matter and dark energy
Harko, Tiberiu; Lobo, Francisco S. N. E-mail: flobo@cii.fc.ul.pt
2013-07-01
We consider a cosmological model in which the two major fluid components of the Universe, dark energy and dark matter, flow with distinct four-velocities. This cosmological configuration is equivalent to a single anisotropic fluid, expanding with a four-velocity that is an appropriate combination of the two fluid four-velocities. The energy density of the single cosmological fluid is larger than the sum of the energy densities of the two perfect fluids, i.e., dark energy and dark matter, respectively, and contains a correction term due to the anisotropy generated by the differences in the four-velocities. Furthermore, the gravitational field equations of the two-fluid anisotropic cosmological model are obtained for a Bianchi type I geometry. By assuming that the non-comoving motion of the dark energy and dark matter induces small perturbations in the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker type cosmological background, and that the anisotropy parameter is small, the equations of the cosmological perturbations due to the non-comoving nature of the two major components are obtained. The time evolution of the metric perturbations is explicitly obtained for the cases of the exponential and power law background cosmological expansion. The imprints of a non-comoving dark energy - dark matter on the Cosmic Microwave Background and on the luminosity distance are briefly discussed, and the temperature anisotropies and the quadrupole are explicitly obtained in terms of the metric perturbations of the flat background metric. Therefore, if there is a slight difference between the four-velocities of the dark energy and dark matter, the Universe would acquire some anisotropic characteristics, and its geometry will deviate from the standard FLRW one. In fact, the recent Planck results show that the presence of an intrinsic large scale anisotropy in the Universe cannot be excluded a priori, so that the model presented in this work can be considered as a
Measuring the dark side (with weak lensing)
Amendola, Luca
2008-04-15
We introduce a convenient parameterization of dark energy models that is general enough to include several modified gravity models and generalized forms of dark energy. In particular we take into account the linear perturbation growth factor, the anisotropic stress and the modified Poisson equation. We discuss the sensitivity of large-scale weak lensing surveys like the proposed DUNE satellite to these parameters (assuming systematic errors can be controlled). We find that a large-scale weak lensing tomographic survey is able to easily distinguish the Dvali-Gabadadze-Porrati model from {Lambda}CDM and to determine the perturbation growth index to an absolute error of 0.02-0.04.
NASA Astrophysics Data System (ADS)
Baltz, Edward Anthony
It is well known that most of the mass in the universe remains unobserved save for its gravitational effect on luminous matter. The nature of this ``dark matter'' remains a mystery. From measurements of the primordial deuterium abundance, the theory of big bang nucleosynthesis predicts that there are not enough baryons to account for the amount of dark matter observed, thus the missing mass must take an exotic form. Several promising candidates have been proposed. In this work I will describe my research along two main lines of inquiry into the dark matter puzzle. The first possibility is that the dark matter is exotic massive particles, such as those predicted by supersymmetric extensions to the standard model of particle physics. Such particles are generically called WIMPs, for weakly interacting massive particles. Focusing on the so-called neutralino in supersymmetric models, I discuss the possible signatures of such particles, including their direct detection via nuclear recoil experiments and their indirect detection via annihilations in the halos of galaxies, producing high energy antiprotons, positrons and gamma rays. I also discuss signatures of the possible slow decays of such particles. The second possibility is that there is a population of black holes formed in the early universe. Any dark objects in galactic halos, black holes included, are called MACHOs, for massive compact halo objects. Such objects can be detected by their gravitational microlensing effects. Several possibilities for sources of baryonic dark matter are also interesting for gravitational microlensing. These include brown dwarf stars and old, cool white dwarf stars. I discuss the theory of gravitational microlensing, focusing on the technique of pixel microlensing. I make predictions for several planned microlensing experiments with ground based and space based telescopes. Furthermore, I discuss binary lenses in the context of pixel microlensing. Finally, I develop a new technique for
Unified Dark Matter scalar field models with fast transition
Bertacca, Daniele; Bruni, Marco; Piattella, Oliver F.; Pietrobon, Davide E-mail: marco.bruni@port.ac.uk E-mail: davide.pietrobon@jpl.nasa.gov
2011-02-01
We investigate the general properties of Unified Dark Matter (UDM) scalar field models with Lagrangians with a non-canonical kinetic term, looking specifically for models that can produce a fast transition between an early Einstein-de Sitter CDM-like era and a later Dark Energy like phase, similarly to the barotropic fluid UDM models in JCAP01(2010)014. However, while the background evolution can be very similar in the two cases, the perturbations are naturally adiabatic in fluid models, while in the scalar field case they are necessarily non-adiabatic. The new approach to building UDM Lagrangians proposed here allows to escape the common problem of the fine-tuning of the parameters which plague many UDM models. We analyse the properties of perturbations in our model, focusing on the the evolution of the effective speed of sound and that of the Jeans length. With this insight, we can set theoretical constraints on the parameters of the model, predicting sufficient conditions for the model to be viable. An interesting feature of our models is that what can be interpreted as w{sub DE} can be < −1 without violating the null energy conditions.
The Dark Matter Problem: A Historical Perspective
NASA Astrophysics Data System (ADS)
Sanders, Robert H.
2010-04-01
1. Introduction; 2. Early history of the dark matter hypothesis; 3. The stability of disk galaxies: the dark halo solutions; 4. Direct evidence: extended rotation curves of spiral galaxies; 5. The maximum disk: light traces mass; 6. Cosmology and the birth of astroparticle physics; 7. Clusters revisited: missing mass found; 8. CDM confronts galaxy rotation curves; 9. The new cosmology: dark matter is not enough; 10. An alternative to dark matter: Modified Newtonian Dynamics; 11. Seeing dark matter: the theory and practice of detection; 12. Reflections: a personal point of view; Appendix; References; Index.
NASA Technical Reports Server (NTRS)
2006-01-01
Dark spots (left) and 'fans' appear to scribble dusty hieroglyphics on top of the Martian south polar cap in two high-resolution Mars Global Surveyor, Mars Orbiter Camera images taken in southern spring. Each image is about 3-kilometers wide (2-miles).
Asymmetric condensed dark matter
Aguirre, Anthony; Diez-Tejedor, Alberto E-mail: alberto.diez@fisica.ugto.mx
2016-04-01
We explore the viability of a boson dark matter candidate with an asymmetry between the number densities of particles and antiparticles. A simple thermal field theory analysis confirms that, under certain general conditions, this component would develop a Bose-Einstein condensate in the early universe that, for appropriate model parameters, could survive the ensuing cosmological evolution until now. The condensation of a dark matter component in equilibrium with the thermal plasma is a relativistic process, hence the amount of matter dictated by the charge asymmetry is complemented by a hot relic density frozen out at the time of decoupling. Contrary to the case of ordinary WIMPs, dark matter particles in a condensate must be lighter than a few tens of eV so that the density from thermal relics is not too large. Big-Bang nucleosynthesis constrains the temperature of decoupling to the scale of the QCD phase transition or above. This requires large dark matter-to-photon ratios and very weak interactions with standard model particles.
Davoudiasl, Hooman; Hooper, Dan; McDermott, Samuel D.
2016-01-22
We describe a general scenario, dubbed “Inflatable Dark Matter”, in which the density of dark matter particles can be reduced through a short period of late-time inflation in the early universe. The overproduction of dark matter that is predicted within many otherwise well-motivated models of new physics can be elegantly remedied within this context, without the need to tune underlying parameters or to appeal to anthropic considerations. Thermal relics that would otherwise be disfavored can easily be accommodated within this class of scenarios, including dark matter candidates that are very heavy or very light. Furthermore, the non-thermal abundance of GUT or Planck scale axions can be brought to acceptable levels, without invoking anthropic tuning of initial conditions. Additionally, a period of late-time inflation could have occurred over a wide range of scales from ~ MeV to the weak scale or above, and could have been triggered by physics within a hidden sector, with small but not necessarily negligible couplings to the Standard Model.
Davoudiasl, Hooman; Hooper, Dan; McDermott, Samuel D.
2016-01-22
We describe a general scenario, dubbed “Inflatable Dark Matter”, in which the density of dark matter particles can be reduced through a short period of late-time inflation in the early universe. The overproduction of dark matter that is predicted within many otherwise well-motivated models of new physics can be elegantly remedied within this context, without the need to tune underlying parameters or to appeal to anthropic considerations. Thermal relics that would otherwise be disfavored can easily be accommodated within this class of scenarios, including dark matter candidates that are very heavy or very light. Furthermore, the non-thermal abundance of GUTmore » or Planck scale axions can be brought to acceptable levels, without invoking anthropic tuning of initial conditions. Additionally, a period of late-time inflation could have occurred over a wide range of scales from ~ MeV to the weak scale or above, and could have been triggered by physics within a hidden sector, with small but not necessarily negligible couplings to the Standard Model.« less
NASA Technical Reports Server (NTRS)
2004-01-01
13 May 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows north polar sand dunes in the summertime. During winter and early spring, north polar dunes are covered with bright frost. When the frost sublimes away, the dunes appear darker than their surroundings. To a geologist, sand has a very specific meaning. A sand grain is defined independently of its composition; it is a particle with a size between 62.5 and 2000 microns. Two thousand microns equals 2 millimeters. The dunes are dark because they are composed of sand grains made of dark minerals and/or rock fragments. Usually, dark grains indicate the presence of unoxidized iron, for example, the dark volcanic rocks of Hawaii, Iceland, and elsewhere. This dune field is located near 71.7oN, 51.3oW. Dune slip faces indicate winds that blow from the upper left toward lower right. This picture covers an area approximately 3 km (1.9 mi) across and is illuminated by sunlight from the lower left.
Cosmological Consequences of Dark Matter Interactions and Vacuum Fluctuations
NASA Astrophysics Data System (ADS)
Boddy, Kimberly K.
This thesis is divided into two parts: interacting dark matter and fluctuations in cosmology. There is an incongruence between the properties that dark matter is expected to possess between the early universe and the late universe. Weakly-interacting dark matter yields the observed dark matter relic density and is consistent with large-scale structure formation; however, there is strong astrophysical evidence in favor of the idea that dark matter has large self-interactions. The first part of this thesis presents two models in which the nature of dark matter fundamentally changes as the universe evolves. In the first model, the dark matter mass and couplings depend on the value of a chameleonic scalar field that changes as the universe expands. In the second model, dark matter is charged under a hidden SU(N) gauge group and eventually undergoes confinement. These models introduce very different mechanisms to explain the separation between the physics relevant for freezeout and for small-scale dynamics. As the universe continues to evolve, it will asymptote to a de Sitter vacuum phase. Since there is a finite temperature associated with de Sitter space, the universe is typically treated as a thermal system, subject to rare thermal fluctuations, such as Boltzmann brains. The second part of this thesis begins by attempting to escape this unacceptable situation within the context of known physics: vacuum instability induced by the Higgs field. The vacuum decay rate competes with the production rate of Boltzmann brains, and the cosmological measures that have a sufficiently low occurrence of Boltzmann brains are given more credence. Upon further investigation, however, there are certain situations in which de Sitter space settles into a quiescent vacuum with no fluctuations. This reasoning not only provides an escape from the Boltzmann brain problem, but it also implies that vacuum states do not uptunnel to higher-energy vacua and that perturbations do not decohere
Light and dark matter in the universe
2010-01-01
This simulation follows the growth of density perturbations in both gas and dark matter components in a volume 1 billion light years on a side beginning shortly after the Big Bang and evolved to half the present age of the universe. It calculates the gravitational clumping of intergalactic gas and dark matter modeled using a computational grid of 64 billion cells and 64 billion dark matter particles. The simulation uses a computational grid of 4096^3 cells and took over 4,000,000 CPU hours to complete. Read more: http://www.anl.gov/Media_Center/News/2010/news100104.html
Effective theory of interacting dark energy
Gleyzes, Jérôme; Mancarella, Michele; Vernizzi, Filippo; Langlois, David E-mail: langlois@apc.univ-paris7.fr E-mail: filippo.vernizzi@cea.fr
2015-08-01
We present a unifying treatment of dark energy and modified gravity that allows distinct conformal-disformal couplings of matter species to the gravitational sector. In this very general approach, we derive the conditions to avoid ghost and gradient instabilities. We compute the equations of motion for background quantities and linear perturbations. We illustrate our formalism with two simple scenarios, where either cold dark matter or a relativistic fluid is nonminimally coupled. This extends previous studies of coupled dark energy to a much broader spectrum of gravitational theories.
Palenik, Mark C.; Dunlap, Brett I.
2015-07-28
Despite the fundamental importance of electron density in density functional theory, perturbations are still usually dealt with using Hartree-Fock-like orbital equations known as coupled-perturbed Kohn-Sham (CPKS). As an alternative, we develop a perturbation theory that solves for the perturbed density directly, removing the need for CPKS. This replaces CPKS with a true Hohenberg-Kohn density perturbation theory. In CPKS, the perturbed density is found in the basis of products of occupied and virtual orbitals, which becomes ever more over-complete as the size of the orbital basis set increases. In our method, the perturbation to the density is expanded in terms of a series of density basis functions and found directly. It is possible to solve for the density in such a way that it makes the total energy stationary even if the density basis is incomplete.
Peebles, P. James E.
2015-01-01
The evidence for the dark matter (DM) of the hot big bang cosmology is about as good as it gets in natural science. The exploration of its nature is now led by direct and indirect detection experiments, to be complemented by advances in the full range of cosmological tests, including judicious consideration of the rich phenomenology of galaxies. The results may confirm ideas about DM already under discussion. If we are lucky, we also will be surprised once again. PMID:24794526
Cosmological constraints on decoupled dark photons and dark Higgs
Berger, Joshua; Jedamzik, Karsten; Walker, Devin G.E.
2016-11-16
Any neutral boson such as a dark photon or dark Higgs that is part of a non-standard sector of particles can mix with its standard model counterpart. When very weakly mixed with the Standard Model, these particles are produced in the early Universe via the freeze-in mechanism and subsequently decay back to standard model particles. In this work, we place constraints on such mediator decays by considering bounds from Big Bang nucleosynthesis and the cosmic microwave background radiation. We find both nucleosynthesis and CMB can constrain dark photons with a kinetic mixing parameter between log ϵ∼−10 to −17 for masses between 1 MeV and 100 GeV. Similarly, the dark Higgs mixing angle ϵ with the Standard Model Higgs is constrained between log ϵ∼−6 to −15. Dramatic improvement on the bounds from CMB spectral distortions can be achieved with proposed experiments such as PIXIE.
Cosmological constraints on decoupled dark photons and dark Higgs
NASA Astrophysics Data System (ADS)
Berger, Joshua; Jedamzik, Karsten; Walker, Devin G. E.
2016-11-01
Any neutral boson such as a dark photon or dark Higgs that is part of a non-standard sector of particles can mix with its standard model counterpart. When very weakly mixed with the Standard Model, these particles are produced in the early Universe via the freeze-in mechanism and subsequently decay back to standard model particles. In this work, we place constraints on such mediator decays by considering bounds from Big Bang nucleosynthesis and the cosmic microwave background radiation. We find both nucleosynthesis and CMB can constrain dark photons with a kinetic mixing parameter between log epsilon ~ -10 to -17 for masses between 1 MeV and 100 GeV . Similarly, the dark Higgs mixing angle epsilon with the Standard Model Higgs is constrained between log epsilon ~ -6 to -15. Dramatic improvement on the bounds from CMB spectral distortions can be achieved with proposed experiments such as PIXIE.
Cosmological Constraints on Decoupled Dark Photons and Dark Higgs
Berger, Joshua; Jedamzik, Karsten; Walker, Devin G.E.
2016-05-23
Any neutral boson such as a dark photon or dark Higgs that is part of a non-standard sector of particles can mix with its standard model counterpart. When very weakly mixed with the Standard Model, these particles are produced in the early Universe via the freeze-in mechanism and subsequently decay back to standard model particles. In this work, we place constraints on such mediator decays by considering bounds from Big Bang nucleosynthesis and the cosmic microwave background radiation. We find both nucleosynthesis and CMB can constrain dark photons with a kinetic mixing parameter between log ϵ ~ -10 to -17 for masses between 1 MeV and 100 GeV. Similarly, the dark Higgs mixing angle ϵ with the Standard Model Higgs is constrained between log ϵ ~ -6 to -15. Dramatic improvement on the bounds from CMB spectral distortions can be achieved with proposed experiments such as PIXIE.
Tauriainen, Johanna; Scharf, Lydia; Frederiksen, Juliet; Naji, Ali; Ljunggren, Hans-Gustaf; Sönnerborg, Anders; Lund, Ole; Reyes-Terán, Gustavo; Hecht, Frederick M.; Deeks, Steven G.; Betts, Michael R.; Buggert, Marcus; Karlsson, Annika C.
2017-01-01
HIV-specific CD8+ T cells demonstrate an exhausted phenotype associated with increased expression of inhibitory receptors, decreased functional capacity, and a skewed transcriptional profile, which are only partially restored by antiretroviral treatment (ART). Expression levels of the inhibitory receptor, T cell immunoglobulin and ITIM domain (TIGIT), the co-stimulatory receptor CD226 and their ligand PVR are altered in viral infections and cancer. However, the extent to which the TIGIT/CD226/PVR-axis is affected by HIV-infection has not been characterized. Here, we report that TIGIT expression increased over time despite early initiation of ART. HIV-specific CD8+ T cells were almost exclusively TIGIT+, had an inverse expression of the transcription factors T-bet and Eomes and co-expressed PD-1, CD160 and 2B4. HIV-specific TIGIThi cells were negatively correlated with polyfunctionality and displayed a diminished expression of CD226. Furthermore, expression of PVR was increased on CD4+ T cells, especially T follicular helper (Tfh) cells, in HIV-infected lymph nodes. These results depict a skewing of the TIGIT/CD226 axis from CD226 co-stimulation towards TIGIT-mediated inhibition of CD8+ T cells, despite early ART. These findings highlight the importance of the TIGIT/CD226/PVR axis as an immune checkpoint barrier that could hinder future “cure” strategies requiring potent HIV-specific CD8+ T cells. PMID:28084312
NASA Astrophysics Data System (ADS)
Baudis, Laura
2016-08-01
More than 80 years after its first postulation in modern form, the existence and distribution of dark matter in our Universe is well established. Dark matter is the gravitational glue that holds together galaxies, galaxy clusters and structures on the largest cosmological scales, and an essential component to explain the observed fluctuations in the cosmic microwave background. Yet its existence is inferred indirectly, through its gravitational influence on luminous matter, and its nature is not known. A viable hypothesis is that dark matter is made of new, elementary particles, with allowed masses and interaction strengths spanning a wide range. Two well-motivated classes of candidates are axions and weakly interacting massive particles (WIMPs), and experimental efforts have now reached sensitivities that allow them to test this hypothesis. Axions, produced non-thermally in the early Universe, can be detected by exploiting their predicted couplings to photons and electrons. WIMPs can be detected directly by looking for their collisions with atomic nuclei ultra-low background detectors, or indirectly, through the observation of their annihilation products such as neutrinos, gamma rays, positrons and antiprotons over the astrophysical background. A complementary method is the production of dark matter particles at colliders such as the Large Hadron Collider, where they could be observed indirectly via missing transverse energy, or via associated particle production. I will review the main experimental efforts to search for dark matter particles, and the existing constraints on the interaction cross sections. I will also discuss future experiments, their complementarity and their ability to measure the properties of these particles.
Astrophysical Probes of Dark Matter
NASA Astrophysics Data System (ADS)
Profumo, S.
2013-08-01
What is the connection between how the dark matter was produced in the early universe and how we can detect it today? Where does the WIMP miracle come from, and is it really a "WIMP" miracle? What brackets the mass range for thermal relics? Where does <συ> come from, and what does it mean? What is the difference between chemical and kinetic decoupling? Why do some people think that dark matter cannot be lighter than 40 GeV? Why is bbar b such a popular annihilation final state? Why is antimatter a good way to look for dark matter? Why should the cosmic-ray positron fraction decline with energy? How do you calculate the flux of neutrinos from dark matter annihilation in a celestial body, and when is it independent of the dark matter pair-annihilation rate? How does dark matter produce photons? -- Read these lecture notes, do the suggested 10 exercises, and you will find answers to all of these questions (and to many more on what You Always Wanted to Know About Dark Matter But Were Afraid to Ask).
Bai, Yang; Rajaraman, Arvind; /UC, Irvine
2012-03-28
We argue that dark matter particles which have strong interactions with the Standard Model particles are not excluded by current astrophysical constraints. These dark matter particles have unique signatures at colliders; instead of missing energy, the dark matter particles produce jets. We propose a new search strategy for such strongly interacting particles by looking for a signal of two trackless jets. We show that suitable cuts can plausibly allow us to find these signals at the LHC even in early data.
On cosmic acceleration without dark energy
Kolb, E.W.; Matarrese, S.; Riotto, A.; /INFN, Padua
2005-06-01
We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion. This invalidates the no-go theorem that there can be no acceleration in our local Hubble patch if the Universe only contains irrotational dust. We then study perturbatively the time behavior of general-relativistic cosmological perturbations, applying, where possible, the renormalization group to regularize the dynamics. We show that an instability occurs in the perturbative expansion involving sub-Hubble modes, which indicates that acceleration in our Hubble patch may originate from the backreaction of cosmological perturbations on observable scales.
Fingerprinting dark energy. II. Weak lensing and galaxy clustering tests
Sapone, Domenico; Amendola, Luca
2010-11-15
The characterization of dark energy is a central task of cosmology. To go beyond a cosmological constant, we need to introduce at least an equation of state and a sound speed and consider observational tests that involve perturbations. If dark energy is not completely homogeneous on observable scales, then the Poisson equation is modified and dark matter clustering is directly affected. One can then search for observational effects of dark energy clustering using dark matter as a probe. In this paper we exploit an analytical approximate solution of the perturbation equations in a general dark energy cosmology to analyze the performance of next-decade large-scale surveys in constraining equation of state and sound speed. We find that tomographic weak lensing and galaxy redshift surveys can constrain the sound speed of the dark energy only if the latter is small, of the order of c{sub s} < or approx. 0.01 (in units of c). For larger sound speeds the error grows to 100% and more. We conclude that large-scale structure observations contain very little information about the perturbations in canonical scalar field models with a sound speed of unity. Nevertheless, they are able to detect the presence of cold dark energy, i.e. a dark energy with nonrelativistic speed of sound.
Automated Lattice Perturbation Theory
Monahan, Christopher
2014-11-01
I review recent developments in automated lattice perturbation theory. Starting with an overview of lattice perturbation theory, I focus on the three automation packages currently "on the market": HiPPy/HPsrc, Pastor and PhySyCAl. I highlight some recent applications of these methods, particularly in B physics. In the final section I briefly discuss the related, but distinct, approach of numerical stochastic perturbation theory.
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.
Density matrix perturbation theory.
Niklasson, Anders M N; Challacombe, Matt
2004-05-14
An orbital-free quantum perturbation theory is proposed. It gives the response of the density matrix upon variation of the Hamiltonian by quadratically convergent recursions based on perturbed projections. The technique allows treatment of embedded quantum subsystems with a computational cost scaling linearly with the size of the perturbed region, O(N(pert.)), and as O(1) with the total system size. The method allows efficient high order perturbation expansions, as demonstrated with an example involving a 10th order expansion. Density matrix analogs of Wigner's 2n+1 rule are also presented.
Dark Matter Annihilation at the Galactic Center
Linden, Timothy Ryan
2013-06-01
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 ve times as much dark matter as baryonic matter. However, e orts 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 rst multiwavelength analysis of the GC, with suitable e ective 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 e orts which have successfully detected an excess in -ray emission from the region immediately surrounding the GC, which is di cult to describe in terms of standard di use 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
Evolution of non-interacting entropic dark energy and its phantom nature
NASA Astrophysics Data System (ADS)
Mathew, Titus K.; Murali, Chinthak; Shejeelammal, J.
2016-04-01
Assuming the form of the entropic dark energy (EDE) as it arises from the surface term in the Einstein-Hilbert’s action, its evolution was analyzed in an expanding flat universe. The model parameters were evaluated by constraining the model using the Union data on Type Ia supernovae. We found that in the non-interacting case, the model predicts an early decelerated phase and a later accelerated phase at the background level. The evolutions of the Hubble parameter, dark energy (DE) density, equation of state parameter and deceleration parameter were obtained. The model hardly seems to be supporting the linear perturbation growth for the structure formation. We also found that the EDE shows phantom nature for redshifts z < 0.257. During the phantom epoch, the model predicts big rip effect at which both the scale factor of expansion and the DE density become infinitely large and the big rip time is found to be around 36 Giga years from now.
Holley-Bockelmann, Kelly; Sinha, Manodeep; Wise, John H. E-mail: manodeep.sinha@vanderbilt.edu
2012-12-10
We explore structure formation in the dark ages (z {approx} 30-6) using two well-known methods for initializing cosmological N-body simulations. Overall, both the Zel'dovich approximation and second-order Lagrangian perturbation theory (2LPT) are known to produce accurate present-day dark matter halo mass functions. However, since the 2LPT method drives more rapid evolution of dense regions, it increases the occurrence of rare massive objects-an effect that is most pronounced at high redshift. We find that 2LPT produces more halos that could harbor Population III stars and their black hole remnants, and they produce them earlier. Although the differences between the 2LPT and Zel'dovich approximation mass functions are nearly erased by z = 6, this small boost to the number and mass of black holes more than doubles the reionized volume of the early universe. We discuss the implications for reionization and massive black hole growth.
Small scale aspects of warm dark matter: Power spectra and acoustic oscillations
Boyanovsky, Daniel; Wu Jun
2011-02-15
We provide a semianalytic derivation of approximate evolution equations for density perturbations of warm dark matter candidates that decoupled while relativistic with arbitrary distribution functions, their solutions at small scales, and a simple numerical implementation that yields their transfer functions and power spectra. Density perturbations evolve through three stages: radiation domination when the particle is relativistic and nonrelativistic and matter domination. An early integrated Sachs-Wolfe effect during the first stage leads to an enhancement of density perturbations and a plateau in the transfer function for k < or approx. k{sub fs}, the free-streaming wave vector. An effective fluid description emerges at small scales which includes the effects of free streaming in initial conditions and inhomogeneities. The transfer function features warm dark matter acoustic oscillations at scales k > or approx. 2k{sub fs}. A simple analytic interpolation of the power spectra between large and small scales and a numerical implementation valid for arbitrary distribution functions is provided. As an application we study the power spectra for two models of sterile neutrinos with m{approx}keV produced nonresonantly and compare our results to those obtained from Boltzmann codes.
Dark degeneracy and interacting cosmic components
Aviles, Alejandro; Cervantes-Cota, Jorge L.
2011-10-15
We study some properties of the dark degeneracy, which is the fact that what we measure in gravitational experiments is the energy-momentum tensor of the total dark sector, and any split into components (as in dark matter and dark energy) is arbitrary. In fact, just one dark fluid is necessary to obtain exactly the same cosmological and astrophysical phenomenology as the {Lambda}CDM model. We work explicitly the first-order perturbation theory and show that beyond the linear order the dark degeneracy is preserved under some general assumptions. Then we construct the dark fluid from a collection of interacting fluids. Finally, we try to break the degeneracy with a general class of couplings to baryonic matter. Nonetheless, we show that these interactions can also be understood in the context of the {Lambda}CDM model as between dark matter and baryons. For this last investigation we choose two independent parametrizations for the interactions, one inspired by electromagnetism and the other by chameleon theories. Then, we constrain them with a joint analysis of CMB and supernovae observational data.
NASA Astrophysics Data System (ADS)
Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Bernard, J.-P.; Bersanelli, M.; Bhatia, R.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Cabella, P.; Cardoso, J.-F.; Catalano, A.; Cayón, L.; Challinor, A.; Chamballu, A.; Chiang, L.-Y.; Chiang, C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Couchot, F.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Dame, T. M.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Gasperis, G.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Dobashi, K.; Donzelli, S.; Doré, O.; Dörl, U.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Finelli, F.; Forni, O.; Fosalba, P.; Frailis, M.; Franceschi, E.; Fukui, Y.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Grenier, I. A.; Gruppuso, A.; Hansen, F. K.; Harrison, D.; Helou, G.; Henrot-Versillé, S.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Hoyland, R. J.; Huffenberger, K. M.; Jaffe, A. H.; Jones, W. C.; Juvela, M.; Kawamura, A.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knox, L.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leonardi, R.; Leroy, C.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; MacTavish, C. J.; Maffei, B.; Maino, D.; Mandolesi, N.; Mann, R.; Maris, M.; Martin, P.; Martínez-González, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, A.; Naselsky, P.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Onishi, T.; Osborne, S.; Pajot, F.; Paladini, R.; Paradis, D.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Poutanen, T.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Reach, W. T.; Reinecke, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, P.; Smoot, G. F.; Starck, J.-L.; Stivoli, F.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Torre, J.-P.; Tristram, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.
2011-12-01
An all sky map of the apparent temperature and optical depth of thermal dust emission is constructed using the Planck-HFI (350μm to 2 mm) andIRAS(100μm) data. The optical depth maps are correlated with tracers of the atomic (Hi) and molecular gas traced by CO. The correlation with the column density of observed gas is linear in the lowest column density regions at high Galactic latitudes. At high NH, the correlation is consistent with that of the lowest NH, for a given choice of the CO-to-H2 conversion factor. In the intermediate NH range, a departure from linearity is observed, with the dust optical depth in excess of the correlation. This excess emission is attributed to thermal emission by dust associated with a dark gas phase, undetected in the available Hi and CO surveys. The 2D spatial distribution of the dark gas in the solar neighbourhood (|bII| > 10°) is shown to extend around known molecular regions traced by CO. The average dust emissivity in the Hi phase in the solar neighbourhood is found to be τD/NHtot = 5.2×10-26 cm2 at 857 GHz. It follows roughly a power law distribution with a spectral index β = 1.8 all the way down to 3 mm, although the SED flattens slightly in the millimetre. Taking into account the spectral shape of the dust optical depth, the emissivity is consistent with previous values derived fromFIRAS measurements at high latitudes within 10%. The threshold for the existence of the dark gas is found at NHtot = (8.0±0.58)×1020 H cm-2 (AV = 0.4mag). Assuming the same high frequency emissivity for the dust in the atomic and the molecular phases leads to an average XCO = (2.54 ± 0.13) × 1020 H2 cm-2/(K km s-1). The mass of dark gas is found to be 28% of the atomic gas and 118% of the CO emitting gas in the solar neighbourhood. The Galactic latitude distribution shows that its mass fraction is relatively constant down to a few degrees from the Galactic plane. A possible explanation for the dark gas lies in a dark molecular phase, where
Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D
2016-09-01
Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.
NASA Astrophysics Data System (ADS)
Wang, B.; Abdalla, E.; Atrio-Barandela, F.; Pavón, D.
2016-09-01
Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.
DAMIC: a novel dark matter experiment
Tiffenberg, Javier; Bertou, Xavier; Butner, Melissa J.; Cancelo, Gustavo; Chavarria, Alvaro; D'Olivo, Juan Carlos; Estrada Vigil, Juan Cruz; Moroni, Guillermo Fernandez; Izraelevitch, Federico; Kilminster, Ben; Lawson, Ian T.; Marsal, Fernando; Molina, Jorge; Privitera, Paolo; Schwarz, Tom; Sofo haro, Miguel; Tiffenberg, Javier; Trillaud, Frederic; Zhou, Jing
2013-10-24
DAMIC (Dark Matter in CCDs) is a novel dark matter experiment that has unique sensitivity to dark matter particles with masses below 10 GeV. Due to its low electronic readout noise (R.M.S. ~3 e-) this instrument is able to reach a detection threshold below 0.5 keV nuclear recoil energy, making the search for dark matter particles with low masses possible. We report on early results and experience gained from a detector that has been running at SNOLAB from Dec 2012. We also discuss the measured and expected backgrounds and present the plan for future detectors to be installed in 2014.
Newtonian perturbations on models with matter creation
NASA Astrophysics Data System (ADS)
Jesus, J. F.; Oliveira, F. A.; Basilakos, S.; Lima, J. A. S.
2011-09-01
Creation of cold dark matter (CCDM) can macroscopically be described by a negative pressure, and, therefore, the mechanism is capable to accelerate the Universe, without the need of an additional dark energy component. In this framework, we discuss the evolution of perturbations by considering a Neo-Newtonian approach where, unlike in the standard Newtonian cosmology, the fluid pressure is taken into account even in the homogeneous and isotropic background equations (Lima, Zanchin, and Brandenberger, MNRAS 291, L1, 1997). The evolution of the density contrast is calculated in the linear approximation and compared to the one predicted by the ΛCDM model. The difference between the CCDM and ΛCDM predictions at the perturbative level is quantified by using three different statistical methods, namely: a simple χ2-analysis in the relevant space parameter, a Bayesian statistical inference, and, finally, a Kolmogorov-Smirnov test. We find that under certain circumstances, the CCDM scenario analyzed here predicts an overall dynamics (including Hubble flow and matter fluctuation field) which fully recovers that of the traditional cosmic concordance model. Our basic conclusion is that such a reduction of the dark sector provides a viable alternative description to the accelerating ΛCDM cosmology.
Dark matter in axion landscape
NASA Astrophysics Data System (ADS)
Daido, Ryuji; Kobayashi, Takeshi; Takahashi, Fuminobu
2017-02-01
If there are a plethora of axions in nature, they may have a complicated potential and create an axion landscape. We study a possibility that one of the axions is so light that it is cosmologically stable, explaining the observed dark matter density. In particular we focus on a case in which two (or more) shift-symmetry breaking terms conspire to make the axion sufficiently light at the potential minimum. In this case the axion has a flat-bottomed potential. In contrast to the case in which a single cosine term dominates the potential, the axion abundance as well as its isocurvature perturbations are significantly suppressed. This allows an axion with a rather large mass to serve as dark matter without fine-tuning of the initial misalignment, and further makes higher-scale inflation to be consistent with the scenario.
GLOBULAR CLUSTERS AND DARK SATELLITE GALAXIES THROUGH THE STREAM VELOCITY
Naoz, Smadar; Narayan, Ramesh
2014-08-10
The formation of purely baryonic globular clusters with no gravitationally bound dark matter is still a theoretical challenge. We show that these objects might form naturally whenever there is a relative stream velocity between baryons and dark matter. The stream velocity causes a phase shift between linear modes of baryonic and dark matter perturbations, which translates to a spatial offset between the two components when they collapse. For a 2σ (3σ) density fluctuation, baryonic clumps with masses in the range 10{sup 5}-2.5 × 10{sup 6} M {sub ☉} (10{sup 5}-4 × 10{sup 6} M {sub ☉}) collapse outside the virial radii of their counterpart dark matter halos. These objects could survive as long-lived, dark-matter-free objects and might conceivably become globular clusters. In addition, their dark matter counterparts, which were deprived of gas, might become dark satellite galaxies.
Present and future evidence for evolving dark energy
Liddle, Andrew R.; Mukherjee, Pia; Parkinson, David; Wang Yun
2006-12-15
We compute the Bayesian evidences for one- and two-parameter models of evolving dark energy, and compare them to the evidence for a cosmological constant, using current data from Type Ia supernova, baryon acoustic oscillations, and the cosmic microwave background. We use only distance information, ignoring dark energy perturbations. We find that, under various priors on the dark energy parameters, {lambda}CDM is currently favored as compared to the dark energy models. We consider the parameter constraints that arise under Bayesian model averaging, and discuss the implication of our results for future dark energy projects seeking to detect dark energy evolution. The model selection approach complements and extends the figure-of-merit approach of the Dark Energy Task Force in assessing future experiments, and suggests a significantly-modified interpretation of that statistic.
Padgett, Miles [University of Glasgow, Glasgow, Scotland
2016-07-12
Optical vortices and orbital angular momentum are currently topical subjects in the optics literature. Although seemingly esoteric, they are, in fact, the generic state of light and arise whenever three or more plane waves interfere. To be observed by eye the light must be monochromatic. Laser speckle is one such example, where the optical energy circulates around each black spot, giving a local orbital angular momentum. This talk with report three on-going studies. First, when considering a volume of interfering waves, the laser specs map out threads of complete darkness embedded in the light. Do these threads form loops? Links? Or even knots? Second, when looking through a rapidly spinning window, the image of the world on the other side is rotated: true or false? Finally, the entanglement of orbital angular momentum states means measuring how the angular position of one photons sets the angular momentum of another: is this an angular version of the EPR (Einstein, Podolsky, and Rosen) paradox?
Baryonic matter perturbations in decaying vacuum cosmology
Marttens, R.F. vom; Zimdahl, W.; Hipólito-Ricaldi, W.S. E-mail: wiliam.ricaldi@ufes.br
2014-08-01
We consider the perturbation dynamics for the cosmic baryon fluid and determine the corresponding power spectrum for a Λ(t)CDM model in which a cosmological term decays into dark matter linearly with the Hubble rate. The model is tested by a joint analysis of data from supernovae of type Ia (SNIa) (Constitution and Union 2.1), baryonic acoustic oscillations (BAO), the position of the first peak of the anisotropy spectrum of the cosmic microwave background (CMB) and large-scale-structure (LSS) data (SDSS DR7). While the homogeneous and isotropic background dynamics is only marginally influenced by the baryons, there are modifications on the perturbative level if a separately conserved baryon fluid is included. Considering the present baryon fraction as a free parameter, we reproduce the observed abundance of the order of 5% independently of the dark-matter abundance which is of the order of 32% for this model. Generally, the concordance between background and perturbation dynamics is improved if baryons are explicitly taken into account.
Effects of tidal gravitational fields in clustering dark energy models
NASA Astrophysics Data System (ADS)
Pace, Francesco; Reischke, Robert; Meyer, Sven; Schäfer, Björn Malte
2017-04-01
We extend a previous work by Reischke et al. by studying the effects of tidal shear on clustering dark energy models within the framework of the extended spherical collapse model and using the Zel'dovich approximation. As in previous works on clustering dark energy, we assumed a vanishing effective sound speed describing the perturbations in dark energy models. To be self-consistent, our treatment is valid only on linear scales since we do not intend to introduce any heuristic models. This approach makes the linear overdensity δc mass dependent and similarly to the case of smooth dark energy, its effects are predominant at small masses and redshifts. Tidal shear has effects of the order of per cent or less, regardless of the model and preserves a well-known feature of clustering dark energy: When dark energy perturbations are included, the models resemble better the Lambda cold dark matter evolution of perturbations. We also showed that effects on the comoving number density of haloes are small and qualitatively and quantitatively in agreement with what were previously found for smooth dark energy models.
Constraints on the coupling between dark energy and dark matter from CMB data
Murgia, R.; Gariazzo, S.; Fornengo, N. E-mail: gariazzo@to.infn.it
2016-04-01
We investigate a phenomenological non-gravitational coupling between dark energy and dark matter, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to dark energy or the opposite. The models are constrained by a whole host of updated cosmological data: cosmic microwave background temperature anisotropies and polarization, high-redshift supernovae, baryon acoustic oscillations, redshift space distortions and gravitational lensing. Both models are found to be compatible with all cosmological observables, but in the case where dark matter decays into dark energy, the tension with the independent determinations of H{sub 0} and σ{sub 8}, already present for standard cosmology, increases: this model in fact predicts lower H{sub 0} and higher σ{sub 8}, mostly as a consequence of the higher amount of dark matter at early times, leading to a stronger clustering during the evolution. Instead, when dark matter is fed by dark energy, the reconstructed values of H{sub 0} and σ{sub 8} nicely agree with their local determinations, with a full reconciliation between high- and low-redshift observations. A non-zero coupling between dark energy and dark matter, with an energy flow from the former to the latter, appears therefore to be in better agreement with cosmological data.
Dark radiation and inflationary freedom
NASA Astrophysics Data System (ADS)
Gariazzo, Stefano
2016-05-01
A relaxed primordial power spectrum (PPS) of scalar perturbations arising from inflation can impact the dark radiation constraints obtained from Cosmic Microwave Background and other cosmological measurements. If inflation produces a non-standard PPS for the initial fluctuations, a fully thermalized light sterile neutrino can be favoured by CMB observations, instead of being strongly disfavoured. In the case of a thermal axion, the constraints on the axion mass are relaxed when the PPS is different from the standard power law. Based on Refs. [1, 2].
Gravitational Waves from a Dark Phase Transition
NASA Astrophysics Data System (ADS)
Schwaller, Pedro
2015-10-01
In this work, we show that a large class of models with a composite dark sector undergo a strong first order phase transition in the early Universe, which could lead to a detectable gravitational wave signal. We summarize the basic conditions for a strong first order phase transition for SU (N ) dark sectors with nf flavors, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at eLISA or in pulsar timing array experiments. The gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors. The discussion includes the twin Higgs and strongly interacting massive particle models as well as symmetric and asymmetric composite dark matter scenarios.
Some topics on scale-invariant perturbations from noninflationary universe
NASA Astrophysics Data System (ADS)
Li, Mingzhe
In this paper, we review some topics on generations of scale-invariant primordial scalar and tensor perturbations in the early universe models different from inflation. The content includes generation of scale-invariant and Gaussian scalar perturbation in the ekpyrotic/cyclic universe, and production scale-invariant tensor perturbation in contracting universe. The main property of the models reviewed in this paper is the nonminimal couplings, include nonminimal couplings between the scalar fields and those to the gravity. By introducing these couplings, it is not difficult to achieve scale-invariances for the perturbations in the early universe models alternative to inflation.
(m, n)-TYPE Holographic Dark Energy Models
NASA Astrophysics Data System (ADS)
Ling, Yi; Pan, Wen-Jian
2013-09-01
We construct (m, n)-type holographic dark energy models at a phenomenological level, which can be viewed as a generalization of agegraphic models with the conformal-like age as the holographic characteristic size. For some values of (m, n) the holographic dark energy can automatically evolve across ω = -1 into a phantom phase even without introducing an interaction between the dark energy and background matter. Our construction is also applicable to the holographic dark energy with generalized future event horizon as the characteristic size. Finally, we address the issue on the stability of our model and show that they are generally stable under the scalar perturbation.
The traces of anisotropic dark energy in light of Planck
Cardona, Wilmar; Kunz, Martin; Hollenstein, Lukas E-mail: lukas.hollenstein@zhaw.ch
2014-07-01
We study a dark energy model with non-zero anisotropic stress, either linked to the dark energy density or to the dark matter density. We compute approximate solutions that allow to characterise the behaviour of the dark energy model and to assess the stability of the perturbations. We also determine the current limits on such an anisotropic stress from the cosmic microwave background data by the Planck satellite, and derive the corresponding constraints on the modified growth parameters like the growth index, the effective Newton's constant and the gravitational slip.
NASA Astrophysics Data System (ADS)
Rong, Shu-Jun; Liu, Qiu-Yu
2012-04-01
The puma model on the basis of the Lorentz and CPT violation may bring an economical interpretation to the conventional neutrinos oscillation and part of the anomalous oscillations. We study the effect of the perturbation to the puma model. In the case of the first-order perturbation which keeps the (23) interchange symmetry, the mixing matrix element Ue3 is always zero. The nonzero mixing matrix element Ue3 is obtained in the second-order perturbation that breaks the (23) interchange symmetry.
Synchrony of plant cellular circadian clocks with heterogeneous properties under light/dark cycles.
Okada, Masaaki; Muranaka, Tomoaki; Ito, Shogo; Oyama, Tokitaka
2017-03-22
Individual cells in a plant can work independently as circadian clocks, and their properties are the basis of various circadian phenomena. The behaviour of individual cellular clocks in Lemna gibba was orderly under 24-h light/dark cycles despite their heterogeneous free-running periods (FRPs). Here, we reveal the entrainment habits of heterogeneous cellular clocks using non-24-h light/dark cycles (T-cycles). The cellular rhythms of AtCCA1::LUC under T = 16 h cycles showed heterogeneous entrainment that was associated with their heterogeneous FRPs. Under T = 12 h cycles, most cells showed rhythms having ~24-h periods. This suggested that the lower limit of entrainment to the light/dark cycles of heterogeneous cellular circadian clocks is set to a period longer than 12 h, which enables them to be synchronous under ~24-h daily cycles without being perturbed by short light/dark cycles. The entrainment habits of individual cellular clocks are likely to be the basis of the circadian behaviour of plant under the natural day-night cycle with noisy environmental fluctuations. We further suggest that modifications of EARLY FLOWERING3 (ELF3) in individual cells deviate the entrainability to shorter T-cycles possibly by altering both the FRPs and light responsiveness.
Kunz, Martin; Liddle, Andrew R.; Parkinson, David; Gao Changjun
2009-10-15
Cosmological observations are normally fit under the assumption that the dark sector can be decomposed into dark matter and dark energy components. However, as long as the probes remain purely gravitational, there is no unique decomposition and observations can only constrain a single dark fluid; this is known as the dark degeneracy. We use observations to directly constrain this dark fluid in a model-independent way, demonstrating, in particular, that the data cannot be fit by a dark fluid with a single constant equation of state. Parametrizing the dark fluid equation of state by a variety of polynomials in the scale factor a, we use current kinematical data to constrain the parameters. While the simplest interpretation of the dark fluid remains that it is comprised of separate dark matter and cosmological constant contributions, our results cover other model types including unified dark energy/matter scenarios.
Dark matter freeze-out in a nonrelativistic sector
NASA Astrophysics Data System (ADS)
Pappadopulo, Duccio; Ruderman, Joshua T.; Trevisan, Gabriele
2016-08-01
A thermally decoupled hidden sector of particles, with a mass gap, generically enters a phase of cannibalism in the early Universe. The Standard Model sector becomes exponentially colder than the hidden sector. We propose the cannibal dark matter framework, where dark matter resides in a cannibalizing sector with a relic density set by 2-to-2 annihilations. Observable signals of cannibal dark matter include a boosted rate for indirect detection, new relativistic degrees of freedom, and warm dark matter.
Condensation of galactic cold dark matter
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. Within 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.
Is Cold Dark Matter a Vacuum Effect?
NASA Astrophysics Data System (ADS)
Houlden, Michael A.
Current theories about the Universe based on an FLRW model conclude that it is composed of ~4% normal matter, ~28 % dark matter and ~68% Dark Energy which is responsible for the well-established accelerated expansion: this model works extremely well. As the Universe expands the density of normal and dark matter decreases while the proportion of Dark Energy increases. This model assumes that the amount of dark matter, whose nature at present is totally unknown, has remained constant. This is a natural assumption if dark matter is a particle of some kind - WIMP, sterile neutrino, lightest supersysmmetric particle or axion, etc. - that must have emerged from the early high temperature phase of the Big Bang. This paper proposes that dark matter is not a particle such as these but a vacuum effect, and that the proportion of dark matter in the Universe is actually increasing with time. The idea that led to this suggestion was that a quantum process (possibly the Higgs mechanism) might operate in the nilpotent vacuum that Rowlands postulates is a dual space to the real space where Standard Model fundamental fermions (and we) reside. This could produce a vacuum quantum state that has mass, which interacts gravitationally, and such states would be `dark matter'. It is proposed that the rate of production of dark matter by this process might depend on local circumstances, such as the density of dark matter and/or normal matter. This proposal makes the testable prediction that the ratio of baryonic to dark matter varies with redshift and offers an explanation, within the framework of Rowlands' ideas, of the coincidence problem - why has cosmic acceleration started in the recent epoch at redshift z ~0.55 when the Dark Energy density first became equal to the matter density?. This process also offers a potential solution to the `missing baryon' problem.
Perturbed nonlinear differential equations
NASA Technical Reports Server (NTRS)
Proctor, T. G.
1974-01-01
For perturbed nonlinear systems, a norm, other than the supremum norm, is introduced on some spaces of continuous functions. This makes possible the study of new types of behavior. A study is presented on a perturbed nonlinear differential equation defined on a half line, and the existence of a family of solutions with special boundedness properties is established. The ideas developed are applied to the study of integral manifolds, and examples are given.
Instability in interacting dark sector: an appropriate holographic Ricci dark energy model
NASA Astrophysics Data System (ADS)
Herrera, Ramón; Hipólito-Ricaldi, W. S.; Videla, Nelson
2016-08-01
In this paper we investigate the consequences of phantom crossing considering the perturbative dynamics in models with interaction in their dark sector. By mean of a general study of gauge-invariant variables in comoving gauge, we relate the sources of instabilities in the structure formation process with the phantom crossing. In order to illustrate these relations and its consequences in more detail, we consider a specific case of an holographic dark energy interacting with dark matter. We find that in spite of the model is in excellent agreement with observational data at background level, however it is plagued of instabilities in its perturbative dynamics. We reconstruct the model in order to avoid these undesirable instabilities, and we show that this implies a modification of the concordance model at background. Also we find drastic changes on the parameters space in our model when instabilities are avoided.
Can cosmic structure form without dark matter?
Dodelson, Scott; Liguori, Michele
2006-12-08
One of the prime pieces of evidence for dark matter is the observation of large overdense regions in the Universe. To account for this observation, perturbations had to have grown since recombination by a factor greater than (1+z*) approximately 1180 where z* is the epoch of recombination. This enhanced growth does not happen in general relativity, and so dark matter is needed in the standard theory. We show here that enhanced growth can occur in alternatives to general relativity, in particular, in Bekenstein's relativistic version of modified Newtonian dynamics.
Cardoso, Hugo F V; Garcia, Susana
2009-02-01
This study attempts to address the issue of relative living standards in Portuguese medieval and early 20th century periods. Since the growth of children provides a good measure of environmental quality for the overall population, the skeletal growth profiles of medieval Leiria and early 20th century Lisbon were compared. Results show that growth in femur length of medieval children did not differ significantly from that of early 20th century children, but after puberty medieval adolescents seem to have recovered, as they have significantly longer femora as adults. This is suggestive of greater potential for catch-up growth in medieval adolescents. We suggest that this results from distinct child labor practices, which impact differentially on the growth of Leiria and Lisbon adolescents. Work for medieval children and adolescents were related to family activities, and care and attention were provided by family members. Conversely, in early 20th century Lisbon children were more often sent to factories at around 12 years of age as an extra source of family income, where they were exploited for their labor. Since medieval and early 20th century children were stunted at an early age, greater potential for catch-up growth in medieval adolescents results from exhausting work being added to modern adolescent's burdens of disease and poor diet, when they entered the labor market. Although early 20th century Lisbon did not differ in overall unfavorable living conditions from medieval Leiria, after puberty different child labor practices may have placed modern adolescents at greater risk of undernutrition and poor growth.
Armendariz-Picon, Cristian; Neelakanta, Jayanth T. E-mail: jtneelak@syr.edu
2014-03-01
If cold dark matter consists of particles, these must be non-interacting and non-relativistic by definition. In most cold dark matter models however, dark matter particles inherit a non-vanishing velocity dispersion from interactions in the early universe, a velocity that redshifts with cosmic expansion but certainly remains non-zero. In this article, we place model-independent constraints on the dark matter temperature to mass ratio, whose square root determines the dark matter velocity dispersion. We only assume that dark matter particles decoupled kinetically while non-relativistic, when galactic scales had not entered the horizon yet, and that their momentum distribution has been Maxwellian since that time. Under these assumptions, using cosmic microwave background and matter power spectrum observations, we place upper limits on the temperature to mass ratio of cold dark matter today (away from collapsed structures). These limits imply that the present cold dark matter velocity dispersion has to be smaller than 54 m/s. Cold dark matter has to be quite cold, indeed.
Yang-Mills condensate as dark energy: A nonperturbative approach
NASA Astrophysics Data System (ADS)
Donà, Pietro; Marcianò, Antonino; Zhang, Yang; Antolini, Claudia
2016-02-01
Models based on the Yang-Mills condensate (YMC) have been advocated for in the literature and claimed as successful candidates for explaining dark energy. Several variations on this simple idea have been considered, the most promising of which are reviewed here. Nevertheless, the previously attained results relied heavily on the perturbative approach to the analysis of the effective Yang-Mills action, which is only adequate in the asymptotically free limit, and were extended into a regime, the infrared limit, in which confinement is expected. We show that if a minimum of the effective Lagrangian in θ =-Fμν aFa μ ν/2 exists, a YMC forms that drives the Universe toward an accelerated de Sitter phase. The details of the models depend weakly on the specific form of the effective Yang-Mills Lagrangian. Using nonperturbative techniques mutated from the functional renormalization-group procedure, we finally show that the minimum in θ of the effective Lagrangian exists. Thus, a YMC can actually take place. The nonperturbative model has properties similar to the ones in the perturbative model. In the early stage of the Universe, the YMC equation of state has an evolution that resembles the radiation component, i.e., wy→1 /3 . However, in the late stage, wy naturally runs to the critical state with wy=-1 , and the Universe transitions from a matter-dominated into a dark energy dominated stage only at latest time, at a redshift whose value depends on the initial conditions that are chosen while solving the dynamical system.
Evidence for dark matter interactions in cosmological precision data?
Lesgourgues, Julien; Marques-Tavares, Gustavo; Schmaltz, Martin E-mail: gusmt@stanford.edu
2016-02-01
We study a two-parameter extension of the cosmological standard model ΛCDM in which cold dark matter interacts with a new form of dark radiation. The two parameters correspond to the energy density in the dark radiation fluid ΔN{sub fluid} and the interaction strength between dark matter and dark radiation. The interactions give rise to a very weak ''dark matter drag'' which damps the growth of matter density perturbations throughout radiation domination, allowing to reconcile the tension between predictions of large scale structure from the CMB and direct measurements of σ{sub 8}. We perform a precision fit to Planck CMB data, BAO, large scale structure, and direct measurements of the expansion rate of the universe today. Our model lowers the χ-squared relative to ΛCDM by about 12, corresponding to a preference for non-zero dark matter drag by more than 3σ. Particle physics models which naturally produce a dark matter drag of the required form include the recently proposed non-Abelian dark matter model in which the dark radiation corresponds to massless dark gluons.
The growth of structure in interacting dark energy models
Caldera-Cabral, Gabriela; Maartens, Roy; Schaefer, Bjoern Malte E-mail: roy.maartens@port.ac.uk
2009-07-01
If dark energy interacts with dark matter, there is a change in the background evolution of the universe, since the dark matter density no longer evolves as a{sup −3}. In addition, the non-gravitational interaction affects the growth of structure. In principle, these changes allow us to detect and constrain an interaction in the dark sector. Here we investigate the growth factor and the weak lensing signal for a new class of interacting dark energy models. In these models, the interaction generalises the simple cases where one dark fluid decays into the other. In order to calculate the effect on structure formation, we perform a careful analysis of the perturbed interaction and its effect on peculiar velocities. Assuming a normalization to today's values of dark matter density and overdensity, the signal of the interaction is an enhancement (suppression) of both the growth factor and the lensing power, when the energy transfer in the background is from dark matter to dark energy (dark energy to dark matter)
Triple unification of inflation, dark matter, and dark energy using a single field
Liddle, Andrew R.; Pahud, Cedric; Urena-Lopez, L. Arturo
2008-06-15
We construct an explicit scenario whereby the same material driving inflation in the early universe can comprise dark matter in the present universe, using a simple quadratic potential. Following inflation and preheating, the density of inflaton/dark matter particles is reduced to the observed level by a period of thermal inflation, of a duration already invoked in the literature for other reasons. Within the context of the string landscape, one can further argue for a nonzero vacuum energy of this field, thus unifying inflation, dark matter, and dark energy into a single fundamental field.
Silk Damping at a Redshift of a Billion: New Limit on Small-Scale Adiabatic Perturbations
NASA Astrophysics Data System (ADS)
Jeong, Donghui; Pradler, Josef; Chluba, Jens; Kamionkowski, Marc
2014-08-01
We study the dissipation of small-scale adiabatic perturbations at early times when the Universe is hotter than T ≃0.5 keV. When the wavelength falls below the damping scale kD-1, the acoustic modes diffuse and thermalize, causing entropy production. Before neutrino decoupling, kD is primarily set by the neutrino shear viscosity, and we study the effect of acoustic damping on the relic neutrino number, primordial nucleosynthesis, dark-matter freeze-out, and baryogenesis. This sets a new limit on the amplitude of primordial fluctuations of ΔR2<0.007 at 104 Mpc-1≲k ≲105 Mpc-1 and a model-dependent limit of ΔR2≲0.3 at k ≲1020-25 Mpc-1.
Linder, Eric V.
2006-04-11
Non-negligible dark energy density at high redshifts would indicate dark energy physics distinct from a cosmological constant or"reasonable'" canonical scalar fields. Such dark energy can be constrained tightly through investigation of the growth of structure, with limits of<~;;2percent of total energy density at z>> 1 for many models. Intermediate dark energy can have effects distinct from its energy density; the dark ages acceleration can be constrained to last less than 5percent of a Hubble e-fold time, exacerbating the coincidence problem. Both the total linear growth, or equivalently sigma 8, and the shape and evolution of the nonlinear mass power spectrum for z<2 (using the Linder-White nonlinear mapping prescription) provide important windows. Probes of growth, such as weak gravitational lensing, can interact with supernovae and CMB distance measurements to scan dark energy behavior over the entire range z=0-1100.
Galactoseismology and the Local Density of Dark Matter
Banik, Nilanjan; Widrow, Lawrence M.; Dodelson, Scott
2016-08-10
We model vertical breathing mode perturbations in the Milky Way's stellar disc and study their effects on estimates of the local dark matter density, surface density, and vertical force. Evidence for these perturbations, which involve compression and expansion of the Galactic disc perpendicular to its midplane, come from the SEGUE, RAVE, and LAMOST surveys. We show that their existence may lead to systematic errors of $10\\%$ or greater in the vertical force $K_z(z)$ at $|z|=1.1\\,{\\rm kpc}$. These errors translate to $\\gtrsim 25\\%$ errors in estimates of the local dark matter density. Using different mono-abundant subpopulations as tracers offers a way out: if the inferences from all tracers in the Gaia era agree, then the dark matter determination will be robust. Disagreement in the inferences from different tracers will signal the breakdown of the unperturbed model and perhaps provide the means for determining the nature of the perturbation.
NASA Technical Reports Server (NTRS)
Criminale, W. O.; Lasseigne, D. G.; Jackson, T. L.
1995-01-01
An initial value approach is used to examine the dynamics of perturbations introduced into a vortex under strain. Both the basic vortex considered and the perturbations are taken as fully three-dimensional. An explicit solution for the time evolution of the vorticity perturbations is given for arbitrary initial vorticity. Analytical solutions for the resulting velocity components are found when the initial vorticity is assumed to be localized. For more general initial vorticity distributions, the velocity components are determined numerically. It is found that the variation in the radial direction of the initial vorticity disturbance is the most important factor influencing the qualitative behavior of the solutions. Transient growth in the magnitude of the velocity components is found to be directly attributable to the compactness of the initial vorticity.
Measurement and Perturbation of Morphogen Lifetime: Effects on Gradient Shape
Drocco, Jeffrey A.; Grimm, Oliver; Tank, David W.; Wieschaus, Eric
2011-01-01
Protein lifetime is of critical importance for most biological processes and plays a central role in cell signaling and embryonic development, where it impacts the absolute concentration of signaling molecules and, potentially, the shape of morphogen gradients. Early conceptual and mathematical models of gradient formation proposed that steady-state gradients are established by an equilibration between the lifetime of a morphogen and its rates of synthesis and diffusion, though whether gradients in fact reach steady state before being read out is a matter of controversy. In any case, this class of models predicts that protein lifetime is a key determinant of both the time to steady state and the spatial extent of a gradient. Using a method that employs repeated photoswitching of a fusion of the morphogen Bicoid (Bcd) and the photoconvertible fluorescent protein Dronpa, we measure and modify the lifetime of Dronpa-Bcd in living Drosophila embryos. We find that the lifetime of Bcd is dynamic, changing from 50 min before mitotic cycle 14 to 15 min during cellularization. Moreover, by measuring total quantities of Bcd over time, we find that the gradient does not reach steady state. Finally, using a nearly continuous low-level conversion to the dark state of Dronpa-Bcd to mimic the effect of increased degradation, we demonstrate that perturbation of protein lifetime changes the characteristic length of the gradient, providing direct support for a mechanism based on synthesis, diffusion, and degradation. PMID:22004733
Perturbed nonlinear differential equations
NASA Technical Reports Server (NTRS)
Proctor, T. G.
1972-01-01
The existence of a solution defined for all t and possessing a type of boundedness property is established for the perturbed nonlinear system y = f(t,y) + F(t,y). The unperturbed system x = f(t,x) has a dichotomy in which some solutions exist and are well behaved as t increases to infinity, and some solution exists and are well behaved as t decreases to minus infinity. A similar study is made for a perturbed nonlinear differential equation defined on a half line, R+, and the existence of a family of solutions with special boundedness properties is established. The ideas are applied to integral manifolds.
NASA Astrophysics Data System (ADS)
Co, Raymond T.; Harigaya, Keisuke; Nomura, Yasunori
2017-03-01
We present a simple and natural dark sector model in which dark matter particles arise as composite states of hidden strong dynamics and their stability is ensured by accidental symmetries. The model has only a few free parameters. In particular, the gauge symmetry of the model forbids the masses of dark quarks, and the confinement scale of the dynamics provides the unique mass scale of the model. The gauge group contains an Abelian symmetry U (1 )D , which couples the dark and standard model sectors through kinetic mixing. This model, despite its simple structure, has rich and distinctive phenomenology. In the case where the dark pion becomes massive due to U (1 )D quantum corrections, direct and indirect detection experiments can probe thermal relic dark matter which is generically a mixture of the dark pion and the dark baryon, and the Large Hadron Collider can discover the U (1 )D gauge boson. Alternatively, if the dark pion stays light due to a specific U (1 )D charge assignment of the dark quarks, then the dark pion constitutes dark radiation. The signal of this radiation is highly correlated with that of dark baryons in dark matter direct detection.
Evolution of perturbations in an inflationary universe
NASA Technical Reports Server (NTRS)
Frieman, J. A.; Will, C. M.
1982-01-01
The evolution of inhomogeneous density perturbations in a model of the very early universe that is dominated for a time by a constant energy density of a false quantum-mechanical vacuum is analyzed. During this period, the universe inflates exponentially and supercools exponentially, until a phase transition back to the true vacuum reheats the matter and radiation. Focus is on the physically measurable, coordinate-independent modes of inhomogeneous perturbations of this model and it is found that all modes either are constant or are exponentially damped during the inflationary era.
Interaction between bosonic dark matter and stars
NASA Astrophysics Data System (ADS)
Brito, Richard; Cardoso, Vitor; Macedo, Caio F. B.; Okawa, Hirotada; Palenzuela, Carlos
2016-02-01
We provide a detailed analysis of how bosonic dark matter "condensates" interact with compact stars, extending significantly the results of a recent Letter [1]. We focus on bosonic fields with mass mB , such as axions, axion-like candidates and hidden photons. Self-gravitating bosonic fields generically form "breathing" configurations, where both the spacetime geometry and the field oscillate, and can interact and cluster at the center of stars. We construct stellar configurations formed by a perfect fluid and a bosonic condensate, and which may describe the late stages of dark matter accretion onto stars, in dark-matter-rich environments. These composite stars oscillate at a frequency which is a multiple of f =2.5 ×1014(mBc2/eV ) Hz . Using perturbative analysis and numerical relativity techniques, we show that these stars are generically stable, and we provide criteria for instability. Our results also indicate that the growth of the dark matter core is halted close to the Chandrasekhar limit. We thus dispel a myth concerning dark matter accretion by stars: dark matter accretion does not necessarily lead to the destruction of the star, nor to collapse to a black hole. Finally, we argue that stars with long-lived bosonic cores may also develop in other theories with effective mass couplings, such as (massless) scalar-tensor theories.
Dark-matter decay and the abundance of ultracompact minihalos
NASA Astrophysics Data System (ADS)
Yang, Yu-Peng; Yang, Gui-Lin; Zong, Hong-Shi
2013-03-01
Ultracompact minihalos would be formed if there are larger density perturbations (0.0003 < δρ/ρ < 0.3) in the earlier epoch. Their density profile is steeper than the standard dark-matter halos. If dark matter can annihilate or decay into standard particles, e.g., photons, these objects would be the potential astrophysical sources. In order to be consistent with observations, as those from Fermi, the abundance of ultracompact minihalos must be constrained. On the other hand, the formation of these objects has very tight relation with the primordial curvature perturbations on smaller scale, so the fraction of ultracompact minihalos is very important for modern cosmology. In previous works, the studies are focused on the dark-matter annihilation for these objects. But if dark matter is not annihilated, the dark-matter decay is another important possible case. On the other hand, the abundance of ultracompact minihalos is related to many other parameters, such as the mass of dark matter, the decay channels and the density profile of dark-matter halos. One of the important aspects of this work is that we investigate the γ-ray signals from nearby ultracompact minihalos due to dark-matter decay and another important aspect is to study in detail how the different decay channels and density profiles affect the constraints on the abundance of ultracompact minihalos.
Scalar perturbations on Lemaitre-Tolman-Bondi spacetimes
Zibin, J. P.
2008-08-15
In recent years there has been growing interest in verifying the horizon-scale homogeneity of the Universe that follows from applying the Copernican principle to the observed isotropy. This program has been stimulated by the discovery that a very large void, centered near us, can explain supernova luminosity distance measurements without dark energy. It is crucial to confront such models with as wide a variety of data as possible. With this application in mind, we develop the relativistic theory of linear scalar perturbations on spherically symmetric dust (Lemaitre-Tolman-Bondi) spacetimes, using the covariant 1+1+2 formalism. We show that the evolution of perturbations is determined by a small set of new linear transfer functions. If decaying modes are ignored (to be consistent with the standard inflationary paradigm), the standard techniques of perturbation theory on homogeneous backgrounds, such as harmonic expansion, can be applied, and results closely paralleling those of familiar cosmological perturbation theory can be obtained.
Perturbing turbulence beyond collapse
NASA Astrophysics Data System (ADS)
Kühnen, Jakob; Scarselli, Davide; Hof, Björn; Nonlinear Dynamics; Turbulence Group Team
2016-11-01
Wall-bounded turbulent flows are considered to be in principle stable against perturbations and persist as long as the Reynolds number is sufficiently high. We show for the example of pipe flow that a specific perturbation of the turbulent flow field disrupts the genesis of new turbulence at the wall. This leads to an immediate collapse of the turbulent flow and causes complete relaminarisation further downstream. The annihilation of turbulence is effected by a steady manipulation of the streamwise velocity component only, greatly simplifying control efforts which usually require knowledge of the highly complex three dimensional and time dependent velocity fields. We present several different control schemes from laboratory experiments which achieve the required perturbation of the flow for total relaminarisation. Transient growth, a linear amplification mechanism measuring the efficiency of eddies in redistributing shear that quantifies the maximum perturbation energy amplification achievable over a finite time in a linearized framework, is shown to set a clear-cut threshold below which turbulence is impeded in its formation and thus permanently annihilated.
Cosmological perturbations in antigravity
NASA Astrophysics Data System (ADS)
Oltean, Marius; Brandenberger, Robert
2014-10-01
We compute the evolution of cosmological perturbations in a recently proposed Weyl-symmetric theory of two scalar fields with oppositely signed conformal couplings to Einstein gravity. It is motivated from the minimal conformal extension of the standard model, such that one of these scalar fields is the Higgs while the other is a new particle, the dilaton, introduced to make the Higgs mass conformally symmetric. At the background level, the theory admits novel geodesically complete cyclic cosmological solutions characterized by a brief period of repulsive gravity, or "antigravity," during each successive transition from a big crunch to a big bang. For simplicity, we consider scalar perturbations in the absence of anisotropies, with potential set to zero and without any radiation. We show that despite the necessarily wrong-signed kinetic term of the dilaton in the full action, these perturbations are neither ghostlike nor tachyonic in the limit of strongly repulsive gravity. On this basis, we argue—pending a future analysis of vector and tensor perturbations—that, with respect to perturbative stability, the cosmological solutions of this theory are viable.
Cosmology with massive neutrinos coupled to dark energy.
Brookfield, A W; van de Bruck, C; Mota, D F; Tocchini-Valentini, D
2006-02-17
Cosmological consequences of a coupling between massive neutrinos and dark energy are investigated. In such models, the neutrino mass is a function of a scalar field, which plays the role of dark energy. The evolution of the background and cosmological perturbations are discussed. We find that mass-varying neutrinos can leave a significant imprint on the anisotropies in the cosmic microwave background and even lead to a reduction of power on large angular scales.
Effective gravitational couplings for cosmological perturbations in generalized Proca theories
NASA Astrophysics Data System (ADS)
De Felice, Antonio; Heisenberg, Lavinia; Kase, Ryotaro; Mukohyama, Shinji; Tsujikawa, Shinji; Zhang, Ying-li
2016-08-01
We consider the finite interactions of the generalized Proca theory including the sixth-order Lagrangian and derive the full linear perturbation equations of motion on the flat Friedmann-Lemaître-Robertson-Walker background in the presence of a matter perfect fluid. By construction, the propagating degrees of freedom (besides the matter perfect fluid) are two transverse vector perturbations, one longitudinal scalar, and two tensor polarizations. The Lagrangians associated with intrinsic vector modes neither affect the background equations of motion nor the second-order action of tensor perturbations, but they do give rise to nontrivial modifications to the no-ghost condition of vector perturbations and to the propagation speeds of vector and scalar perturbations. We derive the effective gravitational coupling Geff with matter density perturbations under a quasistatic approximation on scales deep inside the sound horizon. We find that the existence of intrinsic vector modes allows a possibility for reducing Geff. In fact, within the parameter space, Geff can be even smaller than the Newton gravitational constant G at the late cosmological epoch, with a peculiar phantom dark energy equation of state (without ghosts). The modifications to the slip parameter η and the evolution of the growth rate f σ8 are discussed as well. Thus, dark energy models in the framework of generalized Proca theories can be observationally distinguished from the Λ CDM model according to both cosmic growth and expansion history. Furthermore, we study the evolution of vector perturbations and show that outside the vector sound horizon the perturbations are nearly frozen and start to decay with oscillations after the horizon entry.
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.
Accretion of dark matter by stars.
Brito, Richard; Cardoso, Vitor; Okawa, Hirotada
2015-09-11
Searches for dark matter imprints are one of the most active areas of current research. We focus here on light fields with mass m_{B}, such as axions and axionlike candidates. Using perturbative techniques and full-blown nonlinear numerical relativity methods, we show the following. (i) Dark matter can pile up in the center of stars, leading to configurations and geometries oscillating with a frequency that is a multiple of f=2.5×10^{14}(m_{B}c^{2}/eV) Hz. These configurations are stable throughout most of the parameter space, and arise out of credible mechanisms for dark-matter capture. Stars with bosonic cores may also develop in other theories with effective mass couplings, such as (massless) scalar-tensor theories. We also show that (ii) collapse of the host star to a black hole is avoided by efficient gravitational cooling mechanisms.
NASA Astrophysics Data System (ADS)
Kopp, Joachim; Liu, Jia; Slatyer, Tracy R.; Wang, Xiao-Ping; Xue, Wei
2016-12-01
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 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 even 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. 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.
Quintessence with quadratic coupling to dark matter
Boehmer, Christian G.; Chan, Nyein; Caldera-Cabral, Gabriela; Lazkoz, Ruth; Maartens, Roy
2010-04-15
We introduce a new form of coupling between dark energy and dark matter that is quadratic in their energy densities. Then we investigate the background dynamics when dark energy is in the form of exponential quintessence. The three types of quadratic coupling all admit late-time accelerating critical points, but these are not scaling solutions. We also show that two types of coupling allow for a suitable matter era at early times and acceleration at late times, while the third type of coupling does not admit a suitable matter era.
Asymmetric dark matter in braneworld cosmology
Meehan, Michael T.; Whittingham, Ian B. E-mail: Ian.Whittingham@jcu.edu.au
2014-06-01
We investigate the effect of a braneworld expansion era on the relic density of asymmetric dark matter. We find that the enhanced expansion rate in the early universe predicted by the Randall-Sundrum II (RSII) model leads to earlier particle freeze-out and an enhanced relic density. This effect has been observed previously by Okada and Seto (2004) for symmetric dark matter models and here we extend their results to the case of asymmetric dark matter. We also discuss the enhanced asymmetric annihilation rate in the braneworld scenario and its implications for indirect detection experiments.
Initial conditions for cosmological perturbations
NASA Astrophysics Data System (ADS)
Ashtekar, Abhay; Gupt, Brajesh
2017-02-01
Penrose proposed that the big bang singularity should be constrained by requiring that the Weyl curvature vanishes there. The idea behind this past hypothesis is attractive because it constrains the initial conditions for the universe in geometric terms and is not confined to a specific early universe paradigm. However, the precise statement of Penrose’s hypothesis is tied to classical space-times and furthermore restricts only the gravitational degrees of freedom. These are encapsulated only in the tensor modes of the commonly used cosmological perturbation theory. Drawing inspiration from the underlying idea, we propose a quantum generalization of Penrose’s hypothesis using the Planck regime in place of the big bang, and simultaneously incorporating tensor as well as scalar modes. Initial conditions selected by this generalization constrain the universe to be as homogeneous and isotropic in the Planck regime as permitted by the Heisenberg uncertainty relations.
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
The Dark Energy Survey: More than dark energy - An overview
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 supernovae andmore » 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
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 supernovae 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).
The Dark Energy Survey: more than dark energy - an overview
NASA Astrophysics Data System (ADS)
Dark Energy Survey Collaboration; Abbott, T.; Abdalla, F. B.; Aleksić, J.; Allam, S.; Amara, A.; Bacon, D.; Balbinot, E.; Banerji, M.; Bechtol, K.; Benoit-Lévy, A.; Bernstein, G. M.; Bertin, E.; Blazek, J.; Bonnett, C.; Bridle, S.; Brooks, D.; Brunner, R. J.; Buckley-Geer, E.; Burke, D. L.; Caminha, G. B.; Capozzi, D.; Carlsen, J.; Carnero-Rosell, A.; Carollo, M.; Carrasco-Kind, M.; Carretero, J.; Castander, F. J.; Clerkin, L.; Collett, T.; Conselice, C.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Davis, T. M.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Dodelson, S.; Doel, P.; Drlica-Wagner, A.; Estrada, J.; Etherington, J.; Evrard, A. E.; Fabbri, J.; Finley, D. A.; Flaugher, B.; Foley, R. J.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Giannantonio, T.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Guarnieri, P.; Gutierrez, G.; Hartley, W.; Honscheid, K.; Jain, B.; James, D. J.; Jeltema, T.; Jouvel, S.; Kessler, R.; King, A.; Kirk, D.; Kron, R.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Lima, M.; Lin, H.; Maia, M. A. G.; Makler, M.; Manera, M.; Maraston, C.; Marshall, J. L.; Martini, P.; McMahon, R. G.; Melchior, P.; Merson, A.; Miller, C. J.; Miquel, R.; Mohr, J. J.; Morice-Atkinson, X.; Naidoo, K.; Neilsen, E.; Nichol, R. C.; Nord, B.; Ogando, R.; Ostrovski, F.; Palmese, A.; Papadopoulos, A.; Peiris, H. V.; Peoples, J.; Percival, W. J.; Plazas, A. A.; Reed, S. L.; Refregier, A.; Romer, A. K.; Roodman, A.; Ross, A.; Rozo, E.; Rykoff, E. S.; Sadeh, I.; Sako, M.; Sánchez, C.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Sheldon, E.; Smith, M.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Soumagnac, M.; Suchyta, E.; Sullivan, M.; Swanson, M.; Tarle, G.; Thaler, J.; Thomas, D.; Thomas, R. C.; Tucker, D.; Vieira, J. D.; Vikram, V.; Walker, A. R.; Wechsler, R. H.; Weller, J.; Wester, W.; Whiteway, L.; Wilcox, H.; Yanny, B.; Zhang, Y.; Zuntz, J.
2016-08-01
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 supernovae 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).
Examining the viability of phantom dark energy
NASA Astrophysics Data System (ADS)
Ludwick, Kevin J.
2015-09-01
In the standard cosmological framework of the 0th-order Friedmann-Lemaître-Robertson-Walker (FLRW) metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter w <-1 (known as phantom dark energy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the accepted values for present-day w from Planck and WMAP9 include a significant range of values less than -1 . We find that it is not as obvious as one might think that phantom dark energy has negative kinetic energy categorically. Analogously, we find that field models of quintessence dark energy (wϕ>-1 ) do not necessarily have positive kinetic energy categorically. Staying within the confines of observational constraints and general relativity, for which there is good experimental validation, we consider a few reasonable departures from the standard 0th-order framework in an attempt to see if negative kinetic energy can be avoided in these settings despite an apparent w <-1 . We consider a more accurate description of the universe through the perturbing of the isotropic and homogeneous FLRW metric and the components of the stress-energy tensor, and we consider dynamic w and primordial isocurvature and adiabatic perturbations. We find that phantom dark energy does not necessarily have negative kinetic energy for all relevant length scales at all times, and we also find that, by the same token, quintessence dark energy does not necessarily have positive kinetic energy for all relevant length scales at all times.
DarkSide search for dark matter
Alexander, T.; Alton, D.; Arisaka, K.; Back, H. O.; Beltrame, P.; Benziger, J.; Bonfini, G.; Brigatti, A.; Brodsky, J.; Bussino, S.; Cadonati, L.; Calaprice, F.; Candela, A.; Cao, H.; Cavalcante, P.; Chepurnov, A.; Chidzik, S.; Cocco, A. G.; Condon, C.; D'Angelo, D.; Davini, S.; Vincenzi, M. De; Haas, E. De; Derbin, A.; Pietro, G. Di; Dratchnev, I.; Durben, D.; Empl, A.; Etenko, A.; Fan, A.; Fiorillo, G.; Franco, D.; Fomenko, K.; Forster, G.; Gabriele, F.; Galbiati, C.; Gazzana, S.; Ghiano, C.; Goretti, A.; Grandi, L.; Gromov, M.; Guan, M.; Guo, C.; Guray, G.; Hungerford, E. V.; Ianni, Al; Ianni, An; Joliet, C.; Kayunov, A.; Keeter, K.; Kendziora, C.; Kidner, S.; Klemmer, R.; Kobychev, V.; Koh, G.; Komor, M.; Korablev, D.; Korga, G.; Li, P.; Loer, B.; Lombardi, P.; Love, C.; Ludhova, L.; Luitz, S.; Lukyanchenko, L.; Lund, A.; Lung, K.; Ma, Y.; Machulin, I.; Mari, S.; Maricic, J.; Martoff, C. J.; Meregaglia, A.; Meroni, E.; Meyers, P.; Mohayai, T.; Montanari, D.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B.; Muratova, V.; Nelson, A.; Nemtzow, A.; Nurakhov, N.; Orsini, M.; Ortica, F.; Pallavicini, M.; Pantic, E.; Parmeggiano, S.; Parsells, R.; Pelliccia, N.; Perasso, L.; Perasso, S.; Perfetto, F.; Pinsky, L.; Pocar, A.; Pordes, S.; Randle, K.; Ranucci, G.; Razeto, A.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Saggese, P.; Saldanha, R.; Salvo, C.; Sands, W.; Seigar, M.; Semenov, D.; Shields, E.; Skorokhvatov, M.; Smirnov, O.; Sotnikov, A.; Sukhotin, S.; Suvarov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Thompson, J.; Tonazzo, A.; Unzhakov, E.; Vogelaar, R. B.; Wang, H.; Westerdale, S.; Wojcik, M.; Wright, A.; Xu, J.; Yang, C.; Zavatarelli, S.; Zehfus, M.; Zhong, W.; Zuzel, G.
2013-11-22
The DarkSide staged program utilizes a two-phase time projection chamber (TPC) with liquid argon as the target material for the scattering of dark matter particles. Efficient background reduction is achieved using low radioactivity underground argon as well as several experimental handles such as pulse shape, ratio of ionization over scintillation signal, 3D event reconstruction, and active neutron and muon vetos. The DarkSide-10 prototype detector has proven high scintillation light yield, which is a particularly important parameter as it sets the energy threshold for the pulse shape discrimination technique. The DarkSide-50 detector system, currently in commissioning phase at the Gran Sasso Underground Laboratory, will reach a sensitivity to dark matter spin-independent scattering cross section of 10^{-45} cm^{2} within 3 years of operation.
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.
Kumar, Jason
2014-06-24
We review the theoretical framework underlying models of asymmetric dark matter, describe astrophysical constraints which arise from observations of neutron stars, and discuss the prospects for detecting asymmetric dark matter.
The dark side of cosmology: dark matter and dark energy.
Spergel, David N
2015-03-06
A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales.
Cosmic perturbations through the cyclic ages
Erickson, Joel K.; Gratton, Steven; Steinhardt, Paul J.; Turok, Neil
2007-06-15
We analyze the evolution of cosmological perturbations in the cyclic model, paying particular attention to their behavior and interplay over multiple cycles. Our key results are: (1) galaxies and large scale structure present in one cycle are generated by the quantum fluctuations in the preceding cycle without interference from perturbations or structure generated in earlier cycles and without interfering with structure generated in later cycles; (2) the ekpyrotic phase, an epoch of gentle contraction with equation of state w>>1 preceding the hot big bang, makes the universe homogeneous, isotropic and flat within any given observer's horizon; and (3) although the universe is uniform within each observer's horizon, the structure of the cyclic universe on very large scales is more complex, owing to the effects of superhorizon length perturbations, and cannot be described globally as a Friedmann-Robertson-Walker cosmology. In particular, we show that the ekpyrotic contraction phase is so effective in smoothing, flattening and isotropizing the universe within the horizon that this phase alone suffices to solve the horizon and flatness problems even without an extended period of dark energy domination (a kind of low energy inflation). Instead, the cyclic model rests on a genuinely novel, noninflationary mechanism (ekpyrotic contraction) for resolving the classic cosmological conundrums.
Using Lagrangian perturbation theory for precision cosmology
Sugiyama, Naonori S.
2014-06-10
We explore the Lagrangian perturbation theory (LPT) at one-loop order with Gaussian initial conditions. We present an expansion method to approximately compute the power spectrum LPT. Our approximate solution has good convergence in the series expansion and enables us to compute the power spectrum in LPT accurately and quickly. Non-linear corrections in this theory naturally satisfy the law of conservation of mass because the relation between matter density and the displacement vector of dark matter corresponds to the conservation of mass. By matching the one-loop solution in LPT to the two-loop solution in standard perturbation theory, we present an approximate solution of the power spectrum which has higher order corrections than the two-loop order in standard perturbation theory with the conservation of mass satisfied. With this approximation, we can use LPT to compute a non-linear power spectrum without any free parameters, and this solution agrees with numerical simulations at k = 0.2 h Mpc{sup –1} and z = 0.35 to better than 2%.
Chamseddine, Ali H.; Mukhanov, Viatcheslav E-mail: viatcheslav.Mukhanov@lmu.de
2016-02-01
We modify Einstein General Relativity by adding non-dynamical scalar fields to account simultaneously for both dark matter and dark energy. The dark energy in this case can be distributed in-homogeneously even within horizon scales. Its inhomogeneities can contribute to the late time integrated Sachs-Wolfe effect, possibly removing some of the low multipole anomalies in the temperature fluctuations of the CMB spectrum. The presence of the inhomogeneous dark matter also influences structure formation in the universe.
Yuan, Qiang; Yue, Bin; Chen, Xuelei; Zhang, Bing E-mail: yuebin@bao.ac.cn E-mail: xuelei@cosmology.bao.ac.cn
2011-04-01
It has been proposed that during the formation of the first generation stars there might be a ''dark star'' phase in which the power of the star comes from dark matter annihilation. The adiabatic contraction process to form the dark star would result in a highly concentrated density profile of the host halo at the same time, which may give enhanced indirect detection signals of dark matter. In this work we investigate the extragalactic γ-ray background from dark matter annihilation with such a dark star formation scenario, and employ the isotropic γ-ray data from Fermi-LAT to constrain the model parameters of dark matter. The results suffer from large uncertainties of both the formation rate of the first generation stars and the subsequent evolution effects of the host halos of the dark stars. We find, in the most optimistic case for γ-ray production via dark matter annihilation, the expected extragalactic γ-ray flux will be enhanced by 1-2 orders of magnitude. In such a case, the annihilation cross section of the supersymmetric dark matter can be constrained to the thermal production level, and the leptonic dark matter model which is proposed to explain the positron/electron excesses can be well excluded. Conversely, if the positron/electron excesses are of a dark matter annihilation origin, then the early Universe environment is such that no dark star can form.
Self-interacting complex scalar field as dark matter
Briscese, F.
2011-10-14
We study the viability of a a complex scalar field {chi} with self-interacting potential V = m{sub 0}{sup {chi}/}2|{chi}|{sup 2}+h|{chi}|{sup 4} as dark matter. Due to the self interaction, the scalar field forms a Bose-Einstein condensate at early times that represents dark matter. The self interaction is also responsible of quantum corrections to the scalar field mass that naturally give the dark matter domination at late times without any fine tuning on the energy density of the scalar field at early times. Finally the properties of the spherically symmetric dark matter halos are also discussed.
Nonthermal Supermassive Dark Matter
NASA Technical Reports Server (NTRS)
Chung, Daniel J. H.; Kolb, Edward W.; Riotto, Antonio
1999-01-01
We discuss several cosmological production mechanisms for nonthermal supermassive dark matter and argue that dark matter may he elementary particles of mass much greater than the weak scale. Searches for dark matter should ma be limited to weakly interacting particles with mass of the order of the weak scale, but should extend into the supermassive range as well.
Holographic Dark Energy Density
NASA Astrophysics Data System (ADS)
Saadat, Hassan
2011-06-01
In this article we consider the cosmological model based on the holographic dark energy. We study dark energy density in Universe with arbitrary spatially curvature described by the Friedmann-Robertson-Walker metric. We use Chevallier-Polarski-Linder parametrization to specify dark energy density.
Renormalized Lie perturbation theory
Rosengaus, E.; Dewar, R.L.
1981-07-01
A Lie operator method for constructing action-angle transformations continuously connected to the identity is developed for area preserving mappings. By a simple change of variable from action to angular frequency a perturbation expansion is obtained in which the small denominators have been renormalized. The method is shown to lead to the same series as the Lagrangian perturbation method of Greene and Percival, which converges on KAM surfaces. The method is not superconvergent, but yields simple recursion relations which allow automatic algebraic manipulation techniques to be used to develop the series to high order. It is argued that the operator method can be justified by analytically continuing from the complex angular frequency plane onto the real line. The resulting picture is one where preserved primary KAM surfaces are continuously connected to one another.
Bose-Einstein condensation of dark matter axions.
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.
Covariant Bardeen perturbation formalism
NASA Astrophysics Data System (ADS)
Vitenti, S. D. P.; Falciano, F. T.; Pinto-Neto, N.
2014-05-01
In a previous work we obtained a set of necessary conditions for the linear approximation in cosmology. Here we discuss the relations of this approach with the so-called covariant perturbations. It is often argued in the literature that one of the main advantages of the covariant approach to describe cosmological perturbations is that the Bardeen formalism is coordinate dependent. In this paper we will reformulate the Bardeen approach in a completely covariant manner. For that, we introduce the notion of pure and mixed tensors, which yields an adequate language to treat both perturbative approaches in a common framework. We then stress that in the referred covariant approach, one necessarily introduces an additional hypersurface choice to the problem. Using our mixed and pure tensors approach, we are able to construct a one-to-one map relating the usual gauge dependence of the Bardeen formalism with the hypersurface dependence inherent to the covariant approach. Finally, through the use of this map, we define full nonlinear tensors that at first order correspond to the three known gauge invariant variables Φ, Ψ and Ξ, which are simultaneously foliation and gauge invariant. We then stress that the use of the proposed mixed tensors allows one to construct simultaneously gauge and hypersurface invariant variables at any order.
Amplitudes of Spiral Perturbations
NASA Astrophysics Data System (ADS)
Grosbol, P.; Patsis, P. A.
2014-03-01
It has proven very difficult to estimate the amplitudes of spiral perturbations in disk galaxies from observations due to the variation of mass-to-light ratio and extinction across spiral arms. Deep, near-infrared images of grand-design spiral galaxies obtained with HAWK-I/VLT were used to analyze the azimuthal amplitude and shape of arms, which, even in the K-band may, be significantly biased by the presence of young stellar populations. Several techniques were applied to evaluate the relative importance of young stars across the arms, such as surface brightness of the disk with light from clusters subtracted, number density of clusters detected, and texture of the disk. The modulation of the texture measurement, which correlates with the number density of faint clusters, yields amplitudes of the spiral perturbation in the range 0.1-0.2. This estimate gives a better estimate of the mass perturbation in the spiral arms, since it is dominated by old clusters.
Properties and uncertainties of scalar field models of dark energy with barotropic equation of state
Novosyadlyj, Bohdan; Sergijenko, Olga; Apunevych, Stepan; Pelykh, Volodymyr
2010-11-15
The dynamics of expansion and large scale structure formation in the multicomponent Universe with dark energy modeled by the minimally coupled scalar field with generalized linear barotropic equation of state are analyzed. It is shown that the past dynamics of expansion and future of the Universe - eternal accelerated expansion or turnaround and collapse - are completely defined by the current energy density of a scalar field and relation between its current and early equation of state parameters. The clustering properties of such models of dark energy and their imprints in the power spectrum of matter density perturbations depend on the same relation and, additionally, on the 'effective sound speed' of a scalar field, defined by its Lagrangian. It is concluded that such scalar fields with different values of these parameters are distinguishable in principle. This gives the possibility to constrain them by confronting the theoretical predictions with the corresponding observational data. For that we have used the 7-year Wilkinson Microwave Anisotropy Probe data on cosmic microwave background anisotropies, the Union2 data set on Supernovae Ia and the seventh data release of the Sloan Digital Sky Survey data on luminous red galaxies space distribution. Using the Markov Chain Monte Carlo technique the marginalized posterior and mean likelihood distributions are computed for the scalar fields with two different Lagrangians: Klein-Gordon and Dirac-Born-Infeld ones. The properties of such scalar field models of dark energy with best fitting parameters and uncertainties of their determination are also analyzed in the paper.
Dark microglia: Why are they dark?
Bisht, Kanchan; Sharma, Kaushik; Lacoste, Baptiste; Tremblay, Marie-Ève
2016-01-01
Using transmission electron microscopy (TEM) we recently characterized a microglial phenotype that is induced by chronic stress, fractalkine receptor deficiency, aging, or Alzheimer disease pathology. These 'dark' microglia appear overly active compared with the normal microglia, reaching for synaptic clefts, and extensively engulfing pre-synaptic axon terminals and post-synaptic dendritic spines. From these findings we hypothesized that dark microglia could be specifically implicated in the pathological remodeling of neuronal circuits, which impairs learning, memory, and other essential cognitive functions. In the present addendum we further discuss about the possible causes of their dark appearance under TEM.
Vector field models of modified gravity and the dark sector
Zuntz, J.; Ferreira, P. G.; Zlosnik, T. G; Bourliot, F.; Starkman, G. D.
2010-05-15
We present a comprehensive investigation of cosmological constraints on the class of vector field formulations of modified gravity called generalized Einstein-aether models. Using linear perturbation theory we generate cosmic microwave background and large-scale structure spectra for general parameters of the theory, and then constrain them in various ways. We investigate two parameter regimes: a dark matter candidate where the vector field sources structure formation, and a dark energy candidate where it causes late-time acceleration. We find that the dark matter candidate does not fit the data, and identify five physical problems that can restrict this and other theories of dark matter. The dark energy candidate does fit the data, and we constrain its fundamental parameters; most notably we find that the theory's kinetic index parameter n{sub ae} can differ significantly from its {Lambda}CDM value.
Self-interacting asymmetric dark matter coupled to a light massive dark photon
Petraki, Kalliopi; Pearce, Lauren; Kusenko, Alexander E-mail: lpearce@ucla.edu
2014-07-01
Dark matter (DM) with sizeable self-interactions mediated by a light species offers a compelling explanation of the observed galactic substructure; furthermore, the direct coupling between DM and a light particle contributes to the DM annihilation in the early universe. If the DM abundance is due to a dark particle-antiparticle asymmetry, the DM annihilation cross-section can be arbitrarily large, and the coupling of DM to the light species can be significant. We consider the case of asymmetric DM interacting via a light (but not necessarily massless) Abelian gauge vector boson, a dark photon. In the massless dark photon limit, gauge invariance mandates that DM be multicomponent, consisting of positive and negative dark ions of different species which partially bind in neutral dark atoms. We argue that a similar conclusion holds for light dark photons; in particular, we establish that the multi-component and atomic character of DM persists in much of the parameter space where the dark photon is sufficiently light to mediate sizeable DM self-interactions. We discuss the cosmological sequence of events in this scenario, including the dark asymmetry generation, the freeze-out of annihilations, the dark recombination and the phase transition which gives mass to the dark photon. We estimate the effect of self-interactions in DM haloes, taking into account this cosmological history. We place constraints based on the observed ellipticity of large haloes, and identify the regimes where DM self-scattering can affect the dynamics of smaller haloes, bringing theory in better agreement with observations. Moreover, we estimate the cosmological abundance of dark photons in various regimes, and derive pertinent bounds.
Fan, JiJi; Katz, Andrey; Randall, Lisa; Reece, Matthew
2013-05-24
We point out that current constraints on dark matter imply only that the majority of dark matter is cold and collisionless. A subdominant fraction of dark matter could have much stronger interactions. In particular, it could interact in a manner that dissipates energy, thereby cooling into a rotationally supported disk, much as baryons do. We call this proposed new dark matter component double-disk dark matter (DDDM). We argue that DDDM could constitute a fraction of all matter roughly as large as the fraction in baryons, and that it could be detected through its gravitational effects on the motion of stars in galaxies, for example. Furthermore, if DDDM can annihilate to gamma rays, it would give rise to an indirect detection signal distributed across the sky that differs dramatically from that predicted for ordinary dark matter. DDDM and more general partially interacting dark matter scenarios provide a large unexplored space of testable new physics ideas.
Coupled dark matter-dark energy in light of near universe observations
Honorez, Laura Lopez; Mena, Olga E-mail: beth.ann.reid@gmail.com E-mail: liciaverde@gmail.com
2010-09-01
Cosmological analysis based on currently available observations are unable to rule out a sizeable coupling among the dark energy and dark matter fluids. We explore a variety of coupled dark matter-dark energy models, which satisfy cosmic microwave background constraints, in light of low redshift and near universe observations. We illustrate the phenomenology of different classes of dark coupling models, paying particular attention in distinguishing between effects that appear only on the expansion history and those that appear in the growth of structure. We find that while a broad class of dark coupling models are effectively models where general relativity (GR) is modified — and thus can be probed by a combination of tests for the expansion history and the growth of structure —, there is a class of dark coupling models where gravity is still GR, but the growth of perturbations is, in principle modified. While this effect is small in the specific models we have considered, one should bear in mind that an inconsistency between reconstructed expansion history and growth may not uniquely indicate deviations from GR. Our low redshift constraints arise from cosmic velocities, redshift space distortions and dark matter abundance in galaxy voids. We find that current data constrain the dimensionless coupling to be |ξ| < 0.2, but prospects from forthcoming data are for a significant improvement. Future, precise measurements of the Hubble constant, combined with high-precision constraints on the growth of structure, could provide the key to rule out dark coupling models which survive other tests. We shall exploit as well weak equivalence principle violation arguments, which have the potential to highly disfavour a broad family of coupled models.
Embrace the Dark Side: Advancing the Dark Energy Survey
NASA Astrophysics Data System (ADS)
Suchyta, Eric
The Dark Energy Survey (DES) is an ongoing cosmological survey intended to study the properties of the accelerated expansion of the Universe. In this dissertation, I present work of mine that has advanced the progress of DES. First is an introduction, which explores the physics of the cosmos, as well as how DES intends to probe it. Attention is given to developing the theoretical framework cosmologists use to describe the Universe, and to explaining observational evidence which has furnished our current conception of the cosmos. Emphasis is placed on the dark sector - dark matter and dark energy - the content of the Universe not explained by the Standard Model of particle physics. As its name suggests, the Dark Energy Survey has been specially designed to measure the properties of dark energy. DES will use a combination of galaxy cluster, weak gravitational lensing, angular clustering, and supernovae measurements to derive its state of the art constraints, each of which is discussed in the text. The work described in this dissertation includes science measurements directly related to the first three of these probes. The dissertation presents my contributions to the readout and control system of the Dark Energy Camera (DECam); the name of this software is SISPI. SISPI uses client-server and publish-subscribe communication patterns to coordinate and command actions among the many hardware components of DECam - the survey instrument for DES, a 570 megapixel CCD camera, mounted at prime focus of the Blanco 4-m Telescope. The SISPI work I discuss includes coding applications for DECam's filter changer mechanism and hexapod, as well as developing the Scripts Editor, a GUI application for DECam users to edit and export observing sequence SISPI can load and execute. Next, the dissertation describes the processing of early DES data, which I contributed. This furnished the data products used in the first-completed DES science analysis, and contributed to improving the
Salmela-Aro, Katariina; Upadyaya, Katja; Hakkarainen, Kai; Lonka, Kirsti; Alho, Kimmo
2017-02-01
Recent research shows an increased concern with well-being at school and potential problems associated with students' use of socio-digital technologies, i.e., the mobile devices, computers, social media, and the Internet. Simultaneously with supporting creative social activities, socio-digital participation may also lead to compulsive and addictive behavioral patterns affecting both general and school-related mental health problems. Using two longitudinal data waves gathered among 1702 (53 % female) early (age 12-14) and 1636 (64 % female) late (age 16-18) Finnish adolescents, we examined cross-lagged paths between excessive internet use, school engagement and burnout, and depressive symptoms. Structural equation modeling revealed reciprocal cross-lagged paths between excessive internet use and school burnout among both adolescent groups: school burnout predicted later excessive internet use and excessive internet use predicted later school burnout. Reciprocal paths between school burnout and depressive symptoms were also found. Girls typically suffered more than boys from depressive symptoms and, in late adolescence, school burnout. Boys, in turn, more typically suffered from excessive internet use. These results show that, among adolescents, excessive internet use can be a cause of school burnout that can later spill over to depressive symptoms.
Wang, Y. T.; Xu, L. X.; Gui, Y. X.
2010-10-15
In this paper, we investigate the integrated Sachs-Wolfe effect in the quintessence cold dark matter model with constant equation of state and constant speed of sound in dark energy rest frame, including dark energy perturbation and its anisotropic stress. Comparing with the {Lambda}CDM model, we find that the integrated Sachs-Wolfe (ISW)-power spectrums are affected by different background evolutions and dark energy perturbation. As we change the speed of sound from 1 to 0 in the quintessence cold dark matter model with given state parameters, it is found that the inclusion of dark energy anisotropic stress makes the variation of magnitude of the ISW source uncertain due to the anticorrelation between the speed of sound and the ratio of dark energy density perturbation contrast to dark matter density perturbation contrast in the ISW-source term. Thus, the magnitude of the ISW-source term is governed by the competition between the alterant multiple of (1+3/2xc-circumflex{sub s}{sup 2}) and that of {delta}{sub de}/{delta}{sub m} with the variation of c-circumflex{sub s}{sup 2}.
Cosmological signatures of tilted isocurvature perturbations: reionization and 21cm fluctuations
Sekiguchi, Toyokazu; Sugiyama, Naoshi; Tashiro, Hiroyuki; Silk, Joseph E-mail: hiroyuki.tashiro@asu.edu E-mail: naoshi@nagoya-u.jp
2014-03-01
We investigate cosmological signatures of uncorrelated isocurvature perturbations whose power spectrum is blue-tilted with spectral index 2∼
early formation of small-scale structure, notably dark matter halos and galaxies, and may thereby resolve the shortage of ionizing photons suggested by observations of galaxies at high redshifts (z ≅ 7−8) but that are required to reionize the universe at z ∼ 10. We mainly focus on how the formation of dark matter halos can be modified. Based on the Δχ{sup 2} analysis with other cosmological parameters being fixed, we explore the connection between the spectral shape of CMB anisotropies and the reionization optical depth as a powerful probe of a highly blue-tilted isocurvature primordial power spectrum. We also study the consequences for 21cm line fluctuations due to neutral hydrogens in minihalos. Combination of measurements of the reionization optical depth and 21cm line fluctuations will provide complementary probes of a highly blue-tilted isocurvature power spectrum.
Origin of ΔN{sub eff} as a result of an interaction between dark radiation and dark matter
Bjaelde, Ole Eggers; Das, Subinoy; Moss, Adam E-mail: subinoy@physik.rwth-aachen.de
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 decaying 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.
Dark Forces and Light Dark Matter
Hooper, Dan; Weiner, Neal; Xue, Wei
2012-09-01
We consider a simple class of models in which the dark matter, X, is coupled to a new gauge boson, phi, with a relatively low mass (m_phi \\sim 100 MeV-3 GeV). Neither the dark matter nor the new gauge boson have tree-level couplings to the Standard Model. The dark matter in this model annihilates to phi pairs, and for a coupling of g_X \\sim 0.06 (m_X/10 GeV)^1/2 yields a thermal relic abundance consistent with the cosmological density of dark matter. The phi's produced in such annihilations decay through a small degree of kinetic mixing with the photon to combinations of Standard Model leptons and mesons. For dark matter with a mass of \\sim10 GeV, the shape of the resulting gamma-ray spectrum provides a good fit to that observed from the Galactic Center, and can also provide the very hard electron spectrum required to account for the observed synchrotron emission from the Milky Way's radio filaments. For kinetic mixing near the level naively expected from loop-suppressed operators (epsilon \\sim 10^{-4}), the dark matter is predicted to scatter elastically with protons with a cross section consistent with that required to accommodate the signals reported by DAMA/LIBRA, CoGeNT and CRESST-II.
Cosmological perturbations in a family of deformations of general relativity
Krasnov, Kirill; Shtanov, Yuri E-mail: shtanov@bitp.kiev.ua
2010-06-01
We study linear cosmological perturbations in a previously introduced family of deformations of general relativity characterized by the absence of new degrees of freedom. The homogeneous and isotropic background in this class of theories is unmodified and is described by the usual Friedmann equations. The theory of cosmological perturbations is modified and the relevant deformation parameter has the dimension of length. Gravitational perturbations of the scalar type can be described by a certain relativistic potential related to the matter perturbations just as in general relativity. A system of differential equations describing the evolution of this potential and of the stress-energy density perturbations is obtained. We find that the evolution of scalar perturbations proceeds with a modified effective time-dependent speed of sound, which, contrary to the case of general relativity, does not vanish even at the matter-dominated stage. In a broad range of values of the length parameter controlling the deformation, a specific transition from the regime of modified gravity to the regime of general relativity in the evolution of scalar perturbations takes place during the radiation domination. In this case, the resulting power spectrum of perturbations in radiation and dark matter is suppressed on the comoving spatial scales that enter the Hubble radius before this transition. We estimate the bounds on the deformation parameter for which this suppression does not lead to observable consequences. Evolution of scalar perturbations at the inflationary stage is modified but very slightly and the primordial spectrum generated during inflation is not noticeably different from the one obtained in general relativity.
Dark Atoms: Asymmetry and Direct Detection
Kaplan, David E.; Krnjaic, Gordan Z.; Rehermann, Keith R.; Wells, Christopher M.
2011-10-01
We present a simple UV completion of Atomic Dark Matter (aDM) in which heavy right-handed neutrinos decay to induce both dark and lepton number densities. This model addresses several outstanding cosmological problems: the matter/anti-matter asymmetry, the dark matter abundance, the number of light degrees of freedom in the early universe, and the smoothing of small-scale structure. Additionally, this realization of aDM may reconcile the CoGeNT excess with recently published null results and predicts a signal in the CRESST Oxygen band. We also find that, due to unscreened long-range interactions, the residual un recombined dark ions settle into a diffuse isothermal halo.
Maps of CMB lensing deflection from N-body simulations in Coupled Dark Energy Cosmologies
Carbone, Carmelita; Baldi, Marco; Baccigalupi, Carlo E-mail: marco.baldi5@unibo.it E-mail: bacci@sissa.it
2013-09-01
We produce lensing potential and deflection-angle maps in order to simulate the weak gravitational lensing of the Cosmic Microwave Background (CMB) via ray-tracing through the COupled Dark Energy Cosmological Simulations (CoDECS), the largest suite of N-body simulations to date for interacting Dark Energy cosmologies. The constructed maps faithfully reflect the N-body cosmic structures on a range of scales going from the arcminute to the degree scale, limited only by the resolution and extension of the simulations. We investigate the variation of the lensing pattern due to the underlying Dark Energy (DE) dynamics, characterised by different background and perturbation behaviours as a consequence of the interaction between the DE field and Cold Dark Matter (CDM). In particular, we study in detail the results from three cosmological models differing in the background and perturbations evolution at the epoch in which the lensing cross section is most effective, corresponding to a redshift of ∼ 1, with the purpose to isolate their imprints in the lensing observables, regardless of the compatibility of these models with present constraints. The scenarios investigated here include a reference ΛCDM cosmology, a standard coupled DE (cDE) scenario, and a ''bouncing'' cDE scenario. For the standard cDE scenario, we find that typical differences in the lensing potential result from two effects: the enhanced growth of linear CDM density fluctuations with respect to the ΛCDM case, and the modified nonlinear dynamics of collapsed structures induced by the DE-CDM interaction. As a consequence, CMB lensing highlights the DE impact in the cosmological expansion, even in the degenerate case where the amplitude of the linear matter density perturbations, parametrised through σ{sub 8}, is the same in both the standard cDE and ΛCDM cosmologies. For the ''bouncing'' scenario, we find that the two opposite behaviours of the lens density contrast and of the matter abundance lead to
Pélisson, D; Guitton, D; Goffart, L
1995-01-01
Prior studies have led to the gaze feedback hypothesis, which states that quick orienting movements of the visual axis (gaze shifts) are controlled by a feedback system. We have previously provided evidence for this hypothesis by extending the original study of Mays and Sparks (1980) to the cat with unrestrained head (Pélisson et al. 1989). We showed that cats compensated for a stimulation-induced perturbation of initial gaze position by generating, in the dark, an accurate gaze shift towards the remembered location of a flashed target. In the present study, we investigate goal-directed gaze shifts perturbed "in flight" by a brief stimulation of the superior colliculus. The microstimulation parameters were tuned such that significant perturbations were induced without halting the movement. The ambient light was turned off at the onset of the gaze shift, suppressing any visual feedback. We observed that, following stimulation offset, the gaze shift showed temporal and spatial changes in its trajectory to compensate for the transient perturbation. Such compensations, which occurred "on-line" before gaze shift termination, involved both eye and head movements and had dynamic characteristics resembling those of unperturbed saccadic gaze shifts. These on-line compensations maintained gaze accuracy when the stimulation was applied during the early phase of large and medium (about 60 and 40 degrees) movements. These results are compatible with the notion of a gaze feedback loop providing a dynamic gaze error signal.
Evolution of density perturbations in f(R) gravity
Carloni, S.; Dunsby, P. K. S.; Troisi, A.
2008-01-15
We give a rigorous and mathematically well defined presentation of the covariant and gauge invariant theory of scalar perturbations of a Friedmann-Lemaitre-Robertson-Walker universe for fourth order gravity, where the matter is described by a perfect fluid with a barotropic equation of state. The general perturbations equations are applied to a simple background solution of R{sup n} gravity. We obtain exact solutions of the perturbations equations for scales much bigger than the Hubble radius. These solutions have a number of interesting features. In particular, we find that for all values of n there is always a growing mode for the density contrast, even if the universe undergoes an accelerated expansion. Such behavior does not occur in standard general relativity, where as soon as dark energy dominates, the density contrast experiences an unrelenting decay. This peculiarity is sufficiently novel to warrant further investigation of fourth order gravity models.
Ibarra, Alejandro
2015-07-15
Neutrinos could be key particles to unravel the nature of the dark matter of the Universe. On the one hand, sterile neutrinos in minimal extensions of the Standard Model are excellent dark matter candidates, producing potentially observable signals in the form of a line in the X-ray sky. On the other hand, the annihilation or the decay of dark matter particles produces, in many plausible dark matter scenarios, a neutrino flux that could be detected at neutrino telescopes, thus providing non-gravitational evidence for dark matter. More conservatively, the non-observation of a significant excess in the neutrino fluxes with respect to the expected astrophysical backgrounds can be used to constrain dark matter properties, such as the self-annihilation cross section, the scattering cross section with nucleons and the lifetime.
Implications of the observation of dark matter self-interactions for singlet scalar dark matter
NASA Astrophysics Data System (ADS)
Campbell, Robyn; Godfrey, Stephen; Logan, Heather E.; Peterson, Andrea D.; Poulin, Alexandre
2015-09-01
Evidence for dark matter self-interactions has recently been reported based on the observation of a spatial offset between the dark matter halo and the stars in a galaxy in the cluster Abell 3827. Interpreting the offset as due to dark matter self-interactions leads to a cross section measurement of σDM/m ˜(1 - 1.5 ) cm2 g-1 , where m is the mass of the dark matter particle. We use this observation to constrain singlet scalar dark matter coupled to the standard model and to two-Higgs-doublet models. We show that the most natural scenario in this class of models is very light dark matter, below about 0.1 GeV, whose relic abundance is set by freeze-in, i.e., by slow production of dark matter in the early universe via extremely tiny interactions with the Higgs boson, never reaching thermal equilibrium. We also show that the dark matter abundance can be established through the usual thermal freeze-out mechanism in the singlet scalar extension of the Yukawa-aligned two-Higgs-doublet model, but that it requires rather severe fine tuning of the singlet scalar mass.
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.
NASA Astrophysics Data System (ADS)
Schumann, Marc
2014-10-01
This article reviews the status of the exciting and fastly evolving field of dark matter research as of summer 2013, when it was discussed at the International Cosmic Ray Conference (ICRC) 2013 in Rio de Janeiro. It focuses on the three main avenues to detect weakly interacting massive particle (WIMP) dark matter: direct detection, indirect detection, and collider searches. The article is based on the dark matter rapporteur talk summarizing the presentations given at the conference, filling some gaps for completeness.
Cruz, Norman; Palma, Guillermo; Zambrano, David; Avelino, Arturo E-mail: guillermo.palma@usach.cl E-mail: avelino@fisica.ugto.mx
2013-05-01
We explore a cosmological model composed by a dark matter fluid interacting with a dark energy fluid. The interaction term has the non-linear λρ{sub m}{sup α}ρ{sub e}{sup β} form, where ρ{sub m} and ρ{sub e} are the energy densities of the dark matter and dark energy, respectively. The parameters α and β are in principle not constrained to take any particular values, and were estimated from observations. We perform an analytical study of the evolution equations, finding the fixed points and their stability properties in order to characterize suitable physical regions in the phase space of the dark matter and dark energy densities. The constants (λ,α,β) as well as w{sub m} and w{sub e} of the EoS of dark matter and dark energy respectively, were estimated using the cosmological observations of the type Ia supernovae and the Hubble expansion rate H(z) data sets. We find that the best estimated values for the free parameters of the model correspond to a warm dark matter interacting with a phantom dark energy component, with a well goodness-of-fit to data. However, using the Bayesian Information Criterion (BIC) we find that this model is overcame by a warm dark matter – phantom dark energy model without interaction, as well as by the ΛCDM model. We find also a large dispersion on the best estimated values of the (λ,α,β) parameters, so even if we are not able to set strong constraints on their values, given the goodness-of-fit to data of the model, we find that a large variety of theirs values are well compatible with the observational data used.
A unifying description of dark energy
NASA Astrophysics Data System (ADS)
Gleyzes, Jérôme; Langlois, David; Vernizzi, Filippo
2014-01-01
We review and extend a novel approach that we recently introduced, to describe general dark energy or scalar-tensor models. Our approach relies on an Arnowitt-Deser-Misner (ADM) formulation based on the hypersurfaces where the underlying scalar field is uniform. The advantage of this approach is that it can describe in the same language and in a minimal way a vast number of existing models, such as quintessence, F(R) theories, scalar tensor theories, their Horndeski extensions and beyond. It also naturally includes Horava-Lifshitz theories. As summarized in this review, our approach provides a unified treatment of the linear cosmological perturbations about a Friedmann-Lemaître-Robertson-Walker (FLRW) universe, obtained by a systematic expansion of our general action up to quadratic order. This shows that the behavior of these linear perturbations is generically characterized by five time-dependent functions. We derive the full equations of motion in the Newtonian gauge. In the Horndeski case, we obtain the equation of state for dark energy perturbations in terms of these functions. Our unifying description thus provides the simplest and most systematic way to confront theoretical models with current and future cosmological observations.
The effective field theory of dark energy
Gubitosi, Giulia; Vernizzi, Filippo; Piazza, Federico E-mail: fpiazza@apc.univ-paris7.fr
2013-02-01
We propose a universal description of dark energy and modified gravity that includes all single-field models. By extending a formalism previously applied to inflation, we consider the metric universally coupled to matter fields and we write in terms of it the most general unitary gauge action consistent with the residual unbroken symmetries of spatial diffeomorphisms. Our action is particularly suited for cosmological perturbation theory: the background evolution depends on only three operators. All other operators start at least at quadratic order in the perturbations and their effects can be studied independently and systematically. In particular, we focus on the properties of a few operators which appear in non-minimally coupled scalar-tensor gravity and galileon theories. In this context, we study the mixing between gravity and the scalar degree of freedom. We assess the quantum and classical stability, derive the speed of sound of fluctuations and the renormalization of the Newton constant. The scalar can always be de-mixed from gravity at quadratic order in the perturbations, but not necessarily through a conformal rescaling of the metric. We show how to express covariant field-operators in our formalism and give several explicit examples of dark energy and modified gravity models in our language. Finally, we discuss the relation with the covariant EFT methods recently appeared in the literature.
Do stochastic inhomogeneities affect dark-energy precision measurements?
Ben-Dayan, I; Gasperini, M; Marozzi, G; Nugier, F; Veneziano, G
2013-01-11
The effect of a stochastic background of cosmological perturbations on the luminosity-redshift relation is computed to second order through a recently proposed covariant and gauge-invariant light-cone averaging procedure. The resulting expressions are free from both ultraviolet and infrared divergences, implying that such perturbations cannot mimic a sizable fraction of dark energy. Different averages are estimated and depend on the particular function of the luminosity distance being averaged. The energy flux being minimally affected by perturbations at large z is proposed as the best choice for precision estimates of dark-energy parameters. Nonetheless, its irreducible (stochastic) variance induces statistical errors on Ω(Λ)(z) typically lying in the few-percent range.
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.
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.
NASA Astrophysics Data System (ADS)
Landim, Ricardo G.; Abdalla, Elcio
2017-01-01
We build a model of metastable dark energy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable dark energy is also embedded into a model with SU(2)R symmetry. The dark energy doublet and the dark matter doublet naturally interact with each other. A three-body decay of the dark energy particle into (cold and warm) dark matter can be as long as large fraction of the age of the universe, if the mediator is massive enough, the lower bound being at intermediate energy level some orders below the grand unification scale. Such a decay shows a different form of interaction between dark matter and dark energy, and the model opens a new window to investigate the dark sector from the point-of-view of particle physics.
Dark energy and extended dark matter halos
NASA Astrophysics Data System (ADS)
Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.
2012-03-01
The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even
Drewes, Marco
2014-11-01
We study the damping of an oscillating scalar field in a Friedmann-Robertson-Walker spacetime by perturbative processes, taking into account the back-reaction of the plasma of decay products on the damping rate. The scalar field may be identified with the inflaton, in which case this process resembles the reheating of the universe after inflation. It can also model a modulus that dominates the energy density of the universe at later times. We find that the finite density corrections to the damping rate can have a drastic effect on the thermal history and considerably increase both, the maximal temperature in the early universe and the reheating temperature at the onset of the radiation dominated era. As a result the abundance of some Dark Matter candidates may be considerably larger than previously estimated. We give improved analytic estimates for the maximal and the reheating temperatures and confirm them numerically in a simple model.
The formation of galaxies and quasars in a texture-seeded cold dark matter cosmogony
Gooding, A.K.; Turok, N.; Spergel, D.N. Princeton University Observatory, NJ )
1991-05-01
The nonGaussian perturbations produced by global texture lead to the early formation of stars, quasars, and galaxies. Growth of the density fluctuation in cold dark matter induced by the unwinding of a texture 'knot' is calculated and the evolution of the mass multiplicity function in this galaxy formation model is determined. By z of about 50, about 3 percent of the mass of the universe has formed nonlinear objects of mass greater than 10 to the 6th solar masses - these objects may have reionized the universe. Most objects larger than 10 to the 12th solar masses form by z about 2-3, consistent with the observed epoch of QSO formation. Today, about 35 percent of the mass of the universe is in bound objects of mass greater than 10 to the 12th solar masses. It is found that the slope and the amplitude of the multiplicity function is consistent with the observed galaxy luminosity function. 24 refs.
Signatures of non-gaussianity in the isocurvature modes of primordial black hole dark matter
Young, Sam; Byrnes, Christian T. E-mail: C.Byrnes@sussex.ac.uk
2015-04-01
Primordial black holes (PBHs) are black holes which may have formed very early on during the radiation dominated era in the early universe. We present here a method by which the large scale perturbations in the density of primordial black holes may be used to place tight constraints on non-gaussianity if PBHs account for dark matter (DM) . The presence of local-type non-gaussianity is known to have a significant effect on the abundance of primordial black holes, and modal coupling from the observed CMB scale modes can significantly alter the number density of PBHs that form within different regions of the universe, which appear as DM isocurvature modes. Using the recent Planck constraints on isocurvature perturbations, we show that PBHs are excluded as DM candidates for even very small local-type non-gaussianity, |f{sub NL}|≈0.001 and remarkably the constraint on g{sub NL} is almost as strong. Even small non-gaussianity is excluded if DM is composed of PBHs. If local non-Gaussianity is ever detected on CMB scales, the constraints on the fraction of the universe collapsing into PBHs (which are massive enough to have not yet evaporated) will become much tighter.
Agegraphic dark energy: growth index and cosmological implications
NASA Astrophysics Data System (ADS)
Malekjani, M.; Basilakos, S.; Mehrabi, A.; Davari, Z.; Rezaei, M.
2017-01-01
We study the main cosmological properties of the agegraphic dark energy model at the expansion and perturbation levels. Initially, using the latest cosmological data, we implement a joint likelihood analysis in order to constrain the cosmological parameters. Then, we test the performance of the agegraphic dark energy model at the perturbation level and we define its difference from the usual Lambda cold dark matter (ΛCDM) model. Within this context, we verify that the growth index of matter fluctuations depends on the choice of the considered agegraphic dark energy (homogeneous or clustered). In particular, assuming a homogeneous agegraphic dark energy, we find, for the first time, that the asymptotic value of the growth index is γ ≈ 5/9, which is close to that of the usual Λ cosmology, γ(Λ) ≈ 6/11. Finally, if the distribution of dark energy is clustered, then we obtain γ ≈ 1/2 which is ˜8 per cent smaller than that of the ΛCDM model.
Production regimes for Self-Interacting Dark Matter
Bernal, Nicolás; Chu, Xiaoyong; Garcia-Cely, Camilo; Hambye, Thomas; Zaldivar, Bryan E-mail: xchu@ictp.it E-mail: thambye@ulb.ac.be
2016-03-01
In the context of Self-Interacting Dark Matter as a solution for the small-scale structure problems, we consider the possibility that Dark Matter could have been produced without being in thermal equilibrium with the Standard Model bath. We discuss one by one the following various dark matter production regimes of this kind: freeze-in, reannihilation and dark freeze-out. We exemplify how these mechanisms work in the context of the particularly simple Hidden Vector Dark Matter model. In contrast to scenarios where there is thermal equilibrium with the Standard Model bath, we find two regimes which can easily satisfy all the laboratory and cosmological constraints. These are dark freeze-out with 3-to-2 annihilations and freeze-in via a light mediator. In the first regime, different temperatures in the visible and the Dark Matter sectors allow us to avoid the constraints coming from cosmic structure formation as well as the use of non-perturbative couplings to reproduce the observed relic density. For the second regime, different couplings are responsible for Dark Matter relic density and self-interactions, permitting to surpass BBN, X-ray, CMB and direct detection constraints.
Density perturbations in general modified gravitational theories
De Felice, Antonio; Tsujikawa, Shinji; Mukohyama, Shinji
2010-07-15
We derive the equations of linear cosmological perturbations for the general Lagrangian density f(R,{phi},X)/2+L{sub c}, where R is a Ricci scalar, {phi} is a scalar field, and X=-{partial_derivative}{sup {mu}{phi}{partial_derivative}}{sub {mu}{phi}/}2 is a field kinetic energy. We take into account a nonlinear self-interaction term L{sub c}={xi}({phi}) {open_square}{phi}({partial_derivative}{sup {mu}{phi}{partial_derivative}}{sub {mu}{phi}}) recently studied in the context of ''Galileon'' cosmology, which keeps the field equations at second order. Taking into account a scalar-field mass explicitly, the equations of matter density perturbations and gravitational potentials are obtained under a quasistatic approximation on subhorizon scales. We also derive conditions for the avoidance of ghosts and Laplacian instabilities associated with propagation speeds. Our analysis includes most of modified gravity models of dark energy proposed in literature; and thus it is convenient to test the viability of such models from both theoretical and observational points of view.
NASA Astrophysics Data System (ADS)
Burch, Benjamin P.
The precise phase-space distribution and properties of Galactic dark matter necessary for its direct and indirect detection are currently unknown. Since the distributions of normal and dark matter in the Milky Way are coupled to each other as they both move in the same gravitational potential, constraints on the distribution and properties of dark matter can be derived by studying the distribution of visible matter in the Galaxy and making some general assumptions regarding the phase-space distribution of the dark matter. In this study, the visible components of the Galaxy have been comprehensively reviewed to create an axisymmetric model of the Galaxy that is consistent with the available observations, and the dark matter phase-space distribution is assumed to follow a lowered-isothermal form. Poisson's equations are then solved self-consistently to construct models of the spatial and velocity distribution of Galactic dark matter. The total gravitational potential from normal and dark matter are calculated and compared to the current observations of the rotation curve and to the radial velocity distributions of blue horizontal-branch and blue straggler stars. It is found that this analysis allows for a wide range of parameters for the dark matter. The implications for direct and indirect detection of dark matter are discussed in detail. In the appendices, two additional projects are presented. In Appendix A, the recent observations of the positron fraction and the total electron spectrum in cosmic rays are addressed by considering a nested leaky-box model for the propagation of cosmic rays in the Galaxy. This is found to obviate the need for exotic processes such as the annihilation or decay of dark matter to explain the recent observations. In Appendix B, we discuss a novel dark matter detector involving triggered cavitation in acoustic fields. The theory behind the detector is presented in detail, and we discuss the work than has been done to create a prototype
Planck 2015 results. XIV. Dark energy and modified gravity
NASA Astrophysics Data System (ADS)
Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Battye, R.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Heavens, A.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huang, Z.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Ma, Y.-Z.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marchini, A.; Maris, M.; Martin, P. G.; Martinelli, M.; Martínez-González, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Narimani, A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Salvatelli, V.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Schaefer, B. M.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Viel, M.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, M.; Yvon, D.; Zacchei, A.; Zonca, A.
2016-09-01
We study the implications of Planck data for models of dark energy (DE) and modified gravity (MG) beyond the standard cosmological constant scenario. We start with cases where the DE only directly affects the background evolution, considering Taylor expansions of the equation of state w(a), as well as principal component analysis and parameterizations related to the potential of a minimally coupled DE scalar field. When estimating the density of DE at early times, we significantly improve present constraints and find that it has to be below ~2% (at 95% confidence) of the critical density, even when forced to play a role for z < 50 only. We then move to general parameterizations of the DE or MG perturbations that encompass both effective field theories and the phenomenology of gravitational potentials in MG models. Lastly, we test a range of specific models, such as k-essence, f(R) theories, and coupled DE. In addition to the latest Planck data, for our main analyses, we use background constraints from baryonic acoustic oscillations, type-Ia supernovae, and local measurements of the Hubble constant. We further show the impact of measurements of the cosmological perturbations, such as redshift-space distortions and weak gravitational lensing. These additional probes are important tools for testing MG models and for breaking degeneracies that are still present in the combination of Planck and background data sets. All results that include only background parameterizations (expansion of the equation of state, early DE, general potentials in minimally-coupled scalar fields or principal component analysis) are in agreement with ΛCDM. When testing models that also change perturbations (even when the background is fixed to ΛCDM), some tensions appear in a few scenarios: the maximum one found is ~2σ for Planck TT+lowP when parameterizing observables related to the gravitational potentials with a chosen time dependence; the tension increases to, at most, 3σ when external
Perturbed effects at radiation physics
NASA Astrophysics Data System (ADS)
Külahcı, Fatih; Şen, Zekâi
2013-09-01
Perturbation methodology is applied in order to assess the linear attenuation coefficient, mass attenuation coefficient and cross-section behavior with random components in the basic variables such as the radiation amounts frequently used in the radiation physics and chemistry. Additionally, layer attenuation coefficient (LAC) and perturbed LAC (PLAC) are proposed for different contact materials. Perturbation methodology provides opportunity to obtain results with random deviations from the average behavior of each variable that enters the whole mathematical expression. The basic photon intensity variation expression as the inverse exponential power law (as Beer-Lambert's law) is adopted for perturbation method exposition. Perturbed results are presented not only in terms of the mean but additionally the standard deviation and the correlation coefficients. Such perturbation expressions provide one to assess small random variability in basic variables.
NASA Astrophysics Data System (ADS)
Mondragon, Antonio R.
Observations from the 1930s until the present have established the existence of dark matter with an abundance that is much larger than that of luminous matter. Because none of the known particles of nature have the correct properties to be identified as the dark matter, various exotic candidates have been proposed. The neutralino of supersymmetric theories is the most promising example. Such cold dark matter candidates, however, lead to a conflict between the standard simulations of the evolution of cosmic structure and observations. Simulations predict excessive structure formation on small scales, including density cusps at the centers of galaxies, that is not observed. This conflict still persists in early 2007, and it has not yet been convincingly resolved by attempted explanations that invoke astrophysical phenomena, which would destroy or broaden all small scale structure. We have investigated another candidate that is perhaps more exotic: Lorentz-violating dark matter, which was originally motivated by an unconventional fundamental theory, but which in this dissertation is defined as matter which has a nonzero minimum velocity. Furthermore, the present investigation evolved into the broader goal of exploring the properties of Lorentz-violating matter and the astrophysical consequences-a subject which to our knowledge has not been previously studied. Our preliminary investigations indicated that this form of matter might have less tendency to form small-scale structure. These preliminary calculations certainly established that Lorentz-violating matter which always moves at an appreciable fraction of the speed of light will bind less strongly. However, the much more thorough set of studies reported here lead to the conclusion that, although the binding energy is reduced, the small-scale structure problem is not solved by Lorentz-violating dark matter. On the other hand, when we compare the predictions of Lorentz-violating dynamics with those of classical
Dark microglia: Why are they dark?
Bisht, Kanchan; Sharma, Kaushik; Lacoste, Baptiste; Tremblay, Marie-Ève
2016-01-01
ABSTRACT Using transmission electron microscopy (TEM) we recently characterized a microglial phenotype that is induced by chronic stress, fractalkine receptor deficiency, aging, or Alzheimer disease pathology. These ‘dark’ microglia appear overly active compared with the normal microglia, reaching for synaptic clefts, and extensively engulfing pre-synaptic axon terminals and post-synaptic dendritic spines. From these findings we hypothesized that dark microglia could be specifically implicated in the pathological remodeling of neuronal circuits, which impairs learning, memory, and other essential cognitive functions. In the present addendum we further discuss about the possible causes of their dark appearance under TEM. PMID:28042375
Li, X.Y.; Harko, T.; Cheng, K.S. E-mail: harko@hkucc.hku.hk
2012-06-01
We investigate the structure and stability properties of compact astrophysical objects that may be formed from the Bose-Einstein condensation of dark matter. Once the critical temperature of a boson gas is less than the critical temperature, a Bose-Einstein Condensation process can always take place during the cosmic history of the universe. Therefore we model the dark matter inside the star as a Bose-Einstein condensate. In the condensate dark matter star model, the dark matter equation of state can be described by a polytropic equation of state, with polytropic index equal to one. We derive the basic general relativistic equations describing the equilibrium structure of the condensate dark matter star with spherically symmetric static geometry. The structure equations of the condensate dark matter stars are studied numerically. The critical mass and radius of the dark matter star are given by M{sub crit} ≈ 2(l{sub a}/1fm){sup 1/2}(m{sub χ}/1 GeV){sup −3/2}M{sub s}un and R{sub crit} ≈ 1.1 × 10{sup 6}(l{sub a}/1 fm){sup 1/2}(m{sub χ}/1 GeV){sup −3/2} cm respectively, where l{sub a} and m{sub χ} are the scattering length and the mass of dark matter particle, respectively.
ERIC Educational Resources Information Center
Weston, Anthony
2014-01-01
Environmentalism's wider and wilder possibilities today appear as regions of seeming darkness that bracket or frame acceptable environmental thinking. One of these barely-mentionable darknesses is outer space--the cosmos. Another is the inner and chthonic powers of the land and natural beings generally. This essay aims to bring these two kinds of…
Professor Sean Carroll
2016-07-12
General relativity is inconsistent with cosmological observations unless we invoke components of dark matter and dark energy that dominate the universe. While it seems likely that these exotic substances really do exist, the alternative is worth considering: that Einstein's general relativity breaks down on cosmological scales. I will discuss models of modified gravity, tests in the solar system and elsewhere, and consequences for cosmology.
Simple implementation of general dark energy models
Bloomfield, Jolyon K.; Pearson, Jonathan A. E-mail: jonathan.pearson@durham.ac.uk
2014-03-01
We present a formalism for the numerical implementation of general theories of dark energy, combining the computational simplicity of the equation of state for perturbations approach with the generality of the effective field theory approach. An effective fluid description is employed, based on a general action describing single-scalar field models. The formalism is developed from first principles, and constructed keeping the goal of a simple implementation into CAMB in mind. Benefits of this approach include its straightforward implementation, the generality of the underlying theory, the fact that the evolved variables are physical quantities, and that model-independent phenomenological descriptions may be straightforwardly investigated. We hope this formulation will provide a powerful tool for the comparison of theoretical models of dark energy with observational data.
Dark matter and dark energy: The critical questions
Michael S. Turner
2002-11-19
Stars account for only about 0.5% of the content of the Universe; the bulk of the Universe is optically dark. The dark side of the Universe is comprised of: at least 0.1% light neutrinos; 3.5% {+-} 1% baryons; 29% {+-} 4% cold dark matter; and 66% {+-} 6% dark energy. Now that we have characterized the dark side of the Universe, the challenge is to understand it. The critical questions are: (1) What form do the dark baryons take? (2) What is (are) the constituent(s) of the cold dark matter? (3) What is the nature of the mysterious dark energy that is causing the Universe to speed up.
On the determination of dark energy
Clarkson, Chris
2010-06-23
I consider some of the issues we face in trying to understand dark energy. Huge fluctuations in the unknown dark energy equation of state can be hidden in distance data, so I argue that model-independent tests which signal if the cosmological constant is wrong are valuable. These can be constructed to remove degeneracies with the cosmological parameters. Gravitational effects can play an important role. Even small inhomogeneity clouds our ability to say something definite about dark energy. I discuss how the averaging problem confuses our potential understanding of dark energy by considering the backreaction from density perturbations to second-order in the concordance model: this effect leads to at least a 10% increase in the dynamical value of the deceleration parameter, and could be significantly higher. Large Hubble-scale inhomogeneity has not been investigated in detail, and could conceivably be the cause of apparent cosmic acceleration. I discuss void models which defy the Copernican principle in our Hubble patch, and describe how we can potentially rule out these models.This article is a summary of two talks given at the Invisible Universe Conference, Paris, 2009.
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.
Interacting quintom dark energy with Nonminimal Derivative Coupling
NASA Astrophysics Data System (ADS)
Behrouz, Noushin; Nozari, Kourosh; Rashidi, Narges
2017-03-01
Following our recent work on interacting dark energy models (Nozari and Behrouz, 2016), we study cosmological dynamics of an extended dark energy model in which gravity is non-minimally coupled to the derivatives of a quintessence and a phantom field in a quintom model. There is also a phenomenological interaction between the dark energy and dark matter components. By considering an exponential potential as a self-interaction potential for quintom model, we obtain a scaling solution to alleviate the coincidence problem. The existence and stability of the critical points are discussed in details and it has been shown that in this setup the universe experiences a phantom divide crossing. We compare the model with recent observational data and find some constraints on the model's parameters. We investigate also perturbations around the homogeneous and isotropic background in our Nonminimal Derivative Coupling (NMDC) quintom model.
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.
Essential building blocks of dark energy
NASA Astrophysics Data System (ADS)
Gleyzes, Jerome; Langlois, David; Piazza, Federico; Vernizzi, Filippo
2013-08-01
We propose a minimal description of single field dark energy/modified gravity within the effective field theory formalism for cosmological perturbations, which encompasses most existing models. We start from a generic Lagrangian given as an arbitrary function of the lapse and of the extrinsic and intrinsic curvature tensors of the time hypersurfaces in unitary gauge, i.e. choosing as time slicing the uniform scalar field hypersurfaces. Focusing on linear perturbations, we identify seven Lagrangian operators that lead to equations of motion containing at most two (space or time) derivatives, the background evolution being determined by the time-dependent coefficients of only three of these operators. We then establish a dictionary that translates any existing or future model whose Lagrangian can be written in the above form into our parametrized framework. As an illustration, we study Horndeski's — or generalized Galileon — theories and show that they can be described, up to linear order, by only six of the seven operators mentioned above. This implies, remarkably, that the dynamics of linear perturbations can be more general than that of Horndeski while remaining second order. Finally, in order to make the link with observations, we provide the entire set of linear perturbation equations in Newtonian gauge, the effective Newton constant in the quasi-static approximation and the ratio of the two gravitational potentials, in terms of the time-dependent coefficients of our Lagrangian.
Production of scalar and tensor perturbations in inflationary models
Turner, M.S. NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 )
1993-10-15
Scalar (density) and tensor (gravity-wave) perturbations provide the basis for the fundamental observable consequences of inflation, including CBR anisotropy and the formation of structure in the Universe. These perturbations are nearly scale invariant (Harrison-Zel'dovich spectrum), though a slight deviation from scale invariance ( tilt'') can have significant consequences for both CBR anisotropy and structure formation. In particular, a slightly tilted spectrum of scalar perturbations may improve the agreement of the cold dark matter scenario with the observational data. The amplitude and spectrum of the scalar and tensor perturbations depend upon the shape of the inflationary potential in the small interval where the scalar field responsible for inflation was between about 46 and 54 [ital e]-folds before the end of inflation. By expanding the inflationary potential in a Taylor series over this interval we show that the amplitudes of the perturbations and the power-law slopes of their spectra can be expressed in terms of the value of the potential 50 [ital e]-folds before the end of inflation, [ital V][sub 50], its steepness [ital x][sub 50][equivalent to][ital m][sub Pl][ital V50][sup [prime
Dark matter velocity dispersion effects on CMB and matter power spectra
Piattella, O.F.; Casarini, L.; Fabris, J.C.; Pacheco, J.A. de Freitas E-mail: luciano.casarini@cosmo-ufes.org E-mail: pacheco@oca.eu
2016-02-01
Effects of velocity dispersion of dark matter particles on the CMB TT power spectrum and on the matter linear power spectrum are investigated using a modified CAMB code. Cold dark matter originated from thermal equilibrium processes does not produce appreciable effects but this is not the case if particles have a non-thermal origin. A cut-off in the matter power spectrum at small scales, similar to that produced by warm dark matter or that produced in the late forming dark matter scenario, appears as a consequence of velocity dispersion effects, which act as a pressure perturbation.
Pseudoscalar portal dark matter
NASA Astrophysics Data System (ADS)
Berlin, Asher; Gori, Stefania; Lin, Tongyan; Wang, Lian-Tao
2015-07-01
A fermion dark matter candidate with a relic abundance set by annihilation through a pseudoscalar can evade constraints from direct detection experiments. We present simplified models that realize this fact by coupling a fermion dark sector to a two-Higgs doublet model. These models are generalizations of mixed bino-Higgsino dark matter in the minimal supersymmetric standard model, with more freedom in the couplings and scalar spectra. Annihilation near a pseudoscalar resonance allows a significant amount of parameter space for thermal relic dark matter compared to singlet-doublet dark matter, in which the fermions couple only to the standard model (SM) Higgs doublet. In a general two-Higgs doublet model, there is also freedom for the pseudoscalar to be relatively light and it is possible to obtain thermal relic dark matter candidates even below 100 GeV. In particular, we find ample room to obtain dark matter with mass around 50 GeV and fitting the Galactic center excess in gamma-rays. This region of parameter space can be probed by LHC searches for heavy pseudoscalars or electroweakinos, and possibly by other new collider signals.
Perturbation theory in electron diffraction
NASA Astrophysics Data System (ADS)
Bakken, L. N.; Marthinsen, K.; Hoeier, R.
1992-12-01
The Bloch-wave approach is used for discussing multiple inelastic electron scattering and higher-order perturbation theory in inelastic high-energy electron diffraction. In contrast to previous work, the present work describes three-dimensional diffraction so that higher-order Laue zone (HOLZ) effects are incorporated. Absorption is included and eigenvalues and eigenvectors are calculated from a structure matrix with the inclusion of an absorptive potential. Centrosymmetric as well as non-centrosymmetric crystal structures are allowed. An iteration method with a defined generalized propagation function for solving the inelastic coupling equations is described. It is shown that a similar iteration method with the same propagation function can be used for obtaining higher-order perturbation terms for the wave-function when a perturbation is added to the crystal potential. Finally, perturbation theory by matrix calculations when a general perturbation is added to the structure matrix is considered.
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}).
NASA Astrophysics Data System (ADS)
Ogaz, Sara
2013-10-01
This takes a series of SBC dark measurements over a continuous period of about 6 hours {4 orbits}. The aim is to collect dark images during an extended SBC on-time. Earlier measurements indicate that the dark current increases with SBC on-time and may also be increasing with overall SBC use. The 6-hour time matches the longest time used by any observer. As with all SBC observations this needs continuous SAA free time.This program is executed once per cycle. The last exposures were taken in Mar 2013 under Program 13161.
NASA Astrophysics Data System (ADS)
Fong, Richard; Doroshkevich, Andrei G.; Turchaninov, Victor I.
1995-07-01
The theory of the formation of large-scale structure in the universe through the action of gravitational instability imply the existence of substantial amounts of baryonic dark matter, of the order of 50% of the total baryon content in the universe, in the ``voids'' or under-dense regions seen in the large-scale distribution of galaxies. We discuss also the large-scale structure of dark matter expected in voids and the present and future possibilities for the observation of this baryonic dark matter in ``voids.''
NASA Technical Reports Server (NTRS)
2006-01-01
As winter turns to spring at the south polar ice cap of Mars, the rising sun reveals dark spots and fans emerging from the cold polar night. Using visual images (left) and temperature data (right) from the Thermal Emission Imaging system on NASA's Mars Odyssey orbiter, scientists have built a new model for the origin of the dark markings. Scientists propose the markings come from dark sand and dust strewn by high-speed jets of carbon-dioxide gas. These erupt from under a layer of carbon-dioxide ice that forms each Martian winter.
CMB constraint on non-Gaussianity in isocurvature perturbations
Hikage, Chiaki; Kawasaki, Masahiro; Sekiguchi, Toyokazu; Takahashi, Tomo E-mail: kawasaki@icrr.u-tokyo.ac.jp E-mail: tomot@cc.saga-u.ac.jp
2013-07-01
We study the CMB constraints on non-Gaussianity in CDM isocurvature perturbations. Non-Gaussian isocurvature perturbations can be produced in various models at the very early stage of the Universe. Since the isocurvature perturbations little affect the structure formation at late times, CMB is the best probe of isocurvature non-Gaussianity at least in the near future. In this paper, we focus on non-Gaussian curvature and isocurvature perturbations of the local-type, which are uncorrelated and in the form ζ = ζ{sub G}+(3/5)f{sub NL}(ζ{sub G}{sup 2}−(ζ{sub G}{sup 2})) and S = S{sub G}+f{sub NL}{sup (ISO)}(S{sub G}−(S{sub G}{sup 2})), and constrain the non-linearity parameter of isocurvature perturbations, f{sub NL}{sup (ISO)}, as well as the curvature one f{sub NL}. For this purpose, we employ several state-of-art techniques for the analysis of CMB data and simulation. Assuming that isocurvature perturbations are subdominant, we apply our method to the WMAP 7-year data of temperature anisotropy and obtain constraints on a combination α{sup 2}f{sub NL}{sup (ISO)}, where α is the ratio of the power spectrum of isocurvature perturbations to that of the adiabatic ones. When the adiabatic perturbations are assumed to be Gaussian, we obtained a constraint α{sup 2}f{sub NL}{sup (ISO)} = 40±66 assuming the power spectrum of isocurvature perturbations is scale-invariant. When we assume that the adiabatic perturbations can also be non-Gaussian, we obtain f{sub NL} = 38±24 and α{sup 2}f{sub NL}{sup (ISO)} = −8±72. We also discuss implications of our results for the axion CDM isocurvature model.
Non-Abelian dark matter and dark radiation
NASA Astrophysics Data System (ADS)
Buen-Abad, Manuel A.; Marques-Tavares, Gustavo; Schmaltz, Martin
2015-07-01
We propose a new class of dark matter models with unusual phenomenology. What is ordinary about our models is that dark matter particles are weakly interacting massive particles; they are weakly coupled to the standard model and have weak scale masses. What is unusual is that they come in multiplets of a new dark non-Abelian gauge group with milliweak coupling. The massless dark gluons of this dark gauge group contribute to the energy density of the Universe as a form of weakly self-interacting dark radiation. In this paper we explore the consequences of having (i) dark matter in multiplets, (ii) self-interacting dark radiation, and (iii) dark matter which is weakly coupled to dark radiation. We find that (i) dark matter cross sections are modified by multiplicity factors which have significant consequences for collider searches and indirect detection, and (ii) dark gluons have thermal abundances which affect the cosmic microwave background (CMB) as dark radiation. Unlike additional massless neutrino species the dark gluons are interacting and have vanishing viscosity and (iii) the coupling of dark radiation to dark matter represents a new mechanism for damping the large scale structure power spectrum. A combination of additional radiation and slightly damped structure is interesting because it can remove tensions between global Λ CDM fits from the CMB and direct measurements of the Hubble expansion rate (H0) and large scale structure (σ8).
Contributions to cosmic reionization from dark matter annihilation and decay
NASA Astrophysics Data System (ADS)
Liu, Hongwan; Slatyer, Tracy R.; Zavala, Jesús
2016-09-01
Dark matter annihilation or decay could have a significant impact on the ionization and thermal history of the universe. In this paper, we study the potential contribution of dark matter annihilation (s -wave- or p -wave-dominated) or decay to cosmic reionization, via the production of electrons, positrons and photons. We map out the possible perturbations to the ionization and thermal histories of the universe due to dark matter processes, over a broad range of velocity-averaged annihilation cross sections/decay lifetimes and dark matter masses. We have employed recent numerical studies of the efficiency with which annihilation/decay products induce heating and ionization in the intergalactic medium, and in this work extended them down to a redshift of 1 +z =4 for two different reionization scenarios. We also improve on earlier studies by using the results of detailed structure formation models of dark matter haloes and subhaloes that are consistent with up-to-date N -body simulations, with estimates on the uncertainties that originate from the smallest scales. We find that for dark matter models that are consistent with experimental constraints, a contribution of more than 10% to the ionization fraction at reionization is disallowed for all annihilation scenarios. Such a contribution is possible only for decays into electron/positron pairs, for light dark matter with mass mχ≲100 MeV , and a decay lifetime τχ˜1 024- 1 025 s .
Self-scattering for Dark Matter with an excited state
Schutz, Katelin; Slatyer, Tracy R. E-mail: tslatyer@mit.edu
2015-01-01
Self-interacting dark matter scenarios have recently attracted much attention, as a possible means to alleviate the tension between N-body simulations and observations of the dark matter distribution on galactic and sub-galactic scales. The presence of internal structure for the dark matter—for example, a nearly-degenerate state in the spectrum that could decay, or be collisionally excited or de-excited—has also been proposed as a possible means to address these discrepancies. Such internal structure can be a source of interesting signatures in direct and indirect dark matter searches, for example providing a novel explanation for the 3.5 keV line recently observed in galaxies and galaxy clusters. We analyze a simple model of dark matter self-scattering including a nearly-degenerate excited state, and develop an accurate analytic approximation for the elastic and inelastic s-wave cross sections, which is valid outside the perturbative regime provided the particle velocity is sufficiently low (this condition is also required for the s-wave to dominate over higher partial waves). We anticipate our results will be useful in incorporating inelastic self-scattering into N-body simulations, in order to study the quantitative impact of nearly-degenerate states in the dark matter spectrum on galactic structure and dynamics, and in computing the indirect signatures of multi-state 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.
S-channel dark matter simplified models and unitarity
NASA Astrophysics Data System (ADS)
Englert, Christoph; McCullough, Matthew; Spannowsky, Michael
2016-12-01
The ultraviolet structure of s-channel mediator dark matter simplified models at hadron colliders is considered. In terms of commonly studied s-channel mediator simplified models it is argued that at arbitrarily high energies the perturbative description of dark matter production in high energy scattering can break down. This is analogous to the well documented breakdown of an EFT description of dark matter collider production. With this in mind, to diagnose whether or not the use of simplified models at the LHC is valid, perturbative unitarity of the scattering amplitude in the processes relevant to LHC dark matter searches is studied. The results are as one would expect: at the LHC and future proton colliders the simplified model descriptions of dark matter production are in general valid. As a result of the general discussion, a simple class of 'Fermiophobic Scalar' simplified models is proposed, in which a scalar mediator couples to electroweak vector bosons. The Fermiophobic simplified model is well motivated and exhibits interesting collider and direct detection phenomenology.
DARK MATTER AS AN ACTIVE GRAVITATIONAL AGENT IN CLOUD COMPLEXES
Suarez-Madrigal, Andres; Ballesteros-Paredes, Javier; Colin, Pedro; D'Alessio, Paola
2012-04-01
We study the effect that the dark matter background (DMB) has on the gravitational energy content and, in general, on the star formation efficiency (SFE) of a molecular cloud (MC). We first analyze the effect that a dark matter halo, described by the Navarro-Frenk-White density profile, has on the energy budget of a spherical, homogeneous cloud located at different distances from the halo center. We found that MCs located in the innermost regions of a massive galaxy can feel a contraction force greater than their self-gravity due to the incorporation of the potential of the galaxy's dark matter halo. We also calculated analytically the gravitational perturbation that an MC produces over a uniform DMB (uniform at the scales of an MC) and how this perturbation will affect the evolution of the MC itself. The study shows that the star formation in an MC will be considerably enhanced if the cloud is located in a dense and low velocity dark matter environment. We confirm our results by measuring the SFE in numerical simulations of the formation and evolution of MCs within different DMBs. Our study indicates that there are situations where the dark matter's gravitational contribution to the evolution of the MCs should not be neglected.
NASA Astrophysics Data System (ADS)
Livio, Mario
2010-04-01
1. A brief history of dark matter Vera Rubin; 2. Microlensing towards the Magellanic Clouds Kailash Sahu; 3. Searching for galactic dark matter Harvey Richer; 4. Hot gas in clusters of galaxies and Omega Megan Donahue; 5. Tracking the Baryon density from the Big Bang to the present Gary Steigman; 6. Modified Newtonian dynamics and its implications Bob Sanders; 7. Cosmological parameters and quintessence from radio galaxies Ruth Daly and Eric Guerra; 8. The mass density of the Universe Neta Bahcall; 9. Growth of structure in the Universe John Peacock; 10. Cosmological implications of the most distant supernova (known) Adam Riess; 11. Dynamical probes of the Halo mass function Chris Kochanek; 12. Detection of gravitational waves from inflation Marc Kamionkowski and Andrew Jaffe; 13. Cosmological constant problems and their solution Alex Vilenkin; 14. Dark Matter and dark energy: a physicist's perspective Michael Dine.
Furukawa, Tomonori; Yokoyama, Shuichiro; Ichiki, Kiyotomo; Sugiyama, Naoshi; Mukohyama, Shinji E-mail: shu@a.phys.nagoya-u.ac.jp E-mail: naoshi@a.phys.nagoya-u.ac.jp
2010-05-01
We revisit ghost dark matter, the possibility that ghost condensation may serve as an alternative to dark matter. In particular, we investigate the Friedmann-Robertson-Walker (FRW) background evolution and the large-scale structure (LSS) in the ΛGDM universe, i.e. a late-time universe dominated by a cosmological constant and ghost dark matter. The FRW background of the ΛGDM universe is indistinguishable from that of the standard ΛCDM universe if M∼>1eV, where M is the scale of spontaneous Lorentz breaking. From the LSS we find a stronger bound: M∼>10eV. For smaller M, ghost dark matter would have non-negligible sound speed after the matter-radiation equality, and thus the matter power spectrum would significantly differ from observation. These bounds are compatible with the phenomenological upper bound M∼<100GeV known in the literature.
Nair, Remya; Jhingan, Sanjay E-mail: sanjay.jhingan@gmail.com
2013-02-01
We look for evidence for the evolution in dark energy density by employing Principal Component Analysis (PCA). Distance redshift data from supernovae and baryon acoustic oscillations (BAO) along with WMAP7 distance priors are used to put constraints on curvature parameter Ω{sub k} and dark energy parameters. The data sets are consistent with a flat Universe. The constraints on the dark energy evolution parameters obtained from supernovae (including CMB distance priors) are consistent with a flat ΛCDM Universe. On the other hand, in the parameter estimates obtained from the addition of BAO data the second principal component, which characterize a non-constant contribution from dark energy, is non-zero at 1σ. This could be a systematic effect and future BAO data holds key to making more robust claims.
Cold dark matter: Controversies on small scales.
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.
Cold dark matter: Controversies on small scales
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
Shedding light on baryonic dark matter
NASA Technical Reports Server (NTRS)
Silk, Joseph
1991-01-01
Halo dark matter, if it is baryonic, may plausibly consist of compact stellar remnants. Jeans mass clouds containing 10 to the 6th to 10 to the 8th solar masses could have efficiently formed stars in the early universe and could plausibly have generated, for a suitably top-heavy stellar initial mass function, a high abundance of neutron stars as well as a small admixture of long-lived low mass stars. Within the resulting clusters of dark remnants, which eventually are tidally disrupted when halos eventually form, captures of neutron stars by nondegenerate stars resulted in formation of close binaries. These evolve to produce, by the present epoch, an observable X-ray signal associated with dark matter aggregations in galaxy cluster cores.
Sources and distributions of dark matter
Sikivie, P. |
1995-12-31
In the first section, the author tries to convey a sense of the variety of observational inputs that tell about the existence and the spatial distribution of dark matter in the universe. In the second section, he briefly reviews the four main dark matter candidates, taking note of each candidate`s status in the world of particle physics, its production in the early universe, its effect upon large scale structure formation and the means by which it may be detected. Section 3 concerns the energy spectrum of (cold) dark matter particles on earth as may be observed some day in a direct detection experiment. It is a brief account of work done in collaboration with J. Ipser and, more recently, with I. Tkachev and Y. Wang.
Dark matter detectors as dark photon helioscopes.
An, Haipeng; Pospelov, Maxim; Pradler, Josef
2013-07-26
Light new particles with masses below 10 keV, often considered as a plausible extension of the standard model, will be emitted from the solar interior and can be detected on Earth with a variety of experimental tools. Here, we analyze the new "dark" vector state V, a massive vector boson mixed with the photon via an angle κ, that in the limit of the small mass mV has its emission spectrum strongly peaked at low energies. Thus, we utilize the constraints on the atomic ionization rate imposed by the results of the XENON10 experiment to set the limit on the parameters of this model: κ×mV<3×10(-12) eV. This makes low-threshold dark matter experiments the most sensitive dark vector helioscopes, as our result not only improves current experimental bounds from other searches by several orders of magnitude but also surpasses even the most stringent astrophysical and cosmological limits in a seven-decade-wide interval of mV. We generalize this approach to other light exotic particles and set the most stringent direct constraints on "minicharged" particles.
Elastically Decoupling Dark Matter.
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.
NASA Astrophysics Data System (ADS)
D'Amico, Guido; Kamionkowski, Marc; Sigurdson, Kris
This chapter is intended to provide a brief pedagogical review of dark matter for the newcomer to the subject. We begin with a discussion of the astrophysical evidence for dark matter. The standard weakly interacting massive particle (WIMP) scenario—the motivation, particle models, and detection techniques—is then reviewed. We provide a brief sampling of some recent variations to the standard WIMP scenario, as well as some alternatives (axions and sterile neutrinos). Exercises are provided for the reader.
Helfer, H.L.
2005-10-21
The observations of the extended rotation curves of some galaxies provide important constraints upon the nature of the local dark matter present in the halos of these galaxies. Using these constraints, one can show that the halo dark matter cannot be some population of conventional astronomical objects and (most probably) cannot be a population of exotic non-interacting particles. We suggest that the halos can be regarded as large spatial fluctuations in a classic scalar field.
NASA Astrophysics Data System (ADS)
Frenkel, D.
2013-01-01
This paper discusses the Monte Carlo and Molecular Dynamics methods. Both methods are, in principle, simple. However, simple does not mean risk-free. In the literature, many of the pitfalls in the field are mentioned, but usually as a footnote --and these footnotes are scattered over many papers. The present paper focuses on the "dark side" of simulation: it is one big footnote. I should stress that "dark", in this context, has no negative moral implication. It just means: under-exposed.
Time arrow is influenced by the dark energy.
Allahverdyan, A E; Gurzadyan, V G
2016-05-01
The arrow of time and the accelerated expansion are two fundamental empirical facts of the universe. We advance the viewpoint that the dark energy (positive cosmological constant) accelerating the expansion of the universe also supports the time asymmetry. It is related to the decay of metastable states under generic perturbations, as we show on example of a microcanonical ensemble. These states will not be metastable without dark energy. The latter also ensures a hyperbolic motion leading to dynamic entropy production with the rate determined by the cosmological constant.
Holographic dark energy model from Ricci scalar curvature
Gao Changjun; Wu Fengquan; Chen Xuelei; Shen Yougen
2009-02-15
Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area of the event horizon of the Universe. However, such a model would have a causality problem. In this paper, we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We show that this model does not only avoid the causality problem and is phenomenologically viable, but also naturally solves the coincidence problem of dark energy. Our analysis of the evolution of density perturbations show that the matter power spectra and cosmic microwave background temperature anisotropy is only slightly affected by such modification.
Disformal couplings and the dark sector of the universe
De Bruck, C. van; Morrice, J. E-mail: app12jam@sheffield.ac.uk
2015-04-01
Interactions between dark matter and dark energy, allowing both conformal and and disformal couplings, are studied in detail. We discuss the background evolution, anisotropies in the cosmic microwave background and large scale structures. One of our main findings is that a large conformal coupling is not necessarily disallowed in the presence of a general disformal term. On the other hand, we find that negative disformal couplings very often lead to instabilities in the scalar field. Studying the background evolution and linear perturbations only, our results show that it is observationally challenging to disentangle disformal from purely conformal couplings.
NASA Astrophysics Data System (ADS)
Gibson, C. H.; Schild, R. E.
2011-11-01
Is the accelerating expansion of the Universe true, inferred through observations of distant supernovae, and is the implied existence of an enormous amount of anti- gravitational dark energy material driving the accelerating expansion of the universe also true? To be physically useful these propositions must be falsifiable; that is, subject to observational tests that could render them false, and both fail when viscous, diffusive, astro-biological and turbulence effects are included in the interpretation of observations. A more plausible explanation of negative stresses producing the big bang is turbulence at Planck temperatures. Inflation results from gluon viscous stresses at the strong force transition. Anti-gravitational (dark energy) turbulence stresses are powerful but only temporary. No permanent dark energy is needed. At the plasma-gas transition, viscous stresses cause fragmentation of plasma proto-galaxies into dark matter clumps of primordial gas planets, each of which falsifies dark-energy cold-dark-matter cosmologies. Clumps of these planets form all stars, and explain the alleged accelerating expansion of the universe as a systematic dimming error of Supernovae Ia by light scattered in the hot turbulent atmospheres of evaporated planets surrounding central white dwarf stars.
Matter sourced anisotropic stress for dark energy
NASA Astrophysics Data System (ADS)
Chang, Baorong; Lu, Jianbo; Xu, Lixin
2014-11-01
Usually a dark energy as a perfect fluid is characterized by the ratio of pressure to energy density (w =p /ρ ) and the ratio of their perturbations in its rest frame (cs2=δ p /δ ρ ). However, a dark energy would have other characteristics beyond its equation of state and the effective speed of sound. Here the extra property is the anisotropic stress sourced by matter as a simple extension to the perfect fluid model. At the background level, this anisotropic stress is zero with respect to the cosmological principle, but not at the first-order perturbation. We tested the viability of the existence of this kind of anisotropic stress by using the currently available cosmic observations through the geometrical and dynamical measurements. Using the Markov-chain Monte Carlo method, we found that the upper bounds on the anisotropic stress which enters into the summation of the Newtonian potentials should be of the order O (1 0-3)Δm . We did not find any strong evidence for the existence of this matter-sourced anisotropic stress, even in the 1 σ region.
Chameleon dark energy models with characteristic signatures
Gannouji, Radouane; Moraes, Bruno; Polarski, David; Mota, David F.; Winther, Hans A.; Tsujikawa, Shinji
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. 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.
Dark-matter QCD-axion searches.
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
Dark-matter QCD-axion searches
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
Instability of Interacting Ghost Dark Energy Model in an Anisotropic Universe
NASA Astrophysics Data System (ADS)
Azimi, N.; Barati, F.
2016-07-01
A new dark energy model called "ghost dark energy" was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, ρ Λ = α H, where α is a constant of order {Λ }3_{QCD} and Λ Q C D ˜ 100 M e V is QCD mass scale. In this paper, we investigate about the stability of generalized QCD ghost dark energy model against perturbations in the anisotropic background. At first, the ghost dark energy model of the universe with spatial BI model with/without the interaction between dark matter and dark energy is discussed. In particular, the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy model are obtained. Then, we use the squared sound speed {vs2} the sign of which determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. In conclusion, we find evidence that the ghost dark energy might can not lead to a stable universe favored by observations at the present time in BI universe.
Perturbative gadgets at arbitrary orders
NASA Astrophysics Data System (ADS)
Jordan, Stephen P.; Farhi, Edward
2008-06-01
Adiabatic quantum algorithms are often most easily formulated using many-body interactions. However, experimentally available interactions are generally two-body. In 2004, Kempe, Kitaev, and Regev introduced perturbative gadgets, by which arbitrary three-body effective interactions can be obtained using Hamiltonians consisting only of two-body interactions. These three-body effective interactions arise from the third order in perturbation theory. Since their introduction, perturbative gadgets have become a standard tool in the theory of quantum computation. Here we construct generalized gadgets so that one can directly obtain arbitrary k -body effective interactions from two-body Hamiltonians. These effective interactions arise from the k th order in perturbation theory.
Inflationary perturbations in bimetric gravity
Cusin, Giulia; Durrer, Ruth; Guarato, Pietro; Motta, Mariele E-mail: ruth.durrer@unige.ch E-mail: mariele.motta@unige.ch
2015-09-01
In this paper we study the generation of primordial perturbations in a cosmological setting of bigravity during inflation. We consider a model of bigravity which can reproduce the ΛCDM background and large scale structure and a simple model of inflation with a single scalar field and a quadratic potential. Reheating is implemented with a toy-model in which the energy density of the inflaton is entirely dissipated into radiation. We present analytic and numerical results for the evolution of primordial perturbations in this cosmological setting. We find that the amplitude of tensor perturbations generated during inflation is sufficiently suppressed to avoid the effects of the tensor instability discovered in refs. [1,2] which develops during the cosmological evolution in the physical sector. We argue that from a pure analysis of the tensor perturbations this bigravity model is compatible with present observations. However, we derive rather stringent limits on inflation from the vector and scalar sectors.
Robust stability under additive perturbations
NASA Technical Reports Server (NTRS)
Bhaya, A.; Desoer, C. A.
1985-01-01
A MIMO linear time-invariant feedback system 1S(P,C) is considered which is assumed to be U-stable. The plant P is subjected to an additive perturbation Delta P which is proper but not necessarily stable. It is proved that the perturbed system is U-stable if and only if Delta P(I + Q x Delta P) exp -1 is U-stable.
Relativistic perturbations in ΛCDM: Eulerian and Lagrangian approaches
Villa, Eleonora; Rampf, Cornelius E-mail: cornelius.rampf@port.ac.uk
2016-01-01
We study the relativistic dynamics of a pressure-less and irrotational fluid of dark matter (CDM) with a cosmological constant (Λ), up to second order in cosmological perturbation theory. In our analysis we also account for vector and tensor perturbations and include primordial non-Gaussianity. We consider three gauges: the synchronous-comoving gauge, the Poisson gauge and the total matter gauge, where the first is the unique relativistic Lagrangian frame of reference, and the latters are convenient gauge choices for Eulerian frames. Our starting point is the metric and fluid variables in the Poisson gauge up to second order. We then perform the gauge transformations to the synchronous-comoving gauge and subsequently to the total matter gauge. Our expressions for the metrics, densities, velocities, and the gauge generators are novel and coincide with known results in the limit of a vanishing cosmological constant.
RECONSTRUCTING COSMOLOGICAL MATTER PERTURBATIONS USING STANDARD CANDLES AND RULERS
Alam, Ujjaini; Sahni, Varun; Starobinsky, Alexei A. E-mail: varun@iucaa.ernet.i
2009-10-20
For a large class of dark energy (DE) models, for which the effective gravitational constant is a constant and there is no direct exchange of energy between DE and dark matter (DM), knowledge of the expansion history suffices to reconstruct the growth factor of linearized density perturbations in the non-relativistic matter component on scales much smaller than the Hubble distance. In this paper, we develop a non-parametric method for extracting information about the perturbative growth factor from data pertaining to the luminosity or angular size distances. A comparison of the reconstructed density contrast with observations of large-scale structure and gravitational lensing can help distinguish DE models such as the cosmological constant and quintessence from models based on modified gravity theories as well as models in which DE and DM are either unified or interact directly. We show that for current supernovae (SNe) data, the linear growth factor at z = 0.3 can be constrained to 5% and the linear growth rate to 6%. With future SNe data, such as expected from the Joint Dark Energy Mission, we may be able to constrain the growth factor to 2%-3% and the growth rate to 3%-4% at z = 0.3 with this unbiased, model-independent reconstruction method. For future baryon acoustic oscillation data which would deliver measurements of both the angular diameter distance and the Hubble parameter, it should be possible to constrain the growth factor at z = 2.5%-9%. These constraints grow tighter with the errors on the data sets. With a large quantity of data expected in the next few years, this method can emerge as a competitive tool for distinguishing between different models of dark energy.
Reconstructing cosmological matter perturbations using standard candles and rulers
Alam, Ujjaini; Sahni, Varun; Starobinsky, Alexei A
2008-01-01
For a large class of dark energy (DE) models, for which the effective gravitational constant is a constant and there is no direct exchange of energy between DE and dark matter (DM), knowledge of the expansion history suffices to reconstruct the growth factor of linearized density perturbations in the non-relativistic matter component on scales much smaller than the Hubble distance. In this paper, we develop a non-parametric method for extracting information about the perturbative growth factor from data pertaining to the luminosity or angular size distances. A comparison of the reconstructed density contrast with observations of large-scale structure and gravitational lensing can help distinguish DE models such as the cosmological constant and quintessence from models based on modified gravity theories as well as models in which DE and DM are either unified or interact directly. We show that for current supernovae (SNe) data, the linear growth factor at z = 0.3 can be constrained to 5% and the linear growth rate to 6%. With future SNe data, such as expected from the Joint Dark Energy Mission, we may be able to constrain the growth factor to 2%-3% and the growth rate to 3%-4% at z = 0.3 with this unbiased, model-independent reconstruction method. For future baryon acoustic oscillation data which would deliver measurements of both the angular diameter distance and the Hubble parameter, it should be possible to constrain the growth factor at z = 2.5%-9%. These constraints grow tighter with the errors on the data sets. With a large quantity of data expected in the next few years, this method can emerge as a competitive tool for distinguishing between different models of dark energy.
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.
Non-scale-invariant density perturbations from chaotic extended inflation
Mollerach, S. ); Matarrese, S. )
1992-03-15
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 inflaton field. The spectrum of perturbations is studied for a class of models: it is non-scale-invariant 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.
High order dark wavefront sensing simulations
NASA Astrophysics Data System (ADS)
Ragazzoni, Roberto; Arcidiacono, Carmelo; Farinato, Jacopo; Viotto, Valentina; Bergomi, Maria; Dima, Marco; Magrin, Demetrio; Marafatto, Luca; Greggio, Davide; Carolo, Elena; Vassallo, Daniele
2016-07-01
Dark wavefront sensing takes shape following quantum mechanics concepts in which one is able to "see" an object in one path of a two-arm interferometer using an as low as desired amount of light actually "hitting" the occulting object. A theoretical way to achieve such a goal, but in the realm of wavefront sensing, is represented by a combination of two unequal beams interferometer sharing the same incoming light, and whose difference in path length is continuously adjusted in order to show different signals for different signs of the incoming perturbation. Furthermore, in order to obtain this in white light, the path difference should be properly adjusted vs the wavelength used. While we incidentally describe how this could be achieved in a true optomechanical setup, we focus our attention to the simulation of a hypothetical "perfect" dark wavefront sensor of this kind in which white light compensation is accomplished in a perfect manner and the gain is selectable in a numerical fashion. Although this would represent a sort of idealized dark wavefront sensor that would probably be hard to match in the real glass and metal, it would also give a firm indication of the maximum achievable gain or, in other words, of the prize for achieving such device. Details of how the simulation code works and first numerical results are outlined along with the perspective for an in-depth analysis of the performances and its extension to more realistic situations, including various sources of additional noise.
NASA Astrophysics Data System (ADS)
Kaloper, Nemanja; Padilla, Antonio
2009-10-01
A sizable fraction of the total energy density of the universe may be in heavy particles with a net dark U(1)' charge comparable to its mass. When the charges have the same sign the cancellation between their gravitational and gauge forces may lead to a mismatch between different measures of masses in the universe. Measuring galactic masses by orbits of normal matter, such as galaxy rotation curves or lensing, will give the total mass, while the flows of dark matter agglomerates may yield smaller values if the gauge repulsion is not accounted for. If distant galaxies which house light beacons like SNe Ia contain such dark particles, the observations of their cosmic recession may mistake the weaker forces for an extra `antigravity', and infer an effective dark energy equation of state smaller than the real one. In some cases, including that of a cosmological constant, these effects can mimic w < -1. They can also lead to a local variation of galaxy-galaxy forces, yielding a larger `Hubble Flow' in those regions of space that could be taken for a dynamical dark energy, or superhorizon effects.
DARK MATTER POWERED STARS: CONSTRAINTS FROM THE EXTRAGALACTIC BACKGROUND LIGHT
Maurer, A.; Raue, M.; Kneiske, T.; Horns, D.; Elsaesser, D.; Hauschildt, P. H.
2012-02-01
The existence of predominantly cold non-baryonic dark matter is unambiguously demonstrated by several observations (e.g., structure formation, big bang nucleosynthesis, gravitational lensing, and rotational curves of spiral galaxies). A candidate well motivated by particle physics is a weakly interacting massive particle (WIMP). Self-annihilating WIMPs would affect the stellar evolution especially in the early universe. Stars powered by self-annihilating WIMP dark matter should possess different properties compared with standard stars. While a direct detection of such dark matter powered stars seems very challenging, their cumulative emission might leave an imprint in the diffuse metagalactic radiation fields, in particular in the mid-infrared part of the electromagnetic spectrum. In this work, the possible contributions of dark matter powered stars (dark stars, DSs) to the extragalactic background light (EBL) are calculated. It is shown that existing data and limits of the EBL intensity can already be used to rule out some DS parameter sets.
Effective description of dark matter as a viscous fluid
NASA Astrophysics Data System (ADS)
Floerchinger, Stefan; Garny, Mathias; Tetradis, Nikolaos; Wiedemann, Urs Achim
2016-10-01
Treating dark matter at large scales as an effectively viscous fluid provides an improved framework for the calculation of the density and velocity power spectra compared to the standard assumption of an ideal pressureless fluid. We discuss how this framework can be made concrete through an appropriate coarse-graining procedure. We also review results that demonstrate that it improves the convergence of cosmological perturbation theory.
Farina, Marco
2015-11-09
We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.
Lincoln, Don
2016-07-12
Carl Sagan's oft-quoted statement that there are "billions and billions" of stars in the cosmos gives an idea of just how much "stuff" is in the universe. However scientists now think that in addition to the type of matter with which we are familiar, there is another kind of matter out there. This new kind of matter is called "dark matter" and there seems to be five times as much as ordinary matter. Dark matter interacts only with gravity, thus light simply zips right by it. Scientists are searching through their data, trying to prove that the dark matter idea is real. Fermilab's Dr. Don Lincoln tells us why we think this seemingly-crazy idea might not be so crazy after all.
NASA Astrophysics Data System (ADS)
Bettini, Alessandro
These lectures begin with a brief survey of the astrophysical and cosmological evidence for dark matter. We then consider the three principal theoretically motivated types of dark matter, sterile neutrinos, axions and SUSY WIMPs. In chapter 4 we discuss the motivations for the so-called neutrino minimal standard model, nuMSM, an extension of the SM with three sterile neutrinos with masses similar to the charged fermions. In chapter 5 we briefly recall the strong CP problem of the SM and the solution proposed by Peccei and Quinn leading to the prediction of axions and of their characteristics. We then discuss the experimental status and perspectives. In chapter 6 we assume that the reader to be acquainted with the theoretical motivations for SUSY and move directly to the direct search for dark matter and the description of the principal detector techniques: scintillators, noble fluids and bolometers. We conclude with an outlook on the future perspectives.
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
Stern, Ian P.; Collaboration: ADMX Collaboration; ADMX-HF Collaboration
2014-06-24
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 axions 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.
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 axions 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.
NASA Astrophysics Data System (ADS)
Sellwood, J. A.; Kosowsky, A.
The success of the ΛCDM model on large scales does not extend down to galaxy scales. We list a dozen problems of the dark matter hypothesis, some of which arise in specific models for the formation of structure in the universe, while others are generic and require fine tuning in any dark matter theory. Modifications to the theory, such as adding properties to the DM particles beyond gravitational interactions, or simply a better understanding of the physics of galaxy formation, may resolve some problems, but a number of conspiracies and correlations are unlikely to yield to this approach. The alternative is that mass discrepancies result from of a non-Newtonian law of gravity, a hypothesis which avoids many of the more intractable problems of dark matter. A modified law of gravity is not without formidable difficulties of its own, but it is no longer obvious that they are any more daunting than those facing DM.
Wechsler, Risa
2007-10-30
What is the Universe made of? This question has been asked as long as humans have been questioning, and astronomers and physicists are finally converging on an answer. The picture which has emerged from numerous complementary observations over the past decade is a surprising one: most of the matter in the Universe isn't visible, and most of the Universe isn't even made of matter. In this talk, I will explain what the rest of this stuff, known as 'Dark Energy' is, how it is related to the so-called 'Dark Matter', how it impacts the evolution of the Universe, and how we can study the dark universe using observations of light from current and future telescopes.
Farina, Marco
2015-11-01
We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.
Cosmological implications of the dark matter equation of state
NASA Astrophysics Data System (ADS)
Yang, Weiqiang; Li, Hang; Wu, Yabo; Lu, Jianbo
In this paper, we study a model which is composed of the cosmological constant and dark matter with nonzero equation of state parameter, which could be called as ΛwDM. In the synchronous gauge, we obtain the perturbation equations of dark matter, and deduce the evolution equations of growth factor about the dark matter and baryons. Based on the Markov Chain Monte Carlo (MCMC) method, we constrain this model by the recently available cosmic observations which include cosmic microwave background (CMB) radiation, baryon acoustic oscillation (BAO), type Ia supernovae (SNIa) and fσ8(z) data points from redshift-space distortion (RSD). The results present a tighter constraint on the model than the case without fσ8(z) data. In 3σ regions, we find the dark matter equation of state parameter wdm = 0.00011‑0.00070‑0.00135‑0.00178+0.00069+0.00134+0.00179. The currently available cosmic observations do not favor the nonzero dark matter equation of state parameter, no deviation from the lambda cold dark matter (ΛCDM) model is found in 1σ region.
NASA Astrophysics Data System (ADS)
Walker, Constance E.
2009-05-01
The arc of the Milky Way seen from a truly dark location is part of our planet's natural heritage. More than one fifth of the world population, two thirds of the United States population and one half of the European Union population have already lost naked eye visibility of the Milky Way. This loss, caused by light pollution, is a serious and growing issue that impacts astronomical research, the economy, ecology, energy conservation, human health, public safety and our shared ability to see the night sky. For this reason, "Dark Skies” is a cornerstone project of the International Year of Astronomy. Its goal is to raise public awareness of the impact of artificial lighting on local environments by getting people worldwide involved in a variety of programs that: 1. Teach about dark skies using new technology (e.g., an activity-based planetarium show on DVD, podcasting, social networking on Facebook and MySpace, a Second Life presence) 2. Provide thematic events on light pollution at star parties and observatory open houses (Dark Skies Discovery Sites, Nights in the (National) Parks, Sidewalk Astronomy) 3. Organize events in the arts (e.g., a photography contest) 4. Involve citizen-scientists in naked-eye and digital-meter star hunting programs (e.g., GLOBE at Night, "How Many Stars?", the Great World Wide Star Count and the radio frequency interference equivalent: "Quiet Skies") and 5. Raise awareness about the link between light pollution and public health, economic issues, ecological consequences, energy conservation, safety and security, and astronomy (e.g., The Starlight Initiative, World Night in Defense of Starlight, International Dark Sky Week, International Dark-Sky Communities, Earth Hour, The Great Switch Out, a traveling exhibit, downloadable posters and brochures). The presentation will provide an update, describe how people can become involved and take a look ahead at the program's sustainability. For more information, visit www.darkskiesawareness.org.
Fundamental Particle Structure in the Cosmological Dark Matter
NASA Astrophysics Data System (ADS)
Khlopov, Maxim
2013-11-01
The nonbaryonic dark matter of the universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro-world and mechanisms of its symmetry breaking. Particle candidates for cosmological dark matter are lightest particles that bear new conserved quantum numbers. Dark matter particles may represent ideal gas of noninteracting particles. Self-interacting dark matter weakly or superweakly coupled to ordinary matter is also possible, reflecting nontrivial pattern of particle symmetry in the hidden sector of particle theory. In the early universe the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which macroscopic cosmological defects or primordial nonlinear structures can be originated. Primordial black holes (PBHs) can be not only a candidate for dark matter, but also represent a universal probe for superhigh energy physics in the early universe. Evaporating PBHs turn to be a source of even superweakly interacting particles, while clouds of massive PBHs can serve as nonlinear seeds for galaxy formation. The observed broken symmetry of the three known families may provide a simultaneous solution for the problems of the mass of neutrino and strong CP-violation in the unique framework of models of horizontal unification. Dark matter candidates can also appear in the new families of quarks and leptons and the existence of new stable charged leptons and quarks is possible, hidden in elusive "dark atoms." Such possibility, strongly restricted by the constraints on anomalous isotopes of light elements, is not excluded in scenarios that predict stable double charged particles. The excessive -2 charged particles are bound in these scenarios with primordial helium in O-helium "atoms," maintaining specific nuclear-interacting form of the dark matter, which may provide an interesting solution for the puzzles of the direct dark matter searches. In the context of cosmoparticle physics, studying
Dark-energy thermodynamic models
Besprosvany, Jaime; Izquierdo, German
2010-12-07
We study cosmological consequences of dark-energy thermodynamic models. The assumption that dark energy is conformed of quanta, and an extensivity argument generalize its equation of state. This implies that dark energy and another key component exchange energy. The energy densities of dark energy and the other component then tend asymptotically to a constant, thus explaining the coincidence of dark matter and dark energy today. On the other hand, a model of non-relativistic particles in a Bose-Einstein condensate, with a short-range attractive interaction, produces acceleration. It is shown that the phantom-acceleration regime, at the beginning of the universe, solves the horizon problem.
Lincoln, Don
2014-04-15
Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.
Lincoln, Don
2016-07-12
Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.
Flaugher, Brenna; /Fermilab
2004-11-01
Dark Energy is the dominant constituent of the universe and they have little understanding of it. They describe a new project aimed at measuring the dark energy equation of state parameter, w, to a statistical precision of {approx} 5%, with four separate techniques. The survey will image 5000 deg{sup 2} in the southern sky and collect 300 million galaxies, 30,000 galaxy clusters, and 2000 Type Ia supernovae. The survey will be carried out using a new 3 deg{sup 2} mosaic camera mounted at the prime focus of the 4m Blanco telescope at CTIO.
Higher-order massive neutrino perturbations in large-scale structure
NASA Astrophysics Data System (ADS)
Führer, Florian; Wong, Yvonne Y. Y.
2015-03-01
We develop a higher-order perturbation theory for large-scale structure formation involving a free-streaming hot or warm dark matter species. We focus on the case of mixed cold dark matter and massive neutrinos, although our approach is applicable also to a single warm dark matter species. In order to capture the suppressed growth of neutrino density perturbations on small scales, we account for the full momentum dependence of the phase space distribution using the Vlasov equation, and derive from it a formal closed-form nonlinear equation for the neutrino density. Using a systematic perturbative expansion of this equation we compute high-order corrections to the neutrino density contrast without the explicit need to track the perturbed neutrino momentum distribution. We calculate the leading-order total matter bispectrum for several neutrino masses. Using our result as a benchmark, we test the accuracy of the fluid approximation and a linear approximation used in perturbative and N-body analyses, as well as a new hybrid approach that combines the exact linear evolution with the nonlinear structure of the fluid equations. Aiming at lesssim 1% accuracy, we find that the total matter bispectrum with a low neutrino mass m = 0.046 eV can be reproduced by all but the fluid approximation, while for larger neutrino masses m=0.46 → 0.93 eV only the hybrid approach has the desired accuracy on a large range of scales. This result serves as a cautionary note that approximate nonlinear models of neutrino clustering that reproduce the gross features of some observables may not suffice for precision calculations, nor are they guaranteed to apply to other observables. All of the approximation schemes fail to reproduce the bispectrum of the neutrino density perturbations at better than 20% accuracy across all scales, indicating that an exact treatment of nonlinear neutrino perturbations is necessary.
Galactoseismology and the local density of dark matter
NASA Astrophysics Data System (ADS)
Banik, Nilanjan; Widrow, Lawrence M.; Dodelson, Scott
2017-02-01
We model vertical breathing mode perturbations in the Milky Way's stellar disc and study their effects on estimates of the local dark matter density, surface density, and vertical force. Evidence for these perturbations, which involve compression and expansion of the Galactic disc perpendicular to the mid-plane, comes from three different surveys of stellar kinematics within a few kiloparsecs of the Sun. We show that their existence may lead to systematic errors of 10 per cent or greater in the vertical force Kz(z) at |z| = 1.1 kpc. These errors translate to ≳ 25 per cent errors in estimates of the local dark matter density. Using different mono-abundant subpopulations as tracers offers a way out: if the inferences from all tracers in the Gaia era agree, then the dark matter determination will be robust. Disagreement in the inferences from different tracers will signal the breakdown of the unperturbed model and perhaps provide the means for determining the nature of the perturbation.
Dark Energy and The Dark Matter Relic Abundance
Rosati, Francesca
2004-11-17
Two mechanisms by which the quintessence scalar could enhance the relic abundance of dark matter particles are discussed. These effects can have an impact on supersymmetric candidates for dark matter.
Growth of Cosmic Structure: Probing Dark Energy Beyond Expansion
Huterer, Dragan; Kirkby, David; Bean, Rachel; ...
2014-03-15
The quantity and quality of cosmic structure observations have greatly accelerated in recent years, and further leaps forward will be facilitated by imminent projects. These will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to several pieces of fundamental physics: the primordial perturbations generated by GUT-scale physics; neutrino masses and interactions; the nature of dark matter and dark energy. We focus on the last of these here: the ways that combining probes of growth with those of the cosmic expansionmore » such as distance-redshift relations will pin down the mechanism driving the acceleration of the Universe.« less
Chiral effective theory of dark matter direct detection
NASA Astrophysics Data System (ADS)
Bishara, Fady; Brod, Joachim; Grinstein, Benjamin; Zupan, Jure
2017-02-01
We present the effective field theory for dark matter interactions with the visible sector that is valid at scales of Script O(1 GeV). Starting with an effective theory describing the interactions of fermionic and scalar dark matter with quarks, gluons and photons via higher dimension operators that would arise from dimension-five and dimension-six operators above electroweak scale, we perform a nonperturbative matching onto a heavy baryon chiral perturbation theory that describes dark matter interactions with light mesons and nucleons. This is then used to obtain the coefficients of the nuclear response functions using a chiral effective theory description of nuclear forces. Our results consistently keep the leading contributions in chiral counting for each of the initial Wilson coefficients.
Growth of cosmic structure: Probing dark energy beyond expansion
Huterer, Dragan; Kirkby, David; Bean, Rachel; Connolly, Andrew; Dawson, Kyle; Dodelson, Scott; Evrard, August; Jain, Bhuvnesh; Jarvis, Michael; Linder, Eric; Mandelbaum, Rachel; May, Morgan; Raccanelli, Alvise; Reid, Beth; Rozo, Eduardo; Schmidt, Fabian; Sehgal, Neelima; Slosar, Anže; van Engelen, Alex; Wu, Hao-Yi; Zhao, Gongbo
2015-03-01
The quantity and quality of cosmic structure observations have greatly accelerated in recent years, and further leaps forward will be facilitated by imminent projects. These will enable us to map the evolution of dark and baryonic matter density fluctuations over cosmic history. The way that these fluctuations vary over space and time is sensitive to several pieces of fundamental physics: the primordial perturbations generated by GUT-scale physics; neutrino masses and interactions; the nature of dark matter and dark energy. We focus on the last of these here: the ways that combining probes of growth with those of the cosmic expansion such as distance-redshift relations will pin down the mechanism driving the acceleration of the Universe.
The scalar singlet-triplet dark matter model
Fischer, O.; Van der Bij, J.J. E-mail: vdbij@physik.uni-freiburg.de
2014-01-01
We consider a model for cold dark matter, which combines a real scalar singlet and a real scalar SU(2){sub L} triplet field, both of which are residing in the odd representation of a global Z{sub 2} symmetry. The parameter space of the model is constrained by the inferred dark matter abundance from the WMAP and Planck data, the most recent results from the direct dark matter search experiment LUX, the Z boson decay width from LEP-I and perturbativity of the coupling parameters. The phenomenology of the remaining parameter space is studied. We find that the model allows for DM masses near the electroweak scale and a variety of decay scenarios.
Dark energy and dark matter from primordial QGP
Vaidya, Vaishali Upadhyaya, G. K.
2015-07-31
Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.
Dark energy and dark matter from primordial QGP
NASA Astrophysics Data System (ADS)
Vaidya, Vaishali; Upadhyaya, G. K.
2015-07-01
Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.
Poulsen, P; Kuklo, R M
2001-03-01
We have previously reported the degree of attenuation and perturbation by a Cu jet passing through Comp B explosive. Similar tests have now been performed with high explosive (HE) targets having CJ pressures higher than and lower than the CJ pressure of Comp B. The explosives were LX-14 and TNT, respectively. We found that the measured exit velocity of the jet where it transitions from perturbed to solid did not vary significantly as a function of HE type for each HE thickness. The radial momentum imparted to the perturbed jet segment did vary as a function of HE type, however, and we report the radial spreading of the jet and the penetration of a downstream target as a function of HE type and thickness.
Multi-field inflation and cosmological perturbations
NASA Astrophysics Data System (ADS)
Gong, Jinn-Ouk
We provide a concise review on multi-field inflation and cosmological perturbations. We discuss convenient and physically meaningful bases in terms of which perturbations can be systematically studied. We give formal accounts on the gauge fixing conditions and present the perturbation action in two gauges. We also briefly review nonlinear perturbations.
NASA Astrophysics Data System (ADS)
Baumbach, Christoph; mcissbc
2014-04-01
In reply to the physicsworld.com news story “Dark field illuminates X-ray imaging” (25 February, http://ow.ly/ulJnl), which concerns new research by Robert Cernik and colleagues (Proc. R. Soc. A 10.1098/rspa.2013.0629).
Turner, M.S.
1989-01-01
One of the simplest, yet most profound, questions we can ask about the Universe is, how much stuff is in it, and further what is that stuff composed of. Needless to say, the answer to this question has very important implications for the evolution of the Universe, determining both the ultimate fate and the course of structure formation. Remarkably, at this late date in the history of the Universe we still do not have a definitive answer to this simplest of questions---although we have some very intriguing clues. It is known with certainty that most of the material in the Universe is dark, and we have the strong suspicion that the dominant component of material in the Cosmos is not baryons, but rather is exotic relic elementary particles left over from the earliest, very hot epoch of the Universe. If true, the Dark Matter question is a most fundamental one facing both particle physics and cosmology. The leading particle dark matter candidates are: the axion, the neutralino, and a light neutrino species. All three candidates are accessible to experimental tests, and experiments are now in progress. In addition, there are several dark horse, long shot, candidates, including the superheavy magnetic monopole and soliton stars. 13 refs.
Gómez, M.A.; Jackson, C.B.; Shaughnessy, G. E-mail: chris@uta.edu
2014-12-01
We consider a simplified model of fermionic dark matter which couples exclusively to the right-handed top quark via a renormalizable interaction with a color-charged scalar. We first compute the relic abundance of this type of dark matter and investigate constraints placed on the model parameter space by the latest direct detection data. We also perform a detailed analysis for the production of dark matter at the LHC for this model. We find several kinematic variables that allow for a clean signal extraction and we show that the parameter space of this model will be well probed during LHC Run-II. Finally, we investigate the possibility of detecting this type of dark matter via its annihilations into gamma rays. We compute the continuum and the line emission (which includes a possible ''Higgs in Space!'' line) and its possible discovery by future gamma-ray telescopes. We find that the annihilation spectrum has distinctive features which may distinguish it from other models.
Thermal perturbation of the Sun
NASA Technical Reports Server (NTRS)
Twigg, L. W.; Endal, A. S.
1981-01-01
An investigation of thermal perturbations of the solar convective zone via changes in the mixing length parameter were carried out, with a view toward understanding the possible solar radius and luminosity changes cited in the literature. The results show that: (a) a single perturbation of alpha is probably not the cause of the solar radius change and (b) the parameter W = d lambda nR./d lambda nL. can not be characterized by a single value, as implied in recent work.
Orrell, John
2016-07-12
More than 25 years ago, PNNL scientists began the first underground measurements searching for dark matter using specialized radiation detector technology. Dark matter is yet to be discovered says Physicist John L. Orrell.
Orrell, John
2013-11-20
More than 25 years ago, PNNL scientists began the first underground measurements searching for dark matter using specialized radiation detector technology. Dark matter is yet to be discovered says Physicist John L. Orrell.
Lyman-α forest constraints on decaying dark matter
NASA Astrophysics Data System (ADS)
Wang, Mei-Yu; Croft, Rupert A. C.; Peter, Annika H. G.; Zentner, Andrew R.; Purcell, Chris W.
2013-12-01
We present an analysis of high-resolution N-body simulations of decaying dark matter cosmologies focusing on the statistical properties of the transmitted Lyman-α (Lyα) forest flux in the high-redshift intergalactic medium (IGM). In this type of model a dark matter particle decays into a slightly less massive stable dark matter daughter particle and a comparably light particle. The small mass splitting provides a nonrelativistic kick velocity Vk=cΔM/M to the daughter particle resulting in free-streaming and subsequent damping of small-scale density fluctuations. Current Lyα forest power spectrum measurements probe comoving scales up to ˜2-3h-1Mpc at redshifts z˜2-4, providing one of the most robust ways to probe cosmological density fluctuations on relatively small scales. The suppression of structure growth due to the free-streaming of dark matter daughter particles also has a significant impact on the neutral hydrogen cloud distribution, which traces the underlying dark matter distribution well at high redshift. We exploit Lyα forest power spectrum measurements to constrain the amount of free-streaming of dark matter in such models and thereby place limits on decaying dark matter based only on the dynamics of cosmological perturbations without any assumptions about the interactions of the decay products. We use a suite of dark-matter-only simulations together with the fluctuating Gunn-Peterson approximation to derive the Lyα flux distribution. We argue that this approach should be sufficient for our main purpose, which is to demonstrate the power of the Lyα forest to constrain decaying dark matter models. We find that Sloan Digital Sky Survey 1D Lyα forest power spectrum data place a lifetime-dependent upper limit Vk≲30-70km/s for decay lifetimes ≲10Gyr. This is the most stringent model-independent bound on invisible dark matter decays with small mass splittings. For larger mass splittings (large Vk), Lyα forest data restrict the dark matter
Dark energy and dark matter haloes
NASA Astrophysics Data System (ADS)
Kuhlen, Michael; Strigari, Louis E.; Zentner, Andrew R.; Bullock, James S.; Primack, Joel R.
2005-02-01
We investigate the effect of dark energy on the density profiles of dark matter haloes with a suite of cosmological N-body simulations and use our results to test analytic models. We consider constant equation of state models, and allow both w>=-1 and w < -1. Using five simulations with w ranging from -1.5 to -0.5, and with more than ~1600 well-resolved haloes each, we show that the halo concentration model of Bullock et al. accurately predicts the median concentrations of haloes over the range of w, halo masses and redshifts that we are capable of probing. We find that the Bullock et al. model works best when halo masses and concentrations are defined relative to an outer radius set by a cosmology-dependent virial overdensity. For a fixed power spectrum normalization and fixed-mass haloes, larger values of w lead to higher concentrations and higher halo central densities, both because collapse occurs earlier and because haloes have higher virial densities. While precise predictions of halo densities are quite sensitive to various uncertainties, we make broad comparisons to galaxy rotation curve data. At fixed power spectrum normalization (fixed σ8), w > -1 quintessence models seem to exacerbate the central density problem relative to the standard w=-1 model. For example, models with w~=- 0.5 seem disfavoured by the data, which can be matched only by allowing extremely low normalizations, σ8<~ 0.6. Meanwhile w < -1 models help to reduce the apparent discrepancy. We confirm that the halo mass function of Jenkins et al. provides an excellent approximation to the abundance of haloes in our simulations and extend its region of validity to include models with w < -1.
NASA Astrophysics Data System (ADS)
Bertone, Gianfranco
2013-11-01
Part I. DM in Cosmology: 1. Particle dark matter G. Bertone and J. Silk; 2. Simulations of CDM haloes B. Moore and J. Diemand; 3. MW substructures J. Bullock, M. Kaplinghat and L. Strigari; 4. Gravitational lensing and dark matter Y. Mellier; 5. Dark matter at the centers of galaxies D. Merritt; 6. Modified gravity as an alternative to DM J. Bekenstein; Part II. Candidates: 7. DM production mechanisms G. Gelmini and P. Gondolo; 8. Supersymmetric DM candidates J. Ellis and K. Olive; 9. DM at the EW scale: non-SUSY candidates G. Servant; 10. Non-WIMP candidates J. L. Feng; 11. Axions P. Sikivie; 12. Sterile neutrinos M. Shaposhnikov; Part III. Colliders Searches: 13. SUSY searches at the LHC T. Plehn and G. Polesello; 14. SUSY DM at colliders M. Battaglia and M. E. Peskin; 15. Extra dimensions at the LHC K. Kong, K. Matchev and G. Servant; 16. SUSY tools F. Boudjema, J. Edsjö and P. Gondolo; Part IV. Direct Detection: 17. Direct detection of WIMPs D. G. Cerdeño and A. Green; 18. Annual modulation with NaI(Tl) R. Bernabei and P. Belli; 19. Particle DM and DAMA N. Fornengo; 20. Cryogenic detectors G. Gerbier and J. Gascon; 21. Liquid noble gases E. Aprile and L. Baudis; 22. Directional detectors N. Spooner; 23. Axion searches S. Asztalos; Part V. Indirect Detection and Astrophysical Constraints: 24. Gamma-rays L. Bergström and G. Bertone; 25. Neutrinos F. Halzen and D. Hooper; 26. Antimatter P. Salati, F. Donato and N. Fornengo; 27. Multi-wavelength S. Profumo and P. Ullio; 28. Dark matter and BBN K. Jedamzik and M. Pospelov; 29. Dark matter and stars G. Bertone; Appendix; References; Index.
The phenomenology of maverick dark matter
NASA Astrophysics Data System (ADS)
Krusberg, Zosia Anna Celina
Astrophysical observations from galactic to cosmological scales point to a substantial non-baryonic component to the universe's total matter density. Although very little is presently known about the physical properties of dark matter, its existence offers some of the most compelling evidence for physics beyond the standard model (BSM). In the weakly interacting massive particle (WIMP) scenario, the dark matter consists of particles that possess weak-scale interactions with the particles of the standard model, offering a compelling theoretical framework that allows us to understand the relic abundance of dark matter as a natural consequence of the thermal history of the early universe. From the perspective of particle physics phenomenology, the WIMP scenario is appealing for two additional reasons. First, many theories of BSM physics contain attractive WIMP candidates. Second, the weak-scale interactions between WIMPs and standard model particles imply the possibility of detecting scatterings between relic WIMPs and detector nuclei in direct detection experiments, products of WIMP annihilations at locations throughout the galaxy in indirect detection programs, and WIMP production signals at high-energy particle colliders. In this work, we use an effective field theory approach to study model-independent dark matter phenomenology in direct detection and collider experiments. The maverick dark matter scenario is defined by an effective field theory in which the WIMP is the only new particle within the energy range accessible to the Large Hadron Collider (LHC). Although certain assumptions are necessary to keep the problem tractable, we describe our WIMP candidate generically by specifying only its spin and dominant interaction form with standard model particles. Constraints are placed on the masses and coupling constants of the maverick WIMPs using the Wilkinson Microwave Anisotropy Probe (WMAP) relic density measurement and direct detection exclusion data from both
How dark chocolate is processed
Technology Transfer Automated Retrieval System (TEKTRAN)
This month’s column will continue the theme of “How Is It Processed?” The column will focus on dark chocolate. The botanical name for the cacao tree is Theobroma cacao, which literally means “food of the Gods.” Dark chocolate is both delicious and nutritious. Production of dark chocolate will be des...
Theory and Motivations of Dark Sector Dark Matter and Forces
NASA Astrophysics Data System (ADS)
Schuster, Philip
2017-01-01
We present the theory and motivations underlying ``dark'' or ``hidden'' sector dark matter and new force scenarios. Dark sector scenarios with sub-GeV mass scales have attracted particular attention in the past several years, motivated in part by findings from direct detection, satellite, and LHC experiments, as well as precision measurements. Moreover, these scenarios offer some of the simplest and least explored possibilities for dark matter. As such, sub-GeV dark sector scenarios have become the focus of a broad and growing international program of experiments.
Dynamics of dark energy with a coupling to dark matter
Boehmer, Christian G.; Caldera-Cabral, Gabriela; Maartens, Roy; Lazkoz, Ruth
2008-07-15
Dark energy and dark matter are the dominant sources in the evolution of the late universe. They are currently only indirectly detected via their gravitational effects, and there could be a coupling between them without violating observational constraints. We investigate the background dynamics when dark energy is modeled as exponential quintessence and is coupled to dark matter via simple models of energy exchange. We introduce a new form of dark sector coupling, which leads to a more complicated dynamical phase space and has a better physical motivation than previous mathematically similar couplings.
Ultralight repulsive dark matter and BEC
NASA Astrophysics Data System (ADS)
Fan, JiJi
2016-12-01
Ultralight scalar dark matter with mass at or below the eV scale and pressure from repulsive self-interaction could form a Bose-Einstein condensate in the early Universe and maybe in galaxies as well. It has been suggested to be a possible solution to the cusp/core problem or even to explain MOND phenomenology. In this paper, I initiate a study of possible self-interactions of ultralight scalar dark matter from the particle physics point of view. To protect its mass, the scalar dark matter is identified as a pseudo Nambu-Goldstone boson (pNGB). Quite a few pNGB models with different potentials such as the QCD axion and the dilaton lead to attractive self-interactions. Yet if an axion is a remnant of a 5D gauged U(1) symmetry, its self-interactions could be repulsive provided the masses and charges of the 5D matter contributing to its potential satisfy certain constraints. Collective symmetry breaking could also lead to a repulsive self-interaction yet with too large a strength that is ruled out by Bullet Cluster constraints. I also discuss cosmological and astrophysical constraints on ultralight repulsive dark matter in terms of a parametrization motivated by particle physics considerations.
Falsification of Dark Energy by Fluid Mechanics
NASA Astrophysics Data System (ADS)
Gibson, Carl H.
2012-03-01
The 2011 Nobel Prize in Physics was awarded for the discovery of accelerating super- novae dimness, suggesting a remarkable reversal in the expansion rate of the Universe from a decrease to an increase, driven by anti-gravity forces of a mysterious dark energy material comprising 70% of the Universe mass-energy. Fluid mechanics and Herschel- Planck-Spitzer-Hubble etc. space telescope observations falsify both the accelerating ex- pansion rate and dark energy concepts. Kinematic viscosity is neglected in models of self-gravitational structure formation. Large plasma photon viscosity predicts protosu- perclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the gas protogalaxies fragment into Earth-mass rogue plan- ets in highly persistent, trillion-planet clumps (proto-globular-star-cluster PGCs). PGC planets freeze to form the dark matter of galaxies and merge to form their stars, giving the hydrogen triple-point (14 K) infrared emissions observed. Dark energy is a system- atic dimming error for Supernovae Ia caused by partially evaporated planets feeding hot white dwarf stars at the Chandrasekhar carbon limit. Planet atmospheres may or may not dim light from SNe-Ia events depending on the line of sight.
Sterile neutrinos as subdominant warm dark matter
Palazzo, A.; Cumberbatch, D.; Slosar, A.; Silk, J.
2007-11-15
In light of recent findings which seem to disfavor a scenario with (warm) dark matter entirely constituted of sterile neutrinos produced via the Dodelson-Widrow mechanism, we investigate the constraints attainable for this mechanism by relaxing the usual hypothesis that the relic neutrino abundance must necessarily account for all of the dark matter. We first study how to reinterpret the limits attainable from x-ray nondetection and Lyman-{alpha} forest measurements in the case that sterile neutrinos constitute only a fraction f{sub s} of the total amount of dark matter. Then, assuming that sterile neutrinos are generated in the early universe solely through the Dodelson-Widrow mechanism, we show how the x-ray and Lyman-{alpha} results jointly constrain the mass-mixing parameters governing their production. Furthermore, we show how the same data allow us to set a robust upper limit f{sub s} < or approx. 0.7 at the 2{sigma} level, rejecting the case of dominant dark matter (f{sub s}=1) at the {approx}3{sigma} level.
Testing gravity theories using tensor perturbations
NASA Astrophysics Data System (ADS)
Lin, Weikang; Ishak-Boushaki, Mustapha B.
2017-01-01
Primordial gravitational waves constitute a promising probe of the very early universe physics and the laws of gravity. We study the changes to tensor-mode perturbations that can arise in various modified gravity theories. These include a modified friction and a nonstandard dispersion relation. We introduce a physically motivated parametrization of these effects and use current data to obtain excluded parameter spaces. Taking into account the foreground subtraction, we then perform a forecast analysis focusing on the tensor-mode modified-gravity parameters as constrained by future experiments COrE, Stage-IV and PIXIE. For the tensor-to-scalar ratio r=0.01, we find the minimum detectible modified-gravity effects. In particular, the minimum detectable graviton mass is about 7.8˜9.7×10-33 eV, which is of the same order of magnitude as the graviton mass that allows massive gravity to produce late-time cosmic acceleration. Finally, we study the tensor-mode perturbations in modified gravity during inflation. We find that, the tensor spectral index would be additionally related to the friction parameter ν0 by nT=-3ν0-r/8. In some cases, the future experiments will be able to distinguish this relation from the standard one. In sum, primordial gravitational waves provide a complementary avenue to test gravity theories.
The vacuum's dark particles behave like dark matter and dark energy
NASA Astrophysics Data System (ADS)
Haller, John
2015-04-01
Building on the governing hypothesis that self-information is equal to action, I solve for the time step of the vacuum. The resulting equations (both quantum diffusion and Friedmann's equations) argue that a dark particle, or special black hole, exists at hbar or twice the reduced Planck mass where the Hawking temperature breaks down. It is hypothesized that if neutral hydrogen is nearby the dark particles are able to couple with the background field and thus have a density that looks like dark matter. If hydrogen is not around, the dark particles become frozen leading to a constant density of black body radiation similar to dark energy. If the Universe's dark particles (away from neutral hydrogen) became frozen during the re-ionization of the Universe's history, its BBR density is well within confidence ranges for the cosmological constant. This hypothesis can also explain the recent observations that dark matter decays into dark energy.
VHS Movies: Perturbations for Morphogenesis.
ERIC Educational Resources Information Center
Holmes, Danny L.
This paper discusses the concept of a family system in terms of an interactive system of interrelated, interdependent parts and suggests that VHS movies can act as perturbations, i.e., change promoting agents, for certain dysfunctional family systems. Several distinct characteristics of a family system are defined with particular emphasis on…
Recent Developments in Perturbative QCD
Dixon, Lance J.; /SLAC
2005-07-11
I review recent progress in perturbative QCD on two fronts: extending next-to-next-to-leading order QCD corrections to a broader range of collider processes, and applying twistor-space methods (and related spinoffs) to computations of multi-parton scattering amplitudes.
Adaptation Strategies in Perturbed /s/
ERIC Educational Resources Information Center
Brunner, Jana; Hoole, Phil; Perrier, Pascal
2011-01-01
The purpose of this work is to investigate the role of three articulatory parameters (tongue position, jaw position and tongue grooving) in the production of /s/. Six normal speakers' speech was perturbed by a palatal prosthesis. The fricative was recorded acoustically and through electromagnetic articulography in four conditions: (1) unperturbed,…
Disformal invariance of curvature perturbation
Motohashi, Hayato; White, Jonathan E-mail: jwhite@post.kek.jp
2016-02-01
We show that under a general disformal transformation the linear comoving curvature perturbation is not identically invariant, but is invariant on superhorizon scales for any theory that is disformally related to Horndeski's theory. The difference between disformally related curvature perturbations is found to be given in terms of the comoving density perturbation associated with a single canonical scalar field. In General Relativity it is well-known that this quantity vanishes on superhorizon scales through the Poisson equation that is obtained on combining the Hamiltonian and momentum constraints, and we confirm that a similar result holds for any theory that is disformally related to Horndeski's scalar-tensor theory so long as the invertibility condition for the disformal transformation is satisfied. We also consider the curvature perturbation at full nonlinear order in the unitary gauge, and find that it is invariant under a general disformal transformation if we assume that an attractor regime has been reached. Finally, we also discuss the counting of degrees of freedom in theories disformally related to Horndeski's.
Basics of QCD perturbation theory
Soper, D.E.
1997-06-01
This is an introduction to the use of QCD perturbation theory, emphasizing generic features of the theory that enable one to separate short-time and long-time effects. The author also covers some important classes of applications: electron-positron annihilation to hadrons, deeply inelastic scattering, and hard processes in hadron-hadron collisions. 31 refs., 38 figs.
New results in perturbative QCD
Ellis, R.K.
1985-11-01
Three topics in perturbative QCD important for Super-collider physics are reviewed. The topics are: (2 2) jet phenomena calculated in O( sT); new techniques for the calculation of tree graphs; and colour coherence in jet phenomena. 31 refs., 6 figs.
Dark Energy Coupled with Dark Matter in the Accelerating Universe
NASA Astrophysics Data System (ADS)
Zhang, Yang
2004-06-01
To model the observed Universe containing both dark energy and dark matter, we study the effective Yang Mills condensate model of dark energy and add a non-relativistic matter component as the dark matter, which is generated out of the decaying dark energy at a constant rate Gamma, a parameter of our model. For the Universe driven by these two components, the dynamic evolution still has asymptotic behaviour: the expansion of the Universe is accelerating with an asymptotically constant rate H, and the densities of both components approach to finite constant values. Moreover, OmegaLambdasimeq0.7 for dark energy and Omegamsimeq0.3 for dark matter are achieved if the decay rate Gamma is chosen such that Gamma/H~1.
Unitarisation of EFT amplitudes for dark matter searches at the LHC
NASA Astrophysics Data System (ADS)
Bell, Nicole F.; Busoni, Giorgio; Kobakhidze, Archil; Long, David M.; Schmidt, Michael A.
2016-08-01
We propose a new approach to the LHC dark matter search analysis within the effective field theory framework by utilising the K-matrix unitarisation formalism. This approach provides a reasonable estimate of the dark matter production cross section at high energies, and hence allows reliable bounds to be placed on the cut-off scale of relevant operators without running into the problem of perturbative unitarity violation. We exemplify this procedure for the effective operator D5 in monojet dark matter searches in the collinear approximation. We compare our bounds to those obtained using the truncation method and identify a parameter region where the unitarisation prescription leads to more stringent bounds.
Visible and dark matter from a first-order phase transition in a baryon-symmetric universe
Petraki, Kalliopi; Trodden, Mark; Volkas, Raymond R.
2012-02-28
The similar cosmological abundances observed for visible and dark matter suggest a common origin for both. By viewing the dark matter density as a dark-sector asymmetry, mirroring the situation in the visible sector, we show that the visible and dark matter asymmetries may have arisen simultaneously through a first-order phase transition in the early universe. The additional scalar particles in the theory can mix with the standard Higgs boson and provide other striking signatures.
CMB and matter power spectra with non-linear dark-sector interactions
NASA Astrophysics Data System (ADS)
vom Marttens, R. F.; Casarini, L.; Hipólito-Ricaldi, W. S.; Zimdahl, W.
2017-01-01
An interaction between dark matter and dark energy, proportional to the product of their energy densities, results in a scaling behavior of the ratio of these densities with respect to the scale factor of the Robertson-Walker metric. This gives rise to a class of cosmological models which deviate from the standard model in an analytically tractable way. In particular, it becomes possible to quantify the role of potential dark-energy perturbations. We investigate the impact of this interaction on the structure formation process. Using the (modified) CAMB code we obtain the CMB spectrum as well as the linear matter power spectrum. It is shown that the strong degeneracy in the parameter space present in the background analysis is considerably reduced by considering Planck data. Our analysis is compatible with the ΛCDM model at the 2σ confidence level with a slightly preferred direction of the energy flow from dark matter to dark energy.
Dark solitons near potential and nonlinearity steps
NASA Astrophysics Data System (ADS)
Tsitoura, F.; Anastassi, Z. A.; Marzuola, J. L.; Kevrekidis, P. G.; Frantzeskakis, D. J.
2016-12-01
We study dark solitons near potential and nonlinearity steps and combinations thereof, forming rectangular barriers. This setting is relevant to the contexts of atomic Bose-Einstein condensates (where such steps can be realized by using proper external fields) and nonlinear optics (for beam propagation near interfaces separating optical media of different refractive indices). We use perturbation theory to develop an equivalent particle theory, describing the matter-wave or optical soliton dynamics as the motion of a particle in an effective potential. This Newtonian dynamical problem provides information for the soliton statics and dynamics, including scenarios of reflection, transmission, or quasitrapping at such steps. The case of multiple such steps and its connection to barrier potentials is additionally touched upon. The range of validity of the analytical approximation and radiation effects are also investigated. Our analytical predictions are found to be in very good agreement with the corresponding numerical results, where appropriate.
Testing Lorentz invariance of dark matter
Blas, Diego; Ivanov, Mikhail M.; Sibiryakov, Sergey E-mail: mm.ivanov@physics.msu.ru
2012-10-01
We study the possibility to constrain deviations from Lorentz invariance in dark matter (DM) with cosmological observations. Breaking of Lorentz invariance generically introduces new light gravitational degrees of freedom, which we represent through a dynamical timelike vector field. If DM does not obey Lorentz invariance, it couples to this vector field. We find that this coupling affects the inertial mass of small DM halos which no longer satisfy the equivalence principle. For large enough lumps of DM we identify a (chameleon) mechanism that restores the inertial mass to its standard value. As a consequence, the dynamics of gravitational clustering are modified. Two prominent effects are a scale dependent enhancement in the growth of large scale structure and a scale dependent bias between DM and baryon density perturbations. The comparison with the measured linear matter power spectrum in principle allows to bound the departure from Lorentz invariance of DM at the per cent level.
NASA Astrophysics Data System (ADS)
2003-06-01
Astronomers have used NASA's Chandra X-ray Observatory to make the most detailed probe yet of the distribution of dark matter in a massive cluster of galaxies. Their results indicate that about 80 percent of the matter in the universe consists of cold dark matter - mysterious subatomic particles left over from the dense early universe. Chandra observed a cluster of galaxies called Abell 2029 located about a billion light years from Earth. The cluster is composed of thousands of galaxies enveloped in a gigantic cloud of hot gas, and an amount of dark matter equivalent to more than a hundred trillion Suns. At the center of this cluster is an enormous, elliptically shaped galaxy that is thought to have been formed from the mergers of many smaller galaxies. The X-ray data show that the density of dark matter increases smoothly all the way into the central galaxy of the cluster. This discovery agrees with the predictions of cold dark matter models, and is contrary to other dark matter models that predict a leveling off of the amount of dark matter in the center of the cluster. "I was really surprised at how well we could measure the dark matter so deep into the core of a rich cluster," said Aaron Lewis of the University of California, Irvine, lead author of a paper describing the results in a recent issue of The Astrophysical Journal. "We still have very little idea as to the exact nature of these particles, but our results show that they must behave like cold dark matter." Cold dark matter gets its name from the assumption that the dark matter particles were moving slowly when galaxies and galaxy clusters began to form. Dark matter particles interact with each other and "normal" matter only through gravity. The astronomers' success in placing such tight constraints on the dark matter distribution was partly due to Chandra's ability to make a high resolution intensity and temperature map, and partly due to their choice of a target. The cluster and central galaxy are
Lincoln, Don
2016-07-12
After a century of study, scientists have come to the realization that the ordinary matter made of atoms is a minority in the universe. In order to explain observations, it appears that there exists a new and undiscovered kind of matter, called dark matter, that is five times more prevalent than ordinary matter. The evidence for this new matterâs existence is very strong, but scientists know only a little about its nature. In todayâs video, Fermilabâs Dr. Don Lincoln talks about an exciting and unconventional idea, specifically that dark matter might have a very complex set of structures and interactions. While this idea is entirely speculative, it is an interesting hypothesis and one that scientists are investigating.
Lincoln, Don
2015-04-16
After a century of study, scientists have come to the realization that the ordinary matter made of atoms is a minority in the universe. In order to explain observations, it appears that there exists a new and undiscovered kind of matter, called dark matter, that is five times more prevalent than ordinary matter. The evidence for this new matter’s existence is very strong, but scientists know only a little about its nature. In today’s video, Fermilab’s Dr. Don Lincoln talks about an exciting and unconventional idea, specifically that dark matter might have a very complex set of structures and interactions. While this idea is entirely speculative, it is an interesting hypothesis and one that scientists are investigating.
NASA Technical Reports Server (NTRS)
Friberg, P.; Hjalmarson, A.; Madden, S. C.; Irvine, W. M.
1988-01-01
The first observation of methanol in cold dark clouds TMC 1, L 134 N, and B 335 is reported. In all three clouds, the relative abundance of methanol was found to be in the range of 10 to the -9th (i.e., almost an order of magnitude more abundant than acetaldehyde), with no observable variation between the clouds. Methanol emission showed a complex velocity structure; in TMC 1, clear indications of non-LTE were observed. Dimethyl ether was searched for in L 134 N; the upper limit of the column density of dimethyl ether in L 134 N was estimated to be 4 x 10 to the 12th/sq cm, assuming 5 K rotation temperature and LTE. This limit makes the abundance ratio (CH3)2O/CH3OH not higher than 1/5, indicating that dimethyl ether is not overabundant in this dark cloud.
NASA Astrophysics Data System (ADS)
Doran, Rosa
2015-08-01
Creating awareness about the importance of the protection of our dark skies is the main goal of the Dark Skies Rangers project, a joint effort from the NOAO and the Galileo Teacher Training Program. Hundreds of schools and thousands of students have been reached by this program. We will focus in particular on the experience being developed in Portugal where several municipalities have now received street light auditing produced by students with suggestions on how to enhance the energy efficiency of illumination of specific urban areas. In the International Year of Light we are investing our efforts in exporting the successful Portuguese experience to other countries. The recipe is simple: train teachers, engage students, foster the participation of local community and involve local authorities in the process. In this symposium we hope to draft the cookbook for the near future.
NASA Technical Reports Server (NTRS)
2007-01-01
Using the unique orbit of NASA's Spitzer Space Telescope and a depth-perceiving trick called parallax, astronomers have determined the distance to an invisible Milky Way object called OGLE-2005-SMC-001. This artist's concept illustrates how this trick works: different views from both Spitzer and telescopes on Earth are combined to give depth perception.
Our Milky Way galaxy is heavier than it looks, and scientists use the term 'dark matter' to describe all the 'heavy stuff' in the universe that seems to be present but invisible to our telescopes. While much of this dark matter is likely made up of exotic materials, different from the ordinary particles that make up the world around us, some may consist of dark celestial bodies -- like planets, black holes, or failed stars -- that do not produce light or are too faint to detect from Earth. OGLE-2005-SMC-001 is one of these dark celestial bodies.
Although astronomers cannot see a dark body, they can sense its presence from the way light acts around it. When a dark body like OGLE-2005-SMC-001 passes in front of a bright star, its gravity causes the background starlight to bend and brighten, a process called gravitational microlensing. When the observing telescope, dark body, and star system are closely aligned, the microlensing event reaches maximum, or peak, brightness.
A team of astronomers first sensed OGLE-2005-SMC-001's presence when it passed in front of a star in a neighboring satellite galaxy called the Small Magellanic Cloud. In this artist's rendering, the satellite galaxy is depicted as the fuzzy structure sitting to the left of Earth. Once they detected this microlensing event, the scientists used Spitzer and the principle of parallax to figure out its distance. Humans naturally use parallax to determine distance. Each eye sees the distance of an object differently. The brain takes each eye's perspective and instantaneously calculates how far away the object is.
To determine OGLE
Zurek, Kathryn M.
2008-11-01
We explore multi-component dark matter models where the dark sector consists of multiple stable states with different mass scales, and dark forces coupling these states further enrich the dynamics. The multi-component nature of the dark matter naturally arises in supersymmetric models, where both R parity and an additional symmetry, such as a Z{sub 2}, is preserved. We focus on a particular model where the heavier component of dark matter carries lepton number and annihilates mostly to leptons. The heavier component, which is essentially a sterile neutrino, naturally explains the PAMELA, ATIC and synchrotron signals, without an excess in antiprotons which typically mars other models of weak scale dark matter. The lighter component, which may have a mass from a GeV to a TeV, may explain the DAMA signal, and may be visible in low threshold runs of CDMS and XENON, which search for light dark matter.
Copeland, Edmund J.
2007-11-20
I briefly review attempts that have been made to model dark energy. These include models of a cosmological constant, dynamical models where a scalar field may be responsible for the observed late time acceleration through to the possibility that we are not fully in control of the gravity sector and the acceleration may be some manifestation of modified gravity. In all cases we will see some degree of fine tuning is required with the current models.
NASA Astrophysics Data System (ADS)
McFarlane, Ursuka
2004-06-01
The Waharau Dark Sky weekend event, organized by Keith Edwards and Dean Jonkers of the Auckland Astronomical Society, happens at least twice a year, and is not to be missed. The event isn't catered, there are no speakers or lectures, it's not even organized chaos. It is a weekend of relaxation in the company of like-minded friends, exploring the night skies, checking out the latest skywatching tools, and having fun.
2016-01-01
Abstract Significant literature has an impact on the reader. Reading the novella Heart of Darkness by Joseph Conrad as a young boy rose emotions comparable to those I felt when losing a patient after percutaneous nephrolithotomy (PCNL) as a grown up. The case of a 37-year-old woman with bilateral staghorn and a fatal outcome after PCNL is presented and alternatives are discussed. PMID:27868094
Chamorro-Posada, P; McDonald, G S
2003-05-15
A general dark-soliton solution of the Helmholtz equation (with defocusing Kerr nonlinearity) that has on- and off-axis, gray and black, paraxial and Helmholtz solitons as particular solutions, is reported. Modifications to soliton transverse velocity, width, phase period, and existence conditions are derived and explained in geometrical terms. Simulations verify analytical predictions and also demonstrate spontaneous formation of Helmholtz solitons and transparency of their interactions.
Gurwich, Ilya
2010-06-23
1 construct a general description for neutrino dark energy models, that do not require exotic particles or strange couplings. With the help of the above, this class of models is reduced to a single function with several constraints. It is shown that these models lead to some concrete predictions that can be verified (or disproved) within the next decade, using results from PLANK, EUCLID and JDEM.
Transient gravity perturbations from a double-couple in a homogeneous half-space
NASA Astrophysics Data System (ADS)
Harms, J.
2016-05-01
Seismic waves produced by fault ruptures give rise to gravity perturbations. So far, these perturbations have either been modelled as permanent coseismic gravity change in a half-space or spherical Earth model, or as full time-domain model in infinite space. In this paper, we present the explicit solution of gravity perturbations in time domain produced by a double-couple buried in a homogeneous half-space. This result is especially suited to study gravity perturbations up to a few hundreds of kilometres from the epicentre. It facilitates detailed parametric studies of gravity perturbations from fault rupture, and predicts gravity perturbations of real earthquakes with greatly improved accuracy. The results may serve to develop first designs of gravity-assisted earthquake early-warning systems, made possible by a new generation of ultrasensitive gravity gradiometers, which is currently under development.
Dark matter as a trigger for periodic comet impacts.
Randall, Lisa; Reece, Matthew
2014-04-25
Although statistical evidence is not overwhelming, possible support for an approximately 35×106 yr periodicity in the crater record on Earth could indicate a nonrandom underlying enhancement of meteorite impacts at regular intervals. A proposed explanation in terms of tidal effects on Oort cloud comet perturbations as the Solar System passes through the galactic midplane is hampered by lack of an underlying cause for sufficiently enhanced gravitational effects over a sufficiently short time interval and by the time frame between such possible enhancements. We show that a smooth dark disk in the galactic midplane would address both these issues and create a periodic enhancement of the sort that has potentially been observed. Such a disk is motivated by a novel dark matter component with dissipative cooling that we considered in earlier work. We show how to evaluate the statistical evidence for periodicity by input of appropriate measured priors from the galactic model, justifying or ruling out periodic cratering with more confidence than by evaluating the data without an underlying model. We find that, marginalizing over astrophysical uncertainties, the likelihood ratio for such a model relative to one with a constant cratering rate is 3.0, which moderately favors the dark disk model. Our analysis furthermore yields a posterior distribution that, based on current crater data, singles out a dark matter disk surface density of approximately 10M⊙/pc2. The geological record thereby motivates a particular model of dark matter that will be probed in the near future.
Dark matter and leptogenesis linked by classical scale invariance
NASA Astrophysics Data System (ADS)
Khoze, Valentin V.; Plascencia, Alexis D.
2016-11-01
In this work we study a classically scale invariant extension of the Standard Model that can explain simultaneously dark matter and the baryon asymmetry in the universe. In our set-up we introduce a dark sector, namely a non-Abelian SU(2) hidden sector coupled to the SM via the Higgs portal, and a singlet sector responsible for generating Majorana masses for three right-handed sterile neutrinos. The gauge bosons of the dark sector are mass-degenerate and stable, and this makes them suitable as dark matter candidates. Our model also accounts for the matter-anti-matter asymmetry. The lepton flavour asymmetry is produced during CP-violating oscillations of the GeV-scale right-handed neutrinos, and converted to the baryon asymmetry by the electroweak sphalerons. All the characteristic scales in the model: the electro-weak, dark matter and the leptogenesis/neutrino mass scales, are generated radiatively, have a common origin and related to each other via scalar field couplings in perturbation theory.
ℤ{sub 3} scalar singlet dark matter
Bélanger, Geneviève; Kannike, Kristjan; Pukhov, Alexander; Raidal, Martti E-mail: kristjan.kannike@cern.ch E-mail: martti.raidal@cern.ch
2013-01-01
We consider the minimal scalar singlet dark matter stabilised by a ℤ{sub 3} symmetry. Due to the cubic term in the scalar potential, semi-annihilations, besides annihilations, contribute to the dark matter relic density. Unlike in the ℤ{sub 2} case, the dark matter spin independent direct detection cross section is no more linked to the annihilation cross section. We study the extrema of the potential and show that a too large cubic term would break the ℤ{sub 3} symmetry spontaneously, implying a lower bound on the direct detection cross section, and allowing the whole parameter space to be tested by XENON1T. In a small region of the parameter space the model can avoid the instability of the standard model vacuum up to the unification scale. If the semi-annihilations are large, however, new physics will be needed at TeV scale because the model becomes non-perturbative. The singlet dark matter mass cannot be lower than 53.8 GeV due to the constraint from Higgs boson decay into dark matter.
Dai, D.-C.; Stojkovic, Dejan; Dutta, Sourish
2009-09-15
We examine a dark energy model where a scalar unparticle degree of freedom plays the role of quintessence. In particular, we study a model where the unparticle degree of freedom has a standard kinetic term and a simple mass potential, the evolution is slowly rolling and the field value is of the order of the unparticle energy scale ({lambda}{sub u}). We study how the evolution of w depends on the parameters B (a function of unparticle scaling dimension d{sub u}), the initial value of the field {phi}{sub i} (or equivalently, {lambda}{sub u}) and the present matter density {omega}{sub m0}. We use observational data from type Ia supernovae, baryon acoustic oscillations and the cosmic microwave background to constrain the model parameters and find that these models are not ruled out by the observational data. From a theoretical point of view, unparticle dark energy model is very attractive, since unparticles (being bound states of fundamental fermions) are protected from radiative corrections. Further, coupling of unparticles to the standard model fields can be arbitrarily suppressed by raising the fundamental energy scale M{sub F}, making the unparticle dark energy model free of most of the problems that plague conventional scalar field quintessence models.
Rodríguez-Villalón, Antía; Gas, Elisabet
2009-01-01
Carotenoids are plastidial isoprenoid pigments essential for plant life. High carotenoid levels are found in chloroplasts and chromoplasts, but they are also produced in the etioplasts of seedlings that germinate in the dark. Our recent work has shown that an enhanced production of carotenoids in plastids of dark-grown Arabidopsis thaliana seedlings results in an improved transition to photosynthetic development (greening) upon illumination, illustrating the relevance of regulating etioplast carotenoid biosynthesis for plant fitness. We showed that the biosynthesis of etioplast carotenoids is controlled at the level of phytoene synthase (PSY), the enzyme catalyzing the first committed step of the pathway. Upregulation of PSY is necessary and sufficient to increase the production of carotenoids in dark-grown seedlings, in part because it triggers a feedback mechanism leading to the post-transcriptional accumulation of flux-controlling enzymes of the methylerythritol 4-phosphate (MEP) pathway, which synthesizes the substrates for PSY activity. Based on these and other recent data on the molecular mechanisms controlling deetiolation, we propose a model for the regulation of carotenoid biosynthesis in etioplasts. PMID:19826226
Zhao, HongSheng; Taylor, James E.; Silk, Joseph; Hooper, Dan; /Oxford U. /Fermilab
2005-08-01
Earth-mass dark matter halos are likely to have been the first bound structures to form in the Universe. Whether such objects have survived to the present day in galaxies depends on, among other factors, the rate of encounters with normal stars. In this letter, we estimate the amount of tidal heating and mass loss in microhalos as a result of stellar encounters. We find that while microhalos are only mildly heated in dwarf galaxies of low stellar density, and they should have been completely destroyed in bulge or M32-like regions of high stellar density. In disk galaxies, such as the Milky Way, the disruption rate depends strongly on the orbital parameters of the microhalo; while stochastic radial orbits in triaxial Galactic potential are destroyed first, systems on non-planar retrograde orbits with large pericenters survive the longest. Since many microhalos lose a significant fraction of their material to unbound tidal streams, the final dark matter distribution in the solar neighborhood is better described as a superposition of microstreams rather than as a set of discrete spherical clumps in an otherwise homogeneous medium. Different morphologies of microhalos have implications for direct and indirect dark matter detection experiments.
Stealth dark matter: Dark scalar baryons through the Higgs portal
NASA Astrophysics Data System (ADS)
Appelquist, T.; Brower, R. C.; Buchoff, M. I.; Fleming, G. T.; Jin, X.-Y.; Kiskis, J.; Kribs, G. D.; Neil, E. T.; Osborn, J. C.; Rebbi, C.; Rinaldi, E.; Schaich, D.; Schroeder, C.; Syritsyn, S.; Vranas, P.; Weinberg, E.; Witzel, O.; Lattice Strong Dynamics LSD Collaboration
2015-10-01
We present a new model of stealth dark matter: a composite baryonic scalar of an S U (ND) strongly coupled theory with even ND≥4 . All mass scales are technically natural, and dark matter stability is automatic without imposing an additional discrete or global symmetry. Constituent fermions transform in vectorlike representations of the electroweak group that permit both electroweak-breaking and electroweak-preserving mass terms. This gives a tunable coupling of stealth dark matter to the Higgs boson independent of the dark matter mass itself. We specialize to S U (4 ), and investigate the constraints on the model from dark meson decay, electroweak precision measurements, basic collider limits, and spin-independent direct detection scattering through Higgs exchange. We exploit our earlier lattice simulations that determined the composite spectrum as well as the effective Higgs coupling of stealth dark matter in order to place bounds from direct detection, excluding constituent fermions with dominantly electroweak-breaking masses. A lower bound on the dark baryon mass mB≳300 GeV is obtained from the indirect requirement that the lightest dark meson not be observable at LEP II. We briefly survey some intriguing properties of stealth dark matter that are worthy of future study, including collider studies of dark meson production and decay; indirect detection signals from annihilation; relic abundance estimates for both symmetric and asymmetric mechanisms; and direct detection through electromagnetic polarizability, a detailed study of which will appear in a companion paper.
Numerical Relativity as a tool for studying the Early Universe
NASA Astrophysics Data System (ADS)
Garrison, David
2013-04-01
Numerical simulations are becoming a more effective tool for conducting detailed investigations into the evolution of our universe. In this presentation, I show how the framework of numerical relativity can be used for studying cosmological models. We are working to develop a large-scale simulation of the dynamical processes in the early universe. These take into account interactions of dark matter, scalar perturbations, gravitational waves, magnetic fields and a turbulent plasma. The code described in this report is a GRMHD code based on the Cactus framework and is structured to utilize one of several different differencing methods chosen at run-time. It is being developed and tested on the Texas Learning and Computation Center's Xanadu cluster.
CTE characterization with post-flashed darks
NASA Astrophysics Data System (ADS)
Anderson, Jay
2013-10-01
This internal-orbit calibration program will take a combination of short {100s} and long {800s} darks with various levels of post-flash in order to re-calibrate the WFC3/UVIS CTE model. When a similar set of these images was taken in mid-2012, there were not as many warm pixels as there are now and CTE losses were lower. Furthermore, this program will explore a finer spacing of charge injection to help us understand exactly what happens above the "sweet-spot" background of 12 electrons. Once the model is recalibrated using this data set {which should be taken in early 2014}, we can feel confident in making the pixel-based correction part of the pipeline.The observations will be straightforward. We will take short 100s darks with PF levels of: 0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100, 115, and 130, and 150 electrons -- 30 levels in all. We will also take 800s darks {can't fit longer} with a PF level of about 100e. We should be able to take two shorts and one deep in each orbit, this will take a total of 15 orbits. This will give us 15 long darks, which can be averaged together to get the noise down.It would be best if this program could be scheduled to be executed over the course of only a few days, since I would prefer not to have much change in the dark during acquisition of the data set.
Axion dark matter: strings and their cores
Fleury, Leesa; Moore, Guy D.
2016-01-04
Axions constitute a well-motivated dark matter candidate, and if PQ symmetry breaking occurred after inflation, it should be possible to make a clean prediction for the relation between the axion mass and the axion dark matter density. We show that axion (or other global) string networks in 3D have a network density that depends logarithmically on the string separation-to-core ratio. This logarithm would be about 10 times larger in axion cosmology than what we can achieve in numerical simulations. We simulate axion production in the early Universe, finding that, for the separation-to-core ratios we can achieve, the changing density of the network has little impact on the axion production efficiency.
Axion dark matter: strings and their cores
Fleury, Leesa; Moore, Guy D. E-mail: guy.moore@physik.tu-darmstadt.de
2016-01-01
Axions constitute a well-motivated dark matter candidate, and if PQ symmetry breaking occurred after inflation, it should be possible to make a clean prediction for the relation between the axion mass and the axion dark matter density. We show that axion (or other global) string networks in 3D have a network density that depends logarithmically on the string separation-to-core ratio. This logarithm would be about 10 times larger in axion cosmology than what we can achieve in numerical simulations. We simulate axion production in the early Universe, finding that, for the separation-to-core ratios we can achieve, the changing density of the network has little impact on the axion production efficiency.
How dark matter came to matter
NASA Astrophysics Data System (ADS)
de Swart, J. G.; Bertone, G.; van Dongen, J.
2017-03-01
The history of the dark matter problem can be traced back to at least the 1930s, but it was not until the early 1970s that the issue of 'missing matter' was widely recognized as problematic. In the latter period, previously separate issues involving missing mass were brought together in a single anomaly. We argue that reference to a straightforward accumulation of evidence alone is inadequate to comprehend this episode. Rather, the rise of cosmological research, the accompanying renewed interest in the theory of relativity and changes in the manpower division of astronomy in the 1960s are key to understanding how dark matter came to matter. At the same time, this story may also enlighten us on the methodological dimensions of past practices of physics and cosmology.
Bound-state formation for thermal relic dark matter and unitarity
Harling, Benedict von; Petraki, Kalliopi E-mail: kpetraki@nikhef.nl
2014-12-01
We show that the relic abundance of thermal dark matter annihilating via a long-range interaction, is significantly affected by the formation and decay of dark matter bound states in the early universe, if the dark matter mass is above a few TeV . We determine the coupling required to obtain the observed dark matter density, taking into account both the direct 2-to-2 annihilations and the formation of bound states, and provide an analytical fit. We argue that the unitarity limit on the inelastic cross-section is realized only if dark matter annihilates via a long-range interaction, and we determine the upper bound on the mass of thermal-relic dark matter to be about 197 (139) TeV for (non)-self-conjugate dark matter.
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.
The natural and perturbed troposphere
NASA Technical Reports Server (NTRS)
Stewart, R. W.; Hameed, S.; Pinto, J.
1978-01-01
A quantitative assessment of the chemical and climatic effects of industrial emissions into the atmosphere requires an understanding of the complex interactions of species within the atmosphere and of the atmosphere with other physical systems such as the oceans, lithosphere, and biosphere. The concentration of a particular species is determined by competition between various production and loss processes. The abundances of tropospheric gases are examined. The reactions of the members of the oxygen group are considered along with the models which have been developed to describe the involved relationships. Attention is also given to the natural carbon cycle, perturbations to the carbon cycle, the natural nitrogen cycle, perturbations to the nitrogen cycle, the hydrogen group, the sulfur group, and the halogen group.
BRST quantization of cosmological perturbations
NASA Astrophysics Data System (ADS)
Armendariz-Picon, Cristian; Şengör, Gizem
2016-11-01
BRST quantization is an elegant and powerful method to quantize theories with local symmetries. In this article we study the Hamiltonian BRST quantization of cosmological perturbations in a universe dominated by a scalar field, along with the closely related quantization method of Dirac. We describe how both formalisms apply to perturbations in a time-dependent background, and how expectation values of gauge-invariant operators can be calculated in the in-in formalism. Our analysis focuses mostly on the free theory. By appropriate canonical transformations we simplify and diagonalize the free Hamiltonian. BRST quantization in derivative gauges allows us to dramatically simplify the structure of the propagators, whereas Dirac quantization, which amounts to quantization in synchronous gauge, dispenses with the need to introduce ghosts and preserves the locality of the gauge-fixed action.
Cosmological perturbations in unimodular gravity
Gao, Caixia; Brandenberger, Robert H.; Cai, Yifu; Chen, Pisin E-mail: rhb@hep.physics.mcgill.ca E-mail: chen@slac.stanford.edu
2014-09-01
We study cosmological perturbation theory within the framework of unimodular gravity. We show that the Lagrangian constraint on the determinant of the metric required by unimodular gravity leads to an extra constraint on the gauge freedom of the metric perturbations. Although the main equation of motion for the gravitational potential remains the same, the shift variable, which is gauge artifact in General Relativity, cannot be set to zero in unimodular gravity. This non-vanishing shift variable affects the propagation of photons throughout the cosmological evolution and therefore modifies the Sachs-Wolfe relation between the relativistic gravitational potential and the microwave temperature anisotropies. However, for adiabatic fluctuations the difference between the result in General Relativity and unimodular gravity is suppressed on large angular scales. Thus, no strong constraints on the theory can be derived.
BRST quantization of cosmological perturbations
Armendariz-Picon, Cristian; Şengör, Gizem
2016-11-08
BRST quantization is an elegant and powerful method to quantize theories with local symmetries. In this article we study the Hamiltonian BRST quantization of cosmological perturbations in a universe dominated by a scalar field, along with the closely related quantization method of Dirac. We describe how both formalisms apply to perturbations in a time-dependent background, and how expectation values of gauge-invariant operators can be calculated in the in-in formalism. Our analysis focuses mostly on the free theory. By appropriate canonical transformations we simplify and diagonalize the free Hamiltonian. BRST quantization in derivative gauges allows us to dramatically simplify the structure of the propagators, whereas Dirac quantization, which amounts to quantization in synchronous gauge, dispenses with the need to introduce ghosts and preserves the locality of the gauge-fixed action.
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
R evolution: Improving perturbative QCD
Hoang, Andre H.; Jain, Ambar; Stewart, Iain W.; Scimemi, Ignazio
2010-07-01
Perturbative QCD results in the MS scheme can be dramatically improved by switching to a scheme that accounts for the dominant power law dependence on the factorization scale in the operator product expansion. We introduce the ''MSR scheme'' which achieves this in a Lorentz and gauge invariant way and has a very simple relation to MS. Results in MSR depend on a cutoff parameter R, in addition to the {mu} of MS. R variations can be used to independently estimate (i.) the size of power corrections, and (ii.) higher-order perturbative corrections (much like {mu} in MS). We give two examples at three-loop order, the ratio of mass splittings in the B*-B and D*-D systems, and the Ellis-Jaffe sum rule as a function of momentum transfer Q in deep inelastic scattering. Comparing to data, the perturbative MSR results work well even for Q{approx}1 GeV, and power corrections are reduced compared to MS.
Perturbation growth in accreting filaments
NASA Astrophysics Data System (ADS)
Clarke, S. D.; Whitworth, A. P.; Hubber, D. A.
2016-05-01
We use smoothed particle hydrodynamic simulations to investigate the growth of perturbations in infinitely long filaments as they form and grow by accretion. The growth of these perturbations leads to filament fragmentation and the formation of cores. Most previous work on this subject has been confined to the growth and fragmentation of equilibrium filaments and has found that there exists a preferential fragmentation length-scale which is roughly four times the filament's diameter. Our results show a more complicated dispersion relation with a series of peaks linking perturbation wavelength and growth rate. These are due to gravo-acoustic oscillations along the longitudinal axis during the sub-critical phase of growth. The positions of the peaks in growth rate have a strong dependence on both the mass accretion rate onto the filament and the temperature of the gas. When seeded with a multiwavelength density power spectrum, there exists a clear preferred core separation equal to the largest peak in the dispersion relation. Our results allow one to estimate a minimum age for a filament which is breaking up into regularly spaced fragments, as well as an average accretion rate. We apply the model to observations of filaments in Taurus by Tafalla & Hacar and find accretion rates consistent with those estimated by Palmeirim et al.
Dark Forces and Dark Matter in a Hidden Sector
NASA Astrophysics Data System (ADS)
Andreas, Sarah
2012-01-01
Hidden sectors in connection with GeV-scale dark forces and dark matter are not only a common feature of physics beyond the Standard Model such as string theory and SUSY but are also phenomenologically of great interest regarding recent astrophysical observations. The hidden photon in particular is also searched for and constrained by laboratory experiments, the current status of which will be presented here. Furthermore, several models of hidden sectors containing in addition a dark matter particle will be examined regarding their consistency with the dark matter relic abundance and direct detection experiments.
The dark cube: dark and light character profiles.
Garcia, Danilo; Rosenberg, Patricia
2016-01-01
Background. Research addressing distinctions and similarities between people's malevolent character traits (i.e., the Dark Triad: Machiavellianism, narcissism, and psychopathy) has detected inconsistent linear associations to temperament traits. Additionally, these dark traits seem to have a common core expressed as uncooperativeness. Hence, some researchers suggest that the dark traits are best represented as one global construct (i.e., the unification argument) rather than as ternary construct (i.e., the uniqueness argument). We put forward the dark cube (cf. Cloninger's character cube) comprising eight dark profiles that can be used to compare individuals who differ in one dark character trait while holding the other two constant. Our aim was to investigate in which circumstances individuals who are high in each one of the dark character traits differ in Cloninger's "light" character traits: self-directedness, cooperativeness, and self-transcendence. We also investigated if people's dark character profiles were associated to their light character profiles. Method. A total of 997 participants recruited from Amazon's Mechanical Turk (MTurk) responded to the Short Dark Triad and the Short Character Inventory. Participants were allocated to eight different dark profiles and eight light profiles based on their scores in each of the traits and any possible combination of high and low scores. We used three-way interaction regression analyses and t-tests to investigate differences in light character traits between individuals with different dark profiles. As a second step, we compared the individuals' dark profile with her/his character profile using an exact cell-wise analysis conducted in the ROPstat software (http://www.ropstat.com). Results. Individuals who expressed high levels of Machiavellianism and those who expressed high levels of psychopathy also expressed low self-directedness and low cooperativeness. Individuals with high levels of narcissism, in contrast
Tompson, Lisa
2013-01-01
Objectives: Test the influence of darkness in the street robbery crime event alongside temperature. Methods: Negative binomial regression models tested darkness and temperature as predictors of street robbery. Units of analysis were four 6-hr time intervals in two U.K. study areas that have different levels of darkness and variations of temperature throughout the year. Results: Darkness is a key factor related to robbery events in both study areas. Traversing from full daylight to full darkness increased the predicted volume of robbery by a multiple of 2.6 in London and 1.2 in Glasgow. Temperature was significant only in the London study area. Interaction terms did not enhance the predictive power of the models. Conclusion: Darkness is an important driving factor in seasonal variation of street robbery. A further implication of the research is that time of the day patterns are crucial to understanding seasonal trends in crime data. PMID:25076797
NASA Astrophysics Data System (ADS)
Davini, S.; Agnes, P.; Agostino, L.; Albuquerque, I. F. M.; Alexander, T.; Alton, A. K.; Arisaka, K.; Back, H. O.; Baldin, B.; Biery, K.; Bonfini, G.; Bossa, M.; Bottino, B.; Brigatti, A.; Brodsky, J.; Budano, F.; Bussino, S.; Cadeddu, M.; Cadonati, L.; Cadoni, M.; Calaprice, F.; Canci, N.; Candela, A.; Cao, H.; Cariello, M.; Carlini, M.; Catalanotti, S.; Cavalcante, P.; Chepurnov, A.; Cocco, A. G.; Covone, G.; D'Angelo, D.; D'Incecco, M.; De Cecco, S.; De Deo, M.; De Vincenzi, M.; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, G.; Edkins, E.; Empl, A.; Fan, A.; Fiorillo, G.; Fomenko, K.; Foster, G.; Franco, D.; Gabriele, F.; Galbiati, C.; Giganti, C.; Goretti, A. M.; Granato, F.; Grandi, L.; Gromov, M.; Guan, M.; Guardincerri, Y.; Hackett, B. R.; Herner, K. R.; Hungerford, E. V.; Ianni, Aldo; Ianni, Andrea; James, I.; Jollet, C.; Keeter, K.; Kendziora, C. L.; Kobychev, V.; Koh, G.; Korablev, D.; Korga, G.; Kubankin, A.; Li, X.; Lissia, M.; Lombardi, P.; Luitz, S.; Ma, Y.; Machulin, I. N.; Mandarano, A.; Mari, S. M.; Maricic, J.; Marini, L.; Martoff, C. J.; Meregaglia, A.; Meyers, P. D.; Miletic, T.; Milincic, R.; Montanari, D.; Monte, A.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B. J.; Muratova, V. N.; Musico, P.; Napolitano, J.; Orsini, M.; Ortica, F.; Pagani, L.; Pallavicini, M.; Pantic, E.; Parmeggiano, S.; Pelczar, K.; Pelliccia, N.; Perasso, S.; Pocar, A.; Pordes, S.; Pugachev, D. A.; Qian, H.; Randle, K.; Ranucci, G.; Razeto, A.; Reinhold, B.; Renshaw, A. L.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Sablone, D.; Saggese, P.; Saldanha, R.; Sands, W.; Sangiorgio, S.; Savarese, C.; Segreto, E.; Semenov, D. A.; Shields, E.; Singh, P. N.; Skorokhvatov, M. D.; Smirnov, O.; Sotnikov, A.; Stanford, C.; Suvorov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Tonazzo, A.; Trinchese, P.; Unzhakov, E. V.; Vishneva, A.; Vogelaar, B.; Wada, M.; Walker, S.; Wang, H.; Wang, Y.; Watson, A. W.; Westerdale, S.; Wilhelmi, J.; Wojcik, M. M.; Xiang, X.; Xu, J.; Yang, C.; Yoo, J.; Zavatarelli, S.; Zec, A.; Zhong, W.; Zhu, C.; Zuzel, G.
2016-05-01
The DarkSide program at LNGS aims to perform background-free WIMP searches using two phase liquid argon time projection chambers, with the ultimate goal of covering all parameters down to the so-called neutrino floor. One of the distinct features of the program is the use of underground argon with has a reduced content of the radioactive 39Ar compared to atmospheric argon. The DarkSide Collaboration is currently operating the DarkSide-50 experiment, the first such WIMP detector using underground argon. Operations with underground argon indicate a suppression of 39Ar by a factor (1.4 ± 0.2) × 103 relative to atmospheric argon. The new results obtained with DarkSide-50 and the plans for the next steps of the DarkSide program, the 20t fiducial mass DarkSide-20k detector and the 200 t fiducial Argo, are reviewed in this proceedings.
NASA Astrophysics Data System (ADS)
Davini, Stefano
2014-04-01
A wide range of astrophysical measurements evidence that the stars and gas in all galaxies are immersed in a much larger cloud of non-luminous and non-baryonic dark matter. The nature of the dark matter is still totally unknown, and the resolution of the dark matter puzzle is of fundamental importance to cosmology, astrophysics, and elementary particle physics. One of the major lines of researches directing their efforts at detection of dark matter is direct searches of Weakly Interacting Massive Particles (WIMPs) with detectors operated in deep underground laboratories. The new generation of direct searches of WIMPs promises to probe the most interesting region of parameters for the dark matter candidates. I will review and describe the DarkSide-50 underground Argon detector at Laboratori Nazionali del Gran Sasso.
Review of dark photon searches
NASA Astrophysics Data System (ADS)
Denig, Achim
2016-11-01
Dark Photons are hypothetical extra-U(1) gauge bosons, which are motivated by a number of astrophysical anomalies as well as the presently seen deviation between the Standard Model prediction and the direct measurement of the anomalous magnetic moment of the muon, (g - 2)μ. The Dark Photon does not serve as the Dark Matter particle itself, but acts as a messenger particle of a hypothetical Dark Sector with residual interaction to the Standard Model. We review recent Dark Photon searches, which were carried out in a global effort at various hadron and particle physics facilities. We also comment on the perspectives for future invisble searches, which directly probe the existence of Light Dark Matter particles.
NASA Astrophysics Data System (ADS)
Abrahamse, Augusta
2010-12-01
Future advances in cosmology will depend on the next generation of cosmological observations and how they shape our theoretical understanding of the universe. Current theoretical ideas, however, have an important role to play in guiding the design of such observational programs. The work presented in this thesis concerns the intersection of observation and theory, particularly as it relates to advancing our understanding of the accelerated expansion of the universe (or the dark energy). Chapters 2 - 4 make use of the simulated data sets developed by the Dark Energy Task Force (DETF) for a number of cosmological observations currently in the experimental pipeline. We use these forecast data in the analysis of four quintessence models of dark energy: the PNGB, Exponential, Albrecht-Skordis and Inverse Power Law (IPL) models. Using Markov Chain Monte Carlo sampling techniques we examine the ability of each simulated data set to constrain the parameter space of these models. We examine the potential of the data for differentiating time-varying models from a pure cosmological constant. Additionally, we introduce an abstract parameter space to facilitate comparison between models and investigate the ability of future data to distinguish between these quintessence models. In Chapter 5 we present work towards understanding the effects of systematic errors associated with photometric redshift estimates. Due to the need to sample a vast number of deep and faint galaxies, photometric redshifts will be used in a wide range of future cosmological observations including gravitational weak lensing, baryon accoustic oscillations and type 1A supernovae observations. The uncertainty in the redshift distributions of galaxies has a significant potential impact on the cosmological parameter values inferred from such observations. We introduce a method for parameterizing uncertainties in modeling assumptions affecting photometric redshift calculations and for propagating these
Geometric Hamiltonian structures and perturbation theory
Omohundro, S.
1984-08-01
We have been engaged in a program of investigating the Hamiltonian structure of the various perturbation theories used in practice. We describe the geometry of a Hamiltonian structure for non-singular perturbation theory applied to Hamiltonian systems on symplectic manifolds and the connection with singular perturbation techniques based on the method of averaging.
NASA Technical Reports Server (NTRS)
2005-01-01
20 January 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, acquired during northern summer in December 2004, shows dark, windblown sand dunes in the north polar region of Mars. A vast sea of sand dunes nearly surrounds the north polar cap. These landforms are located near 80.3oN, 144.1oW. Light-toned features in the image are exposures of the substrate that underlies the dune field. The image covers an area about 3 km (1.9 mi) wide and is illuminated by sunlight from the lower left.
Chapline, G
2005-03-08
Event horizons and closed time-like curves cannot exist in the real world for the simple reason that they are inconsistent with quantum mechanics. Following ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago, and the speaker it is now possible to describe in some detail what happens physically when one approaches and crosses a region of space-time where classical general relativity predicts there should be an infinite red shift surface. This quantum critical physics provides a new perspective on a variety of enigmatic astrophysical phenomena including supernovae explosions, gamma ray bursts, positron emission, and dark matter.
Yoo, Jonghee; /Fermilab
2009-12-01
Dark matter is hypothetical matter which does not interact with electromagnetic radiation. The existence of dark matter is only inferred from gravitational effects of astrophysical observations to explain the missing mass component of the Universe. Weakly Interacting Massive Particles are currently the most popular candidate to explain the missing mass component. I review the current status of experimental searches of dark matter through direct detection using terrestrial detectors.
BOOK REVIEW Dark Energy: Theory and Observations Dark Energy: Theory and Observations
NASA Astrophysics Data System (ADS)
Faraoni, Valerio
2011-02-01
The 1998 discovery of what seems an acceleration of the cosmic expansion was made using type Ia supernovae and was later confirmed by other cosmological observations. It has made a huge impact on cosmology, prompting theoreticians to explain the observations and introducing the concept of dark energy into modern physics. A vast literature on dark energy and its alternatives has appeared since then, and this is the first comprehensive book devoted to the subject. This book is addressed to an advanced audience comprising graduate students and researchers in cosmology. Although it contains forty four fully solved problems and the first three chapters are rather introductory, they do not constitute a self-consistent course in cosmology and this book assumes graduate level knowledge of cosmology and general relativity. The fourth chapter focuses on observations, while the rest of this book addresses various classes of models proposed, including the cosmological constant, quintessence, k-essence, phantom energy, coupled dark energy, etc. The title of this book should not induce the reader into believing that only dark energy models are addressed—the authors devote two chapters to discussing conceptually very different approaches alternative to dark energy, including ƒ(R) and Gauss-Bonnet gravity, braneworld and void models, and the backreaction of inhomogeneities on the cosmic dynamics. Two chapters contain a general discussion of non-linear cosmological perturbations and statistical methods widely applicable in cosmology. The final chapter outlines future perspectives and the most likely lines of observational research on dark energy in the future. Overall, this book is carefully drafted, well presented, and does a good job of organizing the information available in the vast literature. The reader is pointed to the essential references and guided in a balanced way through the various proposals aimied at explaining the cosmological observations. Not all classes of
Slow-roll suppression of adiabatic instabilities in coupled scalar field-dark matter models
Corasaniti, Pier Stefano
2008-10-15
We study the evolution of linear density perturbations in the context of interacting scalar field-dark matter cosmologies, where the presence of the coupling acts as a stabilization mechanism for the runaway behavior of the scalar self-interaction potential as in the case of the chameleon model. We show that, in the 'adiabatic' background regime of the system, the rise of unstable growing modes of the perturbations is suppressed by the slow-roll dynamics of the field. Furthermore, the coupled system behaves as an inhomogeneous adiabatic fluid. In contrast, instabilities may develop for large values of the coupling constant, or along nonadiabatic solutions, characterized by a period of high-frequency dumped oscillations of the scalar field. In the latter case, the dynamical instabilities of the field fluctuations, which are typical of oscillatory scalar field regimes, are amplified and transmitted by the coupling to dark matter perturbations.
Dark Matter, Waves, and Identification
NASA Astrophysics Data System (ADS)
Wagner, Orvin
2011-10-01
In 1994 I wrote article for Physics Essays (Waves in Dark Matter) showing how the solar system is organized and stabilized by dark matter standing waves from the dark matter oscillating sun. Wave velocity is apparently inversely proportional to the square root of the dark matter density. At the sun's surface the wave velocity is near 1.25 m/s. More recently I have found local dark matter waves that appear to travel near 25 m/s near April 1 and appear to organize plants. They travel between plants and artificial transmitters and receivers, and penetrate my local hill. From my measurements the local dark matter density is a function of the time of year. The data indicate that dark matter interacts much more than just with gravity as others have surmised. I present experimental proofs and a local dark matter density equation in terms of the measured velocity. The waves and the earth's location may be very important for nature's organization. The observed behavior appears to go a long way towards dark matter identification. These waves also may explain the rings of the gaseous planets in terms of oscillating layers. See the ring article on the web site Darkmatterwaves.com.
Josan, Amandeep S.; Green, Anne M.
2010-10-15
Ultracompact minihalos (UCMHs) are dense dark matter structures, which can form from large density perturbations shortly after matter-radiation equality. If dark matter is in the form of weakly interacting massive particles (WIMPs), then UCMHs may be detected via their gamma-ray emission. We investigate how the Fermi satellite could constrain the abundance of UCMHs and place limits on the power spectrum of the primordial curvature perturbation. Detection by Fermi would put a lower limit on the UCMH halo fraction. The smallest detectable halo fraction f{sub UCMH} > or approx. 10{sup -7} is for M{sub UCMH{approx}}10{sup 3}M{sub {center_dot}}. If gamma-ray emission from UCMHs is not detected, an upper limit can be placed on the halo fraction. The bound is tightest f{sub UCMH} < or approx. 10{sup -5} for M{sub UCMH{approx}}10{sup 5}M{sub {center_dot}}. The resulting upper limit on the power spectrum of the primordial curvature perturbation in the event of nondetection is in the range P{sub R} < or approx. 10{sup -6.5}-10{sup -6} on scales k{approx}10{sup 1}-10{sup 6} Mpc{sup -1}. This is substantially tighter than the existing constraints from primordial black hole formation on these scales; however, it assumes that dark matter is in the form of WIMPs, and UCMHs are not disrupted during the formation of the Milky Way halo.
Testing gravity theories using tensor perturbations
NASA Astrophysics Data System (ADS)
Lin, Weikang; Ishak, Mustapha
2016-12-01
Primordial gravitational waves constitute a promising probe of the very early Universe and the laws of gravity. We study in this work changes to tensor-mode perturbations that can arise in various proposed modified gravity theories. These include additional friction effects, nonstandard dispersion relations involving a massive graviton, a modified speed, and a small-scale modification. We introduce a physically motivated parametrization of these effects and use current available data to obtain exclusion regions in the parameter spaces. Taking into account the foreground subtraction, we then perform a forecast analysis focusing on the tensor-mode modified-gravity parameters as constrained by the future experiments COrE, Stage-IV and PIXIE. For a fiducial value of the tensor-to-scalar ratio r =0.01 , we find that an additional friction of 3.5-4.5% compared to GR will be detected at 3 -σ by these experiments, while a decrease in friction will be more difficult to detect. The speed of gravitational waves needs to be by 5-15% different from the speed of light for detection. We find that the minimum detectable graviton mass is about 7.8 - 9.7 ×10-33 eV , which is of the same order of magnitude as the graviton mass that allows massive gravity theories to produce late-time cosmic acceleration. Finally, we study the tensor-mode perturbations in modified gravity during inflation using our parametrization. We find that, in addition to being related to r , the tensor spectral index would be related to the friction parameter ν0 by nT=-3 ν0-r /8 . Assuming that the friction parameter is unchanged throughout the history of the Universe, and that ν0 is much larger than r , the future experiments considered here will be able to distinguish this modified-gravity consistency relation from the standard inflation consistency relation, and thus can be used as a further test of modified gravity. In summary, tensor-mode perturbations and cosmic-microwave-background B
Conceptual problems in detecting the evolution of dark energy when using distance measurements
NASA Astrophysics Data System (ADS)
Bolejko, K.
2011-01-01
Context. Dark energy is now one of the most important and topical problems in cosmology. The first step to reveal its nature is to detect the evolution of dark energy or to prove beyond doubt that the cosmological constant is indeed constant. However, in the standard approach to cosmology, the Universe is described by the homogeneous and isotropic Friedmann models. Aims: We aim to show that in the perturbed universe (even if perturbations vanish if averaged over sufficiently large scales) the distance-redshift relation is not the same as in the unperturbed universe. This has a serious consequence when studying the nature of dark energy and, as shown here, can impair the analysis and studies of dark energy. Methods: The analysis is based on two methods: the linear lensing approximation and the non-linear Szekeres Swiss-Cheese model. The inhomogeneity scale is ~50 Mpc, and both models have the same density fluctuations along the line of sight. Results: The comparison between linear and non-linear methods shows that non-linear corrections are not negligible. When inhomogeneities are present the distance changes by several percent. To show how this change influences the measurements of dark energy, ten future observations with 2% uncertainties are generated. It is shown the using the standard methods (i.e. under the assumption of homogeneity) the systematics due to inhomogeneities can distort our analysis, and may lead to a conclusion that dark energy evolves when in fact it is constant (or vice versa). Conclusions: Therefore, if future observations are analysed only within the homogeneous framework then the impact of inhomogeneities (such as voids and superclusters) can be mistaken for evolving dark energy. Since the robust distinction between the evolution and non-evolution of dark energy is the first step to understanding the nature of dark energy a proper handling of inhomogeneities is essential.
Identifying Network Perturbation in Cancer
Logsdon, Benjamin A.; Gentles, Andrew J.; Lee, Su-In
2016-01-01
We present a computational framework, called DISCERN (DIfferential SparsE Regulatory Network), to identify informative topological changes in gene-regulator dependence networks inferred on the basis of mRNA expression datasets within distinct biological states. DISCERN takes two expression datasets as input: an expression dataset of diseased tissues from patients with a disease of interest and another expression dataset from matching normal tissues. DISCERN estimates the extent to which each gene is perturbed—having distinct regulator connectivity in the inferred gene-regulator dependencies between the disease and normal conditions. This approach has distinct advantages over existing methods. First, DISCERN infers conditional dependencies between candidate regulators and genes, where conditional dependence relationships discriminate the evidence for direct interactions from indirect interactions more precisely than pairwise correlation. Second, DISCERN uses a new likelihood-based scoring function to alleviate concerns about accuracy of the specific edges inferred in a particular network. DISCERN identifies perturbed genes more accurately in synthetic data than existing methods to identify perturbed genes between distinct states. In expression datasets from patients with acute myeloid leukemia (AML), breast cancer and lung cancer, genes with high DISCERN scores in each cancer are enriched for known tumor drivers, genes associated with the biological processes known to be important in the disease, and genes associated with patient prognosis, in the respective cancer. Finally, we show that DISCERN can uncover potential mechanisms underlying network perturbation by explaining observed epigenomic activity patterns in cancer and normal tissue types more accurately than alternative methods, based on the available epigenomic data from the ENCODE project. PMID:27145341
NASA Astrophysics Data System (ADS)
Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan
2016-02-01
Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system.
Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan
2016-02-11
Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system.
NASA Astrophysics Data System (ADS)
Baer, Howard
2016-06-01
The strong CP problem of QCD is at heart a problem of naturalness: why is the FF ˜ term highly suppressed in the QCD Lagrangian when it seems necessary to explain why there are three and not four light pions? The most elegant solution posits a spontaneously broken Peccei-Quinn (PQ) symmetry which requires the existence of the axion field a. The axion field settles to the minimum of its potential thus removing the offensive term but giving rise to the physical axion whose coherent oscillations can make up the cold dark matter. Only now are experiments such as ADMX beginning to explore QCD axion parameter space. Since a bonafide scalar particle- the Higgs boson- has been discovered, one might expect its mass to reside at the axion scale fa ˜ 1011 GeV. The Higgs mass is elegantly stabilized by supersymmetry: in this case the axion is accompanied by its axino and saxion superpartners. Requiring naturalness also in the electroweak sector implies higgsino-like WIMPs so then we expect mixed axion-WIMP dark matter. Ultimately we would expect detection of both an axion and a WIMP while signals for light higgsinos may show up at LHC and must show up at ILC.
Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan
2016-01-01
Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system. PMID:26864099
Flaugher, B.; Diehl, H. T.; Alvarez, O.; Angstadt, R.; Annis, J. T.; Buckley-Geer, E. J.; Honscheid, K.; Abbott, T. M. C.; Bonati, M.; Antonik, M.; Brooks, D.; Ballester, O.; Cardiel-Sas, L.; Beaufore, L.; Bernstein, G. M.; Bernstein, R. A.; Bigelow, B.; Boprie, D.; Campa, J.; Castander, F. J.; Collaboration: DES Collaboration; and others
2015-11-15
The Dark Energy Camera is a new imager with a 2.°2 diameter field of view mounted at the prime focus of the Victor M. Blanco 4 m telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five-element optical corrector, seven filters, a shutter with a 60 cm aperture, and a charge-coupled device (CCD) focal plane of 250 μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 megapixel focal plane comprises 62 2k × 4k CCDs for imaging and 12 2k × 2k CCDs for guiding and focus. The CCDs have 15 μm × 15 μm pixels with a plate scale of 0.″263 pixel{sup −1}. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 s with 6–9 electron readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.
Flaugher, B.
2015-04-11
The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250-μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. The CCDs have 15μm x 15μm pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.
Flaugher, B.
2015-04-11
The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250-μm thick fully depleted CCDs cooled inside a vacuum Dewar.more » The 570 Mpixel focal plane comprises 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. The CCDs have 15μm x 15μm pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.« less
NASA Astrophysics Data System (ADS)
Jaeckel, Joerg; Mehta, Viraf M.; Witkowski, Lukas T.
2017-01-01
Light pseudo-Nambu-Goldstone bosons (pNGBs) such as, e.g. axion-like particles, that are non-thermally produced via the misalignment mechanism are promising dark matter candidates. An important feature of pNGBs is their periodic potential, whose scale of periodicity controls their couplings. As a consequence of the periodicity the maximal potential energy is limited and, hence, producing the observed dark matter density poses significant constraints on the allowed masses and couplings. In the presence of a monodromy, the field range as well as the range of the potential can be significantly extended. As we argue in this paper this has important phenomenological consequences. The constraints on the masses and couplings are ameliorated and couplings to Standard Model particles could be significantly stronger, thereby opening up considerable experimental opportunities. Yet, monodromy models can also give rise to new and qualitatively different features. As a remnant of the periodicity the potential can feature pronounced ``wiggles''. When the field is passing through them quantum fluctuations are enhanced and particles with non-vanishing momentum are produced. Here, we perform a first analysis of this effect and delineate under which circumstances this becomes important. We briefly discuss some possible cosmological consequences.
Perturbation analyses of intermolecular interactions
NASA Astrophysics Data System (ADS)
Koyama, Yohei M.; Kobayashi, Tetsuya J.; Ueda, Hiroki R.
2011-08-01
Conformational fluctuations of a protein molecule are important to its function, and it is known that environmental molecules, such as water molecules, ions, and ligand molecules, significantly affect the function by changing the conformational fluctuations. However, it is difficult to systematically understand the role of environmental molecules because intermolecular interactions related to the conformational fluctuations are complicated. To identify important intermolecular interactions with regard to the conformational fluctuations, we develop herein (i) distance-independent and (ii) distance-dependent perturbation analyses of the intermolecular interactions. We show that these perturbation analyses can be realized by performing (i) a principal component analysis using conditional expectations of truncated and shifted intermolecular potential energy terms and (ii) a functional principal component analysis using products of intermolecular forces and conditional cumulative densities. We refer to these analyses as intermolecular perturbation analysis (IPA) and distance-dependent intermolecular perturbation analysis (DIPA), respectively. For comparison of the IPA and the DIPA, we apply them to the alanine dipeptide isomerization in explicit water. Although the first IPA principal components discriminate two states (the α state and PPII (polyproline II) + β states) for larger cutoff length, the separation between the PPII state and the β state is unclear in the second IPA principal components. On the other hand, in the large cutoff value, DIPA eigenvalues converge faster than that for IPA and the top two DIPA principal components clearly identify the three states. By using the DIPA biplot, the contributions of the dipeptide-water interactions to each state are analyzed systematically. Since the DIPA improves the state identification and the convergence rate with retaining distance information, we conclude that the DIPA is a more practical method compared with the
The Photosynthetic Dark Reactions Do Not Operate in the Dark.
ERIC Educational Resources Information Center
Lonergan, Thomas A.
2000-01-01
Discusses the common misconception persistent in high school and college level introductory biology texts that "dark reactions" of the Calvin cycle actually occur in the dark. Explains that they are indirectly dependent on the presence of light for their activity. (ASK)
Updates from the DMTPC Dark Matter Search
NASA Astrophysics Data System (ADS)
Lopez, Jeremy
2013-04-01
The motion of Earth through the galactic dark matter halo combined with the rotation of Earth around its axis is expected to create a large daily modulation in the typical directions of WIMP dark matter induced nuclear recoils. This modulation, if found, would provide strong evidence for WIMP interactions with normal matter. To search for this signal, the Dark Matter Time Projection Chamber (DMTPC) collaboration is developing gas TPCs that can measure the directions of low energy nuclear recoils in low pressure CF4 gas. DMTPC detectors use a mesh-based amplification region to measure the ionization profiles of recoils on a two-dimensional readout plane. CCD cameras are used to achieve sub-millimeter spatial resolution for a typical nuclear recoil range of one to several millimeters. This talk will discuss the commissioning and calibration of a prototype DMTPC detector in a surface laboratory at MIT. This detector, the 4-shooter, is testing several new features necessary for a planned 1 m^3 fiducial volume detector currently being designed. Upon completion of surface calibrations in early 2013, the 4-shooter detector will be installed underground at the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico.
Neutrino signals from dark matter
NASA Astrophysics Data System (ADS)
Erkoca, Arif Emre
Large-scale neutrino telescopes will be powerful tools to observe multitude of mysterious phenomena happening in the Universe. The dark matter puzzle is listed as one of them. In this study, indirect detection of dark matter via neutrino signals is presented. The upward muon, the contained muon and the hadronic shower fluxes are calculated, assuming annihilation/decay of the dark matter in the core of the astrophysical objects and in the Galactic center. Direct neutrino production and secondary neutrino production from the decay of Standard Model particles produced in the annihilation/decay of dark matter are studied. The results are contrasted to the ones previously obtained in the literature, illustrating the importance of properly treating muon propagation and energy loss for the upward muon flux. The dependence of the dark matter signals on the density profile, the dark matter mass and the detector threshold are discussed. Different dark matter models (gravitino, Kaluza-Klein and leptophilic) which can account for recent observations of some indirect searches are analyzed regarding their detection in the kilometer size neutrino detectors in the near future. Muon and shower rates and the minimum observation times in order to reach 2sigma detection significance are evaluated, with the result suggesting that the optimum cone half angles chosen about the Galactic center are about 10° (50°) for the muon (shower) events. A detailed analysis shows that for the annihilating dark matter models such as the leptophilic and Kaluza-Klein models, upward and contained muon as well as showers yield promising signals for dark matter detection in just a few years of observation, whereas for decaying dark matter models, the same observation times can only be reached with showers. The analytical results for the final fluxes are also obtained as well as parametric forms for the muon and shower fluxes for the dark matter models considered in this study.
NASA Astrophysics Data System (ADS)
Curtin, David; Tsai, Yuhsin
2014-11-01
In most models of the dark sector, dark matter is charged under some new symmetry to make it stable. We explore the possibility that not just dark matter, but also the force carrier connecting it to the visible sector is charged under this symmetry. This dark mediator then acts as a Double-Dark Portal. We realize this setup in the dark mediator Dark matter model (dmDM), featuring a fermionic DM candidate χ with Yukawa couplings to light scalars ϕ i . The scalars couple to SM quarks via the operator . This can lead to large direct detection signals via the 2 → 3 process χ N → χ N ϕ if one of the scalars has mass ≲ 10 keV. For dark matter Yukawa couplings y χ ˜ 10-3 -10-2, dmDM features a thermal relic dark matter candidate while also implementing the SIDM scenario for ameliorating inconsistencies between dwarf galaxy simulations and observations. We undertake the first systematic survey of constraints on light scalars coupled to the SM via the above operator. The strongest constraints are derived from a detailed examination of the light mediator's effects on stellar astrophysics. LHC experiments and cosmological considerations also yield important bounds. Observations of neutron star cooling exclude the minimal model with one dark mediator, but a scenario with two dark mediators remains viable and can give strong direct detection signals. We explore the direct detection consequences of this scenario and find that a heavy dmDM candidate fakes different WIMPs at different experiments. Large regions of dmDM parameter space are accessible above the irreducible neutrino background.
Stealth Dark Matter: Dark scalar baryons through the Higgs portal
Appelquist, T.; Brower, R. C.; Buchoff, M. I.; Fleming, G. T.; Jin, X. -Y.; Kiskis, J.; Kribs, G. D.; Neil, E. T.; Osborn, J. C.; Rebbi, C.; Rinaldi, E.; Schaich, D.; Schroeder, C.; Syritsyn, S.; Vranas, P.; Weinberg, E.; Witzel, O.
2015-10-23
We present a new model of "Stealth Dark Matter": a composite baryonic scalar of an SU(N_{D}) strongly coupled theory with even N_{D} ≥ 4. All mass scales are technically natural, and dark matter stability is automatic without imposing an additional discrete or global symmetry. Constituent fermions transform in vectorlike representations of the electroweak group that permit both electroweak-breaking and electroweak-preserving mass terms. This gives a tunable coupling of stealth dark matter to the Higgs boson independent of the dark matter mass itself. We specialize to SU(4), and investigate the constraints on the model from dark meson decay, electroweak precision measurements, basic collider limits, and spin-independent direct detection scattering through Higgs exchange. We exploit our earlier lattice simulations that determined the composite spectrum as well as the effective Higgs coupling of stealth dark matter in order to place bounds from direct detection, excluding constituent fermions with dominantly electroweak-breaking masses. A lower bound on the dark baryon mass m_{B} ≳ 300 GeV is obtained from the indirect requirement that the lightest dark meson not be observable at LEP II. Furthermore, we briefly survey some intriguing properties of stealth dark matter that are worthy of future study, including collider studies of dark meson production and decay; indirect detection signals from annihilation; relic abundance estimates for both symmetric and asymmetric mechanisms; and direct detection through electromagnetic polarizability, a detailed study of which will appear in a companion paper.
Stealth Dark Matter: Dark scalar baryons through the Higgs portal
Appelquist, T.; Brower, R. C.; Buchoff, M. I.; ...
2015-10-23
We present a new model of "Stealth Dark Matter": a composite baryonic scalar of an SU(ND) strongly coupled theory with even ND ≥ 4. All mass scales are technically natural, and dark matter stability is automatic without imposing an additional discrete or global symmetry. Constituent fermions transform in vectorlike representations of the electroweak group that permit both electroweak-breaking and electroweak-preserving mass terms. This gives a tunable coupling of stealth dark matter to the Higgs boson independent of the dark matter mass itself. We specialize to SU(4), and investigate the constraints on the model from dark meson decay, electroweak precision measurements,more » basic collider limits, and spin-independent direct detection scattering through Higgs exchange. We exploit our earlier lattice simulations that determined the composite spectrum as well as the effective Higgs coupling of stealth dark matter in order to place bounds from direct detection, excluding constituent fermions with dominantly electroweak-breaking masses. A lower bound on the dark baryon mass mB ≳ 300 GeV is obtained from the indirect requirement that the lightest dark meson not be observable at LEP II. Furthermore, we briefly survey some intriguing properties of stealth dark matter that are worthy of future study, including collider studies of dark meson production and decay; indirect detection signals from annihilation; relic abundance estimates for both symmetric and asymmetric mechanisms; and direct detection through electromagnetic polarizability, a detailed study of which will appear in a companion paper.« less
Statistics of primordial density perturbations from discrete seed masses
NASA Technical Reports Server (NTRS)
Scherrer, Robert J.; Bertschinger, Edmund
1991-01-01
The statistics of density perturbations for general distributions of seed masses with arbitrary matter accretion is examined. Formal expressions for the power spectrum, the N-point correlation functions, and the density distribution function are derived. These results are applied to the case of uncorrelated seed masses, and power spectra are derived for accretion of both hot and cold dark matter plus baryons. The reduced moments (cumulants) of the density distribution are computed and used to obtain a series expansion for the density distribution function. Analytic results are obtained for the density distribution function in the case of a distribution of seed masses with a spherical top-hat accretion pattern. More generally, the formalism makes it possible to give a complete characterization of the statistical properties of any random field generated from a discrete linear superposition of kernels. In particular, the results can be applied to density fields derived by smoothing a discrete set of points with a window function.
Meng, Hongyan; Jiang, Ling; Xu, Bosi; Guo, Wenzhu; Li, Jinglai; Zhu, Xiuqing; Qi, Xiaoquan; Duan, Lixin; Meng, Xianbin; Fan, Yunliu; Zhang, Chunyi
2014-01-01
Interactions among metabolic pathways are important in plant biology. At present, not much is known about how folate metabolism affects other metabolic pathways in plants. Here we report a T-DNA insertion mutant (atdfb-3) of the plastidial folylpolyglutamate synthetase gene (AtDFB) was defective in seed reserves and skotomorphogenesis. Lower carbon (C) and higher nitrogen (N) content in the mutant seeds than that of the wild type were indicative of an altered C and N partitioning capacity. Higher levels of organic acids and sugars were detected in the mutant seeds compared with the wild type. Further analysis revealed that atdfb-3 seeds contained less total amino acids and individual Asn and Glu as well as NO3−. These results indicate significant changes in seed storage in the mutant. Defects in hypocotyl elongation were observed in atdfb-3 in darkness under sufficient NO3− conditions, and further enhanced under NO3− limited conditions. The strong expression of AtDFB in cotyledons and hypocotyl during early developmental stage was consistent with the mutant sensitivity to limited NO3− during a narrow developmental window. Exogenous 5-formyl-tetrahydrofolate completely restored the hypocotyl length in atdfb-3 seedlings with NO3− as the sole N source. Further study demonstrated that folate profiling and N metabolism were perturbed in atdfb-3 etiolated seedlings. The activity of enzymes involved in N reduction and assimilation was altered in atdfb-3. Taken together, these results indicate that AtDFB is required for seed reserves, hypocotyl elongation and N metabolism in darkness, providing novel insights into potential associations of folate metabolism with seed reserve accumulation, N metabolism and hypocotyl development in Arabidopsis. PMID:25000295
Revisiting Black Holes as Dark Matter
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2017-02-01
Could dark matter be made of intermediate-mass black holes formed in the beginning of the universe? A recent study takes a renewed look at this question.Galactic LurkersThe nature of dark matter has long been questioned, but the recent discovery of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) has renewed interest in the possibility that dark matter could consist of primordial black holes in the mass range of 101000 solar masses.The relative amounts of the different constituents of the universe. Dark matter makes up roughly 27%. [ESA/Planck]According to this model, the extreme density of matter present during the universes early expansion led to the formation of a large number of intermediate-mass black holes. These black holes now hide in the halos of galaxies, constituting the mass that weve measured dynamically but remains unseen.LIGOs first gravitational-wave detection revealed the merger of two black holes that were both tens of solar masses in size. If primordial black holes are indeed a major constituent of dark matter, then LIGOs detection is consistent with what we would expect to find: occasional mergers of the intermediate-mass black holes that formed in the early universe and now lurk in galactic halos.Quasar MicrolensingTheres a catch, however. If there truly were a large number of intermediate-mass primordial black holes hiding in galactic halos, they wouldnt go completely unnoticed: we would see signs of their presence in the gravitational microlensing of background quasars. Unseen primordial black holes in a foreground galaxy could cause an image of a background quasar to briefly brighten which would provide us with clear evidence of such black holes despite our not being able to detect them directly.A depiction of quasar microlensing (click for a closer look!). The microlensing object in the foreground galaxy could be a star (as depicted), a primordial black hole, or any other compact object. [NASA
"Phonon" scattering beyond perturbation theory
NASA Astrophysics Data System (ADS)
Qiu, WuJie; Ke, XueZhi; Xi, LiLi; Wu, LiHua; Yang, Jiong; Zhang, WenQing
2016-02-01
Searching and designing materials with intrinsically low lattice thermal conductivity (LTC) have attracted extensive consideration in thermoelectrics and thermal management community. The concept of part-crystalline part-liquid state, or even part-crystalline part-amorphous state, has recently been proposed to describe the exotic structure of materials with chemical- bond hierarchy, in which a set of atoms is weakly bonded to the rest species while the other sublattices retain relatively strong rigidity. The whole system inherently manifests the coexistence of rigid crystalline sublattices and fluctuating noncrystalline substructures. Representative materials in the unusual state can be classified into two categories, i.e., caged and non-caged ones. LTCs in both systems deviate from the traditional T -1 relationship ( T, the absolute temperature), which can hardly be described by small-parameter-based perturbation approaches. Beyond the classical perturbation theory, an extra rattling-like scattering should be considered to interpret the liquid-like and sublattice-amorphization-induced heat transport. Such a kind of compounds could be promising high-performance thermoelectric materials, due to the extremely low LTCs. Other physical properties for these part-crystalline substances should also exhibit certain novelty and deserve further exploration.
Gravitational collapse of Bose-Einstein condensate dark matter halos
NASA Astrophysics Data System (ADS)
Harko, Tiberiu
2014-04-01
We study the mechanisms of the gravitational collapse of the Bose-Einstein condensate dark matter halos, described by the zero temperature time-dependent nonlinear Schrödinger equation (the Gross-Pitaevskii equation), with repulsive interparticle interactions. By using a variational approach, and by choosing an appropriate trial wave function, we reformulate the Gross-Pitaevskii equation with spherical symmetry as Newton's equation of motion for a particle in an effective potential, which is determined by the zero-point kinetic energy, the gravitational energy, and the particles interaction energy, respectively. The velocity of the condensate is proportional to the radial distance, with a time-dependent proportionality function. The equation of motion of the collapsing dark matter condensate is studied by using both analytical and numerical methods. The collapse of the condensate ends with the formation of a stable configuration, corresponding to the minimum of the effective potential. The radius and the mass of the resulting dark matter object are obtained, as well as the collapse time of the condensate. The numerical values of these global astrophysical quantities, characterizing condensed dark matter systems, strongly depend on the two parameters describing the condensate, the mass of the dark matter particle, and of the scattering length, respectively. The stability of the condensate under small perturbations is also studied, and the oscillations frequency of the halo is obtained. Hence these results show that the gravitational collapse of the condensed dark matter halos can lead to the formation of stable astrophysical systems with both galactic and stellar sizes.
Effects of vestibular loss on head stabilization in response to head and body perturbations
NASA Technical Reports Server (NTRS)
Shupert, C. L.; Horak, F. B.; Peterson, B. W. (Principal Investigator)
1996-01-01
Control of head position during postural responses is important to facilitate both the interpretation of vestibular signals and the stabilization of gaze. In these experiments, we compared head stabilization for two different postural tasks: 1) in response to perturbations at the head, and 2) in response to perturbations induced at the support surface, which perturb both body and head position. To determine whether normal vestibular function is necessary for head stabilization in these two tasks, responses to forward and backward mechanical perturbations of the head and body were compared for 13 normal subjects and 4 patients with profound bilateral vestibular loss (two with vestibular loss in adulthood and two in infancy). Normal subjects showed little neck muscle activity for body perturbations, but large, early activations in both neck extensors and flexors for head perturbations. In contrast, vestibular patients showed excessive neck muscle activation for body perturbations and reduced or absent neck muscle activity for head perturbations. Patients with vestibular loss in adulthood also showed increased head acceleration in response to both head and body perturbations, but patients with vestibular loss in infancy showed more normal head accelerations. For body perturbations, the differences in head acceleration between patients and normals were greater for later head acceleration peaks, indicating poor head control during the execution of the postural response. Trunk angle changes were also higher in the patients for forward body perturbations, indicating that poorer control of trunk position could have contributed to their poorer head stabilization. These results indicate that the vestibular system plays an important role in head and trunk stabilization for both head and body perturbations. However, the more normal head accelerations of the patients with infant vestibular loss also indicate that other mechanisms, possibly involving neck reflexes, can at least
Perturbative Methods in Path Integration
NASA Astrophysics Data System (ADS)
Johnson-Freyd, Theodore Paul
This dissertation addresses a number of related questions concerning perturbative "path" integrals. Perturbative methods are one of the few successful ways physicists have worked with (or even defined) these infinite-dimensional integrals, and it is important as mathematicians to check that they are correct. Chapter 0 provides a detailed introduction. We take a classical approach to path integrals in Chapter 1. Following standard arguments, we posit a Feynman-diagrammatic description of the asymptotics of the time-evolution operator for the quantum mechanics of a charged particle moving nonrelativistically through a curved manifold under the influence of an external electromagnetic field. We check that our sum of Feynman diagrams has all desired properties: it is coordinate-independent and well-defined without ultraviolet divergences, it satisfies the correct composition law, and it satisfies Schrodinger's equation thought of as a boundary-value problem in PDE. Path integrals in quantum mechanics and elsewhere in quantum field theory are almost always of the shape ∫ f es for some functions f (the "observable") and s (the "action"). In Chapter 2 we step back to analyze integrals of this type more generally. Integration by parts provides algebraic relations between the values of ∫ (-) es for different inputs, which can be packaged into a Batalin--Vilkovisky-type chain complex. Using some simple homological perturbation theory, we study the version of this complex that arises when f and s are taken to be polynomial functions, and power series are banished. We find that in such cases, the entire scheme-theoretic critical locus (complex points included) of s plays an important role, and that one can uniformly (but noncanonically) integrate out in a purely algebraic way the contributions to the integral from all "higher modes," reducing ∫ f es to an integral over the critical locus. This may help explain the presence of analytic continuation in questions like the
Plasma dark matter direct detection
Clarke, J.D.; Foot, R. E-mail: rfoot@unimelb.edu.au
2016-01-01
Dark matter in spiral galaxies like the Milky Way may take the form of a dark plasma. Hidden sector dark matter charged under an unbroken U(1)' gauge interaction provides a simple and well defined particle physics model realising this possibility. The assumed U(1)' neutrality of the Universe then implies (at least) two oppositely charged dark matter components with self-interactions mediated via a massless 'dark photon' (the U(1)' gauge boson). In addition to nuclear recoils such dark matter can give rise to keV electron recoils in direct detection experiments. In this context, the detailed physical properties of the dark matter plasma interacting with the Earth is required. This is a complex system, which is here modelled as a fluid governed by the magnetohydrodynamic equations. These equations are numerically solved for some illustrative examples, and implications for direct detection experiments discussed. In particular, the analysis presented here leaves open the intriguing possibility that the DAMA annual modulation signal is due primarily to electron recoils (or even a combination of electron recoils and nuclear recoils). The importance of diurnal modulation (in addition to annual modulation) as a means of probing this kind of dark matter is also emphasised.
Optimizing New Dark Energy Experiments
Tyson, J. Anthony
2013-08-26
Next generation “Stage IV” dark energy experiments under design during this grant, and now under construction, will enable the determination of the properties of dark energy and dark matter to unprecedented precision using multiple complementary probes. The most pressing challenge in these experiments is the characterization and understanding of the systematic errors present within any given experimental configuration and the resulting impact on the accuracy of our constraints on dark energy physics. The DETF and the P5 panel in their reports recommended “Expanded support for ancillary measurements required for the long-term program and for projects that will improve our understanding and reduction of the dominant systematic measurement errors.” Looking forward to the next generation Stage IV experiments we have developed a program to address the most important potential systematic errors within these experiments. Using data from current facilities it has been feasible and timely to undertake a detailed investigation of the systematic errors. In this DOE grant we studied of the source and impact of the dominant systematic effects in dark energy measurements, and developed new analysis tools and techniques to minimize their impact. Progress under this grant is briefly reviewed in this technical report. This work was a necessary precursor to the coming generations of wide-deep probes of the nature of dark energy and dark matter. The research has already had an impact on improving the efficiencies of all Stage III and IV dark energy experiments.
Dark energy and the return of the phoenix universe
Lehners, Jean-Luc; Steinhardt, Paul J.
2009-03-15
In cyclic universe models based on a single scalar field (e.g., the radion determining the distance between branes in M theory), virtually the entire Universe makes it through the ekpyrotic smoothing and flattening phase, bounces, and enters a new epoch of expansion and cooling. This stable evolution cannot occur, however, if scale-invariant curvature perturbations are produced by the entropic mechanism because it requires two scalar fields (e.g., the radion and the Calabi-Yau dilaton) evolving along an unstable classical trajectory. In fact, we show here that an overwhelming fraction of the Universe fails to make it through the ekpyrotic phase; nevertheless, a sufficient volume survives and cycling continues forever provided the dark energy phase of the cycle lasts long enough, of order a trillion years. Two consequences are a new role for dark energy and a global structure of the Universe radically different from that of eternal inflation.
Onset of transverse instabilities of confined dark solitons
NASA Astrophysics Data System (ADS)
Hoefer, M. A.; Ilan, B.
2016-07-01
We investigate propagating dark soliton solutions of the two-dimensional defocusing nonlinear Schrödinger or Gross-Pitaevskii (NLS-GP) equation that are transversely confined to propagate in an infinitely long channel. Families of single, vortex, and multilobed solitons are computed using a spectrally accurate numerical scheme. The multilobed solitons are unstable to small transverse perturbations. However, the single-lobed solitons are stable if they are sufficiently confined along the transverse direction, which explains their effective one-dimensional dynamics. The emergence of a transverse modulational instability is characterized in terms of a spectral bifurcation. The critical confinement width for this bifurcation is found to coincide with the existence of a propagating vortex solution and the onset of a "snaking" instability in the dark soliton dynamics that, in turn, give rise to vortex or multivortex excitations. These results shed light on the superfluidic hydrodynamics of dispersive shock waves in Bose-Einstein condensates and nonlinear optics.
Supernova constraints on multi-coupled dark energy
Piloyan, Arpine; Marra, Valerio; Amendola, Luca; Baldi, Marco E-mail: valerio.marra@me.com E-mail: l.amendola@thphys.uni-heidelberg.de
2013-07-01
The persisting consistency of ever more accurate observational data with the predictions of the standard ΛCDM cosmological model puts severe constraints on possible alternative scenarios, but still does not shed any light on the fundamental nature of the cosmic dark sector. As large deviations from a ΛCDM cosmology are ruled out by data, the path to detect possible features of alternative models goes necessarily through the definition of cosmological scenarios that leave almost unaffected the background and — to a lesser extent — the linear perturbations evolution of the universe. In this context, the Multi-coupled DE (McDE) model was proposed by Baldi [9] as a particular realization of an interacting Dark Energy field characterized by an effective screening mechanism capable of suppressing the effects of the coupling at the background and linear perturbation level. In the present paper, for the first time, we challenge the McDE scenario through a direct comparison with real data, in particular with the luminosity distance of Type Ia supernovae. By studying the existence and stability conditions of the critical points of the associated background dynamical system, we select only the cosmologically consistent solutions, and confront their background expansion history with data. Confirming previous qualitative results, the McDE scenario appears to be fully consistent with the adopted sample of Type Ia supernovae, even for coupling values corresponding to an associated scalar fifth-force about four orders of magnitude stronger than standard gravity. Our analysis demonstrates the effectiveness of the McDE background screening, and shows some new non-trivial asymptotic solutions for the future evolution of the universe. Clearly, linear perturbation data and, even more, nonlinear structure formation properties are expected to put much tighter constraints on the allowed coupling range. Nonetheless, our results show how the background expansion history might be
Magnetic brightening of dark excitons in transitional metal dichalcogenides
NASA Astrophysics Data System (ADS)
Zhang, Xiao-Xiao; Lu, Zhengguang; Cao, Ting; Zhang, Fan; Hone, James; Louie, Steven G.; Li, Zhiqiang; Smirnov, Dmitry; Heinz, Tony
Transitional metal dichalcogenides (TMDC) in the MX2 (M = Mo, W, X = S, Se) family represent an excellent platform to study of excitonic effects. At monolayer thickness, these materials exhibit both direct band-gap character and enhanced excitonic interactions. Theoretical studies suggest that both the valence and conduction bands are split and exhibit spin polarized character at the K/K' valleys. The lowest energy band-edge excitons are predicted to have different spin configurations for different materials in this family. When the lowest lying exciton has parallel electron and hole spin, radiative decay is forbidden and the state is dark. Here we demonstrate that by applying an in-plane magnetic field we can perturb the exciton spin configuration and brighten this state, allowing it to undergo radiative decay. We identify such a brightened dark state by the emergence of a new emission peak lying below the absorption peak, with a strength growing with applied in-plane magnetic field. On the other hand, for monolayer MoSe2, where no low-lying dark state is expected, we do not see the growth of a new emission feature under application of an in-plane magnetic field. Our experimental findings are in agreement with the calculated properties of dark excitons based on GW plus Bethe-Salpeter equation approach
Testing coupled dark energy with large scale structure observation
Yang, Weiqiang; Xu, Lixin E-mail: lxxu@dlut.edu.cn
2014-08-01
The coupling between the dark components provides a new approach to mitigate the coincidence problem of cosmological standard model. In this paper, dark energy is treated as a fluid with a constant equation of state, whose coupling with dark matter is Q-bar =3Hξ{sub x}ρ-bar {sub x}. In the frame of dark energy, we derive the evolution equations for the density and velocity perturbations. According to the Markov Chain Monte Carlo method, we constrain the model by currently available cosmic observations which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and fσ{sub 8}(z) data points from redshift-space distortion. The results show the interaction rate in σ regions: ξ{sub x} = 0.00328{sub -0.00328-0.00328-0.00328}{sup +0.000736+0.00549+0.00816}, which means that the recently cosmic observations favor a small interaction rate which is up to the order of 10{sup -2}, meanwhile, the measurement of redshift-space distortion could rule out the large interaction rate in the σ region.
Integrated Sachs-Wolfe effect in interacting dark energy models
Olivares, German; Pavon, Diego; Atrio-Barandela, Fernando
2008-05-15
Models with dark energy decaying into dark matter have been proposed in cosmology to solve the coincidence problem. We study the effect of such coupling on the cosmic microwave background temperature anisotropies. The interaction changes the rate of evolution of the metric potentials and the growth rate of matter density perturbations and modifies the integrated Sachs-Wolfe component of cosmic microwave background temperature anisotropies, enhancing the effect. Cross correlation of galaxy catalogs with cosmic microwave background maps provides a model-independent test to constrain the interaction. We particularize our analysis for a specific interacting model and show that galaxy catalogs with median redshifts z{sub m}=0.1-0.9 can rule out models with an interaction parameter strength of c{sup 2}{approx_equal}0.1 better than 99.95% confidence level. Values of c{sup 2}{<=}0.01 are compatible with the data and may account for the possible discrepancy between the fraction of dark energy derived from Wilkinson microwave anisotropy probe 3 yr data and the fraction obtained from the integrated Sachs-Wolfe effect. Measuring the fraction of dark energy by these two methods could provide evidence of an interaction.
DARK SATELLITES AND THE MORPHOLOGY OF DWARF GALAXIES
Helmi, Amina; Starkenburg, E.; Starkenburg, T. K.; Vera-Ciro, C. A.; Sales, L. V.; De Lucia, G.; Li, Y.-S.
2012-10-10
One of the strongest predictions of the {Lambda}CDM cosmological model is the presence of dark satellites orbiting all types of galaxies. We focus here on the dynamical effects of such satellites on disky dwarf galaxies, and demonstrate that these encounters can be dramatic. Although mergers with M{sub sat} > M{sub d} are not very common, because of the lower baryonic content they occur much more frequently on the dwarf scale than for L{sub *} galaxies. As an example, we present a numerical simulation of a 20% (virial) mass ratio merger between a dark satellite and a disky dwarf (akin to the Fornax dwarf galaxy in luminosity) that shows that the merger remnant has a spheroidal morphology. Perturbations by dark satellites thus provide a plausible path for the formation of dSph systems. The transition from disky to the often amorphous, irregular, or spheroidal morphologies of dwarfs could be a natural consequence of the dynamical heating of hitherto unobservable dark satellites.
Inflationary imprints on dark matter
NASA Astrophysics Data System (ADS)
Nurmi, Sami; Tenkanen, Tommi; Tuominen, Kimmo
2015-11-01
We show that dark matter abundance and the inflationary scale H could be intimately related. Standard Model extensions with Higgs mediated couplings to new physics typically contain extra scalars displaced from vacuum during inflation. If their coupling to Standard Model is weak, they will not thermalize and may easily constitute too much dark matter reminiscent to the moduli problem. As an example we consider Standard Model extended by a Z2 symmetric singlet s coupled to the Standard Model Higgs Φ via λ Φ†Φ s2. Dark matter relic density is generated non-thermally for λ lesssim 10-7. We show that the dark matter yield crucially depends on the inflationary scale. For H~ 1010 GeV we find that the singlet self-coupling and mass should lie in the regime λsgtrsim 10-9 and mslesssim 50 GeV to avoid dark matter overproduction.
Reconstructing and deconstructing dark energy
Linder, Eric V.
2004-06-07
The acceleration of the expansion of the universe, ascribed to a dark energy, is one of the most intriguing discoveries in science. In addition to precise, systematics controlled data, clear, robust interpretation of the observations is required to reveal the nature of dark energy. Even for the simplest question: is the data consistent with the cosmological constant? there are important subtleties in the reconstruction of the dark energy properties. We discuss the roles of analysis both in terms of the Hubble expansion rate or dark energy density {rho}DE(z) and in terms of the dark energy equation of state w(z), arguing that each has its carefully defined place. Fitting the density is best for learning about the density, but using it to probe the equation of state can lead to instability and bias.