Sample records for dark energy equation

  1. Mapping the Dark Energy Equation of State

    E-print Network

    Eric V. Linder

    2003-11-17

    The acceleration of the expansion of the universe has deep implications for structure formation, the composition of the universe, and its fate. Roughly 70% of the energy density is in a dark energy, whose nature remains unknown. Mapping the expansion history through supernovae, mapping the geometry of the universe and formation of structure through redshift surveys, and mapping the distance to recombination through the cosmic microwave background provide complementary, precise probes of the equation of state of the dark energy. Together these next generation maps of the cosmos can reveal not only the value today, but the redshift variation, of the equation of state, providing a critical clue to the underlying physics.

  2. Entropic dark energy and sourced Friedmann equations

    E-print Network

    Ulf H. Danielsson

    2010-03-03

    In this paper we show that a recent attempt to derive dark energy as an entropic force suffers from the same problems as earlier attempts motivated by holography. The possible remedy is again the introduction of source terms.

  3. On the Effective Equation of State of Dark Energy

    E-print Network

    Martin S. Sloth

    2010-12-30

    In an effective field theory model with an ultraviolet momentum cutoff, there is a relation between the effective equation of state of dark energy and the ultraviolet cutoff scale. It implies that a measure of the equation of state of dark energy different from minus one, does not rule out vacuum energy as dark energy. It also indicates an interesting possibility that precise measurements of the infrared properties of dark energy can be used to probe the ultraviolet cutoff scale of effective quantum field theory coupled to gravity. In a toy model with a vacuum energy dominated universe with a Planck scale cutoff, the dark energy effective equation of state is -0.96.

  4. Unified Field Equations Coupling Four Forces and Theory of Dark Matter and Dark Energy

    E-print Network

    Wang, Shouhong

    Unified Field Equations Coupling Four Forces and Theory of Dark Matter and Dark Energy Tian Ma II. Principle of Interaction Dynamics III. Unified Field Equations Coupling Four Forces IV. Duality V, June, 2012, http://arxiv.org/abs/1206.5078 2. Tian Ma & Shouhong Wang, Unified Field Equations Coupling

  5. Dark energy cosmology with generalized linear equation of state

    Microsoft Academic Search

    E. Babichev; V. Dokuchaev; Yu Eroshenko

    2005-01-01

    Dark energy with the usually used equation of state p = wrho, where w = const < 0, is hydrodynamically unstable. To overcome this drawback, we consider the cosmology of a perfect fluid with a linear equation of state of a more general form p = alpha(rho - rho0), where the constants alpha and rho0 are free parameters. This non-homogeneous

  6. Nonparametric reconstruction of the dark energy equation of state

    SciTech Connect

    Heitmann, Katrin [Los Alamos National Laboratory; Holsclaw, Tracy [Los Alamos National Laboratory; Alam, Ujjaini [Los Alamos National Laboratory; Habib, Salman [Los Alamos National Laboratory; Higdon, David [Los Alamos National Laboratory; Sanso, Bruno [UC SANTA CRUZ; Lee, Herbie [UC SANTA CRUZ

    2009-01-01

    The major aim of ongoing and upcoming cosmological surveys is to unravel the nature of dark energy. In the absence of a compelling theory to test, a natural approach is to first attempt to characterize the nature of dark energy in detail, the hope being that this will lead to clues about the underlying fundamental theory. A major target in this characterization is the determination of the dynamical properties of the dark energy equation of state w. The discovery of a time variation in w(z) could then lead to insights about the dynamical origin of dark energy. This approach requires a robust and bias-free method for reconstructing w(z) from data, which does not rely on restrictive expansion schemes or assumed functional forms for w(z). We present a new non parametric reconstruction method for the dark energy equation of state based on Gaussian Process models. This method reliably captures nontrivial behavior of w(z) and provides controlled error bounds. We demollstrate the power of the method on different sets of simulated supernova data. The GP model approach is very easily extended to include diverse cosmological probes.

  7. Periodic Cosmological Evolutions of Equation of State for Dark Energy

    E-print Network

    Kazuharu Bamba; Ujjal Debnath; Kuralay Yesmakhanova; Petr Tsyba; Gulgasyl Nugmanova; Ratbay Myrzakulov

    2012-10-25

    We demonstrate two periodic or quasi-periodic generalizations of the Chaplygin gas (CG) type models to explain the origins of dark energy as well as dark matter by using the Weierstrass $\\wp(t)$, $\\sigma(t)$ and $\\zeta(t)$ functions with two periods being infinite. If the universe can evolve periodically, a non-singular universe can be realized. Furthermore, we examine the cosmological evolution and nature of the equation of state (EoS) of dark energy in the Friedmann-Lema\\^{i}tre-Robertson-Walker cosmology. It is explicitly illustrated that there exist three type models in which the universe always stays in the non-phantom (quintessence) phase, whereas it always evolves in the phantom phase, or the crossing of the phantom divide can be realized. The scalar fields and the corresponding potentials are also analyzed for different types of models.

  8. Gravitational Field Equations and Theory of Dark Matter and Dark Energy

    E-print Network

    Tian Ma; Shouhong Wang

    2012-07-11

    The main objective of this article is to derive a new set of gravitational field equations and to establish a new unified theory for dark energy and dark matter. The new gravitational field equations with scalar potential $\\varphi$ are derived using the Einstein-Hilbert functional, and the scalar potential $\\varphi$ is a natural outcome of the divergence-free constraint of the variational elements. Gravitation is now described by the Riemannian metric $g_{ij}$, the scalar potential $\\varphi$ and their interactions, unified by the new gravitational field equations. Associated with the scalar potential $\\varphi$ is the scalar potential energy density $\\frac{c^4}{8\\pi G} \\Phi=\\frac{c^4}{8\\pi G} g^{ij}D_iD_j \\varphi$, which represents a new type of energy caused by the non-uniform distribution of matter in the universe. The negative part of this potential energy density produces attraction, and the positive part produces repelling force. This potential energy density is conserved with mean zero: $\\int_M \\Phi dM=0$. The sum of this new potential energy density $\\frac{c^4}{8\\pi G} \\Phi$ and the coupling energy between the energy-momentum tensor $T_{ij}$ and the scalar potential field $\\varphi$ gives rise to a new unified theory for dark matter and dark energy: The negative part of this sum represents the dark matter, which produces attraction, and the positive part represents the dark energy, which drives the acceleration of expanding galaxies. In addition, the scalar curvature of space-time obeys $R=\\frac{8\\pi G}{c^4} T + \\Phi$. Furthermore, the new field equations resolve a few difficulties encountered by the classical Einstein field equations.

  9. Equation of state of dark energy in f (R ) gravity

    NASA Astrophysics Data System (ADS)

    Takahashi, Kazufumi; Yokoyama, Jun'ichi

    2015-04-01

    f (R ) gravity is one of the simplest generalizations of general relativity, which may explain the accelerated cosmic expansion without introducing a cosmological constant. Transformed into the Einstein frame, a new scalar degree of freedom appears and it couples with matter fields. In order for f (R ) theories to pass the local tests of general relativity, it has been known that the chameleon mechanism with a so-called thin-shell solution must operate. If the thin-shell constraint is applied to a cosmological situation, it has been claimed that the equation-of-state parameter of dark energy w must be extremely close to -1 . We argue this is due to the incorrect use of the Poisson equation, which is valid only in the static case. By solving the correct Klein-Gordon equation perturbatively, we show that a thin-shell solution exists even if w deviates appreciably from -1 .

  10. Nonparametric reconstruction of the dark energy equation of state

    NASA Astrophysics Data System (ADS)

    Holsclaw, Tracy; Alam, Ujjaini; Sansó, Bruno; Lee, Herbert; Heitmann, Katrin; Habib, Salman; Higdon, David

    2010-11-01

    A basic aim of ongoing and upcoming cosmological surveys is to unravel the mystery of dark energy. In the absence of a compelling theory to test, a natural approach is to better characterize the properties of dark energy in search of clues that can lead to a more fundamental understanding. One way to view this characterization is the improved determination of the redshift-dependence of the dark energy equation of state parameter, w(z). To do this requires a robust and bias-free method for reconstructing w(z) from data that does not rely on restrictive expansion schemes or assumed functional forms for w(z). We present a new nonparametric reconstruction method that solves for w(z) as a statistical inverse problem, based on a Gaussian process representation. This method reliably captures nontrivial behavior of w(z) and provides controlled error bounds. We demonstrate the power of the method on different sets of simulated supernova data; the approach can be easily extended to include diverse cosmological probes.

  11. Nonparametric reconstruction of the dark energy equation of state

    Microsoft Academic Search

    Katrin Heitmann; Tracy Holsclaw; Ujjaini Alam; Salman Habib; David Higdon; Bruno Sanso; Herbie Lee

    2009-01-01

    The major aim of ongoing and upcoming cosmological surveys is to unravel the nature of dark energy. In the absence of a compelling theory to test, a natural approach is to first attempt to characterize the nature of dark energy in detail, the hope being that this will lead to clues about the underlying fundamental theory. A major target in

  12. Nonparametric reconstruction of the dark energy equation of state

    Microsoft Academic Search

    Tracy Holsclaw; Ujjaini Alam; Bruno Sansó; Herbert Lee; Katrin Heitmann; Salman Habib; David Higdon

    2010-01-01

    A basic aim of ongoing and upcoming cosmological surveys is to unravel the mystery of dark energy. In the absence of a compelling theory to test, a natural approach is to better characterize the properties of dark energy in search of clues that can lead to a more fundamental understanding. One way to view this characterization is the improved determination

  13. Probing dark energy perturbations: The dark energy equation of state and speed of sound as measured by WMAP

    Microsoft Academic Search

    Rachel Bean; Olivier Doré

    2004-01-01

    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

  14. Dark Energy with Generalized Equation of State in Bianchi Type-I Cosmological Model

    Microsoft Academic Search

    T. Singh; R. Chaubey

    2011-01-01

    Dark energy with the usually used equation of state p=??, where ?=const<0 is hydrodynamically unstable. To overcome this drawback we consider the cosmology of a perfect fluid with a linear equation\\u000a of state of a more general form p=?(???\\u000a 0), where the constants ? and ?\\u000a 0 are free parameters. The anisotropic Bianchi type-I cosmological model filled with dark energy

  15. Dark-energy equation of state: how far can we go from ??

    E-print Network

    Hrvoje Stefancic

    2006-09-28

    The equation of state of dark energy is investigated to determine how much it may deviate from the equation of state of the cosmological constant (CC). Two aspects of the problem are studied: the "expansion" around the vacuum equation of state and the problem of the crossing of the cosmological constant boundary.

  16. Probing dark energy perturbations: the dark energy equation of state and speed of sound as measured by WMAP

    E-print Network

    Rachel Bean; Olivier Doré

    2003-07-17

    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 speed of sound, from CMB alone, c_{s}^{2}speed of sound.

  17. Perceiving the equation of state of Dark Energy while living in a Cold Spot

    SciTech Connect

    Valkenburg, Wessel, E-mail: w.valkenburg@thphys.uni-heidelberg.de [Institut für Theoretische Teilchenphysik und Kosmologie, RWTH Aachen University, D-52056 Aachen (Germany)

    2012-01-01

    The Cold Spot could be an adiabatic perturbation on the surface of last scattering, in which case it is an over-density with comoving radius of the order of 1 Gpc. We assess the effect that living in a similar structure, without knowing it, has on our perception of the equation of state of Dark Energy. We find that structures of dimensions such that they could cause the Cold Spot on the CMB, affect the perceived equation of state of Dark Energy possibly up to ten percent.

  18. Dynamical mutation of dark energy

    NASA Astrophysics Data System (ADS)

    Abramo, L. R.; Batista, R. C.; Liberato, L.; Rosenfeld, R.

    2008-03-01

    We discuss the intriguing possibility that dark energy may change its equation of state in situations where large dark energy fluctuations are present. We show indications of this dynamical mutation in some generic models of dark energy.

  19. Constraining the Dark Energy Equation of State Using Alternative Cosmic Tracers

    NASA Astrophysics Data System (ADS)

    Chávez, R.; Terlevich, R.; Terlevich, E.; Bresolin, F.; Melnick, J.; Plionis, M.; Basilakos, S.

    2011-10-01

    We propose to use the H II galaxies redshift - distance relation, measured by means of their L(H?)-? correlation, in order to determine the Hubble function to intermediate and high redshifts, in an attempt to constrain the dark energy equation of state parameters solution space, as an alternative to the cosmological use of type a supernovae.

  20. Effect of dark energy sound speed and equation of state on CDM power spectrum

    E-print Network

    Rizwan Ul Haq Ansari; Sanil Unnikrishnan

    2014-07-15

    We study the influence of equation of state $w$ and effective sound speed $c_e$ of the dark energy perturbations on the cold dark matter(CDM) power spectrum.We consider different cases of the equation of state and the effective sound speed, the cold dark matter power spectrum is found to be generically suppressed in these cases as compared to the $\\Lambda$CDM model. The suppression at different length scales depends on the value of $w$ and $c_e$, and the effect of different $w$ is profoundly seen at all length scales. The influence of sound speed is significantly seen only at the intermediate length scales and is negligible at scales very much larger and smaller than the Hubble scale.

  1. Constraints on The Dark Energy Equation of State And The Deceleration Parameter From Recent Cosmic Observations

    E-print Network

    Hassan Amirhashchi

    2015-03-22

    We study the constraints on dark energy equation of state $\\omega^{X}$ and the deceleration parameter $q$ from the recent observational data including Hubble data and the cosmic microwave background (CMB) radiation by using a model-independent deceleration parameter $q(z)=1/2-a/(1+z)^b$ and dark energy equation of state $\\omega^{X}=\\omega_{0}+\\omega_{1}z/(1+z)$ in the scope of anisotropic Bianchi type I space-time. For the cases of Hubble dataset, CMB data, and their combination, our results indicate that the constraints on transition redshift $z_{\\ast}$ are $0.62^{+1.45}_{-0.56}$, $0.34^{+0.13}_{-0.06}$, and $0.60^{+0.20}_{-0.10}$ respectively.

  2. dark matter dark energy inflation

    E-print Network

    Hu, Wayne

    theory dark matter dark energy inflation The National Science Foundation The Kavli Foundation NSF Site Review November 28-29, 2005 #12;dark matter dark energy inflation NSF Site Visit ­ November 28 Gravitation initial conditions beyond single-field slow roll #12;dark matter dark energy inflation NSF Site

  3. Future Type Ia Supernova Data as Tests of Dark Energy from Modified Friedmann Equations

    NASA Astrophysics Data System (ADS)

    Wang, Yun; Freese, Katherine; Gondolo, Paolo; Lewis, Matthew

    2003-09-01

    In the Cardassian model, dark energy density arises from modifications to the Friedmann equation, which becomes H2=g(?M), where g(?M) is a new function of the energy density. The universe is flat, matter dominated, and accelerating. The distance-redshift relation predictions of generalized Cardassian models can be very different from generic quintessence models, and can be differentiated with data from upcoming pencil beam surveys of Type Ia supernovae such as Supernova/Acceleration Probe (SNAP). We have found the interesting result that, once ?m is known to 10% accuracy, SNAP will be able to determine the sign of the time dependence of the dark energy density. Knowledge of this sign (which is related to the weak energy condition) will provide a first discrimination between various cosmological models that fit the current observational data (cosmological constant, quintessence, Cardassian expansion). Further, we have performed Monte Carlo simulations to illustrate how well one can reproduce the form of the dark energy density with SNAP. To be concrete we study a class of two-parameter (n, q) generalized Cardassian models that includes the original Cardassian model (parameterized by n only) as a special case. Examples are given of modified polytropic (MP) Cardassian models that fit current supernova and cosmic microwave background data, and prospects for differentiating between MP Cardassian and other models in future data are discussed. We also note that some Cardassian models can satisfy the weak energy condition w>-1 even with a dark energy component that has an effective equation of state wX<-1.

  4. Properties and uncertainties of scalar field models of dark energy with barotropic equation of state

    SciTech Connect

    Novosyadlyj, Bohdan; Sergijenko, Olga; Apunevych, Stepan; Pelykh, Volodymyr [Astronomical Observatory of Ivan Franko National University of Lviv, Kyryla i Methodia str., 8, Lviv, 79005 (Ukraine); Ya. S. Pidstryhach Institute for Applied Problems of Mechanics and Mathematics, Naukova Street, 3-b, Lviv, 79060 (Ukraine)

    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.

  5. Thermodynamical properties of dark energy

    Microsoft Academic Search

    Yungui Gong; Bin Wang; Anzhong Wang

    2007-01-01

    We have investigated the thermodynamical properties of dark energy. Assuming that the dark energy temperature T˜a-n and considering that the volume of the Universe enveloped by the apparent horizon relates to the temperature, we have derived the dark energy entropy. For dark energy with constant equation of state w>-1 and the generalized Chaplygin gas, the derived entropy can be positive

  6. Thermodynamical properties of dark energy

    Microsoft Academic Search

    Wang Anzhong; Wang Bin; Gong Yungui

    2007-01-01

    We have investigated the thermodynamical properties of dark energy. Assuming that the dark energy temperature Tâa{sup -n} and considering that the volume of the Universe enveloped by the apparent horizon relates to the temperature, we have derived the dark energy entropy. For dark energy with constant equation of state w>-1 and the generalized Chaplygin gas, the derived entropy can be

  7. Reconstruction of the deceleration parameter and the equation of state of dark energy

    SciTech Connect

    Gong Yungui; Wang Anzhong [College of Electronic Engineering, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China) and CASPER, Physics Department, Baylor University, Waco, Texas 76798 (United States); CASPER, Physics Department, Baylor University, Waco, Texas 76798 (United States)

    2007-02-15

    The new 182 gold supernova Ia data, the baryon acoustic oscillation measurement and the shift parameter determined from the Sloan Digital Sky Survey, and the three-year Wilkinson Microwave Anisotropy Probe data are combined to reconstruct the dark energy equation of state parameter w(z) and the deceleration parameter q(z). We find that the strongest evidence of acceleration happens around the redshift z{approx}0.2 and the stringent constraints on w(z) lie in the redshift range z{approx}0.2-0.5. At the sweet spot, -1.2dark energy parametrization w(z)=w{sub 0}+w{sub a}z/(1+z){sup 2} at the 3{sigma} confidence level. The transition redshift z{sub t} when the Universe underwent the transition from deceleration to acceleration is derived to be z{sub t}=0.36{sub -0.08}{sup +0.23}. The combined data is also applied to find out the geometry of the Universe, and we find that at the 3{sigma} confidence level, vertical bar {omega}{sub k} vertical bar < or approx. 0.05 for the simple one-parameter dark energy model, and -0.064<{omega}{sub k}<0.028 for the {lambda}CDM model.

  8. Inference for the dark energy equation of state using Type IA supernova data

    Microsoft Academic Search

    Christopher R. Genovese; Peter Freeman; Larry Wasserman; Robert C. Nichol; Christopher Miller

    2009-01-01

    The surprising discovery of an accelerating universe led cosmologists to posit the existence of “dark energy”—a mysterious energy field that permeates the universe. Understanding dark energy has become the central problem of modern cosmology. After describing the scientific background in depth, we formulate the task as a nonlinear inverse problem that expresses the comoving distance function in terms of the

  9. Detecting features in the dark energy equation of state: a wavelet approach

    SciTech Connect

    Hojjati, Alireza; Pogosian, Levon; Zhao, Gong-Bo, E-mail: alireza_hojjati@sfu.ca, E-mail: levon@sfu.ca, E-mail: gong-bo.zhao@port.ac.uk [Department of Physics, Simon Fraser University, Burnaby, BC, V5A 1S6 (Canada)

    2010-04-01

    We study the utility of wavelets for detecting the redshift evolution of the dark energy equation of state w(z) from the combination of supernovae (SNe), CMB and BAO data. We show that local features in w, such as bumps, can be detected efficiently using wavelets. To demonstrate, we first generate a mock supernovae data sample for a SNAP-like survey with a bump feature in w(z) hidden in, then successfully discover it by performing a blind wavelet analysis. We also apply our method to analyze the recently released ''Constitution'' SNe data, combined with WMAP and BAO from SDSS, and find weak hints of dark energy dynamics. Namely, we find that models with w(z) < ?1 for 0.2 < z < 0.5, and w(z) > ?1 for 0.5 < z < 1, are mildly favored at 95% confidence level. This is in good agreement with several recent studies using other methods, such as redshift binning with principal component analysis (PCA) (e.g. Zhao and Zhang, arXiv: 0908.1568)

  10. Bayesian model selection without evidences: application to the dark energy equation-of-state

    E-print Network

    Hee, Sonke; Hobson, Mike P; Lasenby, Anthony N

    2015-01-01

    A method is presented for Bayesian model selection without explicitly computing evidences, by using a combined likelihood and introducing an integer model selection parameter $n$ so that Bayes factors, or more generally posterior odds ratios, may be read off directly from the posterior of $n$. If the total number of models under consideration is specified a priori, the full joint parameter space $(\\theta, n)$ of the models is of fixed dimensionality and can be explored using standard MCMC or nested sampling methods, without the need for reversible jump MCMC techniques. The posterior on $n$ is then obtained by straightforward marginalisation. We demonstrate the efficacy of our approach by application to several toy models. We then apply it to constraining the dark energy equation-of-state using a free-form reconstruction technique. We show that $\\Lambda$CDM is significantly favoured over all extensions, including the simple $w(z){=}{\\rm constant}$ model.

  11. Test of the Chevallier-Polarski-Linder parametrization for rapid dark energy equation of state transitions

    SciTech Connect

    Linden, Sebastian; Virey, Jean-Marc [Centre de Physique Theorique, CNRS-Luminy Case 907, F-13288 Marseille Cedex 9 (France) and Universite de Provence (France)

    2008-07-15

    We test the robustness and flexibility of the Chevallier-Polarski-Linder (CPL) parametrization of the dark energy equation of state w(z)=w{sub 0}+w{sub a}(z/1+z) in recovering a four-parameter steplike fiducial model. We constrain the parameter space region of the underlying fiducial model where the CPL parametrization offers a reliable reconstruction. It turns out that non-negligible biases leak into the results for recent (z<2.5) rapid transitions, but that CPL yields a good reconstruction in all other cases. The presented analysis is performed with supernova Ia data as forecasted for a space mission like SNAP/JDEM, combined with future expectations for the cosmic microwave background shift parameter R and the baryonic acoustic oscillation parameter A.

  12. Effects of voids on the reconstruction of the equation of state of dark energy

    SciTech Connect

    Lavallaz, Arnaud de; Fairbairn, Malcolm [Department of Physics, King's College London, Strand, London, WC2R 2LS (United Kingdom)

    2011-10-15

    We quantify the effects of the voids known to exist in the Universe upon the reconstruction of the dark energy equation of state w. We show that the effect can start to be comparable with some of the other errors taken into account when analyzing supernova data, depending strongly upon the low redshift cutoff used in the sample. For the supernova data alone, the error induced in the reconstruction of w is much larger than the percent level. When the Baryonic Acoustic Oscillations and the Cosmic Microwave Background data are included in the fit, the effect of the voids upon the determination of w is much lessened but is not much smaller than some of the other errors taken into consideration when performing such fits. We also look at the effect of voids upon the estimation of the equation of state when we allow w to vary over time and show that even when supernova, Cosmic Microwave Background, and Baryonic Acoustic Oscillations data are used to constrain the equation of state, the best fit points in parameter space can change at the 10% level due to the presence of voids, and error-bars increase significantly.

  13. Cosmo-dynamics and dark energy with non-linear equation of state: a quadratic model

    E-print Network

    Kishore N. Ananda; Marco Bruni

    2005-12-08

    We investigate the general relativistic dynamics of Robertson-Walker models with a non-linear equation of state (EoS), focusing on the quadratic case P = P_0 + \\alpha \\rho + \\beta \\rho^2. This may be taken to represent the Taylor expansion of any arbitrary barotropic EoS, P(\\rho). With the right combination of P_0, \\alpha and \\beta, it serves as a simple phenomenological model for dark energy, or even unified dark matter. Indeed we show that this simple model for the EoS can produce a large variety of qualitatively different dynamical behaviors that we classify using dynamical systems theory. An almost universal feature is that accelerated expansion phases are mostly natural for these non-linear EoS's. These are often asymptotically de Sitter thanks to the appearance of an effective cosmological constant. Other interesting possibilities that arise from the quadratic EoS are closed models that can oscillate with no singularity, models that bounce between infinite contraction/expansion and models which evolve from a phantom phase, asymptotically approaching a de Sitter phase instead of evolving to a "Big Rip". In a second paper we investigate the effects of the quadratic EoS in inhomogeneous and anisotropic models, focusing in particular on singularities.

  14. Dark Energy Tomography

    E-print Network

    Yong-Seon Song; Lloyd Knox

    2003-12-08

    We study how parameter error forecasts for tomographic cosmic shear observations are affected by sky coverage, density of source galaxies, inclusion of CMB experiments, simultaneou fitting of non--dark energy parameters, and the parametrization of the history of the dark energy equation-of-state parameter w(z). We find tomographic shear-shear power spectra on large angular scales (l0.04.

  15. Nonparametric reconstruction of the dark energy equation of state from diverse data sets

    SciTech Connect

    Holsclaw, Tracy; Sanso, Bruno; Lee, Herbie [Department of Applied Mathematics and Statistics, University of California, Santa Cruz, California 95064 (United States); Alam, Ujjaini [ISR-1, MS D466, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Heitmann, Katrin [ISR-1, MS D466, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); High Energy Physics Division and Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, Illinois, 60439 (United States); Habib, Salman [T-2, MS B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); High Energy Physics Division and Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, Illinois, 60439 (United States); Higdon, David [CCS-6, MS F600, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

    2011-10-15

    The cause of the accelerated expansion of the Universe poses one of the most fundamental questions in physics today. In the absence of a compelling theory to explain the observations, a first task is to develop a robust phenomenological approach: If the acceleration is driven by some form of dark energy, then the phenomenology is determined by the form of the dark energy equation of state w(z) as a function of redshift. A major aim of ongoing and upcoming cosmological surveys is to measure w and its evolution at high accuracy. Since w(z) is not directly accessible to measurement, powerful reconstruction methods are needed to extract it reliably from observations. We have recently introduced a new reconstruction method for w(z) based on Gaussian process modeling. This method can capture nontrivial w(z) dependences and, most importantly, it yields controlled and unbiased error estimates. In this paper we extend the method to include a diverse set of measurements: baryon acoustic oscillations, cosmic microwave background measurements, and supernova data. We analyze currently available data sets and present the resulting constraints on w(z), finding that current observations are in very good agreement with a cosmological constant. In addition, we explore how well our method captures nontrivial behavior of w(z) by analyzing simulated data assuming high-quality observations from future surveys. We find that the baryon acoustic oscillation measurements by themselves already lead to remarkably good reconstruction results and that the combination of different high-quality probes allows us to reconstruct w(z) very reliably with small error bounds.

  16. Dark Group Dark Energy and Dark Matter

    E-print Network

    De la Macorra, A

    2004-01-01

    We study the possibility that a dark group, a gauge group with particles interacting with the standard model particles only via gravity, is responsible for containing the dark energy and dark matter required by present day observations. We show that it is indeed possible and we determine the constrains for the dark group. The non-perturbative effects generated by a strong gauge coupling constant can de determined and a scalar potential for the dark meson fields is generated parameterizing the dark energy. On the other hand it is the massive particles, e.g. dark baryons, of the dark gauge group that give the corresponding dark matter. The mass of the dark particles is of the order of the condensation scale $\\Lambda_c$ and the temperature is 4-5 times smaller then the photon's temperature. The dark matter is of the warm matter type and it gives good fit to structure formation. The only parameters of the model are the number of particles of the dark group. The conditions to not introduce any fine tuning of the e...

  17. Dark Energy From Fifth Dimension

    Microsoft Academic Search

    H. Alavirad; N. Riazi

    2008-01-01

    Observational evidence for the existence of dark energy is strong. Here we suggest a model which is based on a modified gravitational theory in 5D and interpret the 5th dimension as a manifestation of dark energy in the 4D observable universe. We also obtain an equation of state parameter which varies with time. Finally, we match our model with observations

  18. Thermodynamical properties of dark energy

    SciTech Connect

    Gong Yungui; Wang Bin; Wang Anzhong [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China) and CASPER, Department of Physics, Baylor University, Waco, Texas 76798 (United States); Department of Physics, Fudan University, Shanghai 200433 (China); CASPER, Department of Physics, Baylor University, Waco, Texas 76798 (United States)

    2007-06-15

    We have investigated the thermodynamical properties of dark energy. Assuming that the dark energy temperature T{approx}a{sup -n} and considering that the volume of the Universe enveloped by the apparent horizon relates to the temperature, we have derived the dark energy entropy. For dark energy with constant equation of state w>-1 and the generalized Chaplygin gas, the derived entropy can be positive and satisfy the entropy bound. The total entropy, including those of dark energy, the thermal radiation, and the apparent horizon, satisfies the generalized second law of thermodynamics. However, for the phantom with constant equation of state, the positivity of entropy, the entropy bound, and the generalized second law cannot be satisfied simultaneously.

  19. Thermodynamical properties of dark energy

    E-print Network

    Yungui Gong; Bin Wang; Anzhong Wang

    2007-06-22

    We have investigated the thermodynamical properties of dark energy. Assuming that the dark energy temperature $T\\sim a^{-n}$ and considering that the volume of the Universe enveloped by the apparent horizon relates to the temperature, we have derived the dark energy entropy. For dark energy with constant equation of state $w>-1$ and the generalized Chaplygin gas, the derived entropy can be positive and satisfy the entropy bound. The total entropy, including those of dark energy, the thermal radiation and the apparent horizon, satisfies the generalized second law of thermodynamics. However, for the phantom with constant equation of state, the positivity of entropy, the entropy bound, and the generalized second law cannot be satisfied simultaneously.

  20. Reconstructing and Deconstructing Dark Energy

    E-print Network

    Eric V. Linder

    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.

  1. On Oscillating Dark Energy

    E-print Network

    Eric V. Linder

    2005-11-15

    Distance-redshift data can impose strong constraints on dark energy models even when the equation of state is oscillatory. Despite the double integral dependence of the distance on the equation of state, precision measurement of the distance-redshift relation for z=0-2 is more incisive than the linear growth factor, CMB last scattering surface distance, and the age of the universe in distinguishing oscillatory behavior from an average behavior. While oscillating models might help solve the coincidence problem (since acceleration occurs periodically), next generation observations will strongly constrain such possibilities.

  2. Tommaso Treu, UC Santa Barbara What is the nature of dark energy and dark matter?

    E-print Network

    Glashausser, Charles

    Tommaso Treu, UC Santa Barbara What is the nature of dark energy and dark matter? I will describe on the equation of state of dark energy and flatness comparable to those obtained with the best probes. The second

  3. Correspondence between Ricci and other dark energies

    E-print Network

    Surajit Chattopadhyay; Ujjal Debnath

    2010-09-26

    Purpose of the present paper is to view the correspondence between Ricci and other dark energies. We have considered the Ricci dark energy in presence of dark matter in non-interacting situation. Subsequently, we have derived the pressure and energy density for Ricci dark energy. The equation of state parameter has been generated from these pressure and energy density. Next, we have considered the correspondence between Ricci and other dark energy models, namely tachyonic field, DBI-essence and new agegraphic dark energy without any interaction and investigated possible cosmological consequences.

  4. 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).

  5. Constraining Perturbative Early Dark Energy with Current Observations

    Microsoft Academic Search

    Ujjaini Alam; Ujjaini

    2010-01-01

    In this work, we study a class of early dark energy (EDE) models, in which, unlike in standard dark energy models, a substantial amount of dark energy exists in the matter-dominated era. We self-consistently include dark energy perturbations, and constrain these models using current observations. We consider EDE models in which the dark energy equation of state is at least

  6. The Dark Energy Paradigm

    E-print Network

    Burra G. Sidharth

    2014-12-30

    Though the concept of a dark energy driven accelerating universe was introduced by the author in 1997, to date dark energy itself, as described below has remained a paradigm. A model for the cosmological constant is suggested.

  7. Thermodynamics and dark energy

    NASA Astrophysics Data System (ADS)

    Silva, R.; Gonçalves, R. S.; Alcaniz, J. S.; Silva, H. H. B.

    2012-01-01

    Significant observational effort has been directed to unveiling the nature of the so-called dark energy. However, given the large number of theoretical possibilities, it is possible that this a task cannot be based only on observational data. We discuss some thermodynamic properties of this energy component assuming a general time-dependent equation-of-state parameter w(z) = w0 + waf(z), where w0 and wa are constants and f(z) may assume different forms. We show that very restrictive bounds can be placed on the w0 - wa space when current observational data are combined with the thermodynamic constraints derived.

  8. Measuring the speed of dark: Detecting dark energy perturbations

    NASA Astrophysics Data System (ADS)

    de Putter, Roland; Huterer, Dragan; Linder, Eric V.

    2010-05-01

    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)?-1], degrees of freedom distinct from quintessence (cs?1), and early presence of dark energy [?de(a?1)?0]. Future data may open a new window on dark energy by measuring its spatial as well as time variation.

  9. Inhomogeneous Dark Matter in Nontrivial Interaction with Dark Energy

    Microsoft Academic Search

    Roberto A. Sussman; Israel Quiros; Osmel Martín González

    We study interacting dark energy (DE) and cold dark matter (DM) in the context of an inhomogeneous and anisotropic spacetime.\\u000a DM and DE are modeled as an interactive mixture of inhomogeneous dust (DM) and a generic homogeneous dark energy (DE) fluid.\\u000a By choosing an “equation of state” linking the energy density (?) and pressure (p) of the DE fluid, as

  10. Entropy bounds and dark energy

    NASA Astrophysics Data System (ADS)

    Hsu, Stephen D. H.

    2004-07-01

    Entropy bounds render quantum corrections to the cosmological constant ? finite. Under certain assumptions, the natural value of ? is of order the observed dark energy density ~10-10 eV4, thereby resolving the cosmological constant problem. We note that the dark energy equation of state in these scenarios is w?p/?=0 over cosmological distances, and is strongly disfavored by observational data. Alternatively, ? in these scenarios might account for the diffuse dark matter component of the cosmological energy density. Permanent address: Institute of Theoretical Science and Department of Physics, University of Oregon, Eugene, OR 97403.

  11. Dark Energy and Dark Gravity

    E-print Network

    Ruth Durrer; Roy Maartens

    2007-12-05

    Observations provide increasingly strong evidence that the universe is accelerating. This revolutionary advance in cosmological observations confronts theoretical cosmology with a tremendous challenge, which it has so far failed to meet. Explanations of cosmic acceleration within the framework of general relativity are plagued by difficulties. General relativistic models are nearly all based on a dark energy field with fine-tuned, unnatural properties. There is a great variety of models, but all share one feature in common -- an inability to account for the gravitational properties of the vacuum energy. Speculative ideas from string theory may hold some promise, but it is fair to say that no convincing model has yet been proposed. An alternative to dark energy is that gravity itself may behave differently from general relativity on the largest scales, in such a way as to produce acceleration. The alternative approach of modified gravity (or dark gravity) provides a new angle on the problem, but also faces serious difficulties, including in all known cases severe fine-tuning and the problem of explaining why the vacuum energy does not gravitate. The lack of an adequate theoretical framework for the late-time acceleration of the universe represents a deep crisis for theory -- but also an exciting challenge for theorists. It seems likely that an entirely new paradigm is required to resolve this crisis.

  12. Dark Energy Phenomenology

    E-print Network

    Martin Kunz; Luca Amendola; Domenico Sapone

    2008-06-08

    We discuss the phenomenology of the dark energy in first order perturbation theory, demonstrating that the dark energy cannot be fully constrained unless the dark matter is found, and that there are two functions that characterise the observational properties of the dark sector for cosmological probes. We argue that measuring these two functions should be an important goal for observational cosmology in the next decades.

  13. Alternatives to Dark Matter and Dark Energy

    E-print Network

    Mannheim, P D

    2006-01-01

    We review the underpinnings of the standard Newton-Einstein theory of gravity, and identify where it could possibly go wrong. In particular, we discuss the logical independence from each other of the general covariance principle, the equivalence principle and the Einstein equations, and discuss how to constrain the matter energy-momentum tensor which serves as the source of gravity. We identify the a priori assumption of the validity of standard gravity on all distance scales as the root cause of the dark matter and dark energy problems, and discuss how the freedom currently present in gravitational theory can enable us to construct candidate alternatives to the standard theory in which the dark matter and dark energy problems could then be resolved. We identify three generic aspects of these alternate approaches: that it is a universal acceleration scale which determines when a luminous Newtonian expectation is to fail to fit data, that there is a global cosmological effect on local galactic motions which ca...

  14. On thermodynamical properties of dark energy

    E-print Network

    Gong, Y; Wang, B; Gong, Yungui; Wang, Anzhong; Wang, Bin

    2006-01-01

    We have investigated the thermodynamical properties of the dark energy. Assuming that the dark energy temperature $T\\sim a^{-n}$ and considering that the universe volume enveloped by the apparent horizon relates to the temperature, we have derived the dark energy entropy. For the dark energy with constant equation of state $w>-1$ and the generalized Chaplygin gas dark energy models, the derived entropy can be positive and satisfy the entropy bound. The total entropy, including those of the dark energy, the thermal radiation and the geometric entropy on the apparent horizon, satisfies the generalized second law of thermodynamics. However, for the phantom dark energy with constant equation of state, the positivity of entropy, the entropy bound and the generalized second law cannot be satisfied simultaneously.

  15. Dark Energy Search with Supernovae

    E-print Network

    Yun Wang

    2004-04-25

    To determine the nature of dark energy from observational data, it is important that we use model-independent and optimal methods. We should probe dark energy using its density (allowed to be a free function of cosmic time) instead of its equation of state. We should minimize gravitational lensing effect on supernovae by flux-averaging. We need to include complementary data (for example, from the Cosmic Microwave Background [CMB] and large scale structure [LSS]) in a consistent manner to help break the degeneracy between the dark energy density and the matter density fraction. We should push for ambitious future supernova surveys that can observe a large number of supernovae at the highest possible redshifts. I discuss these and other issues that will be important in our quest to unravel the mystery of the nature of dark energy. Current supernova, CMB, and LSS data already rule out dark energy models with dark energy densities that vary greatly with time; with the cosmological constant model providing an excellent fit to the data. A precise measurement of dark energy density as a free function of cosmic time will have a fundamental impact on particle physics and cosmology.

  16. Cosmology with Ricci dark energy

    NASA Astrophysics Data System (ADS)

    del Campo, Sergio; Fabris, Júlio C.; Herrera, Ramón; Zimdahl, Winfried

    2013-06-01

    We assume the cosmological dark sector to consist of pressureless matter and holographic dark energy with a cutoff length proportional to the Ricci scale. The requirement of separate energy-momentum conservation of the components is shown to establish a relation between the matter fraction and the (necessarily time-dependent) equation-of-state parameter of the dark energy. Focusing on intrinsically adiabatic pressure perturbations of the dark-energy component, the matter perturbations are found as linear combinations of the total energy-density perturbations of the cosmic medium and the relative (nonadiabatic) perturbations of the components. The resulting background dynamics is consistent with observations from supernovae of type Ia, baryonic acoustic oscillations and the differential age of old objects. The perturbation dynamics, on the other hand, is plagued by instabilities which excludes any phantom-type equation of state. The only stable configuration is singled out by a fixed relation between the present matter fraction ?m0 and the present value ?0 of the equation-of-state parameter of the dark energy. However, this instability-avoiding configuration is only marginally consistent with the observationally preferred background values of the mentioned parameters.

  17. Natural Dark Energy

    E-print Network

    Douglas Scott; Ali Frolop

    2007-03-30

    It is now well accepted that both Dark Matter and Dark Energy are required in any successful cosmological model. Although there is ample evidence that both Dark components are necessary, the conventional theories make no prediction for the contributions from each of them. Moreover, there is usually no intrinsic relationship between the two components, and no understanding of the nature of the mysteries of the Dark Sector. Here we suggest that if the Dark Side is so seductive then we should not be restricted to just 2 components. We further suggest that the most natural model has 5 distinct forms of Dark Energy in addition to the usual Dark Matter, each contributing precisely equally to the cosmic energy density budget.

  18. 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.

  19. Dark Energy in the Dark Ages

    SciTech Connect

    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.

  20. What Is the Origin of Dark Energy?

    NASA Astrophysics Data System (ADS)

    Tsujikawa, Shinji

    2007-09-01

    The recent data of Supernova Ia and other observations suggest that the universe has entered the stage of an accelerated expansion after the matter-dominated epoch. The origin of dark energy responsible for this accelerated expansion is a serious mistery. Reviewed are recent theoretical attempts to investigate the origin of dark energy such as scalar field models and modified gravity models. Addressed are also the method to determine the evolution of the equation of state of dark energy from observations.

  1. Possible Equilibria of Interacting Dark Energy Models

    E-print Network

    Micheal S. Berger; Hamed Shojaei

    2008-06-06

    Interacting dark energy and the holographic principle offer a possible way of addressing the cosmic coincidence problem as well as accounting for the size of the dark energy component. The equilibrium points of the Friedmann equations which govern the evolution behavior of dark energy, matter, and curvature components can determine the qualitative behavior of the cosmological models. These possible equilibria and their behavior are examined in a general framework, and some illustrative examples are presented.

  2. Possible equilibria of interacting dark energy models

    SciTech Connect

    Berger, Micheal S.; Shojaei, Hamed [Physics Department, Indiana University, Bloomington, Indiana 47405 (United States)

    2008-06-15

    Interacting dark energy and the holographic principle offer a possible way of addressing the cosmic coincidence problem as well as accounting for the size of the dark energy component. The equilibrium points of the Friedmann equations which govern the evolution behavior of dark energy, matter, and curvature components can determine the qualitative behavior of the cosmological models. These possible equilibria and their behavior are examined in a general framework, and some illustrative examples are presented.

  3. Dark energy survey and camera

    SciTech Connect

    William Wester

    2004-08-16

    The authors describe the Dark Energy Survey and Camera. The survey will image 5000 sq. deg. in the southern sky to collect 300 million galaxies, 30,000 galaxy clusters and 2000 Type Ia supernovae. They expect to derive a value for the dark energy equation of state parameters, w, to a precision of 5% by combining four distinct measurement techniques. They describe the mosaic camera that will consist of CCDs with enhanced sensitivity in the near infrared. The camera will be mounted at the prime focus of the 4m Blanco telescope.

  4. Natural scaling for dark energy

    E-print Network

    L. N. Granda

    2013-08-29

    We propose a dark energy density based on the Gauss-Bonnet 4-dimensional invariant and its modification. This model avoids the necessity of introducing the black hole limit to define the holographic density, since it can be considered as a non-saturated regime. This allows to describe the dark energy with an equation of state and Hubble parameter behaving in a way that can be adjusted very well to recent observations. The model presents quintom behavior without any future finite-time singularities.

  5. Dark Energy, or Worse

    ScienceCinema

    Professor Sean Carroll

    2010-01-08

    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.

  6. Brane-Bulk energy exchange and agegraphic dark energy

    E-print Network

    Ahmad Sheykhi

    2010-02-06

    We consider the agegraphic models of dark energy in a braneworld scenario with brane-bulk energy exchange. We assume that the adiabatic equation for the dark matter is satisfied while it is violated for the agegraphic dark energy due to the energy exchange between the brane and the bulk. Our study shows that with the brane-bulk interaction, the equation of state parameter of agegraphic dark energy on the brane, $w_D$, can have a transition from normal state where $w_D >-1 $ to the phantom regime where $w_D energy always satisfies $w^{\\mathrm{eff}}_D\\geq-1$.

  7. Thermodynamical description of the ghost dark energy model

    E-print Network

    M. Honarvaryan; A. Sheykhi; H. Moradpour

    2015-05-02

    In this paper, we point out thermodynamical description of ghost dark energy and its generalization to the early universe. Thereinafter, we find expressions for the entropy changes of these dark energy candidates. In addition, considering thermal fluctuations, thermodynamics of the dark energy component interacting with a dark matter sector is addressed. {We will also find the effects of considering the coincidence problem on the mutual interaction between the dark sectors, and thus the equation of state parameter of dark energy.} Finally, we derive a relation between the mutual interaction of the dark components of the universe, accelerated with the either ghost dark energy or its generalization, and the thermodynamic fluctuations.

  8. Thermodynamical description of the ghost dark energy model

    E-print Network

    Honarvaryan, M; Moradpour, H

    2015-01-01

    In this paper, we point out thermodynamical description of ghost dark energy and its generalization to the early universe. Thereinafter, we find expressions for the entropy changes of these dark energy candidates. In addition, considering thermal fluctuations, thermodynamics of the dark energy component interacting with a dark matter sector is addressed. {We will also find the effects of considering the coincidence problem on the mutual interaction between the dark sectors, and thus the equation of state parameter of dark energy.} Finally, we derive a relation between the mutual interaction of the dark components of the universe, accelerated with the either ghost dark energy or its generalization, and the thermodynamic fluctuations.

  9. Coupled tachyonic dark energy: a dynamical analysis

    E-print Network

    Landim, Ricardo C G

    2015-01-01

    In this paper we present a dynamical analysis for a coupled tachyonic dark energy with dark matter. The tachyonic field $\\phi$ is considered in the presence of barothropic fluids (matter and radiation) and the autonomous system due to the evolution equations is studied. The three cosmological eras (radiation, matter and dark energy) are described through the critical points, for a generic potential $V(\\phi)$.

  10. Generalizing the cosmic energy equation

    SciTech Connect

    Shtanov, Yuri [Bogolyubov Institute for Theoretical Physics, Kiev 03680 (Ukraine); Department of Physics, Taras Shevchenko Kiev National University, Kiev (Ukraine); Sahni, Varun [Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007 (India)

    2010-11-15

    We generalize the cosmic energy equation to the case when massive particles interact via a modified gravitational potential of the form {phi}(a,r), which is allowed to explicitly depend upon the cosmological time through the expansion factor a(t). Using the nonrelativistic approximation for particle dynamics, we derive the equation for the cosmological expansion which has the form of the Friedmann equation with a renormalized gravitational constant. The generalized Layzer-Irvine cosmic energy equation and the associated cosmic virial theorem are applied to some recently proposed modifications of the Newtonian gravitational interaction between dark-matter particles. We also draw attention to the possibility that the cosmic energy equation may be used to probe the expansion history of the universe thereby throwing light on the nature of dark matter and dark energy.

  11. The Dark Energy Survey

    NASA Astrophysics Data System (ADS)

    Flaugher, Brenna

    2012-03-01

    The Dark Energy Survey Collaboration will soon begin a 5000 sq. deg. imaging survey of the southern galactic cap using a new 520 Megapixel CCD camera, the Dark Energy Camera, with 5 filters (g,r,i,z and Y) mounted on the Blanco 4-meter telescope at Cerro-Tololo Inter-American Observatory. The data will be used to place new and tight constraints on the nature of dark energy via the history of the cosmic expansion rate and the growth of large-scale structure, using the four complementary techniques recommended by the Dark Energy Task Force: weak gravitational lensing, galaxy cluster counts, large-scale structure including baryon acoustic oscillations, and Type Ia supernovae. Installation of the new camera and commissioning on the telescope will take place in early-mid 2012 with the expectation that the survey will begin in late 2012. The science projections and prospects will be described.

  12. Dark Energy in the Dark Ages

    E-print Network

    Eric V. Linder

    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 \\la2% of total energy density at z\\gg1 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 5% 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 zenergy behavior over the entire range z=0-1100.

  13. Quintessence and Dark Energy

    Microsoft Academic Search

    Axel de La Macorra

    2004-01-01

    Dark energy accounts for about 70% of the content of our Universe. Perhaps the best candidate to parametrize the dark energy is a scalar field with only gravitational interactions called quintessence. We first present a generic theoretical approach to quintessence. We show that if the minimum of the scalar potential is at V|min=0 (i.e. there is no arbitrary scale) then

  14. Quintessence and Dark Energy

    Microsoft Academic Search

    Axel de la Macorra

    Dark energy accounts for about 70% of the content of our Universe. Perhaps the best candidate to parametrize the dark energy is a scalar field with only gravitational interactions called quintessence.\\u000a We first present a generic theoretical approach to quintessence. We show that if the minimum of the scalar potential is at V|min=0 (i.e. there is no arbitrary scale) then

  15. Probing Dark Energy with SNAP

    E-print Network

    Eric V. Linder

    2002-10-09

    The distance-redshift relation observed for supernovae has led to the discovery that the expansion of the universe is accelerating. A next generation experiment, the Supernova/Acceleration Probe (SNAP), can investigate the nature of the dark energy responsible, determining its energy density contribution and equation of state. In addition, indications of time variation in the equation of state could provide critical clues to the underlying fundamental physics; we show how SNAP can achieve 3 sigma detection of such time variation in some cases.

  16. Kaluza-Klein Cosmology With Modified Holographic Dark Energy

    E-print Network

    M. Sharif; Farida Khanum

    2011-06-13

    We investigate the compact Kaluza-Klein cosmology in which modified holographic dark energy is interacting with dark matter. Using this scenario, we evaluate equation of state parameter as well as equation of evolution of the modified holographic dark energy. Further, it is shown that the generalized second law of thermodynamics holds without any constraint.

  17. Coupling dark energy to dark matter perturbations

    E-print Network

    Marra, Valerio

    2015-01-01

    This Letter proposes that dark energy in the form of a scalar field could effectively couple to dark matter perturbations. The idea is that dark matter particles could annihilate/interact inside dense clumps and transfer energy to the scalar field, which would then enter an accelerated regime. This hypothesis is interesting as it provides a natural trigger for the onset of the acceleration of the universe, since dark energy starts driving the expansion of the universe when matter perturbations become sufficiently dense. Here we study a possible realization of this general idea by coupling dark energy to dark matter via the linear growth function of matter perturbations. The numerical results show that it is indeed possible to obtain a viable cosmology with the expected series of radiation, matter and dark-energy dominated eras. Moreover, the current density of dark energy is given by the value of the coupling parameters rather than by very special initial conditions for the scalar field. In other words, this ...

  18. UNIFIED THEORY OF DARK ENERGY AND DARK SHOUHONG WANG 2

    E-print Network

    Wang, Shouhong

    UNIFIED THEORY OF DARK ENERGY AND DARK MATTER TIAN MA, 1 SHOUHONG WANG 2 Abstract. The aim of this research report is to derive a uni- fied theory for dark matter and dark energy. Due to the presence of dark energy and dark matter, we postulate that the energy- momentum tensor of the normal matter

  19. Thermodynamics of dark energy interacting with dark matter and radiation

    SciTech Connect

    Jamil, Mubasher [Center for Advanced Mathematics and Physics, National University of Sciences and Technology, Rawalpindi, 46000 (Pakistan); Saridakis, Emmanuel N. [Department of Physics, University of Athens, GR-15771 Athens (Greece); Setare, M. R. [Department of Science, Payame Noor University, Bijar (Iran, Islamic Republic of)

    2010-01-15

    We investigate the validity of the generalized second law of thermodynamics, in the cosmological scenario where dark energy interacts with both dark matter and radiation. Calculating separately the entropy variation for each fluid component and for the apparent horizon itself, we show that the generalized second law is always and generally valid, independently of the specific interaction form, of the fluids equation-of-state parameters and of the background geometry.

  20. Irreversible thermodynamic description of interacting dark energy-dark matter cosmological models

    NASA Astrophysics Data System (ADS)

    Harko, Tiberiu; Lobo, Francisco S. N.

    2013-02-01

    We investigate the interaction between dark energy and dark matter in the framework of irreversible thermodynamics of open systems with matter creation/annihilation. We consider dark energy and dark matter as an interacting two-component (scalar field and “ordinary” dark matter) cosmological fluid in a homogeneous spatially flat and isotropic Friedmann-Robertson-Walker Universe. The thermodynamics of open systems as applied together with the gravitational field equations to the two-component cosmological fluid leads to a generalization of the elementary dark energy-dark matter interaction theory, in which the decay (creation) pressures are explicitly considered as parts of the cosmological fluid stress-energy tensor. Specific models describing coherently oscillating scalar waves, leading to a high particle production at the beginning of the oscillatory period, and models with a constant potential energy scalar field are considered. Furthermore, exact and numerical solutions of the gravitational field equations with dark energy-dark matter interactions are also obtained.

  1. Interacting dark energy: the role of microscopic feedback in the dark sector

    E-print Network

    P. P. Avelino

    2015-03-10

    We investigate the impact on the classical dynamics of dark matter particles and dark energy of a non-minimal coupling in the dark sector, assuming that the mass of the dark matter particles is coupled to a dark energy scalar field. We show that standard results can only be recovered if the space-time variation of the dark energy scalar field is sufficiently smooth on the characteristic length scale of the dark matter particles, and we determine the associated constraint dependent on both the mass and radius of the dark matter particles and the coupling to the dark energy scalar field. We further show, using field theory numerical simulations, that a violation of such constraint results in a microscopic feedback effect strongly affecting the dynamics of dark matter particles, with a potential impact on structure formation and on the space-time evolution of the dark energy equation of state.

  2. LSST: a complementary probe of dark energy

    Microsoft Academic Search

    J. A. Tyson; D. M. Wittman; J. F. Hennawi; D. N. Spergelb

    2003-01-01

    The number of mass clusters and their distribution in redshift are very sensitive to the density of matter ?m and the equation of state of dark energy w. Using weak lens gravitational tomography one can detect clusters of dark matter, weigh them, image their projected mass distribution, and determine their 3-D location. The degeneracy curve in the ?m ? w

  3. Dark energy and dark matter unification via superfluid Chaplygin gas

    NASA Astrophysics Data System (ADS)

    Popov, V. A.

    2010-03-01

    A new model describing the dark sector of the universe is established. The model involves Bose-Einstein condensate (BEC) as dark energy (DE) and an excited state above it as dark matter (DM). The condensate is assumed to have a negative pressure and is embodied as an exotic fluid with Chaplygin equation of state. Excitations are described as a quasiparticle gas. It is shown that the model is not in disagreement with the current observations of the cosmic acceleration. The model predicts increase of the effective cosmological constant and a complete disappearance of the matter at the far future.

  4. Schwarzschild black hole in dark energy background

    NASA Astrophysics Data System (ADS)

    Ishwarchandra, Ngangbam; Ibohal, N.; Yugindro Singh, K.

    2014-10-01

    In this paper we present an exact solution of Einstein's field equations describing the Schwarzschild black hole in dark energy background. It is also regarded as an embedded solution that the Schwarzschild black hole is embedded into the dark energy space producing Schwarzschild-dark energy black hole. It is found that the space-time geometry of Schwarzschild-dark energy solution is non-vacuum Petrov type D in the classification of space-times. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor of the Schwarzschild-dark energy solution. We also find that the energy-momentum tensor of the Schwarzschild-dark energy solution violates the strong energy condition due to the negative pressure leading to a repulsive gravitational force of the matter field in the space-time. It is shown that the time-like vector field for an observer in the Schwarzschild-dark energy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity and the area of the horizons for the Schwarzschild-dark energy black hole.

  5. Schwarzschild black hole in dark energy background

    E-print Network

    Ngangbam Ishwarchandra; Ng. Ibohal; K. Yugindro Singh

    2014-09-27

    In this paper we present an exact solution of Einstein's field equations describing the Schwarzschild black hole in dark energy background. It is also regarded as an embedded solution that the Schwarzschild black hole is embedded into the dark energy space producing Schwarzschild-dark energy black hole. It is found that the space-time geometry of Schwarzschild-dark energy solution is non-vacuum Petrov type $D$ in the classification of space-times. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor of the Schwarzschild-dark energy solution. We also find that the energy-momentum tensor of the Schwarzschild-dark energy solution violates the strong energy condition due to the negative pressure leading to a repulsive gravitational force of the matter field in the space-time. It is shown that the time-like vector field for an observer in the Schwarzschild-dark energy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity and the area of the horizons for the Schwarzschild-dark energy black hole.

  6. Confronting dark energy anisotropic stress

    NASA Astrophysics Data System (ADS)

    Chang, Baorong; Xu, Lixin

    2014-07-01

    We use currently available cosmic observations to probe and constrain an imperfect dark-energy fluid that is characterized by a constant equation of state w and a constant speed of viscosity cvis2. The model parameter space was scanned using the Markov chain Monte Carlo method. The results show that the speed of viscosity cvis2 was not well constrained when currently available data sets are used (including the cosmic microwave background radiation from Planck-2013 and WMAP9, type Ia supernovae, baryon acoustic oscillations, redshift space distortion f?8(z), and gravitational weak lensing from Canada-France Hawaii Telescope Lensing Survey (CFHTLenS). However, the cosmic data sets slightly favor phantom dark energy with a negative speed of viscosity cvis2.

  7. Dark energy from bulk matter

    SciTech Connect

    Bogdanos, C.; Dimitriadis, A.; Tamvakis, K. [Physics Department, University of Ioannina, Ioannina GR451 10 (Greece)

    2007-04-15

    We consider the possibility of getting accelerated expansion and w=-1 crossing in the context of a braneworld cosmological setup, endowed with a bulk energy-momentum tensor. For a given ansatz of the bulk content, we demonstrate that the bulk pressures dominate the dynamics at late times and can lead to accelerated expansion. We also analyze the constraints under which we can get a realistic profile for the effective equation of state and conclude that matter in the bulk has the effect of dark energy on the brane. Furthermore, we show that it is possible to simulate the behavior to a Chaplygin gas using nonexotic bulk matter.

  8. A strategy to measure the dark energy equation of state using the H II galaxy Hubble function and X-ray active galactic nuclei clustering: preliminary results

    NASA Astrophysics Data System (ADS)

    Plionis, M.; Terlevich, R.; Basilakos, S.; Bresolin, F.; Terlevich, E.; Melnick, J.; Chavez, R.

    2011-10-01

    We explore the possibility of setting stringent constraints to the dark energy equation of state using alternative cosmic tracers like (a) the Hubble relation using H II galaxies, which can be observed at much higher redshifts (z? 3.5) than those currently traced by Type Ia supernovae (SNeIa) samples, and (b) the large-scale structure using the clustering of X-ray selected active galactic nuclei (AGN), which have a redshift distribution peaking at z˜ 1. In this paper we use extensive Monte Carlo simulations to define the optimal strategy for the recovery of the dark energy equation of state using the high-redshift (z? 2) Hubble relation, but accounting also for the effects of gravitational lensing, which for such high redshifts can significantly affect the derived cosmological constraints. We investigate the size of the sample of high-z H II galaxies needed to provide useful constraints in the dark energy equation of state. Based on a 'figure of merit' analysis, we provide estimates for the number of 2 ?z? 3.5 tracers needed to reduce the cosmological solution space, presently provided by the Constitution SNIa set, by a desired factor. The analysis is given for any level of rms distance modulus uncertainty and we find that an expected reduction (i.e. by ˜20-40 per cent) of the current level of H II-galaxy-based distance modulus uncertainty does not provide a significant improvement in the derived cosmological constraints. It is much more efficient to increase the number of tracers than to reduce their individual uncertainties. Finally, we propose a framework to put constraints on the dark energy equation of state by using the joint likelihood of the X-ray AGN clustering and of the Hubble relation cosmological analyses. A preliminary joint analysis using the X-ray AGN clustering of the 2XMM survey and the Hubble relation of the Constitution SNIa set provide ?m= 0.31 ± 0.01 and w=-1.06 ± 0.05. We also find that the joint SNIa-2XMM analysis provides significantly more stringent cosmological constraints, increasing the figure of merit by a factor of ˜2, with respect to that of the joint SNIa-baryonic acoustic oscillation analysis.

  9. Cosmic history of viable exponential gravity: Equation of state oscillations and growth index from inflation to dark energy era

    E-print Network

    Kazuharu Bamba; Antonio Lopez-Revelles; R. Myrzakulov; S. D. Odintsov; L. Sebastiani

    2012-11-13

    A generic feature of viable $F(R)$ gravity is investigated: It is demonstrated that during the matter dominated era the large frequency oscillations of the effective dark energy may influence the behavior of higher derivatives of the Hubble parameter with the risk to produce some singular unphysical solutions at high redshift. This behavior is explicitly analyzed for realistic $F(R)$ models, in particular, exponential gravity and a power form model. To stabilize such oscillations, we consider the additional modification of the models via a correction term which does not destroy the viability properties. A detailed analysis on the future evolution of the universe and the evolution history of the growth index of the matter density perturbations are performed. Furthermore, we explore two applications of exponential gravity to the inflationary scenario. We show how it is possible to obtain different numbers of $e$-folds during the early-time acceleration by making different choices of the model parameters in the presence of ultrarelativistic matter, which destabilizes inflation and eventually leads to the exit from the inflationary stage. We execute the numerical analysis of inflation in two viable exponential gravity models. It is proved that at the end of the inflation, the effective energy density and curvature of the universe decrease and thus a unified description between inflation and the $\\Lambda$CDM-like dark energy dominated era can be realized.

  10. Braneworlds and Dark Energy

    E-print Network

    Rui Neves; Cenalo Vaz

    2006-05-18

    In the Randall-Sundrum scenario, we analyse the dynamics of an AdS5 braneworld when conformal matter fields propagate in five dimensions. We show that conformal fields of weight -4 are associated with stable geometries which describe the dynamics of inhomogeneous dust, generalized dark radiation and homogeneous polytropic dark energy on a spherically symmetric 3-brane embedded in the compact AdS5 orbifold. We discuss aspects of the radion stability conditions and of the localization of gravity in the vicinity of the brane.

  11. Dark Energy. What the ...?

    SciTech Connect

    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.

  12. The Dark Side: from Dark Energy & Dark Matter to Washington and Science Policy

    E-print Network

    Collar, Juan I.

    The Dark Side: from Dark Energy & Dark Matter to Washington and Science Policy Presenter: Michael: The Map Room (www.maproom.com )1949 N. Hoyne #12;The Dark Side: from Dark Energy and Dark Matter? What is the nature of the dark energy that is causing the expansion of the Universe to speed up

  13. Braneworld models of dark energy

    NASA Astrophysics Data System (ADS)

    Sahni, Varun; Shtanov, Yuri

    2003-11-01

    We explore a new class of braneworld models in which the scalar curvature of the (induced) brane metric contributes to the brane action. The scalar curvature term arises generically on account of one-loop effects induced by matter fields residing on the brane. Spatially flat braneworld models can enter into a regime of accelerated expansion at late times. This is true even if the brane tension and the bulk cosmological constant are tuned to satisfy the Randall Sundrum constraint on the brane. Braneworld models admit a wider range of possibilities for dark energy than standard LCDM. In these models the luminosity distance can be both smaller and larger than the luminosity distance in LCDM. Whereas models with dL leq dL(LCDM) imply w = p/rho geq -1 and have frequently been discussed in the literature, models with dL > dL(LCDM) have traditionally been ignored, perhaps because, within the general-relativistic framework, the luminosity distance has this property only if the equation of state of matter is strongly negative (w < -1). Within the conventional framework, `phantom energy' with w < -1 is beset with a host of undesirable properties, which makes this model of dark energy unattractive. Braneworld models, on the other hand, have the capacity to endow dark energy with exciting new possibilities (including w < -1) without suffering from the problems faced by phantom energy. For a subclass of parameter values, braneworld dark energy and the acceleration of the universe are transient phenomena. In these models, the universe, after the current period of acceleration, re-enters the matter-dominated regime so that the deceleration parameter q(t) rightarrow 0.5 when t >> t0, where t0 is the present epoch. Such models could help reconcile an accelerating universe with the requirements of string/M-theory.

  14. Gravitational collapse due to dark matter and dark energy in the brane world scenario

    E-print Network

    Soma Nath; Subenoy Chakraborty; Ujjal Debnath

    2005-12-21

    Gravitational collapse of FRW brane world embedded in a conformaly flat bulk is considered for matter cloud consists of dark matter and dark energy with equation of state $p=\\epsilon \\rho$ $(\\epsilon<-{1/3})$. The effect of dark matter and dark energy is being considered first separately and then a combination of them both with and without interaction. In some cases the collapse leads to black hole in some other cases naked singularity appears.

  15. Cosmological Evolution of Pilgrim Dark Energy

    E-print Network

    M. Sharif; M. Zubair

    2014-09-26

    We study pilgrim dark energy model by taking IR cut-offs as particle and event horizons as well as conformal age of the universe. We derive evolution equations for fractional energy density and equation of state parameters for pilgrim dark energy. The phantom cosmic evolution is established in these scenarios which is well supported by the cosmological parameters such as deceleration parameter, statefinder parameters and phase space of $\\omega_\\vartheta$ and $\\omega'_\\vartheta$. We conclude that the consistent value of parameter $\\mu$ is $\\mu<0$ in accordance with the current Planck and WMAP$9$ results.

  16. Dark energy, inflation, and extra dimensions

    SciTech Connect

    Steinhardt, Paul J. [Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544 (United States); Princeton Center for Theoretical Science, Princeton University, Princeton, New Jersey 08544 (United States); Wesley, Daniel [Centre for Theoretical Cosmology, DAMTP, Cambridge University, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)

    2009-05-15

    We consider how accelerated expansion, whether due to inflation or dark energy, imposes strong constraints on fundamental theories obtained by compactification from higher dimensions. For theories that obey the null energy condition (NEC), we find that inflationary cosmology is impossible for a wide range of compactifications; and a dark energy phase consistent with observations is only possible if both Newton's gravitational constant and the dark energy equation of state vary with time. If the theory violates the NEC, inflation and dark energy are only possible if the NEC-violating elements are inhomogeneously distributed in the compact dimensions and vary with time in precise synchrony with the matter and energy density in the noncompact dimensions. Although our proofs are derived assuming general relativity applies in both four and higher dimensions and certain forms of metrics, we argue that similar constraints must apply for more general compactifications.

  17. Dark Energy: fiction or reality?

    SciTech Connect

    Triay, Roland [Centre de Physique Theorique, CNRS Luminy Case 907, 13288 Marseille Cedex 9 (France)

    2010-06-15

    Is Dark Energy justified as an alternative to the cosmological constant LAMBDA in order to explain the acceleration of the cosmic expansion? It turns out that a straightforward dimensional analysis of Einstein equation provides us with clear evidences that the geometrical nature of LAMBDA is the only viable source to this phenomenon, in addition of the application of Ockham's razor principle. This contribution is primarily a review of the main stream in the interpretation of LAMBDA because it is at the origin of such a research program.

  18. Dust of dark energy

    SciTech Connect

    Lim, Eugene A. [ISCAP and Department of Physics, Columbia University, 538 West 120th Street, New York, NY 10027 (United States); Sawicki, Ignacy; Vikman, Alexander, E-mail: eugene.a.lim@gmail.com, E-mail: ignacy.sawicki@nyu.edu, E-mail: alexander.vikman@nyu.edu [CCPP, Department of Physics, New York University, 4 Washington Pl., New York, NY 10003 (United States)

    2010-05-01

    We introduce a novel class of field theories where energy always flows along timelike geodesics, mimicking in that respect dust, yet which possess non-zero pressure. This theory comprises two scalar fields, one of which is a Lagrange multiplier enforcing a constraint between the other's field value and derivative. We show that this system possesses no wave-like modes but retains a single dynamical degree of freedom. Thus, the sound speed is always identically zero on all backgrounds. In particular, cosmological perturbations reproduce the standard behaviour for hydrodynamics in the limit of vanishing sound speed. Using all these properties we propose a model unifying Dark Matter and Dark Energy in a single degree of freedom. In a certain limit this model exactly reproduces the evolution history of ?CDM, while deviations away from the standard expansion history produce a potentially measurable difference in the evolution of structure.

  19. Magnetized anisotropic ghost dark energy cosmological model

    NASA Astrophysics Data System (ADS)

    Das, Kanika; Sultana, Tazmin

    2015-06-01

    We present in this paper a LRS Bianchi type I cosmological model with dark matter and anisotropic ghost dark energy in presence of magnetic field. We have solved the Einstein's field equations with a particular form of Hubble parameter. The physical and geometrical behaviors of the model are discussed. It is observed that the anisotropy of the universe and that of the ghost dark energy tends to zero at late times and the universe becomes spatially homogeneous, isotropic and flat. The coincidence parameter increases with time. We have also studied the statefinder parameters. The results obtained are in agreement with the recent days observations.

  20. Conformal Higgs model: predicted dark energy density

    E-print Network

    R. K. Nesbet

    2014-11-03

    Postulated universal Weyl conformal scaling symmetry provides an alternative to the $\\Lambda$CDM paradigm for cosmology. Recent applications to galactic rotation velocities, Hubble expansion, and a model of dark galactic halos explain qualitative phenomena and fit observed data without invoking dark matter. Significant revision of theory relevant to galactic collisions and clusters is implied, but not yet tested. Dark energy is found to be a consequence of conformal symmetry for the Higgs scalar field of electroweak physics. The present paper tests this implication. The conformal Higgs model acquires a gravitational effect described by a modified Friedmann cosmic evolution equation, shown to fit cosmological data going back to the cosmic microwave background epoch. The tachyonic mass parameter of the Higgs model becomes dark energy in the Friedmann equation. A dynamical model of this parameter, analogous to the Higgs mechanism for gauge boson mass, is derived and tested here. An approximate calculation yields a result consistent with the empirical magnitude inferred from Hubble expansion.

  1. Probing gravitation, dark energy, and acceleration

    SciTech Connect

    Linder, Eric V.

    2004-02-20

    The acceleration of the expansion of the universe arises from unknown physical processes involving either new fields in high energy physics or modifications of gravitation theory. It is crucial for our understanding to characterize the properties of the dark energy or gravity through cosmological observations and compare and distinguish between them. In fact, close consistencies exist between a dark energy equation of state function w(z) and changes to the framework of the Friedmann cosmological equations as well as direct spacetime geometry quantities involving the acceleration, such as ''geometric dark energy'' from the Ricci scalar. We investigate these interrelationships, including for the case of super acceleration or phantom energy where the fate of the universe may be more gentle than the Big Rip.

  2. Virialization in Dark Energy Cosmology

    E-print Network

    Peng Wang

    2005-11-15

    We discuss the issue of energy nonconservation in the virialzation process of spherical collapse model with homogeneous dark energy. We propose an approximation scheme to find the virialization radius. By comparing various schemes and estimating the parameter characterizing the ratio of dark energy to dark matter at the turn-around time, we conclude that the problem of energy nonconservation may have sizable effects in fitting models to observations.

  3. Weak Lensing: Dark Matter, Dark Energy

    SciTech Connect

    Jain, Bhuvnesh (University of Pennsylvania) [University of Pennsylvania

    2006-02-27

    The light rays from distant galaxies are deflected by massive structures along the line of sight, causing the galaxy images to be distorted. Measurements of these distortions, known as weak lensing, provide a way of measuring the distribution of dark matter as well as the spatial geometry of the universe. I will describe the ideas underlying this approach to cosmology. With planned large imaging surveys, weak lensing is a powerful probe of dark energy. I will discuss the observational challenges ahead and recent progress in developing multiple, complementary approaches to lensing measurements.

  4. Dark matter, dark energy and gravity

    NASA Astrophysics Data System (ADS)

    Robson, B. A.

    2015-02-01

    Within the framework of the Generation Model (GM) of particle physics, gravity is identified with the very weak, universal and attractive residual color interactions acting between the colorless particles of ordinary matter (electrons, neutrons and protons), which are composite structures. This gravitational interaction is mediated by massless vector bosons (hypergluons), which self-interact so that the interaction has two additional features not present in Newtonian gravitation: (i) asymptotic freedom and (ii) color confinement. These two additional properties of the gravitational interaction negate the need for the notions of both dark matter and dark energy.

  5. Dipolar dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Blanchet, Luc; Le Tiec, Alexandre

    2009-07-01

    In previous work [L. Blanchet and A. Le Tiec, Phys. Rev. DPRVDAQ1550-7998 78, 024031 (2008)10.1103/PhysRevD.78.024031], a model of dark matter and dark energy based on the concept of gravitational polarization was investigated. This model was shown to recover the concordance cosmological scenario (?-cold dark matter) at cosmological scales, and the phenomenology of the modified Newtonian dynamics at galactic scales. In this article we prove that the model can be formulated with a simple and physically meaningful matter action in general relativity. We also provide alternative derivations of the main results of the model, and some details on the variation of the action.

  6. A phantom menace? Cosmological consequences of a dark energy component with super-negative equation of state

    NASA Astrophysics Data System (ADS)

    Caldwell, R. R.

    2002-10-01

    It is extraordinary that a number of observations indicate that we live in a spatially flat, low matter density Universe, which is currently undergoing a period of accelerating expansion. The effort to explain this current state has focused attention on cosmological models in which the dominant component of the cosmic energy density has negative pressure, with an equation of state /w>=-1. Remarking that most observations are consistent with models right up to the /w=-1 or cosmological constant (/?) limit, it is natural to ask what lies on the other side, at /w<-1. In this regard, we construct a toy model of a ``phantom'' energy component which possesses an equation of state /w<-1. Such a component is found to be compatible with most classical tests of cosmology based on current data, including the recent type 1a SNe data as well as the cosmic microwave background anisotropy and mass power spectrum. If the future observations continue to allow /w<-1, then barring unanticipated systematic effects, the dominant component of the cosmic energy density may be stranger than anything expected.

  7. Observational probes of dark energy

    NASA Astrophysics Data System (ADS)

    Wang, Yun

    2012-07-01

    The cause for the observed acceleration in the expansion of the universe is unknown, and referred to as "dark energy" for convenience. Dark energy could be an unknown energy component, or a modification of Einstein's general relativity. This dictates the measurements that are optimal in unveiling the nature of dark energy: the cosmic expansion history, and the growth history of cosmic large scale structure. I will examine Type Ia supernovae and galaxy clustering as dark energy probes, and discuss recent results and future prospects.

  8. Holographic Dark Energy Model and Scalar-Tensor Theories

    E-print Network

    Yousef Bisabr

    2008-08-10

    We study the holographic dark energy model in a generalized scalar tensor theory. In a universe filled with cold dark matter and dark energy, the effect of potential of the scalar field is investigated in the equation of state parameter. We show that for a various types of potentials, the equation of state parameter is negative and transition from deceleration to acceleration expansion of the universe is possible.

  9. Four LSST Probes of Dark Energy

    NASA Astrophysics Data System (ADS)

    Tyson, J. Anthony; Zhan, H.; Knox, L.; LSST Collaboration

    2007-12-01

    The half-sky LSST six band survey of four billion galaxies will address dark energy physics by exploiting a diversity of precision probes: • Weak lensing tomography (WL) of galaxies vs. redshift, which probes both distances and the evolution of structure vs. redshift, setting multiple independent constraints on the dark energy equation of state. • Spatial correlations of galaxies (Baryon Acoustic Oscillations, BAO) vs. redshift utilizes the "standard ruler” of the peak in the correlation of dark matter revealed in the temperature anisotropies in the cosmic microwave background (CMB). • The redshift distribution of shear peaks due to large structures of dark matter (via WL combined with the optical data) are a potentially sensitive probe of dark energy. • Hundreds of thousands of supernovae are complementary for probing the recent cosmic era when dark energy becomes dominant. When combined with the CMB data these tests form interlocking checks on cosmological models and the physics of dark energy. The combination of BAO with WL is especially powerful. Astrophysical observations are susceptible to systematics, so the LSST is being specifically designed and engineered to minimize and control systematics at a level ten times below the smallest signal of interest. Systematic error experiments using the Subaru telescope are incorporated in these estimates. These diverse probes are complementary, removing degeneracies. The LSST measurements will be obtained from the same set of observations with a powerful facility optimized for this purpose.

  10. Dark energy in hybrid inflation

    SciTech Connect

    Gong, Jinn-Ouk [Department of Physics, KAIST, Daejeon, Republic of Korea (Korea, Republic of); International Center for Astrophysics, KASI, Daejeon (Korea, Republic of); Kim, Seongcheol [Department of Physics, KAIST, Daejeon (Korea, Republic of)

    2007-03-15

    The situation that a scalar field provides the source of the accelerated expansion of the Universe while rolling down its potential is common in both the simple models of the primordial inflation and the quintessence-based dark energy models. Motivated by this point, we address the possibility of causing the current acceleration via the primordial inflation using a simple model based on hybrid inflation. We trigger the onset of the motion of the quintessence field via the waterfall field, and find that the fate of the Universe depends on the true vacuum energy determined by choosing the parameters. We also briefly discuss the variation of the equation of state and the possible implementation of our scenario in supersymmetric theories.

  11. Four LSST probes of Dark Energy

    NASA Astrophysics Data System (ADS)

    Tyson, J. A.; Zhan, H.; Knox, L.; LSST Collaboration

    2006-12-01

    The physics that produces the observed accelerating cosmic expansion is unknown. The half-sky LSST multi-band survey will address the underlying dark energy physics by exploiting a diversity of precision cosmic probes:

    • Weak lensing (WL) of galaxies vs. redshift, which probes both distances and the evolution of structure vs. redshift, thereby setting multiple independent strong constraints on the dark energy equation of state (EOS).
    • Spatial correlations of galaxies vs. redshift (Baryon Acoustic Oscillations, BAO) utilizes the “standard ruler” of the peak in the correlation of dark matter revealed in the temperature anisotropies in the cosmic microwave background (CMB).
    • The redshift distribution of shear peaks due to large structures of dark matter (via WL combined with the optical data) are an exponentially sensitive probe of the dark energy EOS.
    • A million supernovae are complementary for probing the recent cosmic era when dark energy becomes dominant.
    When combined with the CMB data these tests form interlocking checks on cosmological models and the physics of dark energy. The combination of BAO with WL is especially powerful. By simultaneously measuring the distance-redshift and growth-redshift relations, LSST data can tell us whether the recent acceleration is due to dark energy or modified gravity. Astrophysical observations are susceptible to systematics, so the LSST is being specifically designed and engineered to minimize and control systematics at a level ten times below the smallest signal of interest. The diverse techniques above are complementary, removing degeneracies. Much of the power of the LSST comes from the fact that the measurements will be obtained from the same set of observations with a powerful facility optimized for this purpose. Using realistic estimates of systematics from LSST-like observing on the Subaru telescope, we will show projected precision of the LSST survey constraints on the nature of dark energy.

  12. Holographic dark-energy models

    Microsoft Academic Search

    Sergio Del Campo; Júlio. C. Fabris; Ramón Herrera; Winfried Zimdahl

    2011-01-01

    Different holographic dark-energy models are studied from a unifying point of view. We compare models for which the Hubble scale, the future event horizon or a quantity proportional to the Ricci scale are taken as the infrared cutoff length. We demonstrate that the mere definition of the holographic dark-energy density generally implies an interaction with the dark-matter component. We discuss

  13. Interacting dark matter and holographic dark energy in an anisotropic universe

    NASA Astrophysics Data System (ADS)

    Adhav, K. S.; Tayade, G. B.; Bansod, A. S.

    2014-09-01

    In this paper we have studied the anisotropic and homogeneous Bianchi type-I universe filled with interacting Dark matter and Holographic dark energy. Here we discussed two models, in first model the solutions of the field equations are obtained for constant value of deceleration parameter where as in the second model the solutions of the field equations are obtained for special form of deceleration parameter. It is shown that for suitable choice of interaction between dark matter and holographic dark energy there is no coincidence problem (unlike ?CDM). Also, in all the resulting models the anisotropy of expansion dies out very quickly and attains isotropy after some finite time. The Statefinder diagnostic is applied to both the models in order to distinguish between our dark energy models with other existing dark energy models. The physical and geometrical aspects of the models are also discussed.

  14. Dynamical system analysis for DBI dark energy interacting with dark matter

    NASA Astrophysics Data System (ADS)

    Mahata, Nilanjana; Chakraborty, Subenoy

    2015-01-01

    A dynamical system analysis related to Dirac-Born-Infeld (DBI) cosmological model has been investigated in this present work. For spatially flat FRW spacetime, the Einstein field equation for DBI scenario has been used to study the dynamics of DBI dark energy interacting with dark matter. The DBI dark energy model is considered as a scalar field with a nonstandard kinetic energy term. An interaction between the DBI dark energy and dark matter is considered through a phenomenological interaction between DBI scalar field and the dark matter fluid. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables. The potential of the DBI scalar field is assumed to be exponential. Finally, critical points are determined, their nature have been analyzed and corresponding cosmological scenario has been discussed.

  15. On the similarity of Information Energy to Dark Energy

    E-print Network

    M. P. Gough; T. D. Carozzi; A. M. Buckley

    2006-06-19

    Information energy is shown here to have properties similar to those of dark energy. The energy associated with each information bit of the universe is found to be defined identically to the characteristic energy of a cosmological constant. Two independent methods are used to estimate the universe information content of ~10^91 bits, a value that provides an information energy total comparable to that of the dark energy. Information energy is also found to have a significantly negative equation of state parameter, w energy.

  16. arXiv:astro-ph/0703364v227Aug2007 Electromagnetic dark energy

    E-print Network

    Wright, Francis

    arXiv:astro-ph/0703364v227Aug2007 Electromagnetic dark energy Christian Beck School of MathematicalGill University, Montreal, Quebec, Canada (Dated: August 28, 2007) We introduce a new model for dark energy equations, or more generally with the existence of dark energy. The dark energy density consistent

  17. Correspondence between Generalized Dark Energy and Scalar Field Dark Energies

    NASA Astrophysics Data System (ADS)

    Maity, Sayani; Debnath, Ujjal

    2015-07-01

    In this work, we have considered non-flat FRW universe filled with dark matter (with non-zero pressure) and generalized dark energy (GDE) as motivated by the work of Sharif et al. (Mod. Phys. Lett. A 28, 1350180, 2013). Also the dark matter and the dark energy are considered to be interacting. The energy density, pressure and the EoS of the GDE have been calculated for the interacting scenario. For stability analysis of this model, we have also analyzed the sign of square speed of sound. Next we investigate the correspondence between GDE and different other candidates of dark energies such as DBI-essence, tachyonic field, hessenc and electromagnetic field. Also we have reconstructed the potential functions and the scalar fields in this scenario.

  18. Dark Energy in String Theory

    NASA Astrophysics Data System (ADS)

    Greene, Brian; Shiu, Gary

    2014-12-01

    We review the tension between the observational evidence for dark energy and various theoretical considerations. This tension has motivated a reconsideration of the issue of naturalness, and spawned various exotic approaches toward an acceptable solution. We discuss attempts to realize dark energy in string theory, and the perspective on the string landscape that these results have suggested.

  19. The Dark Energy Survey Instrument

    NASA Astrophysics Data System (ADS)

    Flaugher, Brenna; Dark Energy Survey Collaboration

    2006-12-01

    The Dark Energy Survey (DES) is designed to measure the dark energy equation of state parameter, w, to a statistical precision of 5%, with four complementary techniques: galaxy cluster counts, weak lensing, angular power spectrum and type Ia supernovae. We present an overview of the DES instrument (DECam) which will be mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a focal plane of 62 2kx4k CCDs, a five element optical corrector, four filters (g,r,i,z), and the associated infrastructure for operation in a new prime focus cage. To reach redshifts of 1, we plan to use the 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). A CCD packaging and testing facility has been established at Fermilab to produce fully characterized four-side buttable modules. DECam also includes design features to enhance the image quality and the efficiency of operations. DECam will be devoted to the DES for 30% of the time over the five year survey and will otherwise be available to the community as an NOAO facility instrument. Status of the design and prototyping efforts will be described.

  20. Dark Energy and Dark Matter in a Superfluid Universe

    NASA Astrophysics Data System (ADS)

    Huang, Kerson

    2014-04-01

    The vacuum is filled with complex scalar fields, such as the Higgs field. These fields serve as order parameters for superfluidity (quantum phase coherence over oscopic distances), making the entire universe a superfluid. We review a mathematical model consisting of two aspects: (a) emergence of the superfluid during the big bang; (b) observable manifestations of superfluidity in the present universe. The creation aspect requires a self-interacting scalar field that is asymptotically free, i.e. the interaction must grow from zero during the big bang, and this singles out the Halpern-Huang potential, which has exponential behavior for large fields. It leads to an equivalent cosmological constant that decays like a power law, and this gives dark energy without "fine-tuning." Quantum turbulence (chaotic vorticity) in the early universe was able to create all the matter in the universe, fulfilling the inflation scenario. In the present universe, the superfluid can be phenomenologically described by a nonlinear Klein-Gordon equation. It predicts halos around galaxies with higher superfluid density, which is perceived as dark matter through gravitational lensing. In short, dark energy is the energy density of the cosmic superfluid, and dark matter arises from local fluctuations of the superfluid density.

  1. Dark Energy and Dark Matter in a Superfluid Universe

    NASA Astrophysics Data System (ADS)

    Huang, Kerson

    2013-11-01

    The vacuum is filled with complex scalar fields, such as the Higgs field. These fields serve as order parameters for superfluidity (quantum phase coherence over macroscopic distances), making the entire universe a superfluid. We review a mathematical model consisting of two aspects: (a) emergence of the superfluid during the big bang; (b) observable manifestations of superfluidity in the present universe. The creation aspect requires a self-interacting scalar field that is asymptotically free, i.e. the interaction must grow from zero during the big bang, and this singles out the Halpern-Huang potential, which has exponential behavior for large fields. It leads to an equivalent cosmological constant that decays like a power law, and this gives dark energy without "fine-tuning." Quantum turbulence (chaotic vorticity) in the early universe was able to create all the matter in the universe, fulfilling the inflation scenario. In the present universe, the superfluid can be phenomenologically described by a nonlinear Klein-Gordon equation. It predicts halos around galaxies with higher superfluid density, which is perceived as dark matter through gravitational lensing. In short, dark energy is the energy density of the cosmic superfluid, and dark matter arises from local fluctuations of the superfluid density.

  2. Prospects for constraining the dark energy potential

    NASA Astrophysics Data System (ADS)

    Fernandez-Martinez, Enrique; Verde, Licia

    2008-08-01

    We generalize to non-flat geometries the formalism of Simon et al (2005 Phys. Rev. D 71 123001 [astro-ph/0412269]) to reconstruct the dark energy potential. This formalism makes use of quantities similar to the horizon-flow parameters in inflation, can, in principle, be made non-parametric and is general enough to be applied outside the simple, single-scalar-field quintessence. Since currently available and forthcoming data do not allow a non-parametric and exact reconstruction of the potential, we consider a general parametric description in terms of Chebyshev polynomials. We then consider present and future measurements of H(z), baryon acoustic oscillation (BAO) surveys and supernovae type 1A surveys, and investigate their constraints on the dark energy potential. We find that relaxing the flatness assumption increases the errors in the reconstructed dark energy evolution but does not open up significant degeneracies, provided that a modest prior is imposed on the geometry. Direct measurements of H(z), such as those provided by BAO surveys, are crucially important for constraining the evolution of the dark energy potential and the dark energy equation of state, especially for non-trivial deviations from the standard ?CDM (CDM: cold dark matter) model.

  3. Dark Energy: Reason for the Existence of a Classical Universe?

    E-print Network

    Huang, Peng; Li, Miao; Li, Nan

    2015-01-01

    Dark energy is investigated from the perspective of quantum cosmology. By treating the existence of a classical universe as a constraint, it is found that the normal ordering ambiguity factor q in Wheeler-DeWitt equation tends to take its value on domain (-1, 3). Furthermore, to ensure the existence of a classical universe, there must be dark energy in the universe. It is in this sense we propose that dark energy is the reason for the existence of a classical universe.

  4. Cosmological Evolution With Interaction Between Dark Energy And Dark Matter

    E-print Network

    Yu. L. Bolotin; A. Kostenko; O. A. Lemets; D. A. Yerokhin

    2014-08-17

    In this review we consider in detail different theoretical topics associated with interaction in the dark sector. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities. We consider a number of different models (including the holographic dark energy and dark energy in a fractal universe) with interacting dark energy (DE) and dark matter (DM), have done a thorough analysis of these models. The main task of this review was not only to give an idea about the modern set of different models of dark energy, but to show how much can be diverse dynamics of the universe in these models. We find that the dynamics of a Universe that contains interaction in the dark sector can differ significantly from the Standard Cosmological Model (SCM).

  5. Interacting holographic dark energy in Brans-Dicke theory

    E-print Network

    Ahmad Sheykhi

    2009-10-03

    We study cosmological application of interacting holographic energy density in the framework of Brans-Dicke cosmology. We obtain the equation of state and the deceleration parameter of the holographic dark energy in a non-flat universe. As system's IR cutoff we choose the radius of the event horizon measured on the sphere of the horizon, defined as $L=ar(t)$. We find that the combination of Brans-Dicke field and holographic dark energy can accommodate $w_D = -1 $ crossing for the equation of state of \\textit{noninteracting} holographic dark energy. When an interaction between dark energy and dark matter is taken into account, the transition of $w_D$ to phantom regime can be more easily accounted for than when resort to the Einstein field equations is made.

  6. Gravitational Origin of Phantom Dark Energy and Late Cosmic Acceleration

    E-print Network

    S. K. Srivastava

    2007-03-30

    In this letter, dark energy is obtained using dual roles of the Ricci scalar (as a physical field as well as geometry). Dark energy density, obtained here, mimics phantom and the derived Friedmann equation contains a term $\\rho^2_{\\rm de}/2 \\lambda$ with $\\rho_{\\rm de}$ being the dark energy density and $\\lambda$ being the cosmic tension. It is like brane-gravity inspired Friedmann equation, which arises without using the brane-gravity theory. It is found that acceleration is transient for $\\lambda 0$, expansion is found to encounter big-rip problem. It is shown that this problem can be avoided if dark energy behaves as barotropic fluid and generalized Chaplygin gas simultaneously. Moreover, time for transition (from deceleration to acceleration of the universe) is derived as a function of equation of state parameter ${\\rm w}_{\\rm de} = p_[rm de}/\\rho_{\\rm de}$ with $p_{\\rm de}$ being the pressure for dark energy fluid..

  7. Dark goo: bulk viscosity as an alternative to dark energy

    SciTech Connect

    Gagnon, Jean-Sebastien [Technische Universität Darmstadt, Schlossgartenstrasse 2, 64289, Darmstadt (Germany); Lesgourgues, Julien, E-mail: jean-sebastien.gagnon@physik.tu-darmstadt.de, E-mail: julien.lesgourgues@cern.ch [École Polytechnique Fédérale de Lausanne, CH-1015, Lausanne (Switzerland)

    2011-09-01

    We present a simple (microscopic) model in which bulk viscosity plays a role in explaining the present acceleration of the universe. The effect of bulk viscosity on the Friedmann equations is to turn the pressure into an 'effective' pressure containing the bulk viscosity. For a sufficiently large bulk viscosity, the effective pressure becomes negative and could mimic a dark energy equation of state. Our microscopic model includes self-interacting spin-zero particles (for which the bulk viscosity is known) that are added to the usual energy content of the universe. We study both background equations and linear perturbations in this model. We show that a dark energy behavior is obtained for reasonable values of the two parameters of the model (i.e. the mass and coupling of the spin-zero particles) and that linear perturbations are well-behaved. There is no apparent fine tuning involved. We also discuss the conditions under which hydrodynamics holds, in particular that the spin-zero particles must be in local equilibrium today for viscous effects to be important.

  8. Future supernovae observations as a probe of dark energy

    Microsoft Academic Search

    Jochen Weller; Andreas Albrecht

    2002-01-01

    We study the potential impact of improved future supernovae data on our understanding of the dark energy problem. We carefully examine the relative utility of different fitting functions that can be used to parametrize the dark energy models, and provide concrete reasons why a particular choice (based on a parametrization of the equation of state) is better in almost all

  9. Observatory conceptual development for the Joint Dark Energy Mission

    Microsoft Academic Search

    Michael J. Sholl; Gary M. Bernstein; Michael G. Dittman; Joseph M. Howard; Michael L. Lampton; John P. Lehan; J. Eric Mentzell; Robert A. Woodruff

    2009-01-01

    The Joint Dark Energy Mission (JDEM)1,2 is a proposed dark energy space mission that will measure the expansion history of the universe and the growth of its large scale structure. It is intended to provide tight constraints on the equation of state of the universe and test the validity of general relativity. Three complementary observational analyses will be employed: Baryon

  10. Reconstruction of the interaction term between dark matter and dark energy using SNe Ia

    Microsoft Academic Search

    Freddy Cueva Solano; Ulises Nucamendi

    2012-01-01

    We apply a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of dark energy (DE) with constant equation of state (EOS) parameter interacting with dark matter (DM)\\\\@. The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which

  11. Examining the Viability of Phantom Dark Energy

    E-print Network

    Ludwick, Kevin J

    2015-01-01

    In the standard cosmological framework of the 0th-order FLRW metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter $w energy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the value of best fit from Planck and WMAP9 for present-day $w$ is indeed less than $-1$. We find that it is not as obvious as one might think that phantom dark energy has negative 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 $wenergy tensor, and we ...

  12. Prospects in Constraining the Dark Energy Potential

    E-print Network

    Enrique Fernandez-Martinez; Licia Verde

    2008-08-14

    We generalize to non-flat geometries the formalism of Simon et al. (2005) to reconstruct the dark energy potential. This formalism makes use of quantities similar to the Horizon-flow parameters in inflation, can, in principle, be made non-parametric and is general enough to be applied outside the simple, single scalar field quintessence. Since presently available and forthcoming data do not allow a non-parametric and exact reconstruction of the potential, we consider a general parametric description in term of Chebyshev polynomials. We then consider present and future measurements of H(z), Baryon Acoustic Oscillations surveys and Supernovae type 1A surveys, and investigate their constraints on the dark energy potential. We find that, relaxing the flatness assumption increases the errors on the reconstructed dark energy evolution but does not open up significant degeneracies, provided that a modest prior on geometry is imposed. Direct measurements of H(z), such as those provided by BAO surveys, are crucially important to constrain the evolution of the dark energy potential and the dark energy equation of state, especially for non-trivial deviations from the standard LambdaCDM model.

  13. Reconstructing the interaction between dark energy and dark matter using Gaussian processes

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Guo, Zong-Kuan; Cai, Rong-Gen

    2015-06-01

    We present a nonparametric approach to reconstruct the interaction between dark energy and dark matter directly from SNIa Union 2.1 data using Gaussian processes, which is a fully Bayesian approach for smoothing data. In this method, once the equation of state (w ) of dark energy is specified, the interaction can be reconstructed as a function of redshift. For the decaying vacuum energy case with w =-1 , the reconstructed interaction is consistent with the standard ? CDM model, namely, there is no evidence for the interaction. This also holds for the constant w cases from -0.9 to -1.1 and for the Chevallier-Polarski-Linder (CPL) parametrization case. If the equation of state deviates obviously from -1 , the reconstructed interaction exists at 95% confidence level. This shows the degeneracy between the interaction and the equation of state of dark energy when they get constraints from the observational data.

  14. Reconstructing interaction between dark energy and dark matter using Gaussian Processes

    E-print Network

    Cai, Rong-Gen; Yang, Tao

    2015-01-01

    We present a non-parametric approach to reconstruct the interaction between dark energy and dark matter directly from SNIa Union 2.1 data using Gaussian Processes, which is a fully Bayesian approach for smoothing data. In this method, once the equation of state ($w$) of dark energy is specified, the interaction can be reconstructed with respect to redshift. For the decaying vacuum energy case with $w=-1$, the reconstructed interaction is consistent with the $\\Lambda$CDM model, namely, there is no evidence for the interaction. This also holds for the constant $w$ cases from $-0.9$ to $-1.1$ and for the CPL parameterization case. If the equation of state deviates obviously from $-1$, the reconstructed interaction exits at $95\\%$ confidence level. This shows the degeneracy between the interaction and the equation of state of dark energy when they get constraints from the observational data.

  15. Decoupling dark energy from matter

    SciTech Connect

    Brax, Philippe [Institut de Physique Théorique, CEA, IPhT, CNRS, URA 2306, F-91191Gif/Yvette Cedex (France); Bruck, Carsten van de [Department of Applied Mathematics, University of Sheffield, Hounsfield Road, Sheffield S3 7RH (United Kingdom); Davis, Anne-Christine [Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, Cambridge CB3 0WA (United Kingdom); Martin, Jérôme, E-mail: philippe.brax@cea.fr, E-mail: c.vandebruck@sheffield.ac.uk, E-mail: a.c.davis@damtp.cam.ac.uk, E-mail: jmartin@iap.fr [Institut d'Astrophysique de Paris, UMR 7095-CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris (France)

    2009-09-01

    We examine the embedding of dark energy in high energy models based upon supergravity and extend the usual phenomenological setting comprising an observable sector and a hidden supersymmetry breaking sector by including a third sector leading to the acceleration of the expansion of the universe. We find that gravitational constraints on the non-existence of a fifth force naturally imply that the dark energy sector must possess an approximate shift symmetry. When exact, the shift symmetry provides an example of a dark energy sector with a runaway potential and a nearly massless dark energy field whose coupling to matter is very weak, contrary to the usual lore that dark energy fields must couple strongly to matter and lead to gravitational inconsistencies. Moreover, the shape of the potential is stable under one-loop radiative corrections. When the shift symmetry is slightly broken by higher order terms in the Kähler potential, the coupling to matter remains small. However, the cosmological dynamics are largely affected by the shift symmetry breaking operators leading to the appearance of a minimum of the scalar potential such that dark energy behaves like an effective cosmological constant from very early on in the history of the universe.

  16. REPORT OF THE DARK ENERGY TASK FORCE

    E-print Network

    Baumgardt, Holger

    REPORT OF THE DARK ENERGY TASK FORCE (DETF) Dark energy appears to be the dominant component. These circumstances demand an ambitious observational program to determine the dark energy properties as well postulating that 70% of the universe is composed of mysterious "dark energy" that drives the acceleration

  17. Planck priors for dark energy surveys

    E-print Network

    Pia Mukherjee; Martin Kunz; David Parkinson; Yun Wang

    2008-03-11

    Although cosmic microwave background (CMB) anisotropy data alone cannot constrain simultaneously the spatial curvature and the equation of state of dark energy, CMB data provide a valuable addition to other experimental results. However computing a full CMB power spectrum with a Boltzmann code is quite slow; for instance if we want to work with many dark energy and/or modified gravity models, or would like to optimize experiments where many different configurations need to be tested, it is possible to adopt a quicker and more efficient approach. In this paper we consider the compression of the projected Planck CMB data into four parameters, R (scaled distance to last scattering surface), l_a (angular scale of sound horizon at last scattering), Omega_b h^2 (baryon density fraction) and n_s (powerlaw index of primordial matter power spectrum), all of which can be computed quickly. We show that, although this compression loses information compared to the full likelihood, such information loss becomes negligible when more data is added. We also demonstrate that the method can be used for scalar field dark energy independently of the parametrisation of the equation of state, and discuss how this method should be used for other kinds of dark energy models.

  18. Quantum Informational Dark Energy: Dark energy from forgetting

    Microsoft Academic Search

    Jae-Weon Lee; Jungjai Lee; Hyeong-Chan Kim

    2007-01-01

    We suggest that dark energy has a quantum informational origin. Landauer's\\u000aprinciple associated with the erasure of quantum information at a cosmic\\u000ahorizon implies the non-zero vacuum energy having effective negative pressure.\\u000aAssuming the holographic principle, the minimum free energy condition, and the\\u000aGibbons-Hawking temperature for the cosmic event horizon we obtain the\\u000aholographic dark energy with the parameter $d\\\\simeq

  19. Distribution of dark energy in the vicinity of compact objects

    E-print Network

    M. Tsizh; B. Novosyadlyj; Yu. Kulinich

    2014-12-23

    The distribution of dark energy density in the vicinity of compact static objects is analyzed. Dark energy is assumed to be in the form of a scalar field with three parameters: the background density, the equation of state parameter and the effective sound speed. Compact object is assumed to be a homogeneous spherical object of constant radius. We use the solutions of the hydrodynamical equations for dark energy in the gravitational fields of such objects for cases of static distribution of dark energy in the vicinity of star and stationary accretion onto black hole in order to analyze the possibility of constraining of the parameters of dark energy from astrophysical data. We show that dependence of density of dark energy in the vicinity of such object on the effective sound speed, background density and equation of state parameter of dark energy makes it possible to try such tests. Here we exploit the accuracy of determination of masses of Sun and black hole in the center of Milky Way to obtain the lower limit on the effective sound speed of dark energy.

  20. On Dark Energy and Dark Matter (Part I)

    Microsoft Academic Search

    Shlomo Barak; Elia M. Leibowitz

    2008-01-01

    Phenomena currently attributed to Dark Energy (DE) and Dark Matter (DM) are merely a result of the interplay between gravitational energy density, generated by the contraction of space by matter, and the energy density of the Cosmological Microwave Background (CMB), which causes space dilation. In the universe, globally, the gravitational energy density equals the CMB energy density. This leads to

  1. Models for Little Rip Dark Energy

    E-print Network

    Paul H. Frampton; Kevin J. Ludwick; Shin'ichi Nojiri; Sergei D. Odintsov; Robert J. Scherrer

    2012-01-16

    We examine in more detail specific models which yield a little rip cosmology, i.e., a universe in which the dark energy density increases without bound but the universe never reaches a finite-time singularity. We derive the conditions for the little rip in terms of the inertial force in the expanding universe and present two representative models to illustrate in more detail the difference between little rip models and those which are asymptotically de Sitter. We derive conditions on the equation of state parameter of the dark energy to distinguish between the two types of models. We show that coupling between dark matter and dark energy with a little rip equation of state can alter the evolution, changing the little rip into an asymptotic de Sitter expansion. We give conditions on minimally-coupled phantom scalar field models and on scalar-tensor models that indicate whether or not they correspond to a little rip expansion. We show that, counterintuitively, despite local instability, a little-rip cosmology has an infinite lifetime.

  2. Reissner-Nordstrom black hole in dark energy background

    E-print Network

    Ngangbam Ishwarchandra; Ng. Ibohal; K. Yugindro Singh

    2014-11-29

    In this paper we propose a stationary solution of Einstein's field equations describing Reissner-Nordstrom black hole in dark energy background. It is to be regarded as the Reissner-Nordstrom black hole is embedded into the dark energy solution producing Reissner-Nordstrom-dark energy black hole. We find that the space-time geometry of Reissner-Nordstrom-dark energy solution is Petrov type $D$ in the classification of space-times. It is also shown that the embedded space-time possesses an energy-momentum tensor of the electromagnetic field interacting with the dark energy having negative pressure. We find the energy-momentum tensor for dark energy violates the the strong energy condition due to the negative pressure, whereas that of the electromagnetic field obeys the strong energy condition. It is shown that the time-like vector field for an observer in the Reissner-Nordstrom-dark energy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity of the horizons for the embedded dark energy black hole. The characteristic properties of relativistic dark energy based on the de Sitter solution is discussed in an appendix.

  3. Dynamics of dark energy with a coupling to dark matter

    SciTech Connect

    Boehmer, Christian G. [Department of Mathematics, University College London, London WC1E 6BT (United Kingdom); Caldera-Cabral, Gabriela; Maartens, Roy [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 2EG (United Kingdom); Lazkoz, Ruth [Fisika Teorikoa, Euskal Herriko Unibertsitatea, 48080 Bilbao (Spain)

    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.

  4. Understanding Dark Energy

    NASA Astrophysics Data System (ADS)

    Greyber, Howard

    2009-11-01

    By careful analysis of the data from the WMAP satellite, scientists were surprised to determine that about 70% of the matter in our universe is in some unknown form, and labeled it Dark Energy. Earlier, in 1998, two separate international groups of astronomers studying Ia supernovae were even more surprised to be forced to conclude that an amazing smooth transition occurred, from the expected slowing down of the expansion of our universe (due to normal positive gravitation) to an accelerating expansion of the universe that began at at a big bang age of the universe of about nine billion years. In 1918 Albert Einstein stated that his Lambda term in his theory of general relativity was ees,``the energy of empty space,'' and represented a negative pressure and thus a negative gravity force. However my 2004 ``Strong'' Magnetic Field model (SMF) for the origin of magnetic fields at Combination Time (Astro-ph0509223 and 0509222) in our big bang universe produces a unique topology for Superclusters, having almost all the mass, visible and invisible, i.e. from clusters of galaxies down to particles with mass, on the surface of an ellipsoid surrounding a growing very high vacuum. If I hypothesize, with Einstein, that there exists a constant ees force per unit volume, then, gradually, as the universe expands from Combination Time, two effects occur (a) the volume of the central high vacuum region increases, and (b) the density of positive gravity particles in the central region of each Supercluster in our universe decreases dramatically. Thus eventually Einstein's general relativity theory's repulsive gravity of the central very high vacuum region becomes larger than the positive gravitational attraction of all the clusters of galaxies, galaxies, quasars, stars and plasma on the Supercluster shell, and the observed accelerating expansion of our universe occurs. This assumes that our universe is made up mostly of such Superclusters. It is conceivable that the high vacuum region between Superclusters also plays a role in adding extra repulsive gravity force. Note that cosmologist Stephen Hawking comments on his website that ``There is no reason to rule out negative pressure. This is just tension.''

  5. Anisotropic Dark Energy and the Generalized Second Law of Thermodynamics

    E-print Network

    M. Sharif; Farida Khanum

    2011-11-12

    We consider a Bianchi type $I$ model in which anisotropic dark energy is interacting with dark matter and anisotropic radiation. With this scenario, we investigate the validity of the generalized second law of thermodynamics. It is concluded that the validity of this law depends on different parameters like shear, skewness and equation of state.

  6. Structure formation in the presence of dark energy perturbations

    NASA Astrophysics Data System (ADS)

    Abramo, L. R.; Batista, R. C.; Liberato, L.; Rosenfeld, R.

    2007-11-01

    We study non-linear structure formation in the presence of dark energy. The influence of dark energy on the growth of large-scale cosmological structures is exerted both through its background effect on the expansion rate, and through its perturbations. In order to compute the rate of formation of massive objects we employ the spherical collapse formalism, which we generalize to include fluids with pressure. We show that the resulting non-linear evolution equations are identical to the ones obtained in the pseudo-Newtonian approach to cosmological perturbations, in the regime where an equation of state serves to describe both the background pressure relative to density, and the pressure perturbations relative to the density perturbations. We then consider a wide range of constant and time-dependent equations of state (including phantom models) parametrized in a standard way, and study their impact on the non-linear growth of structure. The main effect is the formation of dark energy structure associated with the dark matter halo: non-phantom equations of state induce the formation of a dark energy halo, damping the growth of structures; phantom models, on the other hand, generate dark energy voids, enhancing structure growth. Finally, we employ the Press Schechter formalism to compute how dark energy affects the number of massive objects as a function of redshift (number counts).

  7. Dodging the dark matter degeneracy while determining the dynamics of dark energy

    E-print Network

    Busti, Vinicius C

    2015-01-01

    One of the key issues in cosmology is to establish the nature of dark energy, and to determine whether the equation of state evolves with time. When estimating this from distance measurements there is a degeneracy with the matter density. We show that there exists a simple function of the dark energy equation of state and its first derivative which is independent of this degeneracy at all redshifts, and so is a much more robust determinant of the evolution of dark energy than just its derivative. We show that this function can be well determined at low redshift from supernovae using Gaussian Processes, and that this method is far superior to a variety of parameterisations which are also subject to priors on the matter density. This shows that parametrised models give very biased constraints on the evolution of dark energy.

  8. Can a galaxy redshift survey measure dark energy clustering?

    E-print Network

    Masahiro Takada

    2006-08-23

    (abridged) A wide-field galaxy redshift survey allows one to probe galaxy clustering at largest spatial scales, which carries an invaluable information on horizon-scale physics complementarily to the cosmic microwave background (CMB). Assuming the planned survey consisting of z~1 and z~3 surveys with areas of 2000 and 300 square degrees, respectively, we study the prospects for probing dark energy clustering from the measured galaxy power spectrum, assuming the dynamical properties of dark energy are specified in terms of the equation of state and the effective sound speed c_e in the context of an adiabatic cold dark matter dominated model. The dark energy clustering adds a power to the galaxy power spectrum amplitude at spatial scales greater than the sound horizon, and the enhancement is sensitive to redshift evolution of the net dark energy density, i.e. the equation of state. We find that the galaxy survey, when combined with Planck, can distinguish dark energy clustering from a smooth dark energy model such as the quintessence model (c_e=1), when c_edark energy clustering and the non-relativistic neutrinos implied from the neutrino oscillation experiments, because the two effects both induce a scale-dependent modification in the galaxy power spectrum shape at largest spatial scales accessible from the galaxy survey. It is shown that a wider redshift coverage can efficiently separate the two effects by utilizing the different redshift dependences, where dark energy clustering is apparent only at low redshifts z<1.

  9. Dark Matter and Dark Energy are Mirage

    Microsoft Academic Search

    Gunn Quznetsov

    2010-01-01

    It is known (Quznetsov, 2010) that probabilities of pointlike events are defined by some generalization of Dirac equation. One part of such generalized equation corresponds to the Dirac's leptonic equation, and the other part corresponds to the Dirac's quark equation. The quark part of this equation is invariant under the oscillations of chromatic states. And it turns out that these

  10. New interactions in the dark sector mediated by dark energy

    SciTech Connect

    Brookfield, Anthony W. [Astroparticle Theory and Cosmology Group, Department of Applied Mathematics, University of Sheffield, Hounsfield Road, Sheffield S3 7RH (United Kingdom); Astroparticle Theory and Cosmology Group, Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH (United Kingdom); Bruck, Carsten van de; Hall, Lisa M. H. [Astroparticle Theory and Cosmology Group, Department of Applied Mathematics, University of Sheffield, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

    2008-02-15

    Cosmological observations have revealed the existence of a dark matter sector, which is commonly assumed to be made up of one particle species only. However, this sector might be more complicated than we currently believe: there might be more than one dark matter species (for example, two components of cold dark matter or a mixture of hot and cold dark matter) and there may be new interactions between these particles. In this paper we study the possibility of multiple dark matter species and interactions mediated by a dark energy field. We study both the background and the perturbation evolution in these scenarios. We find that the background evolution of a system of multiple dark matter particles (with constant couplings) mimics a single fluid with a time-varying coupling parameter. However, this is no longer true on the perturbative level. We study the case of attractive and repulsive forces as well as a mixture of cold and hot dark matter particles.

  11. New interactions in the dark sector mediated by dark energy

    E-print Network

    A. W. Brookfield; C. van de Bruck; L. M. H. Hall

    2008-04-10

    Cosmological observations have revealed the existence of a dark matter sector, which is commonly assumed to be made up of one particle species only. However, this sector might be more complicated than we currently believe: there might be more than one dark matter species (for example two components of cold dark matter or a mixture of hot and cold dark matter) and there may be new interactions between these particles. In this paper we study the possibility of multiple dark matter species and interactions mediated by a dark energy field. We study both the background and the perturbation evolution in these scenarios. We find that the background evolution of a system of multiple dark matter particles (with constant couplings) mimics a single fluid with a time-varying coupling parameter. However, this is no longer true on the perturbative level. We study the case of attractive and repulsive forces as well as a mixture of cold and hot dark matter particles.

  12. The integrated Sachs-Wolfe effect in cosmologies with coupled dark matter and dark energy

    E-print Network

    Bjoern Malte Schaefer

    2008-03-14

    The subject of this paper is the derivation of the integrated Sachs-Wolfe (iSW) effect in cosmologies with coupled dark matter and dark energy fluids. These couplings influence the iSW-effect in three ways: The Hubble function assumes a different scaling, the structure growth rate shows a different time evolution, and in addition, the Poisson equation, which relates the density perturbations to fluctuations in the gravitational potential, is changed, due to the violation of the scaling rho ~ a^{-3} of the matter density rho with scale factor a. Exemplarily, I derive the iSW-spectra for a model in which dark matter decays into dark energy, investigate the influence of the dark matter decay rate and the dark energy equation of state on the iSW-signal, and discuss the analogies for gravitational lensing. Quite generally iSW-measurements should reach similar accuracy in determining the dark energy equation of state parameter and the coupling constant.

  13. Dynamical dark energy: Current constraints and forecasts

    NASA Astrophysics Data System (ADS)

    Upadhye, Amol; Ishak, Mustapha; Steinhardt, Paul J.

    2005-09-01

    We consider how well the dark energy equation of state w as a function of redshift z will be measured using current and anticipated experiments. We use a procedure which takes fair account of the uncertainties in the functional dependence of w on z, as well as the parameter degeneracies, and avoids the use of strong prior constraints. We apply the procedure to current data from the Wilkinson Microwave Anisotropy Probe, Sloan Digital Sky Survey, and the supernova searches, and obtain results that are consistent with other analyses using different combinations of data sets. The effects of systematic experimental errors and variations in the analysis technique are discussed. Next, we use the same procedure to forecast the dark energy constraints achievable by the end of the decade, assuming 8 years of Wilkinson Microwave Anisotropy Probe data and realistic projections for ground-based measurements of supernovae and weak lensing. We find the 2? constraints on the current value of w to be ?w0(2?)=0.20, and on dw/dz (between z=0 and z=1) to be ?w1(2?)=0.37. Finally, we compare these limits to other projections in the literature. Most show only a modest improvement; others show a more substantial improvement, but there are serious concerns about systematics. The remaining uncertainty still allows a significant span of competing dark energy models. Most likely, new kinds of measurements, or experiments more sophisticated than those currently planned, are needed to reveal the true nature of dark energy.

  14. The Dark Energy Survey: Overview

    NASA Astrophysics Data System (ADS)

    Frieman, Joshua; Dark Energy Survey Collaboration

    2013-01-01

    The Dark Energy Survey (DES) will employ a new, 570-megapixel digital imager, the Dark Energy Camera, on the Blanco 4-meter telescope at CTIO to carry out 2 multi-band surveys over 525 nights: a wide-area survey of 5000 sq. deg. that will provide grizY measurements of ~200 million galaxies and a time-domain survey in griz over 30 sq. deg. that will yield well-measured light curves for ~4000 type Ia supernovae. The camera saw first light on the telescope in Sept. 2012 and has since been undergoing commissioning and science verification. The aim of the DES project is to probe dark energy using 4 techniques: supernovae, clusters, galaxy clustering (including baryon acoustic oscillations), and weak lensing. I will overview the project, highlighting the science program and setting the context for the other talks in this Special Session.

  15. Dark Energy Camera for Blanco

    SciTech Connect

    Binder, Gary A.; /Caltech /SLAC

    2010-08-25

    In order to make accurate measurements of dark energy, a system is needed to monitor the focus and alignment of the Dark Energy Camera (DECam) to be located on the Blanco 4m Telescope for the upcoming Dark Energy Survey. One new approach under development is to fit out-of-focus star images to a point spread function from which information about the focus and tilt of the camera can be obtained. As a first test of a new algorithm using this idea, simulated star images produced from a model of DECam in the optics software Zemax were fitted. Then, real images from the Mosaic II imager currently installed on the Blanco telescope were used to investigate the algorithm's capabilities. A number of problems with the algorithm were found, and more work is needed to understand its limitations and improve its capabilities so it can reliably predict camera alignment and focus.

  16. Dark energy parameterizations and their effect on dark halos

    E-print Network

    Lamartine Liberato; Rogerio Rosenfeld

    2006-04-19

    There is a plethora of dark energy parameterizations that can fit current supernovae Ia data. However, this data is only sensitive to redshifts up to order one. In fact, many of these parameterizations break down at higher redshifts. In this paper we study the effect of dark energy models on the formation of dark halos. We select a couple of dark energy parameterizations which are sensible at high redshifts and compute their effect on the evolution of density perturbations in the linear and non-linear regimes. Using the Press-Schechter formalism we show that they produce distinguishable signatures in the number counts of dark halos. Therefore, future observations of galaxy clusters can provide complementary constraints on the behavior of dark energy.

  17. Dark energy parametrizations and their effect on dark halos

    NASA Astrophysics Data System (ADS)

    Liberato, Lamartine; Rosenfeld, Rogerio

    2006-07-01

    There are a plethora of dark energy parametrizations that can fit current supernovae Ia data. However, these data are only sensitive to redshifts up to order one. In fact, many of these parametrizations break down at higher redshifts. In this paper we study the effect of dark energy models on the formation of dark halos. We select a couple of dark energy parametrizations which are sensible at high redshifts and compute their effect on the evolution of density perturbations in the linear and non-linear regimes. Using the Press Schechter formalism we show that they produce distinguishable signatures in the number counts of dark halos. Therefore, future observations of galaxy clusters can provide complementary constraints on the behaviour of dark energy.

  18. Astrophysikalisches Institut Potsdam Probes of Dark Energy

    E-print Network

    Astrophysikalisches Institut Potsdam Probes of Dark Energy using Cosmological Simulations Nonlinear component, called dark energy. This unknown energy causes the expansion of the universe to accelerate theoretical model of dark energy has been developed. Instead a number of models have been proposed that range

  19. From Inflation to Dark Energy

    E-print Network

    Robert Brout

    2005-08-04

    It is proposed that after the macroscopic fluctuation of energy density that is responsible for inflation dies away, a class of microscopic fluctuations, always present, survives to give the present day dark energy. This latter is simply a reinterpretation of the causet mechanism of Ahmed, Dodelson, Green and Sorkin, wherein the emergence of space is dropped but only energy considerations are maintained. At postinflation times, energy is exchanged between the "cisplanckian" cosmos and an unknown foam-like transplanckian reservoir. Whereas during inflation, the energy flows only from the latter to the former after inflation it fluctuates in sign thereby accounting for the tiny effective cosmological constant that seems to account for dark energy.

  20. Vacuum energy as dark matter

    NASA Astrophysics Data System (ADS)

    Albareti, F. D.; Cembranos, J. A. R.; Maroto, A. L.

    2014-12-01

    We consider the vacuum energy of massive quantum fields in an expanding universe. We define a conserved renormalized energy-momentum tensor by means of a comoving cutoff regularization. Using exact solutions for de Sitter space-time, we show that in a certain range of mass and renormalization scales there is a contribution to the vacuum energy density that scales as nonrelativistic matter and that such a contribution becomes dominant at late times. By means of the WKB approximation, we find that these results can be extended to arbitrary Robertson-Walker geometries. We study the range of parameters in which the vacuum energy density would be compatible with current limits on dark matter abundance. Finally, by calculating the vacuum energy in a perturbed Robertson-Walker background, we obtain the speed of sound of density perturbations and show that the vacuum energy density contrast can grow on sub-Hubble scales as in standard cold dark matter scenarios.

  1. Constraining dark energy with X-ray galaxy clusters, supernovae and the cosmic microwave background

    Microsoft Academic Search

    David Rapetti; Steven W. Allen; Jochen Weller

    2005-01-01

    We present new constraints on the evolution of dark energy from an analysis of cosmic microwave background, supernova and X-ray galaxy cluster data. Our analysis employs a minimum of priors and exploits the complementary nature of these data sets. We examine a series of dark energy models with up to three free parameters: the current dark energy equation of state

  2. Constraining Dark Energy with X-ray Galaxy Clusters, Supernovae and the Cosmic Microwave Background

    Microsoft Academic Search

    Rapetti

    2005-01-01

    We present new constraints on the evolution of dark energy from an analysis of Cosmic Microwave Background, supernova and X-ray galaxy cluster data. Our analysis employs a minimum of priors and exploits the complementary nature of these data sets. We examine a series of dark energy models with up to three free parameters: the current dark energy equation of state

  3. Constraining Dark Energy with X-ray Clusters, SNe Ia and the CMB

    Microsoft Academic Search

    D. Rapetti; S. W. Allen; J. Weller

    2005-01-01

    In [1] we present new constraints on the evolution of dark energy from an analysis of Cosmic Microwave Background, supernova and X-ray galaxy cluster data. From a combined analysis of all three data sets and assuming that the Universe is at, we examine a series of dark energy models with up to three free parameters: the current dark energy equation

  4. The South Pole Telescope: A white paper for the Dark Energy Task Force

    E-print Network

    Collar, Juan I.

    The South Pole Telescope: A white paper for the Dark Energy Task Force J. E. Carlstrom, C. Chang, T constraints on the nature of dark energy by measuring its impact on the growth of structure, specifically redshifts, the statistical power of the survey yields are sufficient to measure the dark energy equation

  5. Validity of Thermodynamical Laws in Dark Energy Filled Universe

    E-print Network

    Samarpita Bhattacharya; Ujjal Debnath

    2010-12-26

    We have considered the flat FRW model of the universe which is filled with only dark energy. The general descriptions of first and second laws of thermodynamics are investigated on the apparent horizon and event horizon of the universe. We have assumed the equation of state of three different types of dark energy models. We have examined the validity of first and second laws of thermodynamics on apparent and event horizons for these dark energies. For these dark energy models, it has been found that on the apparent horizon, first and second laws are always valid. On the event horizon, the laws are break down for dark energy models 1 and 2. For model 3, first law cannot be satisfied on the event horizon, but second law may be satisfied at the late stage of the evolution of the universe and so the validity of second law on the event horizon depends on the values of the parameters only.

  6. Constraints on the sound speed of dark energy

    E-print Network

    Steen Hannestad

    2005-04-01

    We have studied constraints on the equation of state, $w$, and speed of sound, c_s, of the dark energy from a joint analysis of data from the cosmic microwave background, large scale structure and type-Ia supernovae. We find that current observations have no significant sensitivity to c_s. However, there is a slight difference between models in which there are no dark energy perturbations and models in which dark energy behaves as a fluid. Assuming that there are no dark energy perturbations shifts the allowed region for $w$ to slightly higher values. At present models with and without dark energy perturbations provide roughly equally good fits to observations, but the difference is potentially important for future parameter estimations. Finally, we have also performed error forecasts for future measurements of c_s.

  7. Zero-point energy of vacuum fluctuation as a candidate for dark energy versus a new conjecture of antigravity based on the modified Einstein field equation in general relativity

    E-print Network

    Guang-jiong Ni

    2005-06-02

    In order to clarify why the zero-point energy associated with the vacuum fluctuations cannot be a candidate for the dark energy in the universe, a comparison with the Casimir effect is analyzed in some detail. A principle of epistemology is stressed that it is meaningless to talk about an absolute (isolated) thing. A relative thing can only be observed when it is changing with respect to other things. Then a new conjecture of antigravity --the repulsive force between matter and antimatter derived from the modified Einstein field equation in general relativity-- is proposed. this is due to the particle-antiparticle symmetry based on a new understanding about the essence of special relativity. Its possible consequences in the theory of cosmology are discussed briefly, including a new explanation for the accelerating universe and gamma-ray-bursts.

  8. Dark energy as a kinematic effect

    E-print Network

    Jennen, H

    2015-01-01

    We present a generalization of teleparallel gravity that is consistent with local spacetime kinematics regulated by the de Sitter group $SO(1,4)$. The mathematical structure of teleparallel gravity is shown to be given by a nonlinear Riemann--Cartan geometry without curvature, which inspires us to build the generalization on top of a de Sitter--Cartan geometry with a cosmological function. The cosmological function is given its own dynamics and naturally emerges nonminimally coupled to the gravitational field in a manner akin to teleparallel dark energy models or scalar-tensor theories in general relativity. New in the theory here presented, the cosmological function gives rise to a kinematic contribution in the deviation equation for the world lines of adjacent free-falling particles. While having its own dynamics, dark energy manifests itself in the local kinematics of spacetime.

  9. Vector Fields Resembling Dark Energy

    NASA Astrophysics Data System (ADS)

    Bretón, Nora

    We review how vector fields have been introduced to produce inflationary scenarios in early universes and recently they have been invoked to mimick dark energy. These last approaches have been mostly qualitatives, requiring then to be tested with cosmological probes, in order to seriously be considered as one of the possible causes of the present accelerated expansion of the universe.

  10. Dark Energy and Viscous Cosmology

    E-print Network

    I. Brevik; O. Gorbunova

    2005-08-11

    Singularities in the dark energy universe are discussed, assuming that there is a bulk viscosity in the cosmic fluid. In particular, it is shown how the physically natural assumption of letting the bulk viscosity be proportional to the scalar expansion in a spatially flat FRW universe can drive the fluid into the phantom region (w -1) in the non-viscous case.

  11. The Dark Force: Astrophysical Repulsion from Dark Energy

    E-print Network

    Chiu Man Ho; Stephen D. H. Hsu

    2015-01-23

    Dark energy (i.e., a cosmological constant) leads, in the Newtonian approximation, to a repulsive force which grows linearly with distance. We discuss possible astrophysical effects of this "dark" force. For example, the dark force overcomes the gravitational attraction from an object (e.g., dwarf galaxy) of mass $10^7 M_\\odot$ at a distance of $~ 23$ kpc. It seems possible that observable velocities of bound satellites (rotation curves) could be significantly affected, and therefore used to measure the dark energy density.

  12. LSST as a precision probe of dark energy

    NASA Astrophysics Data System (ADS)

    Tyson, Tony; Wittman, David; Hennawi, Joe; Spergel, David

    2002-04-01

    The distortion of images of high-redshift background galaxies can be used to probe the intervening mass distribution. This weak gravitational lens effect can be used to detect clusters of dark matter, weigh them, image their mass distribution, and determine their 3-D location. The number of mass clusters detected and their redshift distribution are very sensitive to the density of matter ?m and the equation of state of dark energy w. The degeneracy curve in the ?m -- w plane is nearly orthogonal to that from the CMB measurements, so that a combination of CMB data with weak lensing by clusters can yield precision measurements of ?m and w, independently of the supernova observations. The planned Large Synoptic Survey Telescope (LSST) will repeatedly survey 14,000 square degrees of the sky to unprecedented depths. LSST will create a 3-D mass tomographic assay of mass overdensities back to half the age of the universe by measuring the weak gravitational shear and color-redshift of billions of high redshift galaxies. LSST measurements of shear versus source redshift and lens redshift constrain the dark energy density and equation of state. By simultaneously measuring a range of properties of cosmic shear and cluster abundance, the LSST is able to provide a number of independent constraints on the dark energy density and the equation of state. LSST will determine the dark energy equation of state w to within one percent, sharply constraining the nature of dark energy. See the web site http://lssto.org for plots.

  13. LSST: a Complementary Probe of Dark Energy

    E-print Network

    J. A. Tyson; D. M. Wittman; J. F. Hennawi; D. N. Spergel

    2002-09-30

    The number of mass clusters and their distribution in redshift are very sensitive to the density of matter Omega_m and the equation of state of dark energy w. Using weak lens gravitational tomography one can detect clusters of dark matter, weigh them, image their projected mass distribution, and determine their 3-D location. The degeneracy curve in the Omega_m - w plane is nearly orthogonal to that from CMB or SN measurements. Thus, a combination of CMB data with weak lens tomography of clusters can yield precision measurements of Omega_m and w, independently of the SN observations. The Large Synoptic Survey Telescope (LSST) will repeatedly survey 30,000 square degrees of the sky in multiple wavelengths. LSST will create a 3-D tomographic assay of mass overdensities back to half the age of the universe by measuring the shear and color-redshift of billions of high redshift galaxies. By simultaneously measuring several functions of cosmic shear and mass cluster abundance, LSST will provide a number of independent constraints on the dark energy density and the equation of state.

  14. Metamaterial model of tachyonic dark energy

    E-print Network

    Igor I. Smolyaninov

    2014-02-07

    Dark energy with negative pressure and positive energy density is believed to be responsible for the accelerated expansion of the universe. Quite a few theoretical models of dark energy are based on tachyonic fields interacting with itself and normal (bradyonic) matter. Here we propose an experimental model of tachyonic dark energy based on hyperbolic metamaterials. Wave equation describing propagation of extraordinary light inside hyperbolic metamaterials exhibits 2+1 dimensional Lorentz symmetry. The role of time in the corresponding effective 3D Minkowski spacetime is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect bends this spacetime resulting in effective gravitational force between extraordinary photons. We demonstrate that this model has a self-interacting tachyonic sector having negative effective pressure and positive effective energy density. Moreover, a composite multilayer SiC-Si hyperbolic metamaterial exhibits closely separated tachyonic and bradyonic sectors in the long wavelength infrared range. This system may be used as a laboratory model of inflation and late time acceleration of the universe.

  15. REPORT OF THE DARK ENERGY TASK FORCE

    E-print Network

    Hu, Wayne

    REPORT OF THE DARK ENERGY TASK FORCE Andreas Albrecht, University of California, Davis Gary. Suntzeff, Texas A&M University Dark energy appears to be the dominant component of the physical Universe a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among

  16. Signature of the interaction between dark energy and dark matter in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Abdalla, Elcio; Abramo, L. Raul; Sodré, Laerte; Wang, Bin

    2009-03-01

    We investigate the influence of an interaction between dark energy and dark matter upon the dynamics of galaxy clusters. We obtain the general Layser-Irvine equation in the presence of interactions, and find how, in that case, the virial theorem stands corrected. Using optical, X-ray and weak lensing data from 33 relaxed galaxy clusters, we put constraints on the strength of the coupling between the dark sectors. Available data suggests that this coupling is small but positive, indicating that dark energy might be decaying into dark matter. Systematic effects between the several mass estimates, however, should be better known, before definitive conclusions on the magnitude and significance of this coupling could be established.

  17. New holographic dark energy model with non-linear interaction

    E-print Network

    A. Oliveros; Mario A. Acero

    2014-12-23

    In this paper the cosmological evolution of a holographic dark energy model with a non-linear interaction between the dark energy and dark matter components in a FRW type flat universe is analysed. In this context, the deceleration parameter $q$ and the equation state $w_{\\Lambda}$ are obtained. We found that, as the square of the speed of sound remains positive, the model is stable under perturbations since early times; it also shows that the evolution of the matter and dark energy densities are of the same order for a long period of time, avoiding the so--called coincidence problem. We have also made the correspondence of the model with the dark energy densities and pressures for the quintessence and tachyon fields. From this correspondence we have reconstructed the potential of scalar fields and their dynamics.

  18. Studies of dark energy with x-ray observatories

    PubMed Central

    Vikhlinin, Alexey

    2010-01-01

    I review the contribution of Chandra X-ray Observatory to studies of dark energy. There are two broad classes of observable effects of dark energy: evolution of the expansion rate of the Universe, and slow down in the rate of growth of cosmic structures. Chandra has detected and measured both of these effects through observations of galaxy clusters. A combination of the Chandra results with other cosmological datasets leads to 5% constraints on the dark energy equation-of-state parameter, and limits possible deviations of gravity on large scales from general relativity. PMID:20404207

  19. Genesis of Dark Energy: Dark Energy as a Consequence of Cosmological Nuclear Energy

    Microsoft Academic Search

    R. C. Gupta

    2004-01-01

    Recent observations on Type-Ia supernovae and low density measurement of matter (including dark matter) suggest that the present day universe consists mainly of repulsive-gravity type exotic-matter with negative-pressure often referred as dark-energy. But the mystery is about the nature of dark-energy and its puzzling questions such as why, how, where & when about the dark- energy are intriguing. In the

  20. Dark Energy and Dark Matter in General Relativity with local scale invariance

    E-print Network

    Pavan Kumar Aluri; Pankaj Jain; Naveen K. Singh

    2008-10-24

    We consider a generalization of Einstein's general theory of relativity such that it respects local scale invariance. This requires the introduction of a scalar and a vector field in the action. We show that the theory naturally displays both dark energy and dark matter. We solve the resulting equations of motion assuming an FRW metric. The solutions are found to be almost identical to those corresponding to the standard $\\Lambda$CDM model

  1. A Model for Dark Energy decay

    E-print Network

    Elcio Abdalla; Leila Graef; Bin Wang

    2013-08-06

    We discuss a model of non perturbative decay of dark energy into hot and cold dark matter. This model provides a mechanism from the field theory to realize the energy transfer from dark energy into dark matter, which is the requirement to alleviate the coincidence problem. The advantage of the model is the fact that we accommodate a mean life compatible with the age of the universe. We also argue that supersymmetry is a natural set up, though not essential.

  2. Inhomogeneous models of interacting dark matter and dark energy

    Microsoft Academic Search

    Roberto A. Sussman; Israel Quiros; Osmel Martín González

    2005-01-01

    We derive and analyze a class of spherically symmetric cosmological models whose source is an interactive mixture of inhomogeneous cold dark matter (DM) and a generic homogeneous dark energy (DE) fluid. If the DE fluid corresponds to a quintessence scalar field, the interaction term can be associated with a well motivated non-minimal coupling to the DM component. By constructing a

  3. A Single Model of Interacting Dark Energy: Generalized Phantom Energy or Generalized Chaplygin Gas

    Microsoft Academic Search

    Mubasher Jamil

    2010-01-01

    I present a model in which dark energy interacts with matter. The former is represented by a variable equation of state. It\\u000a is shown that the phantom crossing takes place at zero redshift, moreover, stable scaling solution of the Friedmann equations\\u000a is obtained. I show that dark energy is most probably be either generalized phantom energy or the generalized Chaplygin gas,

  4. Modelling dark energy 

    E-print Network

    Jackson, Brendan Marc

    2011-11-23

    One of the most pressing, modern cosmological mysteries is the cause of the accelerated expansion of the universe. The energy density required to cause this large scale opposition to gravity is known to be both far in ...

  5. Inferring "Dark Matter" and "Dark Energy" from Videos Dan Xie , Sinisa Todorovic

    E-print Network

    Zhu, Song Chun

    Inferring "Dark Matter" and "Dark Energy" from Videos Dan Xie , Sinisa Todorovic , and Song.g., grass lawns). Therefore, functional objects can be viewed as "dark matter", emanating "dark energy" that affects people's trajectories in the video. To detect "dark mat- ter" and infer their "dark energy" field

  6. Evolving dark energy with w not = -1.

    PubMed

    Hall, Lawrence J; Nomura, Yasunori; Oliver, Steven J

    2005-09-30

    Theories of evolving quintessence are constructed that generically lead to deviations from the w = -1 prediction of nonevolving dark energy. The small mass scale that governs evolution, m(phi) approximately = 10(-33) eV, is radiatively stable, and the "Why now?" problem is solved. These results rest on seesaw cosmology: Fundamental physics and cosmology can be broadly understood from only two mass scales, the weak scale nu and the Planck scale M. Requiring a scale of dark energy rho(DE)(1/4) governed by nu2/M and a radiatively stable evolution rate m(phi) given by nu4/M3 leads to a distinctive form for the equation of state w(z). Dark energy resides in the potential of a hidden axion field that is generated by a new QCD-like force that gets strong at the scale lambda approximately = nu2/M approximately = rho(DE)(1/4). The evolution rate is given by a second seesaw that leads to the axion mass m(phi) approximately = lambda2/f, with f approximately = M. PMID:16241641

  7. Dark energy with gravitational lens time delays

    E-print Network

    Treu, T; Cyr-Racine, F -Y; Fassnacht, C D; Keeton, C R; Linder, E V; Moustakas, L A; Bradac, M; Buckley-Geer, E; Collett, T; Courbin, F; Dobler, G; Finley, D A; Hjorth, J; Kochanek, C S; Komatsu, E; Koopmans, L V E; Meylan, G; Natarajan, P; Oguri, M; Suyu, S H; Tewes, M; Wong, K C; Zabludoff, A I; Zaritsky, D; Anguita, T; Brunner, R J; Cabanac, R; Falco, E E; Fritz, A; Seidel, G; Howell, D A; Giocoli, C; Jackson, N; Lopez, S; Metcalf, R B; Motta, V; Verdugo, T

    2013-01-01

    Strong lensing gravitational time delays are a powerful and cost effective probe of dark energy. Recent studies have shown that a single lens can provide a distance measurement with 6-7 % accuracy (including random and systematic uncertainties), provided sufficient data are available to determine the time delay and reconstruct the gravitational potential of the deflector. Gravitational-time delays are a low redshift (z~0-2) probe and thus allow one to break degeneracies in the interpretation of data from higher-redshift probes like the cosmic microwave background in terms of the dark energy equation of state. Current studies are limited by the size of the sample of known lensed quasars, but this situation is about to change. Even in this decade, wide field imaging surveys are likely to discover thousands of lensed quasars, enabling the targeted study of ~100 of these systems and resulting in substantial gains in the dark energy figure of merit. In the next decade, a further order of magnitude improvement will...

  8. The Dark Energy Camera (DECam)

    NASA Astrophysics Data System (ADS)

    DePoy, D. L.; Abbott, T.; Annis, J.; Antonik, M.; Barceló, M.; Bernstein, R.; Bigelow, B.; Brooks, D.; Buckley-Geer, E.; Campa, J.; Cardiel, L.; Castander, F.; Castilla, J.; Cease, H.; Chappa, S.; Dede, E.; Derylo, G.; Diehl, H. T.; Doel, P.; DeVicente, J.; Estrada, J.; Finley, D.; Flaugher, B.; Gaztanaga, E.; Gerdes, D.; Gladders, M.; Guarino, V.; Gutierrez, G.; Hamilton, J.; Haney, M.; Holland, S.; Honscheid, K.; Huffman, D.; Karliner, I.; Kau, D.; Kent, S.; Kozlovsky, M.; Kubik, D.; Kuehn, K.; Kuhlmann, S.; Kuk, K.; Leger, F.; Lin, H.; Martinez, G.; Martinez, M.; Merritt, W.; Mohr, J.; Moore, P.; Moore, T.; Nord, B.; Ogando, R.; Olsen, J.; Onal, B.; Peoples, J.; Qian, T.; Roe, N.; Sanchez, E.; Scarpine, V.; Schmidt, R.; Schmitt, R.; Schubnell, M.; Schultz, K.; Selen, M.; Shaw, T.; Simaitis, V.; Slaughter, J.; Smith, C.; Spinka, H.; Stefanik, A.; Stuermer, W.; Talaga, R.; Tarle, G.; Thaler, J.; Tucker, D.; Walker, A.; Worswick, S.; Zhao, A.

    2008-07-01

    We describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey. DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a large mosaic CCD focal plane, a five element optical corrector, five filters (g,r,i,z,Y), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of 62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of view. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms, and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.

  9. Genesis of Dark Energy: Dark Energy as a Consequence of Cosmological Nuclear Energy

    E-print Network

    R. C. Gupta

    2004-12-07

    Recent observations on Type-Ia supernovae and low density measurement of matter (including dark matter) suggest that the present day universe consists mainly of repulsive-gravity type exotic-matter with negative-pressure often referred as dark-energy. But the mystery is about the nature of dark-energy and its puzzling questions such as why, how, where & when about the dark- energy are intriguing. In the present paper the author attempts to answer these questions while making an effort to reveal the genesis of dark-energy, and suggests that the cosmological nuclear-binding-energy liberated during primordial nucleo-synthesis remains trapped for long time and then is released free which manifests itself as dark-energy in the universe. It is also explained why for dark energy the parameter w = -2/3. Noting that w=+1for stiff matter and w=+1/3 for radiation; w = - 2/3 is for dark energy, because -1 is due to deficiency of stiff-nuclear-matter and that this binding energy is ultimately released as radiation contributing +1/3, making w = -1 + 1/3 = -2/3. This thus almost solves the dark-energy mystery of negative-pressure & repulsive-gravity. It is concluded that dark-energy is a consequence of released-free nuclear-energy of cosmos. The proposed theory makes several estimates / predictions, which agree reasonably well with the astrophysical constraints & observations.

  10. Inhomogeneous alternative to dark energy?

    Microsoft Academic Search

    Håvard Alnes; Morad Amarzguioui; Øyvind Grøn

    2006-01-01

    Recently, there have been suggestions that the apparent accelerated expansion of the universe is not caused by repulsive gravitation due to dark energy, but is rather a result of inhomogeneities in the distribution of matter. In this work, we investigate the behavior of a dust-dominated inhomogeneous Lemaître-Tolman-Bondi universe model, and confront it with various astrophysical observations. We find that such

  11. Dark Energy, Gravitation and Electromagnetism

    Microsoft Academic Search

    B. G. Sidharth; B. M. Birla

    2004-01-01

    In the context of the fact that the existence of dark energy causing the\\u000aaccelerated expansion of the universe has been confirmed by the WMAP and the\\u000aSloan Digital Sky Survey, we re-examine gravitation itself, starting with the\\u000aformulation of Sakharov and show that it is possible to obtain gravitation in\\u000aterms of the electromagnetic charge of elementary particles, once

  12. Dark Energy\\/matter Unification

    Microsoft Academic Search

    Aharon Davidson; Yoav Lederer; David Karasik

    2003-01-01

    Let our Universe resemble a 4-dim bubble, floating in a flat (or AdS) 5-dim background, but insist on its evolution being governed by the standard Einstein-Hilbert action. The conserved bulk energy then parameterizes an intriguing deviation from general relativity with an essential built-in Einstein limit. Even an apparently `empty' bubble Universe is effectively infested by a dark (= beyond Einstein)

  13. Dark Energy, Gravitation and Electromagnetism

    E-print Network

    B. G. Sidharth

    2004-01-08

    In the context of the fact that the existence of dark energy causing the accelerated expansion of the universe has been confirmed by the WMAP and the Sloan Digital Sky Survey, we re-examine gravitation itself, starting with the formulation of Sakharov and show that it is possible to obtain gravitation in terms of the electromagnetic charge of elementary particles, once the ZPF and its effects at the Compton scale are taken into account.

  14. About the Geometric Solution to the Problems of Dark Energy

    E-print Network

    Miguel Angel García-Aspeitia

    2011-02-06

    In this paper is proposed a geometric solution to the dark energy, assuming that the space can be divided into regions of size $\\sim L_{p}$ and energy $\\sim E_{p}$. Significantly this assumption generate a energy density similar to the energy density observed for the vaccum energy, the correct solution for the coincidence problem and the state equation characteristic of quintessence in the comoving coordinates. Similarly is studied the ultraviolet and infrarred limits and the amount of dark energy in the Universe.

  15. Dark energy and Josephson junctions

    SciTech Connect

    Branchina, Vincenzo [Department of Physics, University of Catania, Via Santa Sofia 64, I-95123, Catania (Italy); Liberto, Marco Di; Lodato, Ivano, E-mail: vincenzo.branchina@ct.infn.it, E-mail: madiliberto@ssc.unict.it, E-mail: ivlodato@ssc.unict.it [Scuola Superiore di Catania, Via S. Nullo 5/i, Catania (Italy)

    2009-08-01

    It has been recently claimed that dark energy can be (and has been) observed in laboratory experiments by measuring the power spectrum S{sub I}(?) of the noise current in a resistively shunted Josephson junction and that in new dedicated experiments, which will soon test a higher frequency range, S{sub I}(?) should show a deviation from the linear rising observed in the lower frequency region because higher frequencies should not contribute to dark energy. Based on previous work on theoretical aspects of the fluctuation-dissipation theorem, we carefully investigate these issues and show that these claims are based on a misunderstanding of the physical origin of the spectral function S{sub I}(?). According to our analysis, dark energy has never been (and will never be) observed in Josephson junctions experiments. We also predict that no deviation from the linear rising behavior of S{sub I}(?) will be observed in forthcoming experiments. Our findings provide new (we believe definite) arguments which strongly support previous criticisms.

  16. Inhomogeneous alternative to dark energy?

    SciTech Connect

    Alnes, Haavard [Department of Physics, University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo (Norway); Amarzguioui, Morad [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, 0315 Oslo (Norway); Groen, Oyvind [Department of Physics, University of Oslo, P.O. Box 1048 Blindern, 0316 Oslo (Norway); Oslo College, Faculty of Engineering, Cort Adelersgate 30, 0254 Oslo (Norway)

    2006-04-15

    Recently, there have been suggestions that the apparent accelerated expansion of the universe is not caused by repulsive gravitation due to dark energy, but is rather a result of inhomogeneities in the distribution of matter. In this work, we investigate the behavior of a dust-dominated inhomogeneous Lemaitre-Tolman-Bondi universe model, and confront it with various astrophysical observations. We find that such a model can easily explain the observed luminosity distance-redshift relation of supernovae without the need for dark energy, when the inhomogeneity is in the form of an underdense bubble centered near the observer. With the additional assumption that the universe outside the bubble is approximately described by a homogeneous Einstein-de Sitter model, we find that the position of the first peak in the cosmic microwave background (CMB) power spectrum can be made to match the WMAP observations. Whether or not it is possible to reproduce the entire CMB angular power spectrum in an inhomogeneous model without dark energy is still an open question.

  17. Holographic dark energy with varying gravitational constant in Ho?ava-Lifshitz cosmology

    SciTech Connect

    Setare, M.R. [Department of Physics, University of Kurdistan, Pasdaran Ave., Sanandaj (Iran, Islamic Republic of); Jamil, Mubasher, E-mail: rezakord@ipm.ir, E-mail: mjamil@camp.nust.edu.pk [Center for Advanced Mathematics and Physics, National University of Sciences and Technology, Rawalpindi, 46000 (Pakistan)

    2010-02-01

    We investigate the holographic dark energy scenario with a varying gravitational constant in a flat background in the context of Ho?ava-Lifshitz gravity. We extract the exact differential equation determining the evolution of the dark energy density parameter, which includes G variation term. Also we discuss a cosmological implication of our work by evaluating the dark energy equation of state for low redshifts containing varying G corrections.

  18. Leptogenesis in a model of Dark Energy and Dark Matter

    Microsoft Academic Search

    P. Q. Hung

    2006-01-01

    A recent model of dark energy and dark matter was proposed, involving a new gauge group $SU(2)_Z$ whose coupling grows strong at a scale $\\\\Lambda_Z \\\\sim 10^{-3} eV$, a result which is obtained from a simple assumption that its initial value at some high energy scale $M \\\\sim 10^{16} GeV$ is of the order of a typical Standard Model (SM)

  19. A Kinematical Approach to Dark Energy Studies

    SciTech Connect

    Rapetti, David; Allen, Steven W.; Amin, Mustafa A.; Blandford, Roger D.; /KIPAC, Menlo Park

    2006-06-06

    We present and employ a new kinematical approach to cosmological ''dark energy'' studies. We construct models in terms of the dimensionless second and third derivatives of the scale factor a(t) with respect to cosmic time t, namely the present-day value of the deceleration parameter q{sub 0} and the cosmic jerk parameter, j(t). An elegant feature of this parameterization is that all {Lambda}CDM models have j(t) = 1 (constant), which facilitates simple tests for departures from the {Lambda}CDM paradigm. Applying our model to the three best available sets of redshift-independent distance measurements, from type Ia supernovae and X-ray cluster gas mass fraction measurements, we obtain clear statistical evidence for a late time transition from a decelerating to an accelerating phase. For a flat model with constant jerk, j(t) = j, we measure q{sub 0} = -0.81 {+-} 0.14 and j = 2.16{sub -0.75}{sup +0.81}, results that are consistent with {Lambda}CDM at about the 1{sigma} confidence level. A standard ''dynamical'' analysis of the same data, employing the Friedmann equations and modeling the dark energy as a fluid with an equation of state parameter, w (constant), gives {Omega}{sub m} = 0.306{sub -0.040}{sup +0.042} and w = -1.15{sub -0.18}{sup +0.14}, also consistent with {Lambda}CDM at about the 1{sigma} level. In comparison to dynamical analyses, the kinematical approach uses a different model set and employs a minimum of prior information, being independent of any particular gravity theory. The results obtained with this new approach therefore provide important additional information and we argue that both kinematical and dynamical techniques should be employed in future dark energy studies, where possible. Our results provide further interesting support for the concordance {Lambda}CDM paradigm.

  20. Optimal Strategy for Dark Energy Search

    Microsoft Academic Search

    Y. Wang

    2002-01-01

    Most of the energy in the universe is of unknown nature to us. Observers\\/experimentalists face the historical opportunity to probe properties of this dark energy (the most important of which being the time-dependence of its density), and constrain the numerous plausible phenomenological models of dark energy that have been constructed. Based on non-parametric estimates of dark energy density (without imposing

  1. Cosmological Perturbations in Models of Coupled Dark Energy

    E-print Network

    Sirichai Chongchitnan

    2009-02-26

    Models in which dark energy interacts with dark matter have been proposed in the literature to help explain why dark energy should only come to dominate in recent times. In this paper, we present a dynamical framework to calculate cosmological perturbations for a general quintessence potential and interaction term. Our formalism is built upon the powerful phase-space approach often used to analyse the dynamical attractors in the background. We obtain a set of coupled differential equations purely in terms of dimensionless, bounded variables and apply these equations to calculate perturbations in a number of scenarios. Interestingly, in the presence of dark-sector interactions, we find that dark energy perturbations do not redshift away at late times, but can cluster even on small scales. We also clarify the initial conditions for the perturbations in the dark sector, showing that adiabaticity is no longer conserved in the presence of dark-sector interactions, even on large scales. Some issues of instability in the perturbations are also discussed.

  2. Cosmological zoo -- accelerating models with dark energy

    E-print Network

    Marek Szydlowski

    2006-10-09

    ecent observations of type Ia supernovae indicate that the Universe is in an accelerating phase of expansion. The fundamental quest in theoretical cosmology is to identify the origin of this phenomenon. In principle there are two possibilities: 1) the presence of matter which violates the strong energy condition (a substantial form of dark energy), 2) modified Friedmann equations (Cardassian models -- a non-substantial form of dark matter). We classify all these models in terms of 2-dimensional dynamical systems of the Newtonian type. We search for generic properties of the models. It is achieved with the help of Peixoto's theorem for dynamical system on the Poincar{\\'e} sphere. We find that the notion of structural stability can be useful to distinguish the generic cases of evolutional paths with acceleration. We find that, while the $\\Lambda$CDM models and phantom models are typical accelerating models, the cosmological models with bouncing phase are non-generic in the space of all planar dynamical systems. We derive the universal shape of potential function which gives rise to presently accelerating models. Our results show explicitly the advantages of using a potential function (instead of the equation of state) to probe the origin of the present acceleration. We argue that simplicity and genericity are the best guide in understanding our Universe and its acceleration.

  3. Growth Diagnostics for Dark Energy models and EUCLID forecast

    E-print Network

    Sampurnanand; Anjan A. Sen

    2013-12-23

    In this work we introduce a new set of parameters $(r_{g}, s_{g})$ involving the linear growth of matter perturbation that can distinguish and constrain different dark energy models very efficiently. Interestingly, for $\\Lambda$CDM model these parameters take exact value $(1,1)$ at all red shifts whereas for models different from $\\Lambda$CDM, they follow different trajectories in the $(r_{g}, s_{g})$ phase plane. By considering the parametrization for the dark energy equation of state ($w$) and for the linear growth rate ($f_{g}$), we show that different dark energy behaviours with similar evolution of the linear density contrast, can produce distinguishable trajectories in the $(r_{g}, s_{g})$ phase plane. Moreover, one can put stringent constraint on these phase plane using future measurements like EUCLID ruling out some of the dark energy behaviours.

  4. A User-Friendly Dark Energy Model Generator

    E-print Network

    Hinton, Kyle A; Huterer, Dragan

    2015-01-01

    We provide software with a graphical user interface to calculate the phenomenology of a wide class of dark energy models featuring multiple scalar fields. The user chooses a subclass of models and, if desired, initial conditions, or else a range of initial parameters for Monte Carlo. The code calculates the energy density of components in the universe, the equation of state of dark energy, and the linear growth of density perturbations, all as a function of redshift and scale factor. The output also includes an approximate conversion into the average equation of state, as well as the common $(w_0, w_a)$ parametrization. The code is available here: http://github.com/kahinton/Dark-Energy-UI-and-MC

  5. How Sensitive Are Weak Lensing Statistics to Dark Energy Content?

    E-print Network

    Dipak Munshi; Yun Wang

    2002-10-04

    Future weak lensing surveys will directly probe the clustering of dark matter, in addition to providing a test for various cosmological models. Recent studies have provided us with the tools which can be used to construct the complete probability distribution function for convergence fields. It is also possible to construct the bias associated with the hot-spots in convergence maps. These techniques can be used in both the quasi-linear and the highly nonlinear regimes using various well developed numerical methods. We use these results here to study the weak lensing statistics of cosmological models with dark energy. We study how well various classes of dark energy models can be distinguished from models with a cosmological constant. We find that the ratio of the square root of the variance of convergence is complementary to the convergence skewness $S_3$ in probing dark energy equation of state; it can be used to predict the expected difference in weak lensing statistics between various dark energy models, and for choosing optimized smoothing angles to constrain a given class of dark energy models. Our results should be useful for probing dark energy using future weak lensing data with high statistics from galaxy weak lensing surveys and supernova pencil beam surveys.

  6. New Field Theory Effect at Energy Densities Close to the Dark Energy Density

    Microsoft Academic Search

    E. I. Guendelman; A. B. Kaganovich

    2004-01-01

    An alternative gravity and matter fields theory is studied where the consistency condition of equations of motion yields strong correlation between states of ``primordial'' fermion fields and local value of the dark energy. The same ``primordial'' fermion field at different densities can be either in states of regular fermionic matter or in states presumably corresponding to the dark fermionic matter.

  7. Inhomogeneous models of interacting dark matter and dark energy

    Microsoft Academic Search

    Roberto A. Sussman; Israel Quiros; Osmel Martín González

    2005-01-01

    We derive and analyze a class of spherically symmetric cosmological models whose source is an interactive mixture of inhomogeneous\\u000a cold dark matter (DM) and a generic homogeneous dark energy (DE) fluid. If the DE fluid corresponds to a quintessence scalar\\u000a field, the interaction term can be associated with a well motivated non-minimal coupling to the DM component. By constructing\\u000a a

  8. Isotropic turbulence in the dark fluid universe with inhomogeneous equation of state

    NASA Astrophysics Data System (ADS)

    Boko, R. D.; Rodrigues, M. E.; Houndjo, M. J. S.; Chabi Orou, J. B.; Myrzakulov, R.

    2015-07-01

    We investigate the turbulence effect in dark fluid universe with linear inhomogeneous equation of state. Attention is attached to two physical situations. First, we perform the perturbative analysis of turbulence and check its effects around the Big Rip. Later, treating the turbulence energy density as a part of total dark fluid, we study the stability of the system. The result shows that the stability is achieving as the energy density of turbulence decreases, changing into heat (the radiation), in perfect agreement with the avoidance of the Big Rip.

  9. Isotropic turbulence in the dark fluid universe with inhomogeneous equation of state

    E-print Network

    Houndjo, M J S; Aïnamon, C; Chabi-Orou, J B; Myrzakulov, R

    2012-01-01

    We investigate the turbulence effect in dark fluid universe with linear inhomogeneous equation of state. Attention is attached to two physical situations. First, we perform the perturbative analysis of turbulence and check its effects around the Big Rip. Later, treating the turbulence energy density as a part of total dark fluid, we study the stability of the system. The result shows that the stability is achieving as the energy density of turbulence decreases, changing into heat (the radiation), in perfect agreement with the avoidance of the Big Rip.

  10. Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios T. Jenke,1,*

    E-print Network

    Rotter, Stefan

    Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios T. Jenke,1,* G constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded this work, we link these new measurements to dark matter and dark energy searches. Observational cosmology

  11. A divergence-free parametrization for dynamical dark energy

    NASA Astrophysics Data System (ADS)

    Akarsu, Özgür; Dereli, Tekin; Vazquez, J. Alberto

    2015-06-01

    We introduce a new parametrization for the dark energy, led by the same idea to the linear expansion of the equation of state in scale factor a and in redshift z, which diverges neither in the past nor future and contains the same number of degrees of freedom with the former two. We present constraints of the cosmological parameters using the most updated baryon acoustic oscillation (BAO) measurements along with cosmic microwave background (CMB) data and a recent reanalysis of Type Ia supernova (SN) data. This new parametrization allowed us to carry out successive observational analyses by decreasing its degrees of freedom systematically until ending up with a dynamical dark energy model that has the same number of parameters with ?CDM . We found that the dark energy source with a dynamical equation of state parameter equal ?2/3 at the early universe and ?1 today fits the data slightly better than ?.

  12. Unification of Gravitation, Gauge Field and Dark Energy

    E-print Network

    Xin-Bing Huang

    2005-08-26

    This paper is composed of two correlated topics: 1. unification of gravitation with gauge fields; 2. the coupling between the daor field and other fields and the origin of dark energy. After introducing the concept of ``daor field" and discussing the daor geometry, we indicate that the complex daor field has two kinds of symmetry transformations. Hence the gravitation and SU(1,3) gauge field are unified under the framework of the complex connection. We propose a first-order nonlinear coupling equation of the daor field, which includes the coupling between the daor field and SU(1,3) gauge field and the coupling between the daor field and the curvature, and from which Einstein's gravitational equation can be deduced. The cosmological observations imply that dark energy cannot be zero, and which will dominate the doom of our Universe. The real part of the daor field self-coupling equation can be regarded as Einstein's equation endowed with the cosmological constant. It shows that dark energy originates from the self-coupling of the space-time curvature, and the energy-momentum tensor is proportional to the square of coupling constant \\lambda. The dark energy density given by our scenario is in agreement with astronomical observations. Furthermore, the Newtonian gravitational constant G and the coupling constant \\epsilon of gauge field satisfy G= \\lambda^{2}\\epsilon^{2}.

  13. Genesis of Dark Energy: Dark Energy as a Consequence of Cosmological Nuclear Energy

    Microsoft Academic Search

    R. C. Gupta

    2004-01-01

    Recent observations on Type-Ia supernovae and low density measurement of\\u000amatter (including dark matter) suggest that the present day universe consists\\u000amainly of repulsive-gravity type exotic-matter with negative-pressure often\\u000areferred as dark-energy. But the mystery is about the nature of dark-energy and\\u000aits puzzling questions such as why, how, where & when about the dark- energy\\u000aare intriguing. In the

  14. Topology and dark energy: testing gravity in voids.

    PubMed

    Spolyar, Douglas; Sahlén, Martin; Silk, Joe

    2013-12-13

    Modified gravity has garnered interest as a backstop against dark matter and dark energy (DE). As one possible modification, the graviton can become massive, which introduces a new scalar field--here with a Galileon-type symmetry. The field can lead to a nontrivial equation of state of DE which is density and scale dependent. Tension between type Ia supernovae and Planck could be reduced. In voids, the scalar field dramatically alters the equation of state of DE, induces a soon-observable gravitational slip between the two metric potentials, and develops a topological defect (domain wall) due to a nontrivial vacuum structure for the field. PMID:24483641

  15. The Dark Energy Camera (DECam)

    E-print Network

    Honscheid, K; Abbott, T; Annis, J; Antonik, M; Barcel, M; Bernstein, R; Bigelow, B; Brooks, D; Buckley-Geer, E; Campa, J; Cardiel, L; Castander, F; Castilla, J; Cease, H; Chappa, S; Dede, E; Derylo, G; Diehl, T; Doel, P; De Vicente, J; Eiting, J; Estrada, J; Finley, D; Flaugher, B; Gaztañaga, E; Gerdes, D; Gladders, M; Guarino, V; Gutíerrez, G; Hamilton, J; Haney, M; Holland, S; Huffman, D; Karliner, I; Kau, D; Kent, S; Kozlovsky, M; Kubik, D; Kühn, K; Kuhlmann, S; Kuk, K; Leger, F; Lin, H; Martínez, G; Martínez, M; Merritt, W; Mohr, J; Moore, P; Moore, T; Nord, B; Ogando, R; Olsen, J; Onal, B; Peoples, J; Qian, T; Roe, N; Sánchez, E; Scarpine, V; Schmidt, R; Schmitt, R; Schubnell, M; Schultz, K; Selen, M; Shaw, T; Simaitis, V; Slaughter, J; Smith, C; Spinka, H; Stefanik, A; Stuermer, W; Talaga, R; Tarle, G; Thaler, J; Tucker, D; Walker, A; Worswick, S; Zhao, A

    2008-01-01

    In this paper we describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey. DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). It consists of a large mosaic CCD focal plane, a five element optical corrector, five filters (g,r,i,z,Y), a modern data acquisition and control system and the associated infrastructure for operation in the prime focus cage. The focal plane includes of 62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of view and 12 smaller 2K x 2K CCDs for guiding, focus and alignment. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms, and control system for DECam are underway; delivery of the instrument to CTIO is scheduled ...

  16. Holographic Dark Energy Model: State Finder Parameters

    E-print Network

    Nairwita Mazumder; Ritabrata Biswas; Subenoy Chakraborty

    2011-10-30

    In this work, we have studied interacting holographic dark energy model in the background of FRW model of the universe. The interaction is chosen either in linear combination or in product form of the matter densities for dark matter and dark energy. The IR cut off for holographic dark energy is chosen as Ricci's length scale or radius of the future event horizon. The analysis is done using the state finder parameter and coincidence problem has been graphically presented. Finally, universal thermodynamics has been studied using state finder parameters.

  17. New holographic dark energy model inspired by the DGP braneworld

    E-print Network

    A. Sheykhi; M. H. Dehghani; S. Ghaffari

    2015-06-05

    The energy density of the holographic dark energy is based on the area law of entropy, and thus any modification of the area law leads to a modified holographic energy density. Inspired by the entropy expression associated with the apparent horizon of a Friedmann-Robertson-Walker (FRW) Universe in DGP braneworld, we propose a new model for the holographic dark energy in the framework of DGP brane cosmology. We investigate the cosmological consequences of this new model and calculate the equation of state parameter by choosing the Hubble radius, $L = H^{-1}$, as the system's IR cutoff. Our study show that, due to the effects of the extra dimension (bulk), the identification of IR-cutoff with Hubble radius, can reproduce the present acceleration of the Universe expansion. This is in contrast to the ordinary holographic dark energy in standard cosmology which leads to the zero equation of state parameter in the case of choosing the Hubble radius as system's IR cutoff in the absence of interaction between dark matter and dark energy.

  18. Thermodynamics of interacting holographic dark energy

    E-print Network

    Fabiola Arevalo; Paulo Cifuentes; Francisco Pena

    2014-08-21

    The thermodynamics of a scheme of dark matter-dark energy interaction is studied considering a holographic model for the dark energy in a flat Friedmann-Lemaitre-Robertson-Walker background. We obtain a total entropy rate for a general horizon and study the Generalized Second Law of Thermodynamics. In addition, we study two horizons related to the Ricci and Ricci-like model and its effect on an interacting system.

  19. Disformal dark energy at colliders

    E-print Network

    Brax, Philippe; Englert, Christoph

    2015-01-01

    Disformally coupled, light scalar fields arise in many of the theories of dark energy and modified gravity that attempt to explain the accelerated expansion of the universe. They have proved difficult to constrain with precision tests of gravity because they do not give rise to fifth forces around static non-relativistic sources. However, because the scalar field couples derivatively to standard model matter, measurements at high energy particle colliders offer an effective way to constrain and potentially detect a disformally coupled scalar field. Here we derive new constraints on the strength of the disformal coupling from LHC run 1 data and provide a forecast for the improvement of these constraints from run 2. We additionally comment on the running of disformal and standard model couplings in this scenario under the renormalisation group flow.

  20. A regularized free-form estimator for dark energy

    Microsoft Academic Search

    Tarun Deep Saini

    2003-01-01

    We construct a simple, regularized estimator for the dark energy equation of state by using the recently introduced linear response approximation. We show that even a simple regularization substantially improves the performance of the free-form fitting approach. The use of the linear response approximation allows an analytical construction of the maximum likelihood estimator, in a convenient and easy to use

  1. A Regularized Free Form Estimator for Dark Energy

    Microsoft Academic Search

    Tarun Deep Saini

    2003-01-01

    We construct a simple, regularized estimator for the dark energy equation of state by using the recently introduced linear response approximation. We show that even a simple regularization substantially improves the performance of the free form fitting approach. The use of linear response approximation allows an analytic construction of maximum likelihood estimator, in a convenient and easy to use matrix

  2. On dark energy models of single scalar field

    Microsoft Academic Search

    Mingzhe Li; Taotao Qiu; Yifu Cai; Xinmin Zhang

    2012-01-01

    In this paper we revisit the dynamical dark energy model building based on single scalar field involving higher derivative terms. By imposing a degenerate condition on the higher derivatives in curved spacetime, one can select the models which are free from the ghost mode and the equation of state is able to cross the cosmological constant boundary smoothly, dynamically violate

  3. Dark Energy and the Cosmological Constant: A Brief Introduction

    ERIC Educational Resources Information Center

    Harvey, Alex

    2009-01-01

    The recently observed acceleration of the expansion of the universe is a topic of intense interest. The favoured causes are the "cosmological constant" or "dark energy". The former, which appears in the Einstein equations as the term [lambda]g[subscript [mu]v], provides an extremely simple, well-defined mechanism for the acceleration. However,…

  4. Dark Energy and Modified Gravity

    E-print Network

    Ruth Durrer; Roy Maartens

    2008-11-25

    Explanations of the late-time cosmic acceleration within the framework of general relativity are plagued by difficulties. General relativistic models are mostly based on a dark energy field with fine-tuned, unnatural properties. There is a great variety of models, but all share one feature in common -- an inability to account for the gravitational properties of the vacuum energy, and a failure to solve the so-called coincidence problem. Two broad alternatives to dark energy have emerged as candidate models: these typically address only the coincidence problem and not the vacuum energy problem. The first is based on general relativity and attempts to describe the acceleration as an effect of inhomogeneity in the universe. If this alternative could be shown to work, then it would provide a dramatic resolution of the coincidence problem; however, a convincing demonstration of viability has not yet emerged. The second alternative is based on infra-red modifications to general relativity, leading to a weakening of gravity on the largest scales and thus to acceleration. Most examples investigated so far are scalar-tensor or brane-world models, and we focus on the simplest candidates of each type: $f(R)$ models and DGP models respectively. Both of these provide a new angle on the problem, but they also face serious difficulties. However, investigation of these models does lead to valuable insights into the properties of gravity and structure formation, and it also leads to new strategies for testing the validity of General Relativity itself on cosmological scales.

  5. Generalized Ricci dark energy in Horava-Lifshitz gravity

    E-print Network

    Surajit Chattopadhyay

    2011-09-06

    In this letter, we have considered generalized Ricci dark energy in the Horava-Lifshitz gravity. We have reconstructed the Hubble's parameter in terms of fractional densities. We have viewed the equation of state parameter in this situation. Also, we have examined the behavior of deceleration parameter and investigated the nature of the state?nder diagnostics. The equation of state parameter has exhibited quintessence-like behavior and from the plot of the deceleration parameter we have observed an ever accelerating universe.

  6. Leptogenesis in a model of Dark Energy and Dark Matter

    Microsoft Academic Search

    P. Q. Hung

    2006-01-01

    A recent model of dark energy and dark matter was proposed, involving a new\\u000agauge group $SU(2)_Z$ whose coupling grows strong at a scale $\\\\Lambda_Z \\\\sim\\u000a10^{-3} eV$, a result which is obtained from a simple assumption that its\\u000ainitial value at some high energy scale $M \\\\sim 10^{16} GeV$ is of the order of\\u000aa typical Standard Model (SM)

  7. CMB lensing constraints on neutrinos and dark energy

    SciTech Connect

    Putter, Roland de; Zahn, Oliver; Linder, Eric V. [Berkeley Lab and Berkeley Center for Cosmological Physics, University of California, Berkeley, California 94720 (United States)

    2009-03-15

    Signatures of lensing of the cosmic microwave background radiation by gravitational potentials along the line of sight carry with them information on the matter distribution, neutrino masses, and dark energy properties. We examine the constraints that Planck, PolarBear, and CMBpol future data, including from the B-mode polarization or the lensing potential, will be able to place on these quantities. We simultaneously fit for neutrino mass and dark energy equation of state including time variation and early dark energy density, and compare the use of polarization power spectra with an optimal quadratic estimator of the lensing. Results are given as a function of systematics level from residual foreground contamination. A realistic CMBpol experiment can effectively constrain the sum of neutrino masses to within 0.05 eV and the fraction of early dark energy to 0.002. We also present a surprisingly simple prescription for calculating dark energy equation of state constraints in combination with supernova distances from JDEM.

  8. QCD nature of dark energy at finite temperature: cosmological implications

    E-print Network

    K. Azizi; N. Katirci

    2015-06-23

    The Veneziano ghost field has been proposed as an alternative source of dark energy whose energy density is consistent with the cosmological observations. In this model, the energy density of QCD ghost field is expressed in terms of QCD degrees of freedom at zero temperature. We extend this model to finite temperature to search the model predictions from the late time to the early universe. We depict the variations of QCD parameters entering the calculations, dark energy density, equation of state, Hubble and deceleration parameters on temperature from zero to a critical temperature. We compare our results with the observations and theoretical predictions existing at different eras.It is found that this model safely define the universe from quark condensation up to now and its predictions are not in tension with those of the standard cosmology. The finite temperature ghost dark energy predictions on the Hubble parameter slightly better fit to observations compared to those of zero temperature.

  9. QCD nature of dark energy at finite temperature: cosmological implications

    E-print Network

    Azizi, K

    2015-01-01

    The Veneziano ghost field has been proposed as an alternative source of dark energy whose energy density is consistent with the cosmological observations. In this model, the energy density of QCD ghost field is expressed in terms of QCD degrees of freedom at zero temperature. We extend this model to finite temperature to search the model predictions from the late time to the early universe. We depict the variations of QCD parameters entering the calculations, dark energy density, equation of state, Hubble and deceleration parameters on temperature from zero to a critical temperature. We compare our results with the observations and theoretical predictions existing at different eras.It is found that this model safely define the universe from quark condensation up to now and its predictions are not in tension with those of the standard cosmology. The finite temperature ghost dark energy predictions on the Hubble parameter slightly better fit to observations compared to those of zero temperature.

  10. Dark Energy, Expansion History of the Universe, and SNAP

    E-print Network

    Eric V. Linder

    2003-02-03

    This talk presents a pedagogical discussion of how precision distance-redshift observations can map out the recent expansion history of the universe, including the present acceleration and the transition to matter dominated deceleration. The proposed Supernova/Acceleration Probe (SNAP) will carry out observations determining the components and equations of state of the energy density, providing insights into the cosmological model, the nature of the accelerating dark energy, and potentially clues to fundamental high energy physics theories and gravitation. This includes the ability to distinguish between various dynamical scalar field models for the dark energy, as well as higher dimension and alternate gravity theories. A new, advantageous parametrization for the study of dark energy to high redshift is also presented.

  11. Singularity-free dark energy star

    Microsoft Academic Search

    Farook Rahaman; Raju Maulick; Anil Kumar Yadav; Saibal Ray; Ranjan Sharma

    2011-01-01

    We propose a model for an anisotropic dark energy star where we assume that the radial pressure exerted on the system due to the presence of dark energy is proportional to the isotropic perfect fluid matter density. We discuss various physical features of our model and show that the model satisfies all the regularity conditions and is stable as well

  12. Advanced Dark Energy Physics Telescope (ADEPT)

    Microsoft Academic Search

    Charles L. Bennett

    2009-01-01

    In 2006, we proposed to NASA a detailed concept study of ADEPT (the Advanced Dark Energy Physics Telescope), a potential space mission to reliably measure the time-evolution of dark energy by conducting the largest effective volume survey of the universe ever done. A peer-review panel of scientific, management, and technical experts reported back the highest possible 'excellent' rating for ADEPT.

  13. The Dark Energy Survey instrument design

    NASA Astrophysics Data System (ADS)

    Flaugher, B.

    2006-06-01

    We describe a new project, the Dark Energy Survey (DES), aimed at measuring the dark energy equation of state parameter, w, to a statistical precision of ~5%, with four complementary techniques. The survey will use a new 3 sq. deg. mosaic camera (DECam) mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a large mosaic camera, a five element optical corrector, four filters (g,r,i,z), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of 62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the 2.2 deg. diameter field of view. We plan to use the 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). At Fermilab, we will establish a packaging factory to produce four-side buttable modules for the LBNL devices, as well as to test and grade the CCDs. R&D is underway and delivery of DECam to CTIO is scheduled for 2009.

  14. The Dark Energy Survey instrument design

    SciTech Connect

    Flaugher, B.; /Fermilab

    2006-05-01

    We describe a new project, the Dark Energy Survey (DES), aimed at measuring the dark energy equation of state parameter, w, to a statistical precision of {approx}5%, with four complementary techniques. The survey will use a new 3 sq. deg. mosaic camera (DECam) mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a large mosaic camera, a five element optical corrector, four filters (g,r,i,z), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of 62 2K x 4K CCD modules (0.27''/pixel) arranged in a hexagon inscribed within the 2.2 deg. diameter field of view. We plan to use the 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). At Fermilab, we will establish a packaging factory to produce four-side buttable modules for the LBNL devices, as well as to test and grade the CCDs. R&D is underway and delivery of DECam to CTIO is scheduled for 2009.

  15. LISA as a dark energy probe

    NASA Astrophysics Data System (ADS)

    Arun, K. G.; Mishra, Chandra Kant; Van Den Broeck, Chris; Iyer, B. R.; Sathyaprakash, B. S.; Sinha, Siddhartha

    2009-05-01

    Recently, it has been shown that the inclusion of higher signal harmonics in the inspiral signals of binary supermassive black holes (SMBH) leads to dramatic improvements in the parameter estimation with Laser Interferometer Space Antenna (LISA). In particular, the angular resolution becomes good enough to identify the host galaxy or galaxy cluster, in which case the redshift can be determined by electromagnetic means. The gravitational wave signal also provides the luminosity distance with high accuracy, and the relationship between this and the redshift depends sensitively on the cosmological parameters, such as the equation-of-state parameter w = pDE/?DE of dark energy. Using binary SMBH events at z < 1 with appropriate masses and orientations, one would be able to constrain w to within a few per cent. We show that, if the measured sky location is folded into the error analysis, the uncertainty on w goes down by an additional factor of 2-3, leaving weak lensing as the only limiting factor in using LISA as a dark energy probe.

  16. Quasilocal variables in spherical symmetry: Numerical applications to dark matter and dark energy sources

    SciTech Connect

    Sussman, Roberto A. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico (ICN-UNAM), A. P. 70--543, 04510 Mexico D. F. (Mexico)

    2009-01-15

    A numerical approach is considered for spherically symmetric spacetimes that generalize Lemaitre-Tolman-Bondi dust solutions to nonzero pressure ('LTB spacetimes'). We introduce quasilocal (QL) variables that are covariant LTB objects satisfying evolution equations of Friedman-Lemaitre-Robertson-Walker (FLRW) cosmologies. We prove rigorously that relative deviations of the local covariant scalars from the QL scalars are nonlinear, gauge invariant and covariant perturbations on a FLRW formal background given by the QL scalars. The dynamics of LTB spacetimes is completely determined by the QL scalars and these exact perturbations. Since LTB spacetimes are compatible with a wide variety of ''equations of state,'' either single fluids or mixtures, a large number of known solutions with dark matter and dark energy sources in a FLRW framework (or with linear perturbations) can be readily examined under idealized but nontrivial inhomogeneous conditions. Coordinate choices and initial conditions are derived for a numerical treatment of the perturbation equations, allowing us to study nonlinear effects in a variety of phenomena, such as gravitational collapse, nonlocal effects, void formation, dark matter and dark energy couplings, and particle creation. In particular, the embedding of inhomogeneous regions can be performed by a smooth matching with a suitable FLRW solution, thus generalizing the Newtonian 'top hat' models that are widely used in astrophysical literature. As examples of the application of the formalism, we examine numerically the formation of a black hole in an expanding Chaplygin gas FLRW universe, as well as the evolution of density clumps and voids in an interactive mixture of cold dark matter and dark energy.

  17. Dark Energy from Fifth-Dimensional Brans-Dicke Theory

    NASA Astrophysics Data System (ADS)

    Bahrehbakhsh, Amir F.; Farhoudi, Mehrdad; Vakili, Hajar

    2013-08-01

    Following the approach of the induced-matter theory, we investigate the cosmological implications of a five-dimensional Brans-Dicke (BD) theory, and propose to explain the acceleration of the universe. After inducing in a four-dimensional hypersurface, we classify the energy-momentum tensor into two parts in a way that, one part represents all kind of the matter (the baryonic and dark) and the other one contains every extra terms emerging from the scale factor of the fifth dimension and the scalar field, which we consider as the energy-momentum tensor of dark energy. We also separate the energy-momentum conservation equation into two conservation equations, one for matter and the other for dark energy. We perform this procedure for different cases, without interacting term and with two particular (suitable) interacting terms between the two parts. By assuming the parameter of the state equation for dark energy to be constant, the equations of the model admit the power-law solutions. Though, the noninteracting case does not give any accelerated universe, but the interacting cases give both decelerated and accelerated universes. For the interacting cases, we figure out analytically the acceptable ranges of some parameters of the model, and also investigate the data analysis to test the model parameter values consistency with the observational data of the distance modulus of 580 SNe Ia compiled in Union2.1. For one of these interacting cases, the best fitted values suggest that BD coupling constant (?) is ? -7.75, however, it also gives the state parameter of dark energy (wX) equal to ? -0.67. In addition, the model gives the Hubble and deceleration parameters at the present time to be H? ? 69.4 (km/s)/Mpc and q? ? -0.38 (within their confidence intervals), where the scale factor of the fifth dimension shrinks with the time.

  18. Physical Evidence for Dark Energy

    E-print Network

    R. Scranton; A. J. Connolly; R. C. Nichol; A. Stebbins; I. Szapudi; D. J. Eisenstein; N. Afshordi; T. Budavari; I. Csabai; J. A. Frieman; J. E. Gunn; D. Johnston; Y. Loh; R. H. Lupton; C. J. Miller; E. S. Sheldon; R. S. Sheth; A. S. Szalay; M. Tegmark; Y. Xu

    2003-07-20

    We present measurements of the angular cross-correlation between luminous red galaxies from the Sloan Digital Sky Survey and the cosmic microwave background temperature maps from the Wilkinson Microwave Anisotropy Probe. We find a statistically significant achromatic positive correlation between these two data sets, which is consistent with the expected signal from the late Integrated Sachs-Wolfe (ISW) effect. We do not detect any anti-correlation on small angular scales as would be produced from a large Sunyaev-Zel'dovich (SZ) effect, although we do see evidence for some SZ effect for our highest redshift samples. Assuming a flat universe, our preliminary detection of the ISW effect provides independent physical evidence for the existence of dark energy.

  19. Vacuum quantum fluctuation energy in expanding universe and dark energy

    E-print Network

    Shun-Jin Wang

    2014-10-27

    This article is based on the Planckon densely piled vacuum model and the principle of cosmology. With the Planck era as initial conditions and including the early inflation, we have solved the Einstein-Friedmann equations to describe the evolution of the universe. The results are: 1) the ratio of the dark energy density to the vacuum quantum fluctuation energy density is $\\frac{{{\\rho }_{de}}}{{{\\rho }_{vac}}}\\sim{{(\\frac{{{t}_{P}}}{{{T}_{0}}})}^{2}}\\sim{{10}^{-122}} $; 2) at the inflation time ${{t}_{\\inf }}={{10}^{-35}}s$, the calculated universe radiation energy density is $\\rho ({{t}_{\\inf }})\\sim{{10}^{-16}}{{\\rho }_{vac}}$ and the corresponding temperature is ${{E}_{c}}\\sim{{10}^{15}}GeV$ consistent with the GUT phase transition temperature; 3) the expanding universe with vacuum as its environment is a non-equilibrium open system constantly exchanging energy with vacuum; during its expansion, the Planckons in the universe lose quantum fluctuation energy and create the cosmic expansion quanta-cosmons, the energy of cosmons is the lost part of the vacuum quantum fluctuation energy and contributes to the universe energy with the calculated value ${{E}_{\\cos mos}}={{10}^{22}}{{M}_{\\otimes }}{{c}^{2}}$ (where ${{M}_{\\otimes }}$ is solar mass); 4) the total energy of the universe, namely the negative gravity energy plus the positive universe energy is zero; 5) the negative gravity potential and the gravity acceleration related to the creation of cosmons are derived with the nature of outward repulsive force, indicating that the cosmon may be the candidate of the dark energy quantum; 6) both the initial Planck era solution and the infinite asymptotic solution of the Einstein-Friedman equations are unstable: the former tends to expand and the latter tends to shrink, so that the Einstein-Friedman universe will undergo a cyclic evolution of successive expansion and shrinking.

  20. Precision Studies of Dark Energy with LSST

    E-print Network

    J. Anthony Tyson; for the LSST Collaboration

    2006-09-19

    Starting around 2013, data from the Large Synoptic Survey Telescope (LSST) will be analyzed for a wide range of phenomena. By separately tracing the development of mass structure and rate of expansion of the universe, these data will address the physics of dark matter and dark energy, the possible existence of modified gravity on large scales, large extra dimensions, the neutrino mass, and possible self interaction of dark matter particles.

  1. Precision Studies of Dark Energy with LSST

    SciTech Connect

    Tyson, J. Anthony [Department of Physics, University of California, Davis, CA 95616 (United States)

    2006-11-17

    Starting around 2013, data from the Large Synoptic Survey Telescope (LSST) will be analyzed for a wide range of phenomena. By separately tracing the development of mass structure and rate of expansion of the universe, these data will address the physics of dark matter and dark energy, the possible existence of modified gravity on large scales, large extra dimensions, the neutrino mass, and possible self interaction of dark matter particles.

  2. Evolution of entropic dark energy and its phantom nature

    E-print Network

    Titus K. Mathew; Chinthak Murali; Shejeelammal J

    2015-06-06

    Assuming the form of the entropic dark energy as arises form the surface term in the Einstein-Hilbert's action, it's evolution were analyzed in an expanding flat universe. The model parameters were evaluated by constraining model using the Union data on Type Ia supernovae. We found that the model predicts an early decelerated phase and a later accelerated phase at the background level. The evolution of the Hubble parameter, dark energy density, equation of state parameter and deceleration parameter were obtained. The model is diagnosed with $Om$ parameter. The model is hardly seems to be supporting the linear perturbation growth for the structure formation. We also found that the entropic dark energy shows phantom nature for redshifts $zdark energy density become infinitely large and the big rip time is found to be around 36 Giga Years from now.

  3. Evolution of entropic dark energy and its phantom nature

    E-print Network

    Titus K. Mathew; Chinthak Murali; Shejeelammal J

    2015-06-23

    Assuming the form of the entropic dark energy as arises form the surface term in the Einstein-Hilbert's action, it's evolution were analyzed in an expanding flat universe. The model parameters were evaluated by constraining model using the Union data on Type Ia supernovae. We found that the model predicts an early decelerated phase and a later accelerated phase at the background level. The evolution of the Hubble parameter, dark energy density, equation of state parameter and deceleration parameter were obtained. The model is diagnosed with $Om$ parameter. The model is hardly seems to be supporting the linear perturbation growth for the structure formation. We also found that the entropic dark energy shows phantom nature for redshifts $zdark energy density become infinitely large and the big rip time is found to be around 36 Giga Years from now.

  4. Can a galaxy redshift survey measure dark energy clustering?

    SciTech Connect

    Takada, Masahiro [Astronomical Institute, Tohoku University, Sendai 980-8578 (Japan)

    2006-08-15

    A wide-field galaxy redshift survey allows one to probe galaxy clustering at largest spatial scales, which carries invaluable information on horizon-scale physics complementarily to the cosmic microwave background (CMB). Assuming the planned survey consisting of z{approx}1 and z{approx}3 surveys with areas of 2000 and 300 deg.{sup 2}, respectively, we study the prospects for probing dark energy clustering from the measured galaxy power spectrum, assuming the dynamical properties of dark energy are specified in terms of the equation of state and the effective sound speed c{sub e} in the context of an adiabatic cold dark dominated matter model. The dark energy clustering adds a power to the galaxy power spectrum amplitude at spatial scales greater than the sound horizon, and the enhancement is sensitive to redshift evolution of the net dark energy density, i.e. the equation of state. We find that the galaxy survey, when combined with CMB expected from the Planck satellite mission, can distinguish dark energy clustering from a smooth dark energy model such as the quintessence model (c{sub e}=1), when c{sub e} < or approx. 0.04 (0.02) in the case of the constant equation of state w{sub 0}=-0.9 (-0.95). An ultimate full-sky survey of z{approx}1 galaxies allows the detection when c{sub e}(less-or-similar sign)0.08 (0.04) for w{sub 0}=0.9 (-0.95). These forecasts show a compatible power with an all-sky CMB and galaxy cross correlation that probes the integrated Sachs-Wolfe effect. We also investigate a degeneracy between the dark energy clustering and the nonrelativistic neutrinos implied from the neutrino oscillation experiments, because the two effects both induce a scale-dependent modification in the galaxy power spectrum shape at largest spatial scales accessible from the galaxy survey. It is shown that a wider redshift coverage can efficiently separate the two effects by utilizing the different redshift dependences, where dark energy clustering is apparent only at low redshifts z < or approx. 1.

  5. Viscous Dark Energy in $f(T)$ Gravity

    E-print Network

    M. Sharif; Shamaila Rani

    2014-05-18

    We study the bulk viscosity taking dust matter in the generalized teleparallel gravity. We consider different dark energy models in this scenario along with a time dependent viscous model to construct the viscous equation of state parameter for these dark energy models. We discuss the graphical representation of this parameter to investigate the viscosity effects on the accelerating expansion of the universe. It is mentioned here that the behavior of the universe depends upon the viscous coefficients showing the transition from decelerating to accelerating phase. It leads to the crossing of phantom divide line and becomes phantom dominated for specific ranges of these coefficients.

  6. Quintom dark energy models with nearly flat potentials

    SciTech Connect

    Setare, M. R.; Saridakis, E. N. [Department of Science, Payame Noor University, Bijar (Iran, Islamic Republic of); Department of Physics, University of Athens, GR-15771 Athens (Greece)

    2009-02-15

    We examine quintom dark energy models, produced by the combined consideration of a canonical and a phantom field, with nearly flat potentials and dark energy equation-of-state parameter w{sub DE} close to -1. We find that all such models converge to a single expression for w{sub DE}(z), depending only on the initial field values and their derivatives. We show that this quintom paradigm allows for a description of the transition through -1 in the near cosmological past. In addition, we provide the necessary conditions for the determination of the direction of the -1 crossing.

  7. Can we test Dark Energy with Running Fundamental Constants ?

    E-print Network

    Michael Doran

    2005-04-26

    We investigate a link between the running of the fine structure constant $\\alpha$ and a time evolving scalar dark energy field. Employing a versatile parameterization for the equation of state, we exhaustively cover the space of dark energy models. Under the assumption that the change in $\\alpha$ is to first order given by the evolution of the Quintessence field, we show that current Oklo, Quasi Stellar Objects and Equivalence Principle observations restrict the model parameters considerably stronger than observations of the Cosmic Microwave Background, Large Scale Structure and Supernovae Ia combined.

  8. Is dark energy an effect of averaging?

    E-print Network

    Nan Li; Marina Seikel; Dominik J. Schwarz

    2008-01-22

    The present standard model of cosmology states that the known particles carry only a tiny fraction of total mass and energy of the Universe. Rather, unknown dark matter and dark energy are the dominant contributions to the cosmic energy budget. We review the logic that leads to the postulated dark energy and present an alternative point of view, in which the puzzle may be solved by properly taking into account the influence of cosmic structures on global observables. We illustrate the effect of averaging on the measurement of the Hubble constant.

  9. Gravity effects of the quantum vacuum. Dark energy and dark matter

    E-print Network

    Emilio Santos

    2015-05-09

    The stress-energy tensor of the quantum vacuum is studied for the particular case of quantum electrodynamics (QED), that is a fictituous universe where only the electromagnetic and the electron-positron fields exist. The integrals involved are ultraviolet divergent but it is suggested that a natural cut-off may exist. It is shown that, in spite of the fact that the stress-energy tensor of the electromagnetic field alone is traceless (i.e the pressure P equals 1/3 the energy density u), the total QED tensor is proportional to the metric tensor to a good approximation (i. e. P = -u). It is proposed that there is a cosmological constant in Einstein equation that exactly balances the stress-energy of the vacuum. It is shown that vacuum fluctuations give rise to a modified spacetime metric able to explain dark energy. Particular excitations of the vacuum are studied that might explain dark matter.

  10. Dark Energy: Observational Evidence and Theoretical Models

    E-print Network

    Novosyadlyj, B; Shtanov, Yu; Zhuk, A

    2015-01-01

    The book elucidates the current state of the dark energy problem and presents the results of the authors, who work in this area. It describes the observational evidence for the existence of dark energy, the methods and results of constraining of its parameters, modeling of dark energy by scalar fields, the space-times with extra spatial dimensions, especially Kaluza---Klein models, the braneworld models with a single extra dimension as well as the problems of positive definition of gravitational energy in General Relativity, energy conditions and consequences of their violation in the presence of dark energy. This monograph is intended for science professionals, educators and graduate students, specializing in general relativity, cosmology, field theory and particle physics.

  11. Dark energy appears to have caused the expansion of our universe

    Microsoft Academic Search

    Tom Gehrels

    2010-01-01

    A new paradigm based on an equation of Chandrasekhar points directly to a specific multi-verse(http:\\/\\/arXiv.org\\/abs\\/0912.5367 and references there in). Dark energy accelerating the expansion is an essential part of the model -in turn, it shows that dark energy may have caused the expansion to begin with. At the present time, 72

  12. Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter

    E-print Network

    Anil Kumar Yadav; Lallan Yadav

    2010-10-02

    The Bianchi type III dark energy models with constant deceleration parameter are investigated. The equation of state parameter $\\omega$ is found to be time dependent and its existing range for this model is consistent with the recent observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy clustering statistics. The physical aspect of the dark energy models are discussed.

  13. Constraints on the Sound Speed of Dynamical Dark Energy

    E-print Network

    Jun-Qing Xia; Yi-Fu Cai; Tao-Tao Qiu; Gong-Bo Zhao; Xinmin Zhang

    2008-01-16

    In this paper we study the sound speed - $c_s^2$, which is directly related to the classical perturbations - of the dynamical dark energy (DE), especially with an equation of state crossing the cosmological constant boundary in details and show its implications on Cosmic Microwave Background (CMB) Anisotropy. With the present observational data of CMB, Type Ia Supernova (SNIa) and galaxy clustering, we perform a global analysis to constrain the sound speed of dark energy, using the Markov Chain Monte Carlo method. We find that the sound speed of dark energy is weakly constrained by current observations thus the futuristic precision measurements of CMB on a very large angular scale (low multipoles) are necessary.

  14. Statefinder parameters in two dark energy models

    E-print Network

    Grigoris Panotopoulos

    2007-12-07

    The statefinder parameters ($r,s$) in two dark energy models are studied. In the first, we discuss in four-dimensional General Relativity a two fluid model, in which dark energy and dark matter are allowed to interact with each other. In the second model, we consider the DGP brane model generalized by taking a possible energy exchange between the brane and the bulk into account. We determine the values of the statefinder parameters that correspond to the unique attractor of the system at hand. Furthermore, we produce plots in which we show $s,r$ as functions of red-shift, and the ($s-r$) plane for each model.

  15. Direct detection rates of dark matter coupled to dark energy

    SciTech Connect

    Tetradis, N. [Department of Physics, University of Athens, Zographou 157 84 (Greece); Vergados, J. D. [Theoretical Physics Division, University of Ioannina, Ioannina, Gr 451 10 (Greece); Institute of Theoretical Physics, University of Tuebingen, Tuebingen (Germany); Faessler, Amand [Institute of Theoretical Physics, University of Tuebingen, Tuebingen (Germany)

    2007-01-15

    We investigate the effect of a coupling between dark matter and dark energy on the rates for the direct detection of dark matter. The magnitude of the effect depends on the strength {kappa} of this new interaction relative to gravity. The resulting isothermal velocity distribution for dark matter in galaxy halos is still Maxwell-Boltzmann (M-B), but the characteristic velocity and the escape velocity are increased by {radical}(1+{kappa}{sup 2}). We adopt a phenomenological approach and consider values of {kappa} near unity. For such values we find that: (i) The (time averaged) event rate increases for light WIMPs, while it is somewhat reduced for WIMP masses larger than 100 GeV. (ii) The time dependence of the rate arising from the modulation amplitude is decreased compared to the standard M-B velocity distribution. (iii) The average and maximum WIMP energy increase proportionally to 1+{kappa}{sup 2}, which, for sufficiently massive WIMPs, allows the possibility of designing experiments measuring {gamma} rays following nuclear de-excitation.

  16. Why we need to see the dark matter to understand the dark energy

    E-print Network

    Martin Kunz

    2007-10-30

    The cosmological concordance model contains two separate constituents which interact only gravitationally with themselves and everything else, the dark matter and the dark energy. In the standard dark energy models, the dark matter makes up some 20% of the total energy budget today, while the dark energy is responsible for about 75%. Here we show that these numbers are only robust for specific dark energy models and that in general we cannot measure the abundance of the dark constituents separately without making strong assumptions.

  17. G-corrected holographic dark energy model

    E-print Network

    Malekjani, M

    2013-01-01

    Here we investigate the holographic dark energy model in the framework of FRW cosmology where the Newtonian gravitational constant,$G$, is varying with cosmic time. Using the complementary astronomical data which support the time dependency of $G$, the evolutionary treatment of EoS parameter and energy density of dark energy model are calculated in the presence of time variation of $G$. It has been shown that in this case, the phantom regime can be achieved at the present time. We also calculate the evolution of $G$- corrected deceleration parameter for holographic dark energy model and show that the dependency of $G$ on the comic time can influence on the transition epoch from decelerated expansion to the accelerated phase. Finally we perform the statefinder analysis for $G$- corrected holographic model and show that this model has a shorter distance from the observational point in $s-r$ plane compare with original holographic dark energy model.

  18. G-corrected holographic dark energy model

    NASA Astrophysics Data System (ADS)

    Malekjani, M.; Honari-Jafarpour, M.

    2013-08-01

    Here we investigate the holographic dark energy model in the framework of FRW cosmology where the Newtonian gravitational constant, G, is varying with cosmic time. Using the complementary astronomical data which support the time dependency of G, the evolutionary treatment of EoS parameter and energy density of dark energy model are calculated in the presence of time variation of G. It has been shown that in this case, the phantom regime can be achieved at the present time. We also calculate the evolution of G-corrected deceleration parameter for holographic dark energy model and show that the dependency of G on the comic time can influence on the transition epoch from decelerated expansion to the accelerated phase. Finally we perform the statefinder analysis for G-corrected holographic model and show that this model has a shorter distance from the observational point in s- r plane compare with original holographic dark energy model.

  19. New holographic dark energy model inspired by the DGP braneworld

    E-print Network

    Sheykhi, A; Ghaffari, S

    2015-01-01

    The energy density of the holographic dark energy is based on the area law of entropy, and thus any modification of the area law leads to a modified holographic energy density. Inspired by the entropy expression associated with the apparent horizon of a Friedmann-Robertson-Walker (FRW) Universe in DGP braneworld, we propose a new model for the holographic dark energy in the framework of DGP brane cosmology. We investigate the cosmological consequences of this new model and calculate the equation of state parameter by choosing the Hubble radius, $L = H^{-1}$, as the system's IR cutoff. Our study show that, due to the effects of the extra dimension (bulk), the identification of IR-cutoff with Hubble radius, can reproduce the present acceleration of the Universe expansion. This is in contrast to the ordinary holographic dark energy in standard cosmology which leads to the zero equation of state parameter in the case of choosing the Hubble radius as system's IR cutoff in the absence of interaction between dark ma...

  20. Unknowns and unknown unknowns: from dark sky to dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Suto, Yasushi

    2010-07-01

    Answering well-known fundamental questions is usually regarded as the major goal of science. Discovery of other unknown and fundamental questions is, however, even more important. Recognition that "we didn't know anything" is the basic scientific driver for the next generation. Cosmology indeed enjoys such an exciting epoch. What is the composition of our universe ? This is one of the well-known fundamental questions that philosophers, astronomers and physicists have tried to answer for centuries. Around the end of the last century, cosmologists finally recognized that "We didn't know anything". Except for atoms that comprise slightly less than 5% of the universe, our universe is apparently dominated by unknown components; 23% is the known unknown (dark matter), and 72% is the unknown unknown (dark energy). In the course of answering a known fundamental question, we have discovered an unknown, even more fundamental, question: "What is dark matter? What is dark energy?" There are a variety of realistic particle physics models for dark matter, and its experimental detection may be within reach. On the other hand, it is fair to say that there is no widely accepted theoretical framework to describe the nature of dark energy. This is exactly why astronomical observations will play a key role in unveiling its nature. I will review our current understanding of the "dark sky", and then present on-going Japanese project, SuMIRe, to discover even more unexpected questions.

  1. High-resolution temporal constraints on the dynamics of dark energy

    E-print Network

    Gong-Bo Zhao; Dragan Huterer; Xinmin Zhang

    2008-05-18

    We use the recent type Ia supernova, cosmic microwave background and large-scale structure data to shed light on the temporal evolution of the dark energy equation of state $w(z)$ out to redshift one. We constrain the most flexible parametrization of dark energy to date, and include the dark energy perturbations consistently throughout. Interpreting our results via the principal component analysis, we find no significant evidence for dynamical dark energy: the cosmological constant model is consistent with data everywhere between redshift zero and one at 95% C.L.

  2. Reconstruction of Hessence Dark Energy and the Latest Type Ia Supernovae Gold Dataset

    E-print Network

    Hao Wei; Ningning Tang; Shuang Nan Zhang

    2007-02-28

    Recently, many efforts have been made to build dark energy models whose equation-of-state parameter can cross the so-called phantom divide $w_{de}=-1$. One of them is the so-called hessence dark energy model in which the role of dark energy is played by a non-canonical complex scalar field. In this work, we develop a simple method based on Hubble parameter $H(z)$ to reconstruct the hessence dark energy. As examples, we use two familiar parameterizations for $H(z)$ and fit them to the latest 182 type Ia supernovae Gold dataset. In the reconstruction, measurement errors are fully considered.

  3. Collapsing Inhomogeneous Dust Fluid in the Background of Dark Energy

    E-print Network

    Tanwi Bandyopadhyay; Subenoy Chakraborty

    2006-05-11

    In the present work, gravitational collapse of an inhomogeneous spherical star model, consisting of inhomogeneous dust fluid (dark matter) in the background of dark energy is considered. The collapsing process is examined first separately for both dark matter and dark energy and then under the combined effect of dark matter and dark energy with or without interaction. The dark energy is considered in the form of perfect fluid and both marginally and non-marginally bound cases are considered for the collapsing model. Finally dark energy in the form of anisotropic fluid is investigated and it is found to be similar to ref. [12

  4. The Tensor to Scalar Ratio of Phantom Dark Energy Models

    E-print Network

    A. E. Schulz; Martin White

    2001-04-06

    We investigate the anisotropies in the cosmic microwave background in a class of models which possess a positive cosmic energy density but negative pressure, with a constant equation of state w = p/rho < -1. We calculate the temperature and polarization anisotropy spectra for both scalar and tensor perturbations by modifying the publicly available code CMBfast. For a constant initial curvature perturbation or tensor normalization, we have calculated the final anisotropy spectra as a function of the dark energy density and equation of state w and of the scalar and tensor spectral indices. This allows us to calculate the dependence of the tensor-to-scalar ratio on w in a model with phantom dark energy, which may be important for interpreting any future detection of long-wavelength gravitational waves.

  5. Lectures on Dark Energy and Cosmic Acceleration

    NASA Astrophysics Data System (ADS)

    Frieman, Joshua A.

    2008-09-01

    The discovery ten years ago that the expansion of the Universe is accelerating put in place the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% dark energy. Yet the underlying cause of cosmic acceleration remains a mystery: it could arise from the repulsive gravity of dark energy-for example, the quantum energy of the vacuum-or it may signal that General Relativity breaks down on cosmological scales and must be replaced. In these lectures, I present the observational evidence for cosmic acceleration and what it has revealed about dark energy, discuss a few of the theoretical ideas that have been proposed to explain acceleration, and describe the key observational probes that we hope will shed light on this enigma in the coming years. Based on five lectures given at the XII Ciclo de Cursos Especiais at the Observatorio Nacional, Rio de Janeiro, Brazil, 1-5 October 2007.

  6. Probing dark energy through scale dependence

    NASA Astrophysics Data System (ADS)

    Motta, Mariele; Sawicki, Ignacy; Saltas, Ippocratis D.; Amendola, Luca; Kunz, Martin

    2013-12-01

    We consider the consequences of having no prior knowledge of the true dark energy model for the interpretation of cosmological observations. The magnitude of redshift-space distortions and weak-lensing shear is determined by the metric on the geodesics of which galaxies and light propagate. We show that, given precise enough observations, we can use these data to completely reconstruct the metric on our past light cone and therefore to measure the scale and time dependence of the anisotropic stress and the evolution of the gravitational potentials in a model-independent manner. Since both dark matter and dark energy affect the visible sector only through the gravitational field they produce, they are inseparable without a model for dark energy: galaxy bias cannot be measured and therefore the distribution of dark matter determined; the peculiar velocity of dark matter can be identified with that of the galaxies only when the equivalence principle holds. Given these limitations, we show how one can nonetheless build tests for classes of dark energy models which depend on making measurements at multiple scales at a particular redshift. They are null tests on the model-independent observables, do not require modeling evolution in time, and do not require any parametrization of the free functions of these models—such as the sound speed. We show that one in principle could rule out or constrain the whole class of the most general scalar-tensor theories even without assuming the quasistatic limit.

  7. Holographic dark energy with time depend gravitational constant in the non-flat Ho$\\check{r}$ava-Lifshitz cosmology

    E-print Network

    Kh. Saaidi; A. Aghamohammadi; M. R. Setare

    2010-10-25

    We study the holographic dark energy on the subject of Ho$\\check{r}$ava-Lifshitz gravity with a time dependent gravitational constant (G(t)), in the non-flat space-time. We obtain the differential equation that specify the evolution of the dark energy density parameter based on varying gravitational constant. we find out a relation for the state parameter of the dark energy equation to low redshifts which containing varying $G$ correction.

  8. Galaxy Formation With Dark Matter and Dark Energy

    E-print Network

    David E. Rosenberg

    2012-06-12

    Eliptical and bulge galaxies share a tight correlation of velocity distribution to both luminosity and black hole mass. There are similar orbital speeds for all galaxies of a given luminosity including dark matter (DM) at large radii. The halo surface density of DM is constant for almost all types of galaxies and ranges 14 mag. down to dwarf spherical galaxies. There are supermassive black holes or giant, pure disk galaxies at high redshift inexplicable with hierarchical clustering or collapse dynamics. These and a myriad of other galaxy formation problems are explainable by an initial shell which caused the Planck cosmic microwave background radiation. A reduction in the energy-density of primordial galactic black holes is necessary to explain dark energy.

  9. Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios

    NASA Astrophysics Data System (ADS)

    Jenke, T.; Cronenberg, G.; Burgdörfer, J.; Chizhova, L. A.; Geltenbort, P.; Ivanov, A. N.; Lauer, T.; Lins, T.; Rotter, S.; Saul, H.; Schmidt, U.; Abele, H.

    2014-04-01

    We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton's inverse square law of gravity is understood at micron distances on an energy scale of 10-14 eV. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant ? >5.8×108 at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength gsgp>3.7×10-16 (5.3×10-16) at a Yukawa length of ? =20 ?m (95% C.L.).

  10. Cosmological analysis of pilgrim dark energy in loop quantum cosmology

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul

    2015-05-01

    The proposal of pilgrim dark energy is based on the speculation that phantom-like dark energy (with strong enough resistive force) can prevent black hole formation in the universe. We explore this phenomenon in the loop quantum cosmology framework by taking pilgrim dark energy with a Hubble horizon. We evaluate the cosmological parameters such as the Hubble parameter, the equation of state parameter, the squared speed of sound, and also cosmological planes like - and - on the basis of the pilgrim dark energy parameter () and the interacting parameter (). It is found that the values of the Hubble parameter lie in the range . It is mentioned here that the equation of state parameter lies within the ranges for and for , respectively. Also, the - planes provide a CDM limit, and freezing and thawing regions for all cases of . It is also interesting to mention here that the - planes lie in the range (). In addition, the - planes also correspond to CDM for all cases of . Finally, it is remarked that all the above constraints of the cosmological parameters (corresponding to and ) show consistency with different observational data like Planck, WP, BAO, , SNLS, and nine-year WMAP.

  11. Cosmological Analysis of Pilgrim Dark Energy in Loop Quantum Cosmology

    E-print Network

    Jawad, Abdul

    2015-01-01

    The proposal of pilgrim dark energy is based on speculation that phantom-like dark energy (with strong enough resistive force) can prevent black hole formation in the universe. We explore this phenomenon in loop quantum cosmology framework by taking Hubble horizon as an infra-red cutoff in pilgrim dark energy. We evaluate the cosmological parameters such as Hubble, equation of state parameter, squared speed of sound and also cosmological planes like $\\omega_{\\vartheta}-\\omega'_{\\vartheta}$ and $r-s$ on the basis of pilgrim dark energy parameter ($u$) and interacting parameter ($d^2$). It is found that values of Hubble parameter lies in the range $74^{+0.005}_{-0.005}$. It is mentioned here that equation state parameter lies within the ranges $-1\\mp0.00005$ for $u=2, 1$ and $(-1.12,-1), (-5,-1)$ for $u=-1,-2$, respectively. Also, $\\omega_{\\vartheta}-\\omega'_{\\vartheta}$ planes provide $\\Lambda$CDM limit, freezing and thawing regions for all cases of $u$. It is also interesting to mention here that $\\omega_{\\va...

  12. COBE-DMR-Normalized Dark Energy Cosmogony

    E-print Network

    Pia Mukherjee; Anthony J. Banday; Alain Riazuelo; Krzysztof M. Górski; Bharat Ratra

    2003-08-19

    Likelihood analyses of the COBE-DMR sky maps are used to determine the normalization of the inverse-power-law-potential scalar field dark energy model. Predictions of the DMR-normalized model are compared to various observations to constrain the allowed range of model parameters. Although the derived constraints are restrictive, evolving dark energy density scalar field models remain an observationally-viable alternative to the constant cosmological constant model.

  13. DARK MATTER AND DARK ENERGY AS EFFECTS OF QUANTUM GRAVITY Max I. Fomitchev1

    E-print Network

    Giles, C. Lee

    DARK MATTER AND DARK ENERGY AS EFFECTS OF QUANTUM GRAVITY Max I. Fomitchev1 Submitted March 12th of high matter density expected in the early Universe I show that primordial inflation and dark energy (i. Subject headings: cosmology: dark matter ­ galaxies: kinematics and dynamics ­ X-rays: galaxies: clusters

  14. Dark Energy, Dark Matter and Science with Constellation-X

    NASA Technical Reports Server (NTRS)

    Cardiff, Ann Hornschemeier

    2005-01-01

    Constellation-X, with more than 100 times the collecting area of any previous spectroscopic mission operating in the 0.25-40 keV bandpass, will enable highthroughput, high spectral resolution studies of sources ranging from the most luminous accreting supermassive black holes in the Universe to the disks around young stars where planets form. This talk will review the updated Constellation-X science case, released in booklet form during summer 2005. The science areas where Constellation-X will have major impact include the exploration of the space-time geometry of black holes spanning nine orders of magnitude in mass and the nature of the dark energy and dark matter which govern the expansion and ultimate fate of the Universe. Constellation-X will also explore processes referred to as "cosmic feedback" whereby mechanical energy, radiation, and chemical elements from star formation and black holes are returned to interstellar and intergalactic medium, profoundly affecting the development of structure in the Universe, and will also probe all the important life cycles of matter, from stellar and planetary birth to stellar death via supernova to stellar endpoints in the form of accreting binaries and supernova remnants. This talk will touch upon all these areas, with particular emphasis on Constellation-X's role in the study of Dark Energy.

  15. Dark Energy Found Stifling Growth in Universe

    NASA Astrophysics Data System (ADS)

    2008-12-01

    WASHINGTON -- For the first time, astronomers have clearly seen the effects of "dark energy" on the most massive collapsed objects in the universe using NASA's Chandra X-ray Observatory. By tracking how dark energy has stifled the growth of galaxy clusters and combining this with previous studies, scientists have obtained the best clues yet about what dark energy is and what the destiny of the universe could be. This work, which took years to complete, is separate from other methods of dark energy research such as supernovas. These new X-ray results provide a crucial independent test of dark energy, long sought by scientists, which depends on how gravity competes with accelerated expansion in the growth of cosmic structures. Techniques based on distance measurements, such as supernova work, do not have this special sensitivity. Scientists think dark energy is a form of repulsive gravity that now dominates the universe, although they have no clear picture of what it actually is. Understanding the nature of dark energy is one of the biggest problems in science. Possibilities include the cosmological constant, which is equivalent to the energy of empty space. Other possibilities include a modification in general relativity on the largest scales, or a more general physical field. People Who Read This Also Read... Chandra Data Reveal Rapidly Whirling Black Holes Ghostly Glow Reveals a Hidden Class of Long-Wavelength Radio Emitters Powerful Nearby Supernova Caught By Web Cassiopeia A Comes Alive Across Time and Space To help decide between these options, a new way of looking at dark energy is required. It is accomplished by observing how cosmic acceleration affects the growth of galaxy clusters over time. "This result could be described as 'arrested development of the universe'," said Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., who led the research. "Whatever is forcing the expansion of the universe to speed up is also forcing its development to slow down." Vikhlinin and his colleagues used Chandra to observe the hot gas in dozens of galaxy clusters, which are the largest collapsed objects in the universe. Some of these clusters are relatively close and others are more than halfway across the universe. The results show the increase in mass of the galaxy clusters over time aligns with a universe dominated by dark energy. It is more difficult for objects like galaxy clusters to grow when space is stretched, as caused by dark energy. Vikhlinin and his team see this effect clearly in their data. The results are remarkably consistent with those from the distance measurements, revealing general relativity applies, as expected, on large scales. "For years, scientists have wanted to start testing how gravity works on large scales and now, we finally have," said William Forman, a co-author of the study from the Smithsonian Astrophysical Observatory. "This is a test that general relativity could have failed." When combined with other clues -- supernovas, the study of the cosmic microwave background, and the distribution of galaxies -- this new X-ray result gives scientists the best insight to date on the properties of dark energy. The study strengthens the evidence that dark energy is the cosmological constant. Although it is the leading candidate to explain dark energy, theoretical work suggests it should be about 10 raised to the power of 120 times larger than observed. Therefore, alternatives to general relativity, such as theories involving hidden dimensions, are being explored. "Putting all of this data together gives us the strongest evidence yet that dark energy is the cosmological constant, or in other words, that 'nothing weighs something'," said Vikhlinin. "A lot more testing is needed, but so far Einstein's theory is looking as good as ever." These results have consequences for predicting the ultimate fate of the universe. If dark energy is explained by the cosmological constant, the expansion of the universe will cont

  16. Report of the Dark Energy Task Force

    SciTech Connect

    Albrecht, Andreas; /UC, Davis; Bernstein, Gary; /Pennsylvania U.; Cahn, Robert; /LBL, Berkeley; Freedman, Wendy L.; /Carnegie Inst. Observ.; Hewitt, Jacqueline; /MIT; Hu,Wayne; /KICP, Chicago; Huth, John; /Harvard U.; Kamionkowski, Marc; /Caltech; Kolb, Edward W.; /Fermilab /Chicago U., Astron. Astrophys. Ctr.; Knox, Lloyd; /UC, Davis; Mather, John C.; /NASA, Goddard /Princeton U.; ,

    2006-09-01

    Dark energy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed phenomenon that most directly demonstrates that our theories of fundamental particles and gravity are either incorrect or incomplete. Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among the very most compelling of all outstanding problems in physical science. These circumstances demand an ambitious observational program to determine the dark energy properties as well as possible.

  17. Dark energy and future singularity of the universe in Kaluza-Klein space time

    NASA Astrophysics Data System (ADS)

    Samnata, G. C.

    2014-10-01

    The dark energy model with the equation of state is studied in Kaluza-Klein space time. The model comprises and provides realization of several types of singularities in different parameter regimes. We discuss the finite-time singularities into four classes and explicitly present the models which give rise to these singularities by assuming the form of the equation of state of dark energy. Also, we discussed the models in terms of the cosmological redshift and some observational parameters.

  18. Observational Constraints on the Nature of Dark Energy: First Cosmological Results from the ESSENCE Supernova Survey

    Microsoft Academic Search

    W. Michael Wood-Vasey; G. Miknaitis; C. W. Stubbs; S. Jha; A. G. Riess; P. M. Garnavich; R. P. Kirshner; C. Aguilera; A. C. Becker; J. W. Blackman; S. Blondin; P. Challis; A. Clocchiatti; A. Conley; R. Covarrubias; T. M. Davis; A. V. Filippenko; R. J. Foley; A. Garg; M. Hicken; K. Krisciunas; B. Leibundgut; W. Li; T. Matheson; A. Miceli; G. Narayan; G. Pignata; J. L. Prieto; A. Rest; M. E. Salvo; B. P. Schmidt; R. C. Smith; J. Sollerman; J. Spyromilio; J. L. Tonry; N. B. Suntzeff; A. Zenteno

    2007-01-01

    We present constraints on the dark energy equation-of-state parameter, w=P\\/(rhoc2), using 60 SNe Ia from the ESSENCE supernova survey. We derive a set of constraints on the nature of the dark energy assuming a flat universe. By including constraints on (OmegaM, w) from baryon acoustic oscillations, we obtain a value for a static equation-of-state parameter w=-1.05+0.13-0.12 (stat 1 sigma)+\\/-0.13 (sys)

  19. Effective dark energy models and dark energy models with bounce in frames of F( T) gravity

    NASA Astrophysics Data System (ADS)

    Astashenok, Artyom V.

    2014-05-01

    Various cosmological models in frames of F( T) gravity are considered. The general scheme of constructing effective dark energy models with various evolution is presented. It is showed that these models in principle are compatible with ?CDM model. The dynamics of universe governed by F( T) gravity can mimics ?CDM evolution in past but declines from it in a future. We also construct some dark energy models with the "real" (non-effective) equation-of-state parameter w such that w?-1. It is showed that in F( T) gravity the Universe filled phantom field not necessarily ends its existence in singularity. There are two possible mechanisms permitting the final singularity. Firstly due to the nonlinear dependence between energy density and H 2 ( H is the Hubble parameter) the universe can expands not so fast as in the general relativity and in fact Little Rip regime take place instead Big Rip. We also considered the models with possible bounce in future. In these models the universe expansion can mimics the dynamics with future singularity but due to bounce in future universe begin contracts.

  20. Dark MaGICC: the effect of dark energy on disc galaxy formation. Cosmology does matter

    NASA Astrophysics Data System (ADS)

    Penzo, C.; Macciò, A. V.; Casarini, L.; Stinson, G. S.; Wadsley, J.

    2014-07-01

    We present the Dark MaGICC (Making Galaxies in a Cosmological Context) project, which aims to investigate the effect of dark energy (DE) modelling on disc galaxy formation via hydrodynamical cosmological simulations. Dark MaGICC includes four dynamical DE scenarios with time varying equations of state, one with a self-interacting Ratra-Peebles model. In each scenario, we simulate three disc galaxies with high resolution using smoothed particle hydrodynamics. The baryonic physics model is the same used in the MaGICC project, and we varied only the background cosmology. We find that the DE parametrization has a surprisingly important impact on galaxy evolution and on structural properties of galaxies at z = 0, in striking contrast with predictions from pure N-body simulations. The different background evolutions can (depending on the behaviour of the DE equation of state) either enhance or quench star formation with respect to a ? cold dark matter model, at a level similar to the variation of the stellar feedback parametrization, with strong effects on the final galaxy rotation curves. While overall stellar feedback is still the driving force in shaping galaxies, we show that the effect of the DE parametrization plays a larger role than previously thought, especially at lower redshifts. For this reason, the influence of DE parametrization on galaxy formation must be taken into account, especially in the era of precision cosmology.

  1. The transient and the late time attractor tachyon dark energy: Can we distinguish it from quintessence ?

    E-print Network

    Amna Ali; M. Sami; A. A. Sen

    2009-05-15

    The string inspired tachyon field can serve as a candidate of dark energy. Its equation of state parameter $w$ varies from 0 to -1. In case of tachyon field potential $V(\\phi)\\to 0$ slower(faster) than $1/\\phi^2$ at infinity, dark energy(dark matter) is a late time attractor. We investigate the tachyon dark energy models under the assumption that $w$ is close to -1. We find that all the models exhibit unique behavior around the present epoch which is exactly same as that of the thawing quintessence.

  2. The transient and the late time attractor tachyon dark energy: Can we distinguish it from quintessence ?

    E-print Network

    Ali, Amna; Sen, A A

    2009-01-01

    The string inspired tachyon field can serve as a candidate of dark energy. Its equation of state parameter $w$ varies from 0 to -1. In case of tachyon field potential $V(\\phi)\\to 0$ slower(faster) than $1/\\phi^2$ at infinity, dark energy(dark matter) is a late time attractor. We investigate the tachyon dark energy models under the assumption that $w$ is close to -1. We find that all the models exhibit unique behavior around the present epoch which is exactly same as that of the thawing quintessence.

  3. Covariant extrinsic gravity and the geometric origin of dark energy

    NASA Astrophysics Data System (ADS)

    Jalalzadeh, S.; Rostami, T.

    2015-01-01

    In this paper, we construct the covariant or model independent induced Einstein-Yang-Mills field equations on a four-dimensional brane embedded isometrically in an D-dimensional bulk space, assuming the matter fields are confined to the brane. Applying this formalism to cosmology, we derive the generalized Friedmann equations. We derive the density parameter of dark energy in terms of width of the brane, normal curvature radii and the number of extra large dimensions. We show that dark energy could actually be the manifestation of the local extrinsic shape of the brane. It is shown that the predictions of this model are in good agreement with observation if we consider an 11-dimensional bulk space.

  4. Observational constraint on dynamical evolution of dark energy

    SciTech Connect

    Gong, Yungui [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Cai, Rong-Gen [Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Chen, Yun; Zhu, Zong-Hong, E-mail: gongyg@cqupt.edu.cn, E-mail: cairg@itp.ac.cn, E-mail: chenyun@mail.bnu.edu.cn, E-mail: zhuzh@bnu.edu.cn [Department of Astronomy, Beijing Normal University, Beijing 100875 (China)

    2010-01-01

    We use the Constitution supernova, the baryon acoustic oscillation, the cosmic microwave background, and the Hubble parameter data to analyze the evolution property of dark energy. We obtain different results when we fit different baryon acoustic oscillation data combined with the Constitution supernova data to the Chevallier-Polarski-Linder model. We find that the difference stems from the different values of ?{sub m0}. We also fit the observational data to the model independent piecewise constant parametrization. Four redshift bins with boundaries at z = 0.22, 0.53, 0.85 and 1.8 were chosen for the piecewise constant parametrization of the equation of state parameter w(z) of dark energy. We find no significant evidence for evolving w(z). With the addition of the Hubble parameter, the constraint on the equation of state parameter at high redshift is improved by 70%. The marginalization of the nuisance parameter connected to the supernova distance modulus is discussed.

  5. Viscous Dark Energy and Generalized Second Law of Thermodynamics

    Microsoft Academic Search

    M. R. Setare; A. Sheykhi

    2010-01-01

    We examine the validity of the generalized second law of thermodynamics in a non-flat universe in the presence of viscous dark energy. First we assume that the universe is filled only with viscous dark energy. Then, we extend our study to the case where there is an interaction between viscous dark energy and pressureless dark matter. We examine the time

  6. Logarithm of the scale factor as a generalised coordinate in a lagrangian for dark matter and dark energy

    E-print Network

    Debashis Gangopadhyay; Somnath Mukherjee

    2008-08-14

    A lagrangian for the $k-$ essence field is set up with canonical kinetic terms and incorporating the scaling relation of [1]. There are two degrees of freedom, {\\it viz.},$q(t)= ln\\enskip a(t)$ ($a(t)$ is the scale factor) and the scalar field $\\phi$, and an interaction term involving $\\phi$ and $q(t)$.The Euler-Lagrange equations are solved for $q$ and $\\phi$. Using these solutions quantities of cosmological interest are determined. The energy density $\\rho$ has a constant component which we identify as dark energy and a component behaving as $a^{-3}$ which we call dark matter. The pressure $p$ is {\\it negative} for time $t\\to \\infty$ and the sound velocity $c_{s}^{2}={\\partial p\\over\\partial\\rho} << 1$. When dark energy dominates, the deceleration parameter $Q\\to -1$ while in the matter dominated era $Q\\sim {1\\over 2}$. The equation of state parameter $w={p\\over \\rho}$ is shown to be consistent with $w={p\\over\\rho}\\sim -1$ for dark energy domination and during the matter dominated era we have $w\\sim 0$. Bounds for the parameters of the theory are estimated from observational data. Keywords: k-essence models, dark matter, dark energy PACS No: 98.80.-k

  7. 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.

  8. Dark Energy as a Signature of Extra Dimensions

    Microsoft Academic Search

    Baojiu Li; Ming-Chung Chu; Kai-Chung Cheung; Alfred Tang

    2005-01-01

    One of the most important and surprising discoveries in cosmology in recent years is the realization that our Universe is dominated by a mysterious dark energy, which leads to an accelerating expansion of space-time. A simple generalization of the standard Friedmann-Robertson-Walker equations based on General Relativity and the Cosmological Principles with the inclusion of a number of closed extra dimensions

  9. A Regularized Free Form Estimator for Dark Energy

    Microsoft Academic Search

    Tarun Deep Saini

    2003-01-01

    We construct a simple, regularized estimator for the dark energy equation of\\u000astate by using the recently introduced linear response approximation. We show\\u000athat even a simple regularization substantially improves the performance of the\\u000afree form fitting approach. The use of linear response approximation allows an\\u000aanalytic construction of maximum likelihood estimator, in a convenient and easy\\u000ato use matrix

  10. Probing the dynamics of dark energy with novel parametrizations

    Microsoft Academic Search

    Jing-Zhe Ma; Xin Zhang

    2011-01-01

    We point out that the CPL parametrization has a problem that the equation of state w(z) diverges in the far future, so that this model can only properly describe the past evolution but cannot depict the future evolution. To overcome such a difficulty, in this Letter we propose two novel parametrizations for dark energy, the logarithm form w(z)=w0+w1(ln(2+z)1+z?ln2) and the

  11. Dark energy from a scale-free distribution

    Microsoft Academic Search

    G. Iannone; O. Luongo

    2011-01-01

    We investigate some intriguing consequences of characterizing dark energy by the so-called scale-free statistics in a flat Friedman-Robertson-Walker cosmology. We adopt a toy model, derived from a power law distribution, being P(k)~k-gamma, with 2equation of state around the value

  12. Dark energy constraints from the cosmic age and supernova

    Microsoft Academic Search

    Bo Feng; Xiulian Wang; Xinmin Zhang

    2005-01-01

    Using the low limit of cosmic ages from globular cluster and the white dwarfs: t0>12Gyr, together with recent new high redshift supernova observations from the HST\\/GOODS program and previous supernova data, we give a considerable estimation of the equation of state for dark energy, with uniform priors as weak as 0.2?m0.4 or 0.1?mh20.16. We find cosmic age limit plays a

  13. Anticipations of dark energy in the work of Schrödinger

    NASA Astrophysics Data System (ADS)

    Halpern, Paul

    2015-04-01

    I'll examine the advocacy by Schrödinger of a cosmological constant, or its equivalent, beginning with his 1917 paper ``Concerning a System of Solutions to the Generally Covariant Equations for Gravitation,'' and continuing with his efforts in the 1940s toward a unified field theory. I'll discuss Schrödinger's idea that electromagnetism as well as gravitation was attenuated at long distances due to such a construct. I'll remark how these ideas anticipated modern discussions about dark energy.

  14. Isotropic and anisotropic dark energy models

    NASA Astrophysics Data System (ADS)

    Saha, Bijan

    2014-03-01

    In this review we discuss the evolution of the universe filled with dark energy with or without perfect fluid. In doing so we consider a number of cosmological models, namely Bianchi type I, III, V, VI0, VI and FRW ones. For the anisotropic cosmological models we have used proportionality condition as an additional constrain. The exact solutions to the field equations in quadrature are found in case of a BVI model. It was found that the proportionality condition used here imposed severe restriction on the energy-momentum tensor, namely it leads to isotropic distribution of matter. Anisotropic BVI0, BV, BIII and BIDE models with variable EoS parameter ? have been investigated by using a law of variation for the Hubble parameter. In this case the matter distribution remains anisotropic, though depending on the concrete model there appear different restrictions on the components of energy-momentum tensor. That is why we need an extra assumption such as variational a law for the Hubble parameter. It is observed that, at the early stage, the EoS parameter v is positive i.e. the universe was matter dominated at the early stage but at later time, the universe is evolving with negative values, i.e., the present epoch. DE model presents the dynamics of EoS parameter ? whose range is in good agreement with the acceptable range by the recent observations. A spatially homogeneous and anisotropic locally rotationally symmetric Bianchi-I space time filled with perfect fluid and anisotropic DE possessing dynamical energy density is studied. In the derived model, the EoS parameter of DE (?( de)) is obtained as time varying and it is evolving with negative sign which may be attributed to the current accelerated expansion of Universe. The distance modulus curve of derived model is in good agreement with SNLS type Ia supernovae for high redshift value which in turn implies that the derived model is physically realistic. A system of two fluids within the scope of a spatially flat and isotropic FRW model is studied. The role of the two fluids, either minimally or directly coupled in the evolution of the dark energy parameter, has been investigated. In doing so we have used three different ansatzs regarding the scale factor that gives rise to a variable decelerating parameter. It is observed that, in the non-interacting case, both the open and flat universes can cross the phantom region whereas in the interacting case only the open universe can cross the phantom region. The stability and acceptability of the obtained solution are also investigated.

  15. Can strong gravitational lensing constrain dark energy?

    SciTech Connect

    Lee, Seokcheon [Institute of Physics, Academia Sinica, Taipei, Taiwan 11529 (China); Ng, K.-W. [Institute of Physics, Academia Sinica, Taipei, Taiwan 11529 (China); Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan 11529 (China)

    2007-08-15

    We discuss the ratio of the angular diameter distances from the source to the lens, D{sub ds}, and to the observer at present, D{sub s}, for various dark energy models. It is well known that the difference of D{sub s}s between the models is apparent and this quantity is used for the analysis of Type Ia supernovae. However we investigate the difference between the ratio of the angular diameter distances for a cosmological constant, (D{sub ds}/D{sub s}){sup {lambda}}, and that for other dark energy models, (D{sub ds}/D{sub s}){sup other}, in this paper. It has been known that there is lens model degeneracy in using strong gravitational lensing. Thus, we investigate the model independent observable quantity, Einstein radius ({theta}{sub E}), which is proportional to both D{sub ds}/D{sub s} and velocity dispersion squared, {sigma}{sub v}{sup 2}. D{sub ds}/D{sub s} values depend on the parameters of each dark energy model individually. However, (D{sub ds}/D{sub s}){sup {lambda}}-(D{sub ds}/D{sub s}){sup other} for the various dark energy models, is well within the error of {sigma}{sub v} for most of the parameter spaces of the dark energy models. Thus, a single strong gravitational lensing by use of the Einstein radius may not be a proper method to investigate the property of dark energy. However, better understanding to the mass profile of clusters in the future or other methods related to arc statistics rather than the distances may be used for constraints on dark energy.

  16. Does cosmological structure formation require dark energy?

    Microsoft Academic Search

    S. Sarkar

    2009-01-01

    Precision measurements of anisotropies in the cosmic microwave background and of the clustering of large-scale structure have supposedly established that the universe is presently dominated by ``dark energy'' which has negative pressure and behaves similarly to a cosmological constant. This is based on the assumption that the primordial density perturbation has a nearly scale-invariant power-law spectrum and that the dark

  17. Thermodynamics and New Holographic Dark Energy

    NASA Astrophysics Data System (ADS)

    Sharif, Muhammad; Saleem, Rabia

    2015-01-01

    We check the validity of the generalized second law of thermodynamics on apparent as well as on a horizon of fixed radius l. We take non-interacting dark matter and new holographic dark energy in flat Kaluza-Klein universe. It turns out that the generalized second law of thermodynamics is valid for a specific range depending upon the values of parameters but does not hold on horizon with fixed radius l.

  18. Energy Conservation Equations of Motion

    E-print Network

    Vinokurov, Nikolay A

    2015-01-01

    A conventional derivation of motion equations in mechanics and field equations in field theory is based on the principle of least action with a proper Lagrangian. With a time-independent Lagrangian, a function of coordinates and velocities that is called energy is constant. This paper presents an alternative approach, namely derivation of a general form of equations of motion that keep the system energy, expressed as a function of generalized coordinates and corresponding velocities, constant. These are Lagrange equations with addition of gyroscopic forces. The important fact, that the energy is defined as the function on the tangent bundle of configuration manifold, is used explicitly for the derivation. The Lagrangian is derived from a known energy function. A development of generalized Hamilton and Lagrange equations without the use of variational principles is proposed. The use of new technique is applied to derivation of some equations.

  19. Dynamics of dark energy in the gravitational fields of matter inhomogeneities

    NASA Astrophysics Data System (ADS)

    Novosyadlyj, Bohdan; Kulinich, Yurij; Tsizh, Maksym

    2014-09-01

    We study the dynamical properties and space distribution of dark energy in the weak and strong gravitational fields caused by inhomogeneities of matter in the static world of galaxies and clusters. We show that the dark energy in the weak gravitational fields of matter density perturbations can condense or dilute, but amplitudes of its perturbations remain very small on all scales. We illustrate also how the "accretion" of the phantom dark energy onto the matter overdensity forms the dark energy underdensity. We analyze the behavior of dark energy in the gravitational fields of stars and black holes with the Schwarzschild metric. It is shown that, in the case of stars, the static solution of the differential equations for energy-momentum conservation exists and describes the distribution of density of dark energy inside and outside of a star. We have found that for stars and galaxies its value differs slightly from the average and is a bit higher for the quintessential scalar field as dark energy and a bit lower for the phantom one. The difference grows with the decrease of the effective sound speed of dark energy and is large in the neighborhood of neutron stars. We obtain and analyze also the solutions of equations that describe the stationary accretion of the dark energy as a test component onto the Schwarzschild black hole. It is shown that the rate of change of mass of the dark energy is positive in the case of quintessential dark energy and is negative in the case of the phantom one.

  20. New Perspectives: Wave Mechanical Interpretations of Dark Matter, Baryon and Dark Energy

    NASA Astrophysics Data System (ADS)

    Russell, Esra

    We model the cosmic components: dark matter, dark energy and baryon distributions in the Cosmic Web by means of highly nonlinear Schrodinger type and reaction diffusion type wave mechanical descriptions. The construction of these wave mechanical models of the structure formation is achieved by introducing the Fisher information measure and its comparison with highly nonlinear term which has dynamical analogy to infamous quantum potential in the wave equations. Strikingly, the comparison of this nonlinear term and the Fisher information measure provides a dynamical distinction between lack of self-organization and self-organization in the dynamical evolution of the cosmic components. Mathematically equivalent to the standard cosmic fluid equations, these approaches make it possible to follow the evolution of the matter distribution even into the highly nonlinear regime by circumventing singularities. Also, numerical realizations of the emerging web-like patterns are presented from the nonlinear dynamics of the baryon component while dark energy component shows Gaussian type dynamics corresponding to soliton-like solutions.

  1. Dark energy from a scale-free distribution

    NASA Astrophysics Data System (ADS)

    Iannone, G.; Luongo, O.

    2011-05-01

    We investigate some intriguing consequences of characterizing dark energy by the so-called scale-free statistics in a flat Friedman-Robertson-Walker cosmology. We adopt a toy model, derived from a power law distribution, being P(k)~k-?, with 2equation of state around the value w~- 1 for higher redshift. In addition, we test the equation of state with the modern cosmological data and we make a comparison with the observational constraints.

  2. Dynamics of dark energy models and centre manifolds

    E-print Network

    Christian G. Boehmer; Nyein Chan; Ruth Lazkoz

    2011-11-27

    We analyse dark energy models where self-interacting three-forms or phantom fields drive the accelerated expansion of the Universe. The dynamics of such models is often studied by rewriting the cosmological field equations in the form of a system of autonomous differential equations, or simply a dynamical system. Properties of these systems are usually studied via linear stability theory. In situations where this method fails, for instance due to the presence of zero eigenvalues in the Jacobian, centre manifold theory can be applied. We present a concise introduction and show explicitly how to use this theory in two concrete examples.

  3. Formation of Dark Matter Haloes in a Homogeneous Dark Energy Universe

    Microsoft Academic Search

    Lucio Marassi

    2010-01-01

    Several independent cosmological tests have shown evidences that the energy density of the universe is dominated by a dark energy component, which causes the present accelerated expansion. The large scale structure formation can be used to probe dark energy models, and the mass function of dark matter haloes is one of the best statistical tools to perform this study. We

  4. Prepared for submission to JCAP Interacting dark energy collapse

    E-print Network

    Prepared for submission to JCAP Interacting dark energy collapse with matter components separation dark energy scenario. Following the usual assumption of a single radius of collapse for all species, we how we can discriminate between different quintessence models. Keywords: dark matter simulations, dark

  5. Probing the dynamical behavior of dark energy

    SciTech Connect

    Cai, Rong-Gen; Su, Qiping; Zhang, Hong-Bo, E-mail: cairg@itp.ac.cn, E-mail: sqp@itp.ac.cn, E-mail: hbzhang@itp.ac.cn [Key Laboratory of Frontiers in Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100190 (China)

    2010-04-01

    We investigate dynamical behavior of the equation of state of dark energy w{sub de} by employing the linear-spline method in the region of low redshifts from observational data (SnIa, BAO, CMB and 12 H(z) data). The redshift is binned and w{sub de} is approximated by a linear expansion of redshift in each bin. We leave the divided points of redshift bins as free parameters of the model, the best-fitted values of divided points will represent the turning positions of w{sub de} where w{sub de} changes its evolving direction significantly (if there exist such turnings in our considered region). These turning points are natural divided points of redshift bins, and w{sub de} between two nearby divided points can be well approximated by a linear expansion of redshift. We find two turning points of w{sub de} in z element of (0,1.8) and one turning point in z element of (0,0.9), and w{sub de}(z) could be oscillating around w = ?1. Moreover, we find that there is a 2? deviation of w{sub de} from around z = 0.9 in both correlated and uncorrelated estimates.

  6. Axion-dilaton cosmology and dark energy

    SciTech Connect

    Catena, Riccardo; Moeller, Jan, E-mail: catena@sissa.it, E-mail: janmoe@mail.desy.de [Deutsches Elektronen-Synchrotron DESY, Theory Group, Notkestrasse 85, D-22603 Hamburg (Germany)

    2008-03-15

    We discuss a class of flat FRW cosmological models based on D = 4 axion-dilaton gravity universally coupled to cosmological background fluids. In particular, we investigate the possibility of recurrent acceleration, which was recently shown to be generically realized in a wide class of axion-dilaton models, but in the absence of cosmological background fluids. We observe that, once we impose the existence of radiation- and matter-dominated earlier stages of cosmic evolution, the axion-dilaton dynamics is altered significantly with respect to the case of pure axion-dilaton gravity. Explicit computations are done considering a universal metric coupling between the dilaton and the matter fields. As a result we find that during the matter-dominated epoch the scalar fields remain either frozen, due to the large expansion rate, or enter a cosmological scaling regime. In both cases, oscillations of the effective equation of state around the acceleration boundary value are impossible. Models which enter an oscillatory stage in the low redshift regime, on the other hand, are disfavored by observations. We also comment on the viability of the axion-dilaton system as a candidate for dynamical dark energy. In a certain subclass of models, an intermediate scaling regime is succeeded by eternal acceleration. We also briefly discuss the issue of dependence on initial conditions.

  7. Constraining Dark Energy with DEEP2

    E-print Network

    Marc Davis; Brian F. Gerke; Jeffrey A. Newman

    2004-08-18

    The DEEP2 survey has now completed half of its planned three-year lifespan, and we have collected approximately 50% of the data, putting us exactly on schedule. The survey plan calls for spectroscopic coverage by July of 2005 of \\~60,000 galaxies over 3.5 square degrees to a limiting magnitude of R_{AB}=24.1; the great majority of these objects are at 0.7equation of state parameter of the Dark Energy, w. By counting the number of virialized groups and clusters we find in redshift space as a function of their redshift and internal velocity dispersion, we probe both the volume element and the growth of structure at z~1, each of which depends on w. Studies of early DEEP2 data indicate that the method is likely to work, and preliminary indications are that a total of ~250 small groups will be counted in the full survey, leading to a constraint \\delta w ~ 0.1 if combined with both the velocity dispersion distribution of z~0 clusters from the Sloan Digital Sky Survey and an independent measurement of \\sigma_8. We also provide a general description of the DEEP2 observations and target selection, including the algorithm by which galaxies are placed on slitmasks, to provide context for discussion of DEEP2 cluster samples.

  8. A new look at dark energy

    E-print Network

    Riazi, N

    2015-01-01

    The origin of the dark energy which is assumed to be responsible for the observed accelerated expansion of the universe still remains a scientific dilemma. Here we propose a tentative origin for this energy, if it is coming from a distribution of specific quantum particles.

  9. Cosmic Acceleration, Dark Energy, and Fundamental Physics

    Microsoft Academic Search

    Michael S. Turner; Dragan Huterer

    2007-01-01

    A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic acceleration is a highly elastic ( p˜-rho), very smooth form of energy called ``dark energy'' accounting for about 75% of the Universe.

  10. Evolution of dark energy perturbations in scalar-tensor cosmologies

    SciTech Connect

    Bueno Sanchez, J. C.; Perivolaropoulos, L. [Department of Physics, University of Ioannina, Ioannina (Greece)

    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.

  11. Evolution of entropic dark energy and its phantom nature

    E-print Network

    Mathew, Titus K; J, Shejeelammal

    2015-01-01

    Assuming the form of the entropic dark energy as arises form the surface term in the Einstein-Hilbert's action, it's evolution were analyzed in an expanding flat universe. The model parameters were evaluated by constraining model using the Union data on Type Ia supernovae. We found that the model predicts an early decelerated phase and a later accelerated phase at the background level. The evolution of the Hubble parameter, dark energy density, equation of state parameter and deceleration parameter were obtained. The model is diagnosed with $Om$ parameter. The model is hardly seems to be supporting the linear perturbation growth for the structure formation. We also found that the entropic dark energy 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 dark energy density become infinitely large and the big rip time is found to be around 36 Giga Years from now.

  12. Dynamics of Bianchi I Universe with Magnetized Anisotropic Dark Energy

    E-print Network

    M. Sharif; M. Zubair

    2010-05-25

    We study Bianchi type $I$ cosmological model in the presence of magnetized anisotropic dark energy. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS $p=\\omega{\\rho}$ and a uniform magnetic field of energy density $\\rho_B$. We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar. The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as anisotropic fluid do not approach isotropy through the evolution of the universe.

  13. Galaxy surveys, inhomogeneous reionization, and dark energy

    E-print Network

    Jonathan R. Pritchard; Steven R. Furlanetto; Marc Kamionkowski

    2007-01-17

    We examine the effect of inhomogeneous reionization on the galaxy power spectrum and the consequences for probing dark energy. To model feedback during reionization, we apply an ansatz setting the galaxy overdensity proportional to the underlying ionization field. Thus, inhomogeneous reionization may leave an imprint in the galaxy power spectrum. We evolve this imprint to low redshift and use the Fisher-matrix formalism to assess the effect on parameter estimation. We show that a combination of low- (z=0.3) and high- (z=3) redshift galaxy surveys can constrain the size of cosmological HII regions during reionization. This imprint can also cause confusion when using baryon oscillations or other features of the galaxy power spectrum to probe the dark energy. We show that when bubbles are large, and hence detectable, our ability to constrain w can be degraded by up to 50%. When bubbles are small, the imprint has little or no effect on measuring dark-energy parameters.

  14. Dark energy in flows of galaxies

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.

    2015-06-01

    It has traditionally been taken for granted that Hubble's law is the key relation in cosmology, while it is surprisingly mysterious on the local scales of 1-30 Mpc where it was originally discovered. The progress in observational cosmology and, in particular, the discovery of dark energy have changed the views, and now we see that Hubble's law works hardly at truly cosmological distances, but it rules very well on local scales. Recent observations with the HST, in combination with a theory model of the local expansion flows, give a clear evidence to the presence of dark energy in the local universe. It is dark energy that dominates the dynamics of the local flows and introduces to them the approximately linear velocity-distance relation with nearly universal expansion time-rate.

  15. Neutrino dark energy-revisiting the stability issue

    SciTech Connect

    Bjaelde, Ole Eggers; Hannestad, Steen [Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C (Denmark); Brookfield, Anthony W; Van de Bruck, Carsten [Department of Applied Mathematics, Astro-Particle Theory and Cosmology Group, Hounsfield Road, Hicks Building, University of Sheffield, Sheffield S3 7RH (United Kingdom); Mota, David F [Institute for Theoretical Physics, University of Heidelberg, D-69120 Heidelberg (Germany); Schrempp, Lily [Deutsches Elektron-Synchroton DESY, Hamburg, Notkestrasse 85, 22607 Hamburg (Germany); Tocchini-Valentini, Domenico, E-mail: oeb@phys.au.dk, E-mail: php04awb@sheffield.ac.uk, E-mail: C.vandebruck@sheffield.ac.uk, E-mail: sth@phys.au.dk, E-mail: d.mota@thphys.uni-heidelberg.de, E-mail: lily.schrempp@desy.de, E-mail: dtv@skysrv.pha.jhu.edu [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)

    2008-01-15

    A coupling between a light scalar field and neutrinos has been widely discussed as a mechanism for linking (time varying) neutrino masses and the present energy density and equation of state of dark energy. However, it has been pointed out that the viability of this scenario in the non-relativistic neutrino regime is threatened by the strong growth of hydrodynamic perturbations associated with a negative adiabatic sound speed squared. In this paper we revisit the stability issue in the framework of linear perturbation theory in a model independent way. The criterion for the stability of a model is translated into a constraint on the scalar-neutrino coupling, which depends on the ratio of the energy densities in neutrinos and cold dark matter. We illustrate our results by providing meaningful examples for both stable and unstable models.

  16. Correspondence Between Einstein-Aether Gravity and Scalar Field Dark Energies

    NASA Astrophysics Data System (ADS)

    Debnath, Ujjal

    2015-07-01

    Here we briefly discuss the Einstein-Aether gravity theory by modification of Einstein-Hilbert action. We find the modified Friedmann equations and then we find the effective energy density and pressure for Einstein-Aether gravity sector. These can be treated as dark energy provided some restrictions on the free function F( K), where K is proportional to H 2. Subsequently, we study the correspondence between the effective dark energy coming from Einstein-Aether gravity with other dark energies like k-essence, tachyon, dilaton, hessence and DBI-essence dark energy and construct the scalar field and corresponding scalar potentials which describe the dynamics of the scalar fields graphically. So finally, if the Einstein-Aether gravity behaves like other dark energy models, in this situation, the scalar field increases and potential decreases.

  17. Importance of supernovae at z>1.5 to probe dark energy

    NASA Astrophysics Data System (ADS)

    Linder, Eric V.; Huterer, Dragan

    2003-04-01

    The accelerating expansion of the universe suggests that an unknown component with strongly negative pressure, called dark energy, currently dominates the dynamics of the universe. Such a component makes up ˜70% of the energy density of the universe yet has not been predicted by the standard model of particle physics. The best method for exploring the nature of this dark energy is to map the recent expansion history, at which type Ia supernovae have proved adept. We examine here the depth of survey necessary to provide a precise and qualitatively complete description of dark energy. A realistic analysis of parameter degeneracies, allowance for natural time variation of the dark energy equation of state, and systematic errors in astrophysical observations all demonstrate the importance of a survey covering the full range 0dark energy.

  18. Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios

    E-print Network

    T. Jenke; G. Cronenberg; J. Burgdörfer; L. A. Chizhova; P. Geltenbort; A. N. Ivanov; T. Lauer; T. Lins; S. Rotter; H. Saul; U. Schmidt; H. Abele

    2014-04-15

    We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of the Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate, that Newton's inverse square law of Gravity is understood at micron distances on an energy scale of~$10^{-14}$~eV. At this level of precision we are able to provide constraints on any possible gravity-like interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant~$\\beta > 5.8\\times10^8$ at~95% confidence level~(C.L.), and an attractive (repulsive) dark matter axion-like spin-mass coupling is excluded for the coupling strength $g_sg_p > 3.7\\times10^{-16}$~($5.3\\times10^{-16}$)~at a Yukawa length of~$\\lambda = 20$~{\\textmu}m~(95% (C.L.).

  19. Dark Energy: A Crisis for Fundamental Physics

    ScienceCinema

    Stubbs, Christopher [Harvard University, Cambridge, Massachusetts, USA

    2010-09-01

    Astrophysical observations provide robust evidence that our current picture of fundamental physics is incomplete. The discovery in 1998 that the expansion of the Universe is accelerating (apparently due to gravitational repulsion between regions of empty space!) presents us with a profound challenge, at the interface between gravity and quantum mechanics. This "Dark Energy" problem is arguably the most pressing open question in modern fundamental physics. The first talk will describe why the Dark Energy problem constitutes a crisis, with wide-reaching ramifications. One consequence is that we should probe our understanding of gravity at all accessible scales, and the second talk will present experiments and observations that are exploring this issue.

  20. Dark energy from conformal symmetry breaking

    E-print Network

    F. Darabi

    2013-06-18

    The breakdown of conformal symmetry in a conformally invariant scalar-tensor gravitational model is revisited in the cosmological context. Although the old scenario of conformal symmetry breaking in cosmology containing scalar field has already been used in many earlier works, it seems that no special attention has been paid for the investigation on the possible connection between the breakdown of conformal symmetry and the existence of dark energy. In this paper, it is shown that the old scenario of conformal symmetry breaking in cosmology, if properly interpreted, not only has a potential ability to describe the origin of dark energy as a symmetry breaking effect, but also may resolve the coincidence problem.

  1. Can dark energy viscosity be detected with the Euclid survey?

    E-print Network

    Domenico Sapone; Elisabetta Majerotto; Martin Kunz; Bianca Garilli

    2015-05-07

    Recent work has demonstrated that it is important to constrain the dynamics of cosmological perturbations, in addition to the evolution of the background, if we want to distinguish among different models of the dark sector. Especially the anisotropic stress of the (possibly effective) dark energy fluid has been shown to be an important discriminator between modified gravity and dark energy models. In this paper we use approximate analytical solutions of the perturbation equations in the presence of viscosity to study how the anisotropic stress affects the weak lensing and galaxy power spectrum. We then forecast how sensitive the photometric and spectroscopic Euclid surveys will be to both the speed of sound and the viscosity of our effective dark energy fluid when using weak lensing tomography and the galaxy power spectrum. We find that Euclid alone can only constrain models with very small speed of sound and viscosity, while it will need the help of other observables in order to give interesting constraints on models with a sound speed close to one. This conclusion is also supported by the expected Bayes factor between models.

  2. Is dark energy dynamical? Prospects for an answer

    SciTech Connect

    Linder, Eric V.; Miquel, Ramon [Physics Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States)

    2004-12-15

    Recent data advances offer the exciting prospect of a first look at whether dark energy has a dynamical equation of state or not. While formally theories exist with a constant equation of state, they are nongeneric--Einstein's cosmological constant is a notable exception. So limits on the time variation, w{sup '}, directly tell us crucial physics. Two recent improvements in supernova data from the Hubble space telescope allow important steps forward in constraining the dynamics of dark energy, possessing the ability to exclude models with w{sup '} > or approx. 1, if the universe truly has a cosmological constant. These data bring us much closer to the 'systematics' era, where further improvements will come predominantly from more accurate, not merely more, observations. We examine the possible gains and point out the complementary roles of space and ground based observations in the near future. To achieve the leap to precision understanding of dark energy in the next generation will require specially designed space based measurements; we estimate the confidence level of detection of dynamics (e.g., distinguishing between w{sup '}=0 and w{sup '}=1) will be {approx}1.8{sigma} after the ongoing generation, improving to more than 6.5{sigma} in the dedicated space generation.

  3. Chaotic scalar fields as models for dark energy Christian Beck*

    E-print Network

    Beck, Christian

    Chaotic scalar fields as models for dark energy Christian Beck* Kavli Institute for Theoretical stochastically quantized self-interacting scalar fields as suitable models to generate dark energy is the exis- tence of vacuum energy or, in a more general setting, of dark energy. The observations suggest

  4. Viscous dark energy and generalized second law of thermodynamics

    E-print Network

    M. R. Setare; A. Sheykhi

    2011-03-05

    We examine the validity of the generalized second law of thermodynamics in a non-flat universe in the presence of viscous dark energy. At first we assume that the universe filled only with viscous dark energy. Then, we extend our study to the case where there is an interaction between viscous dark energy and pressureless dark matter. We examine the time evolution of the total entropy, including the entropy associated with the apparent horizon and the entropy of the viscous dark energy inside the apparent horizon. Our study show that the generalized second law of thermodynamics is always protected in a universe filled with interacting viscous dark energy and dark matter in a region enclosed by the apparent horizon. Finally, we show that the the generalized second law of thermodynamics is fulfilled for a universe filled with interacting viscous dark energy and dark matter in the sense that we take into account the Casimir effect.

  5. Thermodynamical description of the interacting new agegraphic dark energy

    E-print Network

    A. Sheykhi; M. R. Setare

    2010-09-30

    We describe the thermodynamical interpretation of the interaction between new agegraphic dark energy and dark matter in a non-flat universe. When new agegraphic dark energy and dark matter evolve separately, each of them remains in thermodynamic equilibrium. As soon as an interaction between them is taken into account, their thermodynamical interpretation changes by a stable thermal fluctuation. We obtain a relation between the interaction term of the dark components and this thermal fluctuation.

  6. arXiv:0908.1408v1[astro-ph.CO]10Aug2009 Hiding dark energy transitions at low redshift

    E-print Network

    Hu, Wayne

    arXiv:0908.1408v1[astro-ph.CO]10Aug2009 Hiding dark energy transitions at low redshift Michael allowable and theoretically possible to have large fluctu- ations in the dark energy equation of state it is well known that at high redshifts (z 1) order unity deviations may still exist in the dark energy

  7. Reconstructing generalized ghost condensate model with dynamical dark energy parametrizations and observational datasets

    E-print Network

    Jingfei Zhang; Xin Zhang; Hongya Liu

    2007-03-21

    Observations of high-redshift supernovae indicate that the universe is accelerating at the present stage, and we refer to the cause for this cosmic acceleration as ``dark energy''. In particular, the analysis of current data of type Ia supernovae (SNIa), cosmic large-scale structure (LSS), and the cosmic microwave background (CMB) anisotropy implies that, with some possibility, the equation-of-state parameter of dark energy may cross the cosmological-constant boundary ($w=-1$) during the recent evolution stage. The model of ``quintom'' has been proposed to describe this $w=-1$ crossing behavior for dark energy. As a single-real-scalar-field model of dark energy, the generalized ghost condensate model provides us with a successful mechanism for realizing the quintom-like behavior. In this paper, we reconstruct the generalized ghost condensate model in the light of three forms of parametrization for dynamical dark energy, with the best-fit results of up-to-date observational data.

  8. Dark energy from Gauss-Bonnet and nonminimal couplings

    NASA Astrophysics Data System (ADS)

    Granda, L. N.; Jimenez, D. F.

    2014-12-01

    We consider a scalar-tensor model of dark energy with Gauss-Bonnet and nonminimal couplings. Exact cosmological solutions were found in the absence of potential that give equations of state of dark energy consistent with current observational constraints, but with different asymptotic behaviors depending on the couplings of the model. A detailed reconstruction procedure is given for the scalar potential and the Gauss-Bonnet coupling for any given cosmological scenario. In particular we consider conditions for the existence of a variety of cosmological solutions with accelerated expansion, including quintessence, phantom, de Sitter, and Little Rip. For the case of quintessence and phantom we have found a scalar potential of the Albrecht-Skordis type, where the potential is an exponential with a polynomial factor.

  9. arXiv:0706.2986v1[astro-ph]20Jun2007 DARK MATTER AND DARK ENERGY

    E-print Network

    Steidel, Chuck

    arXiv:0706.2986v1[astro-ph]20Jun2007 DARK MATTER AND DARK ENERGY MARC KAMIONKOWSKI California, and/or the introduction of some negative-pressure "dark energy," again, the nature of which remains Press. kamion@tapir.caltech.edu 1 #12;Dark Matter and Dark Energy 2 eries may help us understand the new

  10. Cosmological electromagnetic fields and dark energy

    Microsoft Academic Search

    Jose Beltrán Jiménez; Antonio L. Maroto

    2009-01-01

    We show that the presence of a temporal electromagnetic field on cosmological scales generates an effective cosmological constant which can account for the accelerated expansion of the universe. Primordial electromagnetic quantum fluctuations produced during electroweak scale inflation could naturally explain the presence of this field and also the measured value of the dark energy density. The behavior of the electromagnetic

  11. Late Time Phase Transition as Dark Energy

    Microsoft Academic Search

    A. de la Macorra

    2003-01-01

    We study the possibility that the quintessence field responsible for the dark energy and the present day acceleration of the universe is given by a condensate field generated at a late phase transition scale determined by the condensation scale. We show that the quintessence field can be described naturally by the condensates of a non-abelian gauge group. The non-perturbative effects

  12. Report from the Dark Energy Task Force

    Microsoft Academic Search

    Andreas Albrecht

    2006-01-01

    Understanding the observed cosmic acceleration is widely ranked among the very most compelling of all outstanding problems in physical science. Many believe that nothing short of a revolution will be required in order to integrate the cosmic acceleration (often attributed to ``dark energy'') with our understanding of fundamental physics. The DETF was formed at the request of DOE, NASA and

  13. Geometrical Constraints on Dark Energy Models

    Microsoft Academic Search

    Ruth Lazkoz; Euskal Herriko Unibertsitatea

    2007-01-01

    This contribution intends to give a pedagogical introduction to the topic of dark energy (the mysterious agent supposed to drive the observed late time acceleration of the Universe) and to various observational tests which require only assumptions on the geometry of the Universe. Those tests are the supernovae luminosity, the CMB shift, the direct Hubble data, and the baryon acoustic

  14. Stringy Model of Cosmological Dark Energy

    NASA Astrophysics Data System (ADS)

    Aref'eva, Irina Ya.

    2007-11-01

    A string field theory (SFT) nonlocal model of the cosmological dark energy providing w<-1 is briefly surveyed. We summarize recent developments and open problems, as well as point out some theoretical issues related with others applications of the SFT nonlocal models in cosmology, in particular, in inflation and cosmological singularity.

  15. Stringy Model of Cosmological Dark Energy

    SciTech Connect

    Aref'eva, Irina Ya. [Steklov Mathematical Institute of Russian Academy of Sciences, Gubkin st., 8, 119991, Moscow (Russian Federation)

    2007-11-20

    A string field theory (SFT) nonlocal model of the cosmological dark energy providing w<-1 is briefly surveyed. We summarize recent developments and open problems, as well as point out some theoretical issues related with others applications of the SFT nonlocal models in cosmology, in particular, in inflation and cosmological singularity.

  16. Distance measurements from supernovae and dark energy constraints

    SciTech Connect

    Wang Yun [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks Street, Norman, Oklahoma 73019 (United States)

    2009-12-15

    Constraints on dark energy from current observational data are sensitive to how distances are measured from Type Ia supernova (SN Ia) data. We find that flux averaging of SNe Ia can be used to test the presence of unknown systematic uncertainties, and yield more robust distance measurements from SNe Ia. We have applied this approach to the nearby+SDSS+ESSENCE+SNLS+HST set of 288 SNe Ia, and the 'Constitution' set of 397 SNe Ia. Combining the SN Ia data with cosmic microwave background anisotropy data from Wilkinson Microwave Anisotropy Probe 5 yr observations, the Sloan Digital Sky Survey baryon acoustic oscillation measurements, the data of 69 gamma-ray bursts (GRBs) , and the Hubble constant measurement from the Hubble Space Telescope project SHOES, we measure the dark energy density function X(z){identical_to}{rho}{sub X}(z)/{rho}{sub X}(0) as a free function of redshift (assumed to be a constant at z>1 or z>1.5). Without the flux averaging of SNe Ia, the combined data using the Constitution set of SNe Ia seem to indicate a deviation from a cosmological constant at {approx}95% confidence level at 0 < or apporx. z < or approx. 0.8; they are consistent with a cosmological constant at {approx}68% confidence level when SNe Ia are flux averaged. The combined data using the nearby+SDSS+ESSENCE+SNLS+HST data set of SNe Ia are consistent with a cosmological constant at 68% confidence level with or without flux averaging of SNe Ia, and give dark energy constraints that are significantly more stringent than that using the Constitution set of SNe Ia. Assuming a flat Universe, dark energy is detected at >98% confidence level for z{<=}0.75 using the combined data with 288 SNe Ia from nearby+SDSS+ESSENCE+SNLS+HST, independent of the assumptions about X(z{>=}1). We quantify dark energy constraints without assuming a flat Universe using the dark energy figure of merit for both X(z) and a dark energy equation-of-state linear in the cosmic scale factor.

  17. Dark energy and the BOOMERANG data.

    PubMed

    Amendola, L

    2001-01-01

    The recent high-quality BOOMERANG data allow the testing of many competing cosmological models. Here I present a seven-parameter likelihood analysis of dark energy models with exponential potential and explicit coupling to dark matter. The BOOMERANG data constrain the dimensionless coupling beta to be smaller than 0.1, an order of magnitude better than previous limits. In terms of the constant xi of nonminimally coupled theories, this amounts to xi<0.01. On the other hand, BOOMERANG does not have enough sensitivity to put constraints on the potential slope. PMID:11177790

  18. Evolution of spherical overdensities in holographic dark energy models

    NASA Astrophysics Data System (ADS)

    Naderi, Tayebe; Malekjani, Mohammad; Pace, Francesco

    2015-02-01

    In this work, we investigate the spherical collapse model in flat Friedmann-Robertson-Walker (FRW) dark energy universes. We consider the holographic dark energy (HDE) model as a dynamical dark energy scenario with a slowly time-varying equation-of-state parameter wde in order to evaluate the effects of the dark energy component on structure formation in the universe. We first calculate the evolution of density perturbations in the linear regime for both phantom and quintessence behaviour of the HDE model and compare the results with standard Einstein-de Sitter and ? cold dark matter (?CDM) models. We then calculate the evolution of two characterizing parameters in the spherical collapse model, i.e. the linear density threshold ?c and the virial overdensity parameter ?vir. We show that in HDE cosmologies the growth factor g(a) and the linear overdensity parameter ?c fall behind the values for a ?CDM universe while the virial overdensity ?vir is larger in HDE models than in the ?CDM model. We also show that the ratio between the radius of the spherical perturbations at the virialization and turn-around time is smaller in HDE cosmologies than that predicted in a ?CDM universe. Hence, the growth of structures starts earlier in HDE models than in ?CDM cosmologies and more concentrated objects can form in this case. It has been shown that the non-vanishing surface pressure leads to smaller virial radius and larger virial overdensity ?vir. We compare the predicted number of haloes in HDE cosmologies and find out that in general this value is smaller than for ?CDM models at higher redshifts and we compare different mass function prescriptions. Finally, we compare the results of the HDE models with observations.

  19. Constraints on generalized dark energy from recent observations

    Microsoft Academic Search

    Kiyotomo Ichiki; Tomo Takahashi

    2007-01-01

    Effects of a generalized dark energy fluid are investigated on cosmic density fluctuations such as a cosmic microwave background. As a general dark energy fluid, we take into consideration the possibility of the anisotropic stress for dark energy, which has not been discussed much in the literature. We comprehensively study its effects on the evolution of density fluctuations along with

  20. Loop Quantum Corrections to Statefinder Parameters of Dark Energy

    E-print Network

    Mubasher Jamil; D. Momeni; Ratbay Myrzakulov

    2013-05-17

    In this short letter, we presented the explicit forms of the statefinder parameters for the Friedmann-Robertson-Walker (FRW) Universe in the loop quantum cosmology (LQC) for Holographic dark energy and New-Agegraphic dark energy. Numerically we investigated cosmological implications of these parameters for models of dark energy.

  1. Automation of Calibration System for Dark Energy Survey

    E-print Network

    Automation of Calibration System for Dark Energy Survey Jason Wise1, J. P. Rheault1, D. L. DePoy1 1 from gravitational interactions. The Dark Energy Survey (DES) is a sky survey designed to find the reason for this acceleration. It will use the Dark Energy Camera (DECam), which is a 570 Megapixel camera

  2. Discriminating between models for the dark energy Duane A. Dicus

    E-print Network

    Repko, Wayne

    Discriminating between models for the dark energy Duane A. Dicus Center for Particle Physics a substantial dark energy component, which is usually interpreted in terms of a cosmological constant. Here we examine how much the form of this dark energy can be modified while still retaining an acceptable fit

  3. A Dark Energy Model with Generalized Uncertainty Principle in the Emergent, Intermediate and Logamediate Scenarios of the Universe

    E-print Network

    Rahul Ghosh; Surajit Chattopadhyay; Ujjal Debnath

    2011-10-22

    This work is motivated by the work of Kim et al (2008), which considered the equation of state parameter for the new agegraphic dark energy based on generalized uncertainty principle coexisting with dark matter without interaction. In this work, we have considered the same dark energy inter- acting with dark matter in emergent, intermediate and logamediate scenarios of the universe. Also, we have investigated the statefinder, kerk and lerk parameters in all three scenarios under this inter- action. The energy density and pressure for the new agegraphic dark energy based on generalized uncertainty principle have been calculated and their behaviors have been investigated. The evolu- tion of the equation of state parameter has been analyzed in the interacting and non-interacting situations in all the three scenarios. The graphical analysis shows that the dark energy behaves like quintessence era for logamediate expansion and phantom era for emergent and intermediate expansions of the universe.

  4. Dark matter interacts with variable vacuum energy

    E-print Network

    Iván E. Sánchez G

    2014-09-21

    We investigate a spatially flat Friedmann-Robertson-Walker (FRW) scenario with two interacting components, dark matter and variable vacuum energy (VVE) densities, plus two decoupled components, one is a baryon term while the other behaves as a radiation component. We consider a linear interaction in the derivative dark component density. We apply the $\\chi^2$ method to the observational Hubble data for constraining the cosmological parameters and analyze the amount of dark energy in the radiation era for the model. It turns out that our model fulfills the severe bound of $\\Omega_{x}(z\\simeq 1100)Euclid and CMBPol experiments, reported for the behavior of the dark energy at early times, and fulfills the stringent bound $\\Omega_{x}(z\\simeq 10^{10})<0.04$ at $2\\sigma$ level in the big-bang nucleosynthesis epoch. We also examine the cosmic age problem at high redshift associated with the old quasar APM 08279+5255 and estimate the age of the universe today.

  5. Collapse Dynamics of a Star of Dark Matter and Dark Energy

    E-print Network

    Subenoy Chakraborty; Tanwi Bandyopadhyay

    2006-09-12

    In this work, we study the collapse dynamics of an inhomogeneous spherically symmetric star made of dark matter (DM) and dark energy (DE). The dark matter is taken in the form of a dust cloud while anisotropic fluid is chosen as the candidate for dark energy. It is investigated how dark energy modifies the collapsing process and is examined whether dark energy has any effect on the Cosmic Censorship Conjecture. The collapsing star is assumed to be of finite radius and the space time is divided into three distinct regions $\\Sigma$ and $V^{\\pm}$, where $\\Sigma$ represents the boundary of the star and $V^{-}(V^{+})$ denotes the interior (exterior) of the star. The junction conditions for matching $V^{\\pm}$ over $\\Sigma$ are specified. Role of Dark energy in the formation of apparent horizon is studied and central singularity is analyzed.

  6. Friedmann cosmology with bulk viscosity: a concrete model for dark energy

    E-print Network

    X H Meng; X Dou

    2008-12-29

    The universe content is considered as a non-perfect fluid with bulk viscosity and can be described by a general equation of state (endowed some deviation from the conventionally assumed cosmic perfect fluid model). An explicitly bulk viscosity dark energy model is proposed to confront consistently with the current observational data sets by statistical analysis and is shown consistent with (not deviated away much from) the concordant $\\Lambda$ Cold Dark Matter (CDM) model by comparing the decelerating parameter. Also we compare our relatively simple viscosity dark energy model with a more complicated one by contrast with the concordant $\\Lambda$CDM model and find our model improves for the viscosity dark energy model building. Finally we discuss the perspectives of dark energy probes for the coming years with observations.

  7. Probing dark energy with the CMB: projected constraints from WMAP and Planck

    E-print Network

    A. Balbi; C. Baccigalupi; F. Perrotta; S. Matarrese; N. Vittorio

    2003-06-18

    We investigate the accuracy attainable by forthcoming space-based observations of the cosmic microwave background (CMB) temperature and polarization anisotropy in constraining the dark energy density parameter $\\Oq$ and equation of state $\\wq=p_{\\rm Q}/\\rho_{\\rm Q}$. Despite degeneracies among parameters, it is possible for high precision observations such as those from WMAP and Planck to provide interesting information on the nature of the dark energy. Furthermore, we show that imposing a flat universe constraint makes it possible to obtain tight limits in the space of dark energy parameters even from the CMB alone.

  8. Interacting viscous dark energy in a Bianchi type-III universe

    NASA Astrophysics Data System (ADS)

    Amirhashchi, Hassan

    2014-09-01

    We study the evolution of the equation of state of viscous dark energy in the scope of Bianchi type III space-time. We consider a case where the dark energy is minimally coupled to the perfect fluid, as well as in direct interaction with it. The viscosity and the interaction between the two fluids are parameterized by constants ?0 and ?, respectively. We have made a detailed investigation of the cosmological implications of this parametrization. To differentiate between different dark energy models, we have performed a geometrical diagnostic by using the statefinder pair {s, r}.

  9. Probing dark energy with the shear-ratio geometric test

    E-print Network

    A. N. Taylor; T. D. Kitching; D. J. Bacon; A. F. Heavens

    2006-11-15

    We adapt the Jain--Taylor (2003) shear-ratio geometric lensing method to measure the dark energy equation of state, and its time derivative from dark matter haloes in cosmologies with arbitrary spatial curvature. The full shear-ratio covariance matrix is calculated for lensed sources, including the intervening large-scale structure and photometric redshift errors as additional sources of noise, and a maximum likelihood method for applying the test is presented. Combining with the expected results from the CMB we design an optimal survey for probing dark energy. A targeted survey imaging 60 of the largest clusters in a hemisphere with 5-band optical photometric redshifts to a median galaxy depth of zm=0.9 could measure w0 to a marginal 1-sigma error of $\\Delta$w0=0.5. We marginalize over all other parameters including wa, where the equation of state is parameterized in terms of scale factor a as w(a)=w0+wa(1-a). For higher accuracy a large-scale photometric redshift survey is required. Such a near-future 5-band survey covering 10,000 square degrees to z_m=0.7 could measure w0 to $\\Delta$w0=0.075 and $\\Delta$wa=0.33. A stronger combined constraint is measured at a pivot redshift zp=0.27 of $\\Delta$w(zp)=0.0298. We compare and combine the geometric test with the cosmological and dark energy parameters measured from planned Baryon Acoustic Oscillation (BAO) and supernova Type Ia experiments, and find that the geometric test results combine with a significant reduction in errors due to different degeneracies. A combination of geometric lensing, CMB and BAO experiments could achieve a pivot redshift constraint of $\\Delta$w(zp)=0.020 at zp=0.62. Simple relations are presented that show how our lensing results can be scaled to other telescope classes and survey parameters.

  10. Coupled dark energy: a dynamical analysis with complex scalar field

    E-print Network

    Landim, Ricardo C G

    2015-01-01

    The dynamical analysis for coupled dark energy with dark matter is presented, where a complex scalar field is taken into account and it is considered in the presence of a barothropic fluid. We consider three dark energy candidates: quintessence, phantom and tachyon. The critical points are found and their stabilities analyzed, leading to the three cosmological eras (radiation, matter and dark energy), for a generic potential. The results presented here enlarge the previous analyses found in the literature.

  11. Cosmic inflation, deceleration, acceleration, dark matter, and dark `energy' in one coherent package

    E-print Network

    Ellis, Homer

    Cosmic inflation, deceleration, acceleration, dark matter, and dark `energy' in one coherent to (mis)represent a uniform negative net mass density of gravitationally attractive and gravitationally, baryonic particles of primordial matter and as the continuously created, invisible particles of the `dark

  12. $\\alpha $-Attractors: Planck, LHC and Dark Energy

    E-print Network

    Carrasco, John Joseph M; Linde, Andrei

    2015-01-01

    We develop four-parameter supergravity models of inflation and dark energy, constrained so that ${\\delta\\rho\\over \\rho}$, $n_s$ and the cosmological constant $\\Lambda $ take their known observable values, but where the mass of gravitino $m_{3/2}$ and the tensor-to-scalar ratio $r$ are free parameters. We focus on generalized cosmological $\\alpha$-attractor models, with logarithmic Kahler potentials, a nilpotent goldstino and spontaneously broken supersymmetry at the de Sitter minimum. The future data on B-modes will specify the parameter $\\alpha$, measuring the geometry of the Kahler, manifold. The string landscape idea for dark energy is supported in these models via an incomplete cancellation of the universal positive goldstino and negative gravitino contribution. The scale of SUSY breaking M related to the mass of gravitino in our models is a controllable parameter, independent on the scale of inflation, it will be constrained by LHC data and future collider Energy-frontier experiments.

  13. Genesis of Dark Energy: Dark Energy as Consequence of Release and Two-stage Tracking Cosmological Nuclear Energy

    E-print Network

    R. C. Gupta; Anirudh Pradhan

    2009-07-28

    Recent observations on Type-Ia supernovae and low density ($\\Omega_{m} = 0.3$) measurement of matter including dark matter suggest that the present-day universe consists mainly of repulsive-gravity type `exotic matter' with negative-pressure often said `dark energy' ($\\Omega_{x} = 0.7$). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the dark energy, are intriguing. In the present paper the authors attempt to answer these questions while making an effort to reveal the genesis of dark energy and suggest that `the cosmological nuclear binding energy liberated during primordial nucleo-synthesis remains trapped for a long time and then is released free which manifests itself as dark energy in the universe'. It is also explained why for dark energy the parameter $w = - {2/3}$. Noting that $ w = 1$ for stiff matter and $w = {1/3}$ for radiation; $w = - {2/3}$ is for dark energy because $"-1"$ is due to `deficiency of stiff-nuclear-matter' and that this binding energy is ultimately released as `radiation' contributing $"+ {1/3}"$, making $w = -1 + {1/3} = - {2/3}$. When dark energy is released free at $Z = 80$, $w = -{2/3}$. But as on present day at $Z = 0$ when radiation strength has diminished to $\\delta \\to 0$, $w = -1 + \\delta{1/3} = - 1$. This, thus almost solves the dark-energy mystery of negative pressure and repulsive-gravity. The proposed theory makes several estimates /predictions which agree reasonably well with the astrophysical constraints and observations. Though there are many candidate-theories, the proposed model of this paper presents an entirely new approach (cosmological nuclear energy) as a possible candidate for dark energy.

  14. Modified holographic Ricci dark energy model and statefinder diagnosis in flat universe

    E-print Network

    Mathew, Titus K; Divakaran, Divya

    2012-01-01

    Evolution of the universe with modified holographic Ricci dark energy model is considered. Dependency of the equation of state parameter and deceleration parameter on the redshift and model parameters are obtained. It is shown that the density evolution of both non-relativistic matter and dark energy are the same until recent times. The evolutionary trajectories of the model for different model parameters are obtained in the statefinder planes, r-s and r-q planes. The present statefinder parameters are obtained for different model parameter values, using that the model is differentiated from other standard models like $\\Lambda$CDM model etc. We have also shown that the evolutionary trajectories are depending on the model parameters, and at past times the dark energy is behaving like cold dark matter, with equation of state equal to zero.

  15. Dark Energy Constraints from Baryon Acoustic Oscillations

    E-print Network

    Yun Wang

    2006-04-25

    Baryon acoustic oscillations (BAO) in the galaxy power spectrum allows us to extract the scale of the comoving sound horizon at recombination, a cosmological standard ruler accurately determined by the cosmic microwave background anisotropy data. We examine various issues important in the use of BAO to probe dark energy. We find that assuming a flat universe, and priors on Omega_m, Omega_m h^2, and Omega_b h^2 as expected from the Planck mission, the constraints on dark energy parameters (w_0,w') scale much less steeply with survey area than (area)^{-1/2} for a given redshift range. The constraints on the dark energy density rho_X(z), however, do scale roughly with (area)^{-1/2} due to the strong correlation between H(z) and Omega_m (which reduces the effect of priors on Omega_m). Dark energy constraints from BAO are very sensitive to the assumed linear scale of matter clustering and the redshift accuracy of the survey. For a BAO survey with 0.5<= z <= 2, sigma(R)=0.4 (corresponding to k_{max}(z=0)=0.086 h Mpc^{-1}), and sigma_z/(1+z)=0.001, (sigma_{w_0},sigma_{w'})=(0.115, 0.183) and (0.069, 0.104) for survey areas of 1000 (deg)^2 and 10000 (deg)^2 respectively. We find that it is critical to minimize the bias in the scale estimates in order to derive reliable dark energy constraints. For a 1000 (10000) square degree BAO survey, a 1-sigma bias in ln H(z) leads to a 2-sigma (3-sigma) bias in w'. The bias in w' due to the same scale bias from ln D_A(z) is slightly smaller and opposite in sign. The results from this paper will be useful in assessing different proposed BAO surveys and guiding the design of optimal dark energy detection strategies.

  16. Cosmic inflation, deceleration, acceleration, dark matter, and dark 'energy' in one coherent package

    E-print Network

    Homer G. Ellis

    2015-03-15

    In creating his gravitational field equations Einstein assumed without justification that inertial mass, even in its equivalent form as energy, is a source of gravity. Giving up that assumption allows modifying the field equations to a form in which a positive cosmological constant is seen to (mis)represent a uniform negative net mass density of gravitationally attractive and gravitationally repulsive matter. Field equations with both positive and negative active gravitational mass densities of both primordial and continuously created matter incorporated, along with two scalar fields to 'relax the constraints' on the space-time geometry, yield cosmological solutions that exhibit inflation, deceleration, coasting, acceleration, and a 'big bounce' instead of a 'big bang', and provide good fits to a Hubble diagram of type Ia supernovae data. The repulsive matter is identified as the back sides of the 'drainholes' introduced by the author in 1973 as solutions of those same field equations. Drainholes are topological tunnels in space which gravitationally attract on their front, entrance sides and repel more strongly on their back, exit sides. The front sides serve both as the gravitating cores of the visible, baryonic particles of primordial matter and as the continuously created, invisible particles of the 'dark matter' needed to hold together the large scale structures seen in the universe; the back sides serve as the misnamed 'dark energy' driving the current acceleration of the expansion of the universe. Formation of cosmic voids, walls, filaments, and nodes is attributed to expulsion of drainhole entrances from regions populated by drainhole exits, and accumulation of the entrances on boundaries separating those regions.

  17. Phantom dark energy with varying-mass dark matter particles: acceleration and cosmic coincidence problem

    E-print Network

    Genly Leon; Emmanuel N. Saridakis

    2009-04-09

    We investigate several varying-mass dark-matter particle models in the framework of phantom cosmology. We examine whether there exist late-time cosmological solutions, corresponding to an accelerating universe and possessing dark energy and dark matter densities of the same order. Imposing exponential or power-law potentials and exponential or power-law mass dependence, we conclude that the coincidence problem cannot be solved or even alleviated. Thus, if dark energy is attributed to the phantom paradigm, varying-mass dark matter models cannot fulfill the basic requirement that led to their construction.

  18. Dark energy fingerprints in the nonminimal Wu-Yang wormhole structure

    E-print Network

    Balakin, Alexander B

    2014-01-01

    We discuss new exact solutions to nonminimally extended Einstein-Yang-Mills equations describing spherically symmetric static wormholes supported by the gauge field of the Wu-Yang type in a dark energy environment. We focus on the analysis of three types of exact solutions to the gravitational field equations. Solutions of the first type relate to the model, in which the dark energy is anisotropic, i.e., the radial and tangential pressures do not coincide. Solutions of the second type correspond to the isotropic pressure tensor; in particular, we discuss the exact solution, for which the dark energy is characterized by the equation of state for a string gas. Solutions of the third type describe the dark energy model with constant pressure and energy density. For the solutions of the third type we consider in detail the problem of horizons and find constraints for the parameters of nonminimal coupling and for the constitutive parameters of the dark energy equation of state, which guarantee that the nonminimal ...

  19. Possible Effects of Dark Energy on the Detection of Dark Matter Particles

    E-print Network

    Peihong Gu; Xiao-Jun Bi; Zhi-Hai Lin; Xinmin Zhang

    2005-03-14

    We study in this paper the possible influence of the dark energy on the detection of the dark matter particles. In models of dark energy described by a dynamical scalar field such as the Quintessence, its interaction with the dark matter will cause the dark matter particles such as the neutralino vary as a function of space and time. Given a specific model of the Quintessence and its interaction in this paper we calculate numerically the corrections to the neutralino masses and the induced spectrum of the neutrinos from the annihilation of the neutralinos pairs in the core of the Sun. This study gives rise to a possibility of probing for dark energy in the experiments of detecting the dark matter particles.

  20. Modified GBIG Scenario as an Alternative for Dark Energy

    E-print Network

    Kourosh Nozari; Narges Rashidi

    2009-09-02

    We construct a DGP-inspired braneworld model where induced gravity on the brane is modified in the spirit of $f(R)$ gravity and stringy effects are taken into account by incorporation of the Gauss-Bonnet term in the bulk action. We explore cosmological dynamics of this model and we show that this scenario is a successful alternative for dark energy proposal. Interestingly, it realizes the phantom-like behavior without introduction of any phantom field on the brane and the effective equation of state parameter crosses the cosmological constant line naturally in the same way as observational data suggest.

  1. Modified GBIG scenario as an alternative for dark energy

    SciTech Connect

    Nozari, Kourosh; Rashidi, Narges, E-mail: knozari@umz.ac.ir, E-mail: n.rashidi@umz.ac.ir [Department of Physics, Faculty of Basic Sciences, University of Mazandaran, P.O. Box 47416-95447, Babolsar (Iran, Islamic Republic of)

    2009-09-01

    We construct a DGP-inspired braneworld model where induced gravity on the brane is modified in the spirit of f(R) gravity and stringy effects are taken into account by incorporation of the Gauss–Bonnet term in the bulk action. We explore cosmological dynamics of this model and we show that this scenario is a successful alternative for dark energy proposal. Interestingly, it realizes the phantom-like behavior without introduction of any phantom field on the brane and the effective equation of state parameter crosses the cosmological constant line naturally in the same way as observational data suggest.

  2. Probing the dynamics of dark energy with novel parametrizations

    NASA Astrophysics Data System (ADS)

    Ma, Jing-Zhe; Zhang, Xin

    2011-05-01

    We point out that the CPL parametrization has a problem that the equation of state w(z) diverges in the far future, so that this model can only properly describe the past evolution but cannot depict the future evolution. To overcome such a difficulty, in this Letter we propose two novel parametrizations for dark energy, the logarithm form w(z)=w+w(ln(2+z)1+z-ln2) and the oscillating form w(z)=w+w(sin(1+z)1+z-sin(1)), successfully avoiding the future divergency problem in the CPL parametrization, and use them to probe the dynamics of dark energy in the whole evolutionary history. Our divergency-free parametrizations are proven to be very successful in exploring the dynamical evolution of dark energy and have powerful prediction capability for the ultimate fate of the universe. Constraining the CPL model and the new models with the current observational data, we show that the new models are more favored. The features and the predictions for the future evolution in the new models are discussed in detail.

  3. Probing dark energy dynamics from current and future cosmological observations

    SciTech Connect

    Zhao Gongbo [Institute of Cosmology and Gravitation, Dennis Sciama Building, Burnaby Road, Portsmouth, PO1 3FX (United Kingdom); Department of Physics, Simon Fraser University, Burnaby, BC, V5A 1S6 (Canada); Zhang Xinmin [Theoretical Physics Division, Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918-4, Beijing 100049 (China); Theoretical Physics Center for Science Facilities (TPCSF), Chinese Academy of Sciences (China)

    2010-02-15

    We report the constraints on the dark energy equation-of-state w(z) using the latest 'Constitution' SNe sample combined with the WMAP5 and Sloan Digital Sky Survey data. Assuming a flat Universe, and utilizing the localized principal component analysis and the model selection criteria, we find that the {Lambda}CDM model is generally consistent with the current data, yet there exists a weak hint of the possible dynamics of dark energy. In particular, a model predicting w(z)<-1 at z is an element of [0.25,0.5) and w(z)>-1 at z is an element of [0.5,0.75), which means that w(z) crosses -1 in the range of z is an element of [0.25,0.75), is mildly favored at 95% confidence level. Given the best fit model for current data as a fiducial model, we make future forecast from the joint data sets of Joint Dark Energy Mission, Planck, and Large Synoptic Survey Telescope, and we find that the future surveys can reduce the error bars on the w bins by roughly a factor of 10 for a 5-w-bin model.

  4. Distinguishing interacting dark energy from wCDM with CMB, lensing, and baryon acoustic oscillation data

    NASA Astrophysics Data System (ADS)

    Väliviita, Jussi; Palmgren, Elina

    2015-07-01

    We employ the Planck 2013 CMB temperature anisotropy and lensing data, and baryon acoustic oscillation (BAO) data to constrain a phenomenological wCDM model, where dark matter and dark energy interact. We assume time-dependent equation of state parameter for dark energy, and treat dark matter and dark energy as fluids whose energy-exchange rate is proportional to the dark-matter density. The CMB data alone leave a strong degeneracy between the interaction rate and the physical CDM density parameter today, ?c, allowing a large interaction rate |?| ~ H0. However, as has been known for a while, the BAO data break this degeneracy. Moreover, we exploit the CMB lensing potential likelihood, which probes the matter perturbations at redshift z ~ 2 and is very sensitive to the growth of structure, and hence one of the tools for discerning between the ?CDM model and its alternatives. However, we find that in the non-phantom models (wde>?1), the constraints remain unchanged by the inclusion of the lensing data and consistent with zero interaction, ?0.14 < ?/H0 < 0.02 at 95% CL. On the contrary, in the phantom models (wdeenergy transfer from dark energy to dark matter is moderately favoured over the non-interacting model; 0?0.57 < ?/H0 < ?0.1 at 95% CL with CMB+BAO, while addition of the lensing data shifts this to ?0.46 < ?/H0 < ?0.01.

  5. Atom-interferometry constraints on dark energy

    E-print Network

    Paul Hamilton; Matt Jaffe; Philipp Haslinger; Quinn Simmons; Holger Müller; Justin Khoury

    2015-07-02

    If dark energy --- which drives the accelerated expansion of the universe --- consists of a light scalar field, it might be detectable as a "fifth force" between normal-matter objects, in potential conflict with precision tests of gravity. Chameleon fields and other theories with screening mechanisms, however, can evade these tests by suppressing the forces in regions of high density, such as the laboratory. Using a cesium matter-wave interferometer near a spherical mass in an ultra-high vacuum chamber, we reduce the screening mechanism by probing the field with individual atoms rather than bulk matter. Thus, we constrain a wide class of dark energy theories, including a range of chameleon and other theories that reproduce the observed cosmic acceleration.

  6. Dark energy simulacrum in nonlinear electrodynamics

    SciTech Connect

    Labun, Lance; Rafelski, Johann [Department of Physics, University of Arizona, Tucson, Arizona, 85721 (Unites States) and Ludwig-Maximillians-Universitaet Muenchen, 85748 Garching (Germany)

    2010-03-15

    Quasiconstant external fields in nonlinear electromagnetism generate a global contribution proportional to g{sup {mu}{nu}}in the energy-momentum tensor, thus a simulacrum of dark energy. To provide a thorough understanding of the origin and strength of its effects, we undertake a complete theoretical and numerical study of the energy-momentum tensor T{sup {mu}{nu}}for nonlinear electromagnetism. The Euler-Heisenberg nonlinearity due to quantum fluctuations of spinor and scalar matter fields is considered and contrasted with the properties of classical nonlinear Born-Infeld electromagnetism. We address modifications of charged particle kinematics by strong background fields.

  7. Gauss Bonnet dark energy Chaplygin Gas Model

    E-print Network

    Karimkhani, Elahe; Khodam-Mohammadi, Abdolhossein

    2015-01-01

    In this work we incorporate GB dark energy density and its modification, MGB, with Chaplygin gas component. We show that, presence of Chaplygin gas provides us a feature to obtain an exact solution for scalar field and potential of scalar field. Investigation on squared of sound speed provides a lower limit for constant parameters of MGB model. Also, we could find some bounds for free parameters of model.

  8. Dark Energy from $\\alpha$-Attractors

    E-print Network

    Linder, Eric V

    2015-01-01

    A class of inflation theories called $\\alpha$-attractors has been investigated recently with interesting properties interpolating between quadratic potentials, the Starobinsky model, and an attractor limit. Here we examine their use for late time cosmic acceleration. We generalize the class and demonstrate how it can interpolate between thawing and freezing dark energy, and reduce the fine tuning of initial conditions, allowing $w\\approx-1$ for a prolonged period or as a de Sitter attractor.

  9. Power Law Entropy Corrected New-Agegraphic Dark Energy in Ho?ava-Lifshitz Cosmology

    E-print Network

    K. Karami; A. Sheykhi; Mubasher Jamil; R. Myrzakulov; S. Ghaffari; A. Abdolmaleki

    2012-03-31

    We investigate the new agegraphic dark energy (NADE) model with power-law corrected entropy in the framework of Ho\\v{r}ava-Lifshitz cosmology. For a non-flat universe containing the interacting power-law entropy-corrected NADE (PLECNADE) with dark matter, we obtain the differential equation of the evolution of density parameter as well as the deceleration parameter. To study parametric behavior, we used an interesting form of state parameter as function of redshift $\\omega_{\\Lambda}(z)=\\omega_0+\\omega_1 z$. We found that phantom crossing occurs for the state parameter for a non-zero coupling parameter, thus supporting interacting dark energy model.

  10. An inhomogeneous alternative to dark energy?

    E-print Network

    Havard Alnes; Morad Amarzguioui; Oyvind Gron

    2006-04-18

    Recently, there have been suggestions that the apparent accelerated expansion of the universe is not caused by repulsive gravitation due to dark energy, but is rather a result of inhomogeneities in the distribution of matter. In this work, we investigate the behaviour of a dust dominated inhomogeneous Lemaitre-Tolman-Bondi universe model, and confront it with various astrophysical observations. We find that such a model can easily explain the observed luminosity distance-redshift relation of supernovae without the need for dark energy, when the inhomogeneity is in the form of an underdense bubble centered near the observer. With the additional assumption that the universe outside the bubble is approximately described by a homogeneous Einstein-de Sitter model, we find that the position of the first CMB peak can be made to match the WMAP observations. Whether or not it is possible to reproduce the entire CMB angular power spectrum in an inhomogeneous model without dark energy, is still an open question.

  11. Redshift drift exploration for interacting dark energy

    E-print Network

    Geng, Jia-Jia; Zhang, Jing-Fei; Zhang, Xin

    2015-01-01

    By detecting redshift drift in the spectra of Lyman-$\\alpha$ forest of distant quasars, Sandage-Loeb (SL) test directly measures the expansion of the universe, covering the "redshift desert" of $2 \\lesssim z \\lesssim5$. Thus this method is definitely an important supplement to the other geometric measurements and will play a crucial role in cosmological constraints. In this paper, we quantify the ability of SL test signal by a CODEX-like spectrograph for constraining interacting dark energy. Four typical interacting dark energy models are considered: (\\romannumeral1) $Q=\\gamma H\\rho_c$, (\\romannumeral2) $Q=\\gamma H\\rho_{de}$, (\\romannumeral3) $Q=\\gamma H_0\\rho_c$, and (\\romannumeral4) $Q=\\gamma H_0\\rho_{de}$. The results show that for all the considered interacting dark energy models, relative to the current joint SN+BAO+CMB+$H_0$ observations, the constraints on $\\Omega_m$ and $H_0$ would be improved by about 60\\% and 30--40\\%, while the constraints on $w$ and $\\gamma$ would be slightly improved, with a 30-y...

  12. Prospects in Constraining the Dark Energy Potential

    E-print Network

    Fernandez-Martinez, Enrique

    2008-01-01

    We generalize to non-flat geometries the formalism of Simon et al. (2005) to reconstruct the dark energy potential. This formalism makes use of quantities similar to the Horizon-flow parameters in inflation, can, in principle, be made non-parametric and is general enough to be applied outside the simple, single scalar field quintessence. Since presently available and forthcoming data do not allow a non-parametric and exact reconstruction of the potential, we consider a general parametric description in term of Chebyshev polynomials. We then consider present and future measurements of H(z), Baryon Acoustic Oscillations surveys and Supernovae type 1A surveys, and investigate their constraints on the dark energy potential. We find that, relaxing the flatness assumption increases the errors on the reconstructed dark energy evolution but does not open up significant degeneracies, provided that a modest prior on geometry is imposed. Direct measurements of H(z), such as those provided by BAO surveys, are crucially i...

  13. Genesis of Dark Energy: Dark Energy as Consequence of Release and Two-stage Tracking Cosmological Nuclear Energy

    E-print Network

    Gupta, R C

    2009-01-01

    Recent observations on Type-Ia supernovae and low density ($\\Omega_{m} = 0.3$) measurement of matter including dark matter suggest that the present day universe consists mainly of repulsive-gravity type `exotic matter' with negative-pressure often said `dark energy' ($\\Omega_{x} = 0.7$). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the dark energy, are intriguing. In the present paper the authors attempt to answer these questions while making an effort to reveal the genesis of dark energy and suggest that `the cosmological nuclear binding energy liberated during primordial nucleo-synthesis remains trapped for a long time and then is released free which manifests itself as dark energy in the universe'. It is also explained why for dark energy the parameter $ w = - {2/3}$. Noting that $ w = 1$ for stiff matter and $ w = {1/3}$ for radiation; $w = -{2/3}$ is for dark energy because "-1" is due to `dificiency of stiff-nuclear-matter' and that this ...

  14. Genesis of Dark Energy: Dark Energy as Consequence of Release and Two-Stage Tracking of Cosmological Nuclear Energy

    Microsoft Academic Search

    R. C. Gupta; Anirudh Pradhan

    2010-01-01

    Recent observations on Type-Ia supernovae and low density (?\\u000a m\\u000a =0.3) measurement of matter including dark matter suggest that the present-day universe consists mainly of repulsive-gravity\\u000a type ‘exotic matter’ with negative-pressure often said ‘dark energy’ (?\\u000a x\\u000a =0.7). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the\\u000a dark

  15. DARK FLUID: A UNIFIED FRAMEWORK FOR MODIFIED NEWTONIAN DYNAMICS, DARK MATTER, AND DARK ENERGY

    SciTech Connect

    Zhao Hongsheng [Scottish University Physics Alliance, University of St. Andrews, KY16 9SS (United Kingdom); Li Baojiu, E-mail: hz4@st-andrews.ac.u, E-mail: b.li@damtp.cam.ac.u [Department of Applied Math and Theoretical Physics, Cambridge University, CB3 0WA (United Kingdom)

    2010-03-20

    Empirical theories of dark matter (DM) like modified Newtonian dynamics (MOND) gravity and of dark energy (DE) like f(R) gravity were motivated by astronomical data. But could these theories be branches rooted from a more general and hence generic framework? Here we propose a very generic Lagrangian of such a framework based on simple dimensional analysis and covariant symmetry requirements, and explore various outcomes in a top-down fashion. The desired effects of quintessence plus cold DM particle fields or MOND-like scalar field(s) are shown to be largely achievable by one vector field only. Our framework preserves the covariant formulation of general relativity, but allows the expanding physical metric to be bent by a single new species of dark fluid flowing in spacetime. Its non-uniform stress tensor and current vector are simple functions of a vector field with variable norm, not coupled with the baryonic fluid and the four-vector potential of the photon fluid. The dark fluid framework generically branches into a continuous spectrum of theories with DE and DM effects, including the f(R) gravity, tensor-vector-scalar-like theories, Einstein-Aether, and nuLAMBDA theories as limiting cases. When the vector field degenerates into a pure scalar field, we obtain the physics for quintessence. Choices of parameters can be made to pass Big Bang nucleosynthesis, parameterized post-Newtonian, and causality constraints. In this broad setting we emphasize the non-constant dynamical field behind the cosmological constant effect, and highlight plausible corrections beyond the classical MOND predictions.

  16. Dynamical systems analysis of an interacting dark energy model in the brane scenario

    NASA Astrophysics Data System (ADS)

    Biswas, Sujay Kr.; Chakraborty, Subenoy

    2015-03-01

    In this paper, we investigate the background dynamics in brane cosmology when dark energy is coupled to dark matter by a suitable interaction. Here we consider an homogeneous and isotropic Friedmann-Robertson-Walker brane model and the evolution equations are reduced to an autonomous system by suitable transformation of variables. The nature of critical points are analyzed by evaluating the eigenvalues of linearized Jacobi matrix. Finally, the classical stability of the model is also studied.

  17. A Laboratory Search for Dark Energy

    E-print Network

    Yasunori Fujii; Kensuke Homma

    2010-02-24

    The discovery of the accelerating universe indicates strongly the presence of a scalar field which is not only expected to solve today's version of the cosmological constant problem, or the fine-tuning and the coincidence problems, but also provides a way to understand dark energy. It has also been shown that Jordan's scalar-tensor theory is now going to be re-discovered in the new lights. In this letter we suggest a way to search for the extremely light scalar field by means of a laboratory experiment on the low-energy photon-photon interactions with the quasi-parallel incident beams.

  18. A Terrestrial, Atom Interferometer, Experiment Searching for Dark Energy Density and Other Dark Contents of the Vacuum

    E-print Network

    Wechsler, Risa H.

    1 A Terrestrial, Atom Interferometer, Experiment Searching for Dark Energy Density and Other Dark way to investigate the nature of dark energy and at the same time to look for unknown contents, as in Fig. 5, there is an additional force on the atoms caused by dark energy, FDE shift of A is now

  19. Comparison of piecewise-constant methods for dark energy

    E-print Network

    Savvas Nesseris; Domenico Sapone

    2014-09-18

    We compare four different methods that can be used to analyze the type Ia supernovae (SnIa) data, ie to use piecewise-constant functions in terms of: the dark energy equation of state $w(z)$, the deceleration parameter $q(z)$, the Hubble parameter $H(z)$ and finally the luminosity distance $d_L$. These four quantities cover all aspects of the accelerating Universe, ie the phenomenological properties of dark energy, the expansion rate (first and second derivatives) of the Universe and the observations themselves. For the first two cases we also perform principal component analysis (PCA) so as to decorrelate the parameters, while for the last two cases we use novel analytic expressions to find the best-fit parameters. In order to test the methods we create mock SnIa data (2000 points, uniform in redshift $z\\in[0,1.5]$) for three fiducial cosmologies: the cosmological constant model ($\\Lambda$CDM), a linear expansion of the dark energy equation of state parameter $w(a)=w_0+w_a(1-a)$ and the Hu-Sawicki $f(R)$ model. We find that if we focus on the two mainstream approaches for the PCA, i.e. $w(z)$ and $q(z)$, then the best piecewise-constant scheme is always $w(z)$. Finally, to our knowledge the piecewise-constant method for $H(z)$ is new in the literature, while for the rest three methods we present several new analytic expressions.

  20. Dark Energy and the Hierarchy Problem

    SciTech Connect

    Chen, Pisin

    2006-12-06

    The well-known hierarchy between the Planck scale (>> 1019GeV) and the TeV scale, namely a ratio of {approx} 10{sup 16} between the two, is coincidentally repeated in a inverted order between the TeV scale and the dark energy scale at {approx} 10{sup -3} eV implied by the observations. We argue that this is not a numerical coincidence. The same brane-world setups to address the first hierarchy problem may also in principle address this second hierarchy issue. Specifically, we consider supersymmetry in the bulk and its breaking on the brane and resort to the Casimir energy induced by the bulk graviton-gravitino mass-shift on the brane as the dark energy. For the ADD model we found that our notion is sensible only if the number of extra dimension n = 2. We extend our study to the Randall-Sundrum model. Invoking the chirality-flip on the boundaries for SUSY-breaking, the zero-mode gravitino contribution to the Casimir energy does give rise to the double hierarchy. Unfortunately since the higher Kaluza-Klein modes acquire relative mass-shifts at the TeV level, the zero-mode contribution to Casimir energy is overshadowed.

  1. Cool Dark Cosmic Dust as a Reservoir of Absorbed Energy

    E-print Network

    I. Simonia

    2005-07-22

    The conception of cool dark cosmic dust has been proposed. The process of accumulation of absorbed energy by dust of such kind is considered. The conception of accumulation horizon is introduced. The possible role of cool dark cosmic dust is discussed for solution of the problem of dark matter. The other aspects of the problem are also considered.

  2. New Light on Dark Energy

    NASA Astrophysics Data System (ADS)

    2008-01-01

    Using ESO's Very Large Telescope Interferometer, astronomers have probed the inner parts of the disc of material surrounding a young stellar object, witnessing how it gains its mass before becoming an adult. ESO PR Photo 03/08 ESO PR Photo 03a/08 The disc around MWC 147 (Artist's Impression) The astronomers had a close look at the object known as MWC 147, lying about 2,600 light years away towards the constellation of Monoceros ('the Unicorn'). MWC 147 belongs to the family of Herbig Ae/Be objects. These have a few times the mass of our Sun and are still forming, increasing in mass by swallowing material present in a surrounding disc. MWC 147 is less than half a million years old. If one associated the middle-aged, 4.6 billion year old Sun with a person in his early forties, MWC 147 would be a 1-day-old baby [1]. The morphology of the inner environment of these young stars is however a matter of debate and knowledge of it is important to better understand how stars and their cortège of planets form. The astronomers Stefan Kraus, Thomas Preibisch, and Keiichi Ohnaka have used the four 8.2-m Unit Telescopes of ESO's Very Large Telescope to this purpose, combining the light from two or three telescopes with the MIDI and AMBER instruments. "With our VLTI/MIDI and VLTI/AMBER observations of MWC147, we combine, for the first time, near- and mid-infrared interferometric observations of a Herbig Ae/Be star, providing a measurement of the disc size over a wide wavelength range [2]," said Stefan Kraus, lead-author of the paper reporting the results. "Different wavelength regimes trace different temperatures, allowing us to probe the disc's geometry on the smaller scale, but also to constrain how the temperature changes with the distance from the star." The near-infrared observations probe hot material with temperatures of up to a few thousand degrees in the innermost disc regions, while the mid-infrared observations trace cooler dust further out in the disc. The observations show that the temperature changes with radius are much steeper than predicted by the currently favoured models, indicating that most of the near-infrared emission emerges from hot material located very close to the star, that is, within one or two times the Earth-Sun distance (1-2 AU). This also implies that dust cannot exist so close to the star, since the strong energy radiated by the star heats and ultimately destroys the dust grains. ESO PR Photo 03/08 ESO PR Photo 03b/08 The Region Around MWC 147 "We have performed detailed numerical simulations to understand these observations and reached the conclusion that we observe not only the outer dust disc, but also measure strong emission from a hot inner gaseous disc. This suggests that the disc is not a passive one, simply reprocessing the light from the star," explained Kraus. "Instead, the disc is active, and we see the material, which is just transported from the outer disc parts towards the forming star." ESO PR Photo 03/08 ESO PR Photo 03c/08 Close-up on MWC 147 The best-fit model is that of a disc extending out to 100 AU, with the star increasing in mass at a rate of seven millionths of a solar mass per year. "Our study demonstrates the power of ESO's VLTI to probe the inner structure of discs around young stars and to reveal how stars reach their final mass," said Stefan Kraus. More Information The authors report their results in a paper in the Astrophysical Journal ("Detection of an inner gaseous component in a Herbig Be star accretion disk: Near- and mid-infrared spectro-interferometry and radiative transfer modeling of MWC 147", by Stefan Kraus, Thomas Preibisch, Keichii Ohnaka").

  3. On the holographic dark energy in chameleon scalar-tensor cosmology

    NASA Astrophysics Data System (ADS)

    Saaidi, K.; Sheikhahmadi, H.; Golanbari, T.; Rabiei, S. W.

    2013-11-01

    We study the holographic dark energy (HDE) model in generalized Brans-Dicke scenario with a non-minimal coupling between the scalar field and matter Lagrangian namely Chameleon Brans Dicke (CBD) mechanism. In this study we consider the interacting and non-interacting cases for two different cutoffs. The physical quantities of the model such as, equation of state (EoS) parameter, deceleration parameter and the evolution equation of dimensionless parameter of dark energy are obtained. We shall show that this model can describe the dynamical evolution of fraction parameter of dark energy in all epochs. Also we find the EoS parameter can cross the phantom divide line by suitable choices of parameters without any mines kinetic energy term.

  4. On the Similarity of Information Energy to Dark Energy

    Microsoft Academic Search

    M. P. Gough; T. D. Carozzi; A. M. Buckley

    2006-01-01

    Information energy is shown here to have properties similar to those of dark\\u000aenergy. The energy associated with each information bit of the universe is\\u000afound to be defined identically to the characteristic energy of a cosmological\\u000aconstant. Two independent methods are used to estimate the universe information\\u000acontent of ~10^91 bits, a value that provides an information energy total

  5. The growth of structure in interacting dark energy models

    SciTech Connect

    Caldera-Cabral, Gabriela; Maartens, Roy [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX (United Kingdom); Schaefer, Bjoern Malte, E-mail: gaby.calderacabral@port.ac.uk, E-mail: roy.maartens@port.ac.uk, E-mail: spirou@ita.uni-heidelberg.de [Astronomisches Recheninstitut, Zentrum für Astronomie, Universität Heidelberg, Mönchhofstraße 12, 69120 Heidelberg (Germany)

    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)

  6. Can the Existence of Dark Energy Be Directly Detected?

    E-print Network

    Martin L. Perl

    2008-10-06

    The majority of astronomers and physicists accept the reality of dark energy and also believe that it can only be studied indirectly through observation of the motions of stars and galaxies. In this paper I open the experimental question of whether it is possible to directly detect dark energy through the presence of dark energy density. Two thirds of this paper outlines the major aspects of dark energy density as now comprehended by the astronomical and physics community. The final third summarizes various proposals for direct detection of dark energy density or its possible effects. At this time I do not have a fruitful answer to the question: Can the Existence of Dark Energy Be Directly Detected?

  7. Holographic field theory models of dark energy in interaction with dark matter

    E-print Network

    Sandro M. R. Micheletti

    2011-10-07

    We discuss two lagrangian interacting dark energy models in the context of the holographic principle. The potentials of the interacting fields are constructed. The models are compared with CMB distance information, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. For both models the results are consistent with a non vanishing interaction between dark sectors - with more than three standard deviations of confidence for one of them. Moreover, in both cases, the sign of coupling is consistent with dark energy decaying into dark matter, alleviating the coincidence problem.

  8. Understanding the Fundamental Properties of Dark Matter & Dark Energy in Structure formation and Cosmology

    SciTech Connect

    Ellis, Richard, S.

    2008-02-01

    This program is concerned with developing and verifying the validityof observational methods for constraining the properties of dark matter and dark energy in the universe. Excellent progress has been made in comparing observational projects involving weak gravitational lensing using both ground and space-based instruments, in further constraining the nature of dark matter via precise measures of its distribution in clusters of galaxies using strong gravitational lensing, in demonstrating the possible limitations of using distant supernovae in future dark energy missions, and in investigating the requirement for ground-based surveys of baryonic acoustic oscillations.

  9. Holographic dark energy in Brans-Dicke theory with log correction

    E-print Network

    Ahmad Sheykhi; Kayoomars Karami; Mubasher Jamil; E. Kazemi; M. Haddad

    2011-11-01

    In the derivation of holographic dark energy density, the area law of the black hole entropy plays a crucial role. However, the entropy-area relation can be modified from the inclusion of quantum effects, motivated from the loop quantum gravity, string theory and black hole physics. In this paper, we study cosmological implication of the interacting entropy-corrected holographic dark energy model in the framework of Brans-Dicke cosmology. We obtain the equation of state and the deceleration parameters of the entropy-corrected holographic dark energy in a non-flat Universe. As system's IR cutoff we choose the radius of the event horizon measured on the sphere of the horizon, defined as $L=ar(t)$. We find out that when the entropy-corrected holographic dark energy is combined with the Brans-Dicke field, the transition from normal state where $w_D >-1 $ to the phantom regime where $w_D <-1 $ for the equation of state of interacting dark energy can be more easily achieved for than when resort to the Einstein field equations is made.

  10. Dark and composite rogue waves in the coupled Hirota equations

    NASA Astrophysics Data System (ADS)

    Chen, Shihua

    2014-08-01

    The intriguing dark and composite rogue wave dynamics in a coupled Hirota system are unveiled, based on the exact explicit rational solutions obtained under the assumption of equal background height. It is found that a dark rogue wave state would occur as a result of the strong coupling between two field components with large wavenumber difference, and there would appear plenty of composite structures that are attributed to the specific wavenumber difference and the free choice of three independent structural parameters. The coexistence of different fundamental rogue waves in such a coupled system is also demonstrated.

  11. Interacting dark energy and the cosmic coincidence problem

    SciTech Connect

    Berger, Micheal S.; Shojaei, Hamed [Physics Department, Indiana University, Bloomington, Indiana 47405 (United States)

    2006-04-15

    The introduction of an interaction for dark energy to the standard cosmology offers a potential solution to the cosmic coincidence problem. We examine the conditions on the dark energy density that must be satisfied for this scenario to be realized. Under some general conditions we find a stable attractor for the evolution of the Universe in the future. Holographic conjectures for the dark energy offer some specific examples of models with the desired properties.

  12. Solvable K-essence Cosmologies and Modified Chaplygin Gas Unified Models of Dark Energy and Dark Matter

    E-print Network

    M. Sharif; K. R. Yesmakhanova; S. Rani; R. Myrzakulov

    2012-07-30

    This paper is devoted to the investigation of modified Chaplygin gas model in the context of solvable k-essence cosmologies. For this purpose, we construct equations of state parameter of this model for some particular values of the parameter $n$. The graphical behavior of these equations are also discussed by using power law form of potential. The relationship between k-essence and modified Chaplygin gas model shows viable results in the dark energy scenario. We conclude that the universe behaves as a cosmological constant, quintessence phase or phantom phase depending upon $n$.

  13. Inflation and New Agegraphic Dark Energy

    E-print Network

    Cheng-Yi Sun; Rui-Hong Yue

    2011-04-23

    In the note, we extend the discussion of the new agegraphic dark energy (NADE) model to include the inflation stage. Usually, in the inflation models, for convenience the conformal time $\\eta$ is set to be zero at the end of inflation. This is incompatible with the NADE model since $\\eta=0$ indicates the divergence of NADE. To avoid the difficulty, we can redefine the conformal time as $\\eta+\\delta$. However, we find that the positive constant $\\delta$ must be so large that NADE can not become dominated at present time.

  14. Inflation and new agegraphic dark energy

    SciTech Connect

    Sun Chengyi [Institute of Modern Physics, Northwest University, Xian, 710069 (China); Yue Ruihong [Faculty of Science, Ningbo University, Ningbo 315211 (China)

    2011-05-15

    In the note, we extend the discussion of the new agegraphic dark energy (NADE) model to include the inflation stage. Usually, in the inflation models, for convenience the conformal time {eta} is set to be zero at the end of inflation. This is incompatible with the NADE model since {eta}=0 indicates the divergence of NADE. To avoid the difficulty, we can redefine the conformal time as {eta}+{delta}. However, we find that the positive constant {delta} must be so large that NADE cannot become dominated at present time.

  15. Holographic Foam, Dark Energy and Infinite Statistics

    E-print Network

    Y. Jack Ng

    2007-09-30

    Quantum fluctuations of spacetime give rise to quantum foam, and black hole physics dictates that the foam is of holographic type. Applied to cosmology, the holographic model requires the existence of dark energy which, we argue, is composed of an enormous number of inert ``particles'' of extremely long wavelength. These "particles" necessarily obey infinite statistics in which all representations of the particle permutation group can occur. For every boson or fermion in the present observable universe there could be $\\sim 10^{31}$ such "particles". We also discuss the compatibility between the holographic principle and infinite statistics.

  16. The Dark Energy Survey CCD imager design

    SciTech Connect

    Cease, H.; DePoy, D.; Diehl, H.T.; Estrada, J.; Flaugher, B.; Guarino, V.; Kuk, K.; Kuhlmann, S.; Schultz, K.; Schmitt, R.L.; Stefanik, A.; /Fermilab /Ohio State U. /Argonne

    2008-06-01

    The Dark Energy Survey is planning to use a 3 sq. deg. camera that houses a {approx} 0.5m diameter focal plane of 62 2kx4k CCDs. The camera vessel including the optical window cell, focal plate, focal plate mounts, cooling system and thermal controls is described. As part of the development of the mechanical and cooling design, a full scale prototype camera vessel has been constructed and is now being used for multi-CCD readout tests. Results from this prototype camera are described.

  17. Geometrical constraints on dark energy models

    E-print Network

    Ruth Lazkoz

    2007-10-15

    This contribution intends to give a pedagogical introduction to the topic of dark energy (the mysterious agent supposed to drive the observed late time acceleration of the Universe) and to various observational tests which require only assumptions on the geometry of the Universe. Those tests are the supernovae luminosity, the CMB shift, the direct Hubble data, and the baryon acoustic oscillations test. An historical overview of Cosmology is followed by some generalities on FRW spacetimes (the best large-scale description of the Universe), and then the test themselves are discussed. A convenient section on statistical inference is included as well.

  18. Modified gravity models of dark energy

    E-print Network

    Shinji Tsujikawa

    2010-12-31

    We review recent progress of modified gravity models of dark energy--based on f(R) gravity, scalar-tensor theories, braneworld gravity, Galileon gravity, and other theories. In f(R) gravity and Brans-Dicke theory it is possible to design viable models consistent with local gravity constraints under a chameleon mechanism, while satisfying conditions for the cosmological viability. The Dvali-Gabadazde-Porrati braneworld model can be compatible with local gravity constraints through a nonlinear field self-interaction arising from a brane-bending mode, but the self-accelerating solution contains a ghost mode in addition to the tension with observational data about the cosmic expansion history. The extension of the field self-interaction to more general forms satisfying a Galilean symmetry in the flat space-time allows a possibility to avoid the appearance of ghosts and Laplacian instabilities, while the late-time cosmic acceleration can be realized by the field kinetic energy. We study the evolution of cosmological perturbations in those models to place constraints on model parameters from the observations of large-scale structure, cosmic microwave background, and weak lensing. We also briefly review other modified gravitational models of dark energy-- such as those based on Gauss-Bonnet gravity and Lorentz-violating theories.

  19. Statefinder diagnosis and the interacting ghost model of dark energy

    E-print Network

    M. Malekjani; A. Khodam-Mohammadi

    2012-02-19

    A new model of dark energy namely "ghost dark energy model" has recently been suggested to interpret the positive acceleration of cosmic expansion. The energy density of ghost dark energy is proportional to the hubble parameter. In this paper we perform the statefinder diagnostic tool for this model both in flat and non-flat universe. We discuss the dependency of the evolutionary trajectories in $s-r$ and $q-r$ planes on the interaction parameter between dark matter and dark energy as well as the spatial curvature parameter of the universe. Eventually, in the light of SNe+BAO+OHD+CMB observational data, we plot the evolutionary trajectories in $s-r$ and $q-r$ planes for the best fit values of the cosmological parameters and compare the interacting ghost model with other dynamical dark energy models. We show that the evolutionary trajectory of ghost dark energy in statefinder diagram is similar to holographic dark energy model. It has been shown that the statefinder location of $\\Lambda$CDM is in good agreement with observation and therefore the dark energy models whose current statefinder values are far from the $\\Lambda$CDM point can be ruled out.

  20. Dark matter and dark energy in the Universe: Astrophysical reasons and theoretical models

    Microsoft Academic Search

    S. Apunevych; Yu. Kulinich; B. Novosyadlyj; V. Pelykh

    2009-01-01

    The general review on the problem of dark matter and dark energy in observable Universe is given. The problem is treated from\\u000a the point of view of research fields on the boundary of which this fundamental task is situated, namely, the astrophysics\\u000a and theoretical physics. We emphasize that interdisciplinary nature of “dark sector” of Universe problem can assist in its

  1. The future of the local large scale structure: the roles of dark matter and dark energy

    Microsoft Academic Search

    Yehuda Hoffman; Ofer Lahav; Gustavo Yepes; Yaniv Dover

    2007-01-01

    We study the distinct effects of dark matter and dark energy on the future evolution of nearby large scale structures using constrained N-body simulations. We contrast a model of cold dark matter and a cosmological constant (LambdaCDM) with an open CDM (OCDM) model with the same matter density Omegam = 0.3 and the same Hubble constant h = 0.7. Already

  2. Dark energy and dark matter in the Universe: in three volumes.

    NASA Astrophysics Data System (ADS)

    Shulga, Valery; Zhdanov, Valery; Alexandrov, Alexander; Berczik, Peter; Pavlenko, Elena; Pavlenko, Yakiv; Pilyugin, Leonid; Tsvetkova, Victoria

    2014-07-01

    This monograph is the second issue of a three volume edition under the general title Dark Energy and Dark Matter in the Universe. It concentrates mainly on astrophysical aspects of the dark matter and invisible mass problem including those of gravitational lensing, mass distribution, and chemical abundance in the Universe, physics of compact stars and models of the galactic evolution. The monograph is intended for science professionals, educators and graduate students, specializing in extragalactic astronomy, cosmology and general relativity.

  3. On the growth of perturbations in interacting dark energy and dark matter fluids

    E-print Network

    N. A. Koshelev

    2010-10-18

    The covariant generalizations of the background dark sector coupling suggested in G. Mangano, G. Miele and V. Pettorino, Mod. Phys. Lett. A 18, 831 (2003) are considered. The evolution of perturbations is studied with detailed attention to interaction rate that is proportional to the product of dark matter and dark energy densities. It is shown that some classes of models with coupling of this type do not suffer from early time instabilities in strong coupling regime.

  4. Dark energy from primordial inflationary quantum fluctuations.

    PubMed

    Ringeval, Christophe; Suyama, Teruaki; Takahashi, Tomo; Yamaguchi, Masahide; Yokoyama, Shuichiro

    2010-09-17

    We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the Universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale. PMID:20867625

  5. The Hawking temperature in the context of dark energy for Reissner-Nordstrom and Kerr background

    NASA Astrophysics Data System (ADS)

    Manna, Goutam; Gangopadhyay, Debashis

    2014-03-01

    For emergent gravity metrics, the presence of dark energy modifies the Hawking temperature. We show that for the spherically symmetric Reissner-Nordstrom background metric, the emergent metric can be mapped into a Robinson-Trautman black hole. Allowed values of the dark energy density follow from rather general conditions. For some allowed values of the dark energy density this black hole can have zero Hawking temperature, i.e. the black hole does not radiate. For a Kerr background along , the emergent black hole metric satisfies Einstein's equations for large and always radiates. Our analysis is done in the context of emergent gravity metrics having -essence scalar fields with a Born-Infeld type lagrangian. In both cases the scalar field also satisfies the emergent gravity equations of motion for and.

  6. Limits of dark energy measurements from CMB lensing-ISW-galaxy count correlations

    E-print Network

    Benjamin Gold

    2005-03-10

    I discuss several issues that arise when trying to constrain the dark energy equation of state using correlations of the integrated Sachs-Wolfe effect with galaxy counts and lensing of the cosmic microwave background. These techniques are complementary to others such as galaxy shear surveys, and can use data that will already be obtained from currently planned observations. In regimes where cosmic variance and shot noise are the dominant sources of error, constraints could be made on the mean equation of state to within 0.33 and its first derivative to within 1.0. Perhaps more interesting is that the determination of dark energy parameters by these types of experiments depends strongly on the presence or absence of perturbations in the dark energy fluid.

  7. Dissipative or conservative cosmology with dark energy?

    SciTech Connect

    Szydlowski, Marek [Astronomical Observatory, Jagiellonian University, Orla 171, 30-244 Krakow (Poland); Marc Kac Complex Systems Research Center, Jagiellonian University, Reymonta 4, 30-059 Krakow (Poland)], E-mail: uoszydlo@cyf-kr.edu.pl; Hrycyna, Orest [Department of Theoretical Physics, Faculty of Philosophy, John Paul II Catholic University of Lublin, Al. Raclawickie 14, 20-950 Lublin (Poland)], E-mail: hrycyna@kul.lublin.pl

    2007-12-15

    All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analyzed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property-acceleration-is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in a one-dimensional potential which is parameterized by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We characterize the class of dark energy models that admit late time de Sitter attractor solution in terms of the potential function of corresponding conservative system. We argue that inclusion of dissipation effects makes the model more realistic because of its structural stability. We also confront viscous models with SNIa observations. The best fitted models are obtained by minimizing the {chi}{sup 2} function which is illustrated by residuals and {chi}{sup 2} levels in the space of model independent parameters. The general conclusion is that SNIa data supports the viscous model without the cosmological constant. The obtained values of {chi}{sup 2} statistic are comparable for both the viscous model and {lambda}CDM model. The Bayesian information criteria are used to compare the models with different power-law parameterization of viscous effects. Our result of this analysis shows that SNIa data supports viscous cosmology more than the {lambda}CDM model if the coefficient in viscosity parameterization is fixed. The Bayes factor is also used to obtain the posterior probability of the model.

  8. Bright, dark, and mixed vector soliton solutions of the general coupled nonlinear Schrödinger equations.

    PubMed

    Agalarov, Agalar; Zhulego, Vladimir; Gadzhimuradov, Telman

    2015-04-01

    The reduction procedure for the general coupled nonlinear Schrödinger (GCNLS) equations with four-wave mixing terms is proposed. It is shown that the GCNLS system is equivalent to the well known integrable families of the Manakov and Makhankov U(n,m)-vector models. This equivalence allows us to construct bright-bright and dark-dark solitons and a quasibreather-dark solution with unconventional dynamics: the density of the first component oscillates in space and time, whereas the density of the second component does not. The collision properties of solitons are also studied. PMID:25974564

  9. Probing Dark Energy with Constellation-X

    SciTech Connect

    Rapetti, David; Allen, Steven W.; /KIPAC, Menlo Park

    2006-09-08

    Constellation-X (Con-X) will carry out two powerful and independent sets of tests of dark energy based on X-ray observations of galaxy clusters, providing comparable accuracy to other leading dark energy probes. The first group of tests will measure the absolute distances to clusters, primarily using measurements of the X-ray gas mass fraction in the largest, dynamically relaxed clusters, but with additional constraining power provided by follow-up observations of the Sunyaev-Zel'dovich (SZ) effect. As with supernovae studies, such data determine the transformation between redshift and true distance, d(z), allowing cosmic acceleration to be measured directly. The second, independent group of tests will use the exquisite spectroscopic capabilities of Con-X to determine scaling relations between X-ray observables and mass. Together with forthcoming X-ray and SZ cluster surveys, these data will help to constrain the growth of structure, which is also a strong function of cosmological parameters.

  10. Effects of shear and rotation on the spherical collapse model for clustering dark energy

    NASA Astrophysics Data System (ADS)

    Pace, Francesco; Batista, Ronaldo C.; Del Popolo, Antonino

    2014-11-01

    In the framework of the spherical collapse model, we study the influence of shear and rotation terms for dark matter fluid in clustering dark energy models. We evaluate, for different equations of state, the effects of these terms on the linear overdensity threshold parameter, ?c, and on the virial overdensity, ?V. The evaluation of their effects on ?c allows us to infer the modifications occurring on the mass function. Due to ambiguities in the definition of the halo mass in the case of clustering dark energy, we consider two different situations: the first is the classical one where the mass is of the dark matter halo only, while the second one is given by the sum of the mass of dark matter and dark energy. As previously found, the spherical collapse model becomes mass dependent and the two additional terms oppose the collapse of the perturbations, especially on galactic scales, with respect to the spherical non-rotating model, while on cluster scales the effects of shear and rotation become negligible. The values for ?c and ?V are higher than the standard spherical model. Regarding the effects of the additional non-linear terms on the mass function, we evaluate the number density of haloes. As expected, major differences appear at high masses and redshifts. In particular, quintessence (phantom) models predict more (less) objects with respect to the ? colddarkmatter model, and the mass correction due to the contribution of the dark energy component has negligible effects on the overall number of structures.

  11. Dark matter and dark energy from the solution of the strong CP problem.

    PubMed

    Mainini, Roberto; Bonometto, Silvio A

    2004-09-17

    The Peccei-Quinn (PQ) solution of the strong CP problem requires the existence of axions, which are viable candidates for dark matter. If the Nambu-Goldstone potential of the PQ model is replaced by a potential V(|Phi|) admitting a tracker solution, the scalar field |Phi| can account for dark energy, while the phase of Phi yields axion dark matter. If V is a supergravity (SUGRA) potential, the model essentially depends on a single parameter, the energy scale Lambda. Once we set Lambda approximately equal to 10(10) GeV at the quark-hadron transition, |Phi| naturally passes through values suitable to solve the strong CP problem, later growing to values providing fair amounts of dark matter and dark energy. PMID:15447249

  12. Detecting dark matter-dark energy coupling with the halo mass function

    E-print Network

    P. M. Sutter; P. M. Ricker

    2008-10-03

    We use high-resolution simulations of large-scale structure formation to analyze the effects of interacting dark matter and dark energy on the evolution of the halo mass function. Using a chi-square likelihood analysis, we find significant differences in the mass function between models of coupled dark matter-dark energy and standard concordance cosmology Lambda-CDM out to redshift z=1.5. We also find a preliminary indication that the Dark Energy Survey should be able to distinguish these models from Lambda-CDM within its mass and redshift contraints. While we can distinguish the effects of these models from Lambda-CDM cosmologies with different fundamental parameters, DES will require independent measurements of sigma-8 to confirm these effects.

  13. Observational constraints on a unified dark matter and dark energy model based on generalized Chaplygin gas

    Microsoft Academic Search

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

    2010-01-01

    We study a generalized version of Chaplygin gas as unified model of dark matter and dark energy. Using realistic theoretical models and the currently available observational data from the age of the universe, the expansion history based on the type Ia supernovae, the matter power spectrum, the cosmic microwave background radiation anisotropy power spectra, and the perturbation growth factor we

  14. Constraints on unified models for dark matter and dark energy using H( z)

    Microsoft Academic Search

    Júlio C. Fabris; Paulo L. C. de Oliveira; Hermano Velten

    2011-01-01

    The differential age data of astrophysical objects that have evolved passively during the history of the universe (e.g. red galaxies) allows us to test theoretical cosmological models through the predicted Hubble function expressed in terms of the redshift z, H( z). We use the observational data for H( z) to test unified scenarios for dark matter and dark energy. Specifically,

  15. Coincidences of Dark Energy with Dark Matter: Clues for a Simple Alternative?

    Microsoft Academic Search

    HongSheng Zhao

    2007-01-01

    A rare coincidence of scales in standard particle physics is needed to explain why Lambda or the negative pressure of cosmological dark energy (DE) coincides with the positive pressure P0 of random motion of dark matter (DM) in bright galaxies. Recently Zlosnik and coworkers proposed to modify the Einstein curvature by adding nonlinear pressure from a medium flowing with a

  16. Holographic field theory models of dark energy in interaction with dark matter

    Microsoft Academic Search

    Sandro M. R. Micheletti

    2010-01-01

    We discuss two lagrangian interacting dark energy models in the context of the holographic principle. The potentials of the interacting fields are constructed. The models are compared with CMB distance information, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. For both models the results are consistent with a non vanishing interaction between dark sectors - with more than

  17. Effects of f(R) Dark Energy on Dissipative Anisotropic Collapsing Fluid

    Microsoft Academic Search

    M. Sharifand; H. Rizwana Kausar

    2010-01-01

    The purpose of this paper is to study the effects of dark energy on dynamics of the collapsing fluid within the framework of metric f(R) gravity. The fluid distribution is assumed to be locally anisotropic and undergoing dissipation in the form of heat flow, null radiations and shear viscosity. For this purpose, we take general spherical symmetric spacetime. Dynamical equations

  18. Testing the interaction of dark energy to dark matter through the analysis of virial relaxation of clusters Abell Clusters A586 and A1689 using realistic density profiles

    E-print Network

    Testing the interaction of dark energy to dark matter through the analysis of virial relaxation´onoma de Madrid Cantoblanco, 28049 Madrid SPAIN Interaction between dark energy and dark matter is probed for evidence and possible strategies for de- tection of dark energy and dark matter are among the most pressing

  19. Spherical collapse model and cluster formation beyond the {lambda} cosmology: Indications for a clustered dark energy?

    SciTech Connect

    Basilakos, Spyros; Sanchez, Juan Carlos Bueno; Perivolaropoulos, Leandros [Academy of Athens, Research Center for Astronomy and Applied Mathematics, Soranou Efesiou 4, 11527 Athens (Greece); Department of Physics, University of Ioannina, 45110 Ioannina (Greece)

    2009-08-15

    We generalize the small scale dynamics of the Universe by taking into account models with an equation of state which evolves with time, and provide a complete formulation of the cluster virialization attempting to address the nonlinear regime of structure formation. In the context of the current dark energy models, we find that galaxy clusters appear to form at z{approx}1-2, in agreement with previous studies. Also, we investigate thoroughly the evolution of spherical matter perturbations, as the latter decouple from the background expansion and start to 'turn around' and finally collapse. Within this framework, we find that the concentration parameter depends on the choice of the considered dark energy (homogeneous or clustered). In particular, if the distribution of the dark energy is clustered then we produce more concentrated structures with respect to the homogeneous dark energy. Finally, comparing the predicted concentration parameter with the observed concentration parameter, measured for four massive galaxy clusters, we find that the scenario which contains a pure homogeneous dark energy is unable to reproduce the data. The situation becomes somewhat better in the case of an inhomogeneous (clustered) dark energy.

  20. Covariance of dark energy parameters and sound speed constraints from large HI surveys

    E-print Network

    A. Torres-Rodriguez; C. M. Cress; K. Moodley

    2008-04-15

    An interesting probe of the nature of dark energy is the measure of its sound speed, $c_s$. We review the significance for constraining sound speed models of dark energy using large neutral hydrogen (HI) surveys with the Square Kilometre Array (SKA). Our analysis considers the effect on the sound speed measurement that arises from the covariance of $c_s$ with the dark energy density, $\\Omega_\\LLambda$, and a time-varying equation of state, $w(a)=w_0+(1-a)w_a$. We find that the approximate degeneracy between dark energy parameters that arises in power spectrum observations is lifted through redshift tomography of the HI-galaxy angular power spectrum, resulting in sound speed constraints that are not severely degraded. The cross-correlation of the galaxy and the integrated Sachs-Wolfe (ISW) effect spectra contributes approximately 10 percent of the information that is needed to distinguish variations in the dark energy parameters, and most of the discriminating signal comes from the galaxy auto-correlation spectrum. We also find that the sound speed constraints are weakly sensitive to the HI bias model. These constraints do not improve substantially for a significantly deeper HI survey since most of the clustering sensitivity to sound speed variations arises from $z \\lsim 1.5$. A detection of models with sound speeds close to zero, $c_s \\lsim 0.01,$ is possible for dark energy models with $w\\gsim -0.9$.

  1. 9/24/09 2:12 PMErasing Dark Energy SEEDMAGAZINE.COM Page 1 of 23http://seedmagazine.com/content/article/erasing_dark_energy/

    E-print Network

    Temple, Blake

    9/24/09 2:12 PMErasing Dark Energy § SEEDMAGAZINE.COM Page 1 of 23http://seedmagazine.com/content/article/erasing_dark_energy » Follow us on Twitter » Erasing Dark Energy Wide Angle / by Veronique Greenwood / September 24, 2009 Why do we need dark energy to explain the observable universe? Two mathematicians propose an alternate

  2. The coincidence problem in the scenario of dark energy interacting with two fluids

    E-print Network

    Norman Cruz; Samuel Lepe; Francisco Pena

    2009-10-07

    A cosmological model of dark energy interacting with dark matter and another general component of the universe is considered. The evolution equations for coincidence parameters r and s, which represent the ratios between the dark energy and the matter and the other cosmic fluid, respectively, are analyzed in terms of the stability of stationary solutions. The obtained general results allow to shed some light on the coincidence problem and in the equations of state of the three interacting fluids, due to the constraints imposes by the stability of the solutions. We found that for an interaction proportional to the sum of the DE density and the third fluid density, the hypothetical fluid must have positive pressure, which leads naturally to a cosmological scenario with radiation, unparticle or even some form of warm DM as the third interacting fluid.

  3. Thermodynamical Behaviors of Nonflat Brans-Dicke Gravity with Interacting New Agegraphic Dark Energy

    NASA Astrophysics Data System (ADS)

    Wu, Ya-Bo; Zhang, Xue; Lu, Jian-Bo; Zhao, Yue-Yue; Lu, Jun-Wang; Yu, Fang

    2014-12-01

    The dynamical behaviors of Brans-Dicke gravity with the interacting new agegraphic dark energy (NADE) model are studied in this paper. First of all, by considering the dark energy density ?de = 3n2??-2, the evolutions of the equation of state and the deceleration parameter can be described in the framework of Friedmann-Robertson-Walker universe. Moreover, the field equations of the Brans-Dicke gravity can be cast to the form of the first law of thermodynamics with the so-called entropy production term d˜ {S}. Furthermore, the generalized second law of thermodynamics can be given in nonflat Brans-Dicke gravity with the interacting NADE enclosed by the dynamical apparent horizon with Hawking temperature. Finally, when the interaction between NADE and dark matter is considered as a fluctuation around the thermal equilibrium, it can be written to a form of logarithmic correction, and the expression of the interaction term can be obtained.

  4. Dark Energy, Anthropic Selection Effects, Entropy and Life

    Microsoft Academic Search

    Chas A. Egan

    2010-01-01

    According to the standard LCDM model, the matter and dark energy densities (rho_m and rho_DE) are only comparable for a brief time. We address the cosmic coincidence problem under LCDM and generalized dark energy models by considering the temporal distribution of terrestrial planets. We compare the Sun to representative stellar samples in 11 properties plausibly related to life. We find

  5. Evolution of the horizons for dark energy universe

    E-print Network

    Ritabrata Biswas; Nairwita Mazumder; Subenoy Chakraborty

    2011-06-12

    Recent observational evidences of accelerating phase of the universe strongly demand that the dominating matter in the universe is in the form of dark energy. In this work, we study the evolution of the apparent and event horizons for various dark energy models and examine their behavior across phantom barrier line.

  6. Revealing Dark Energy with the Next Generations of Supernova Surveys

    Microsoft Academic Search

    E. Linder

    2002-01-01

    The accelerating expansion of the universe suggests that an unknown component with strongly negative pressure, called dark energy, currently dominates the dynamics of the universe. The best method for exploring the nature of this dark energy is to map the recent expansion history, at which Type Ia supernovae have proved adept. We examine here the depth of survey necessary to

  7. Logarithmic entropy corrected holographic dark energy with nonminimal kinetic coupling

    NASA Astrophysics Data System (ADS)

    Amani, Ali R.; Sadeghi, J.; Farajollahi, H.; Pourali, M.

    2012-01-01

    In this paper, we have considered a cosmological model with the non--minimal kinetic coupling terms and investigated its cosmological implications with respect to the logarithmic entropy-- corrected holographic dark energy (LECHDE). The correspondence between LECHDE in flat FRW cosmology and the phantom dark energy model with the aim to interpret the current universe acceleration is also examined.

  8. Observatory conceptual development for the Joint Dark Energy Mission

    NASA Astrophysics Data System (ADS)

    Sholl, Michael J.; Bernstein, Gary M.; Content, David A.; Dittman, Michael G.; Howard, Joseph M.; Lampton, Michael L.; Lehan, John P.; Mentzell, J. Eric; Woodruff, Robert A.

    2009-08-01

    The Joint Dark Energy Mission (JDEM)1,2 is a proposed dark energy space mission that will measure the expansion history of the universe and the growth of its large scale structure. It is intended to provide tight constraints on the equation of state of the universe and test the validity of general relativity. Three complementary observational analyses will be employed: Baryon Acoustic Oscillations, Type 1a Supernovae and Gravitational Weak Lensing. An observatory designed for efficient accommodation of these techniques combines wide-field, diffraction-limited observations, ultra-stable point spread function, and spectroscopy. In this paper we discuss optical configurations capable of simultaneous wide-field imaging and spectroscopy, using either afocal or focal telescope configurations. Spectroscopy may be performed by an integral field unit (IFU), grism or prism spectrometer. We present a flowdown of weak lensing image stability requirements (the most demanding technique optically) to telescope thermo-mechanical stability limits, based on variations in the optical transfer function of combinations of Zernike modes, and the sensitivity of these mode combinations to thermo-mechanical drift of the telescope. We apply our formalism to a representative threemirror anastigmat telescope and find quantitative relations between the second moments of the image and the required stability of the telescope over a typical weak lensing observation.

  9. Dark Energy Survey: understanding the acceleration of the Universe

    NASA Astrophysics Data System (ADS)

    Hao, Jiangang

    2013-04-01

    The Dark Energy Survey (DES) is a next generation optical survey aimed at understanding the expansion rate of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. Using a new 570 Megapixel CCD camera mounted on the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory in Chile, the survey will image over 5000 square-degrees of the southern galactic cap with 5 filters (g, r, i, z, Y) in 5 years and improve the constraints on the evolution of the equation of state of Dark Energy by a factor of 3 - 5. After achieving first light on Sept. 12, 2012, the DES is moving forward at amazing speed. Commissioning was carried out in Sept-Oct., 2012, followed by Science Verification that was successfully completed by February 2013. During the Science Verification, DES has been focusing on three patches of the sky, imaging a couple of hundred square degrees at full DES depth. Of the three patches, one is along the southern celestial equatorial region, overlapping with many existing optical surveys for better calibration, and the other two are overlapping with the South Pole Telescope (SPT) Sunyaev-Zel'dovich survey in the southern sky. The official survey will start in Sept. 2013 and a lot of exciting science is just ahead.

  10. Observational constraints on holographic dark energy with varying gravitational constant

    SciTech Connect

    Lu, Jianbo; Xu, Lixin [Institute of Theoretical Physics, School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian, 116024 (China); Saridakis, Emmanuel N. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing, 400065 (China); Setare, M.R., E-mail: lvjianbo819@163.com, E-mail: msaridak@phys.uoa.gr, E-mail: rezakord@ipm.ir, E-mail: lxxu@dlut.edu.cn [Department of Science of Bijar, University of Kurdistan, Bijar (Iran, Islamic Republic of)

    2010-03-01

    We use observational data from Type Ia Supernovae (SN), Baryon Acoustic Oscillations (BAO), Cosmic Microwave Background (CMB) and observational Hubble data (OHD), and the Markov Chain Monte Carlo (MCMC) method, to constrain the cosmological scenario of holographic dark energy with varying gravitational constant. We consider both flat and non-flat background geometry, and we present the corresponding constraints and contour-plots of the model parameters. We conclude that the scenario is compatible with observations. In 1? we find ?{sub ?0} = 0.72{sup +0.03}{sub ?0.03}, ?{sub k0} = ?0.0013{sup +0.0130}{sub ?0.0040}, c = 0.80{sup +0.19}{sub ?0.14} and ?{sub G}?G'/G = ?0.0025{sup +0.0080}{sub ?0.0050}, while for the present value of the dark energy equation-of-state parameter we obtain w{sub 0} = ?1.04{sup +0.15}{sub ?0.20}.

  11. Observational constraints on a variable dark energy model

    SciTech Connect

    Movahed, M. Sadegh [Department of Physics, Sharif University of Technology, P.O.Box 11365-9161, Tehran (Iran, Islamic Republic of); Institute for Studies in theoretical Physics and Mathematics, P.O.Box 19395-5531, Tehran (Iran, Islamic Republic of); Iran Space Agency, P.O.Box 199799-4313, Tehran (Iran, Islamic Republic of); Rahvar, Sohrab [Department of Physics, Sharif University of Technology, P.O.Box 11365-9161, Tehran (Iran, Islamic Republic of); Institute for Studies in theoretical Physics and Mathematics, P.O.Box 19395-5531, Tehran (Iran, Islamic Republic of)

    2006-04-15

    We study the effect of a phenomenological parameterized quintessence model on low, intermediate and high redshift observations. At low and intermediate redshifts, we use the Gold sample of supernova Type Ia (SNIa) data and recently observed size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), to put constraint on the parameters of the quintessence model. At the high redshift, the same fitting procedure is done using WAMP data, comparing the location of acoustic peak with that obtain from the dark energy model. As a complementary analysis in a flat universe, we combine the results from the SNIa, CMB and SDSS. The best fit values for the model parameters are {omega}{sub m}=0.27{sub -0.02}{sup +0.02} (the present matter content) and w{sub 0}=-1.45{sub -0.60}{sup +0.35} (dark energy equation of state). Finally we calculate the age of universe in this model and compare it with the age of old stars and high redshift objects.

  12. Generalized dark-bright vector soliton solution to the mixed coupled nonlinear Schrödinger equations

    NASA Astrophysics Data System (ADS)

    Manikandan, N.; Radhakrishnan, R.; Aravinthan, K.

    2014-08-01

    We have constructed a dark-bright N-soliton solution with 4N+3 real parameters for the physically interesting system of mixed coupled nonlinear Schrödinger equations. Using this as well as an asymptotic analysis we have investigated the interaction between dark-bright vector solitons. Each colliding dark-bright one-soliton at the asymptotic limits includes more coupling parameters not only in the polarization vector but also in the amplitude part. Our present solution generalizes the dark-bright soliton in the literature with parametric constraints. By exploiting the role of such coupling parameters we are able to control certain interaction effects, namely beating, breathing, bouncing, attraction, jumping, etc., without affecting other soliton parameters. Particularly, the results of the interactions between the bound state dark-bright vector solitons reveal oscillations in their amplitudes under certain parametric choices. A similar kind of effect was also observed experimentally in the BECs. We have also characterized the solutions with complicated structure and nonobvious wrinkle to define polarization vector, envelope speed, envelope width, envelope amplitude, grayness, and complex modulation. It is interesting to identify that the polarization vector of the dark-bright one-soliton evolves on a spherical surface instead of a hyperboloid surface as in the bright-bright case of the mixed coupled nonlinear Schrödinger equations.

  13. The CHASE laboratory search for chameleon dark energy

    E-print Network

    Jason H. Steffen; for the GammeV-CHASE collaboration

    2010-11-17

    A scalar field is a favorite candidate for the particle responsible for dark energy. However, few theoretical means exist that can simultaneously explain the observed acceleration of the Universe and evade tests of gravity. The chameleon mechanism, whereby the properties of a particle depend upon the local environment, is one possible avenue. We present the results of the Chameleon Afterglow Search (CHASE) experiment, a laboratory probe for chameleon dark energy. CHASE marks a significant improvement other searches for chameleons both in terms of its sensitivity to the photon/chameleon coupling as well as its sensitivity to the classes of chameleon dark energy models and standard power-law models. Since chameleon dark energy is virtually indistinguishable from a cosmological constant, CHASE tests dark energy models in a manner not accessible to astronomical surveys.

  14. On the nature of dark energy: the lattice Universe

    NASA Astrophysics Data System (ADS)

    Villata, M.

    2013-05-01

    There is something unknown in the cosmos. Something big. Which causes the acceleration of the Universe expansion, that is perhaps the most surprising and unexpected discovery of the last decades, and thus represents one of the most pressing mysteries of the Universe. The current standard ?CDM model uses two unknown entities to make everything fit: dark energy and dark matter, which together would constitute more than 95 % of the energy density of the Universe. A bit like saying that we have understood almost nothing, but without openly admitting it. Here we start from the recent theoretical results that come from the extension of general relativity to antimatter, through CPT symmetry. This theory predicts a mutual gravitational repulsion between matter and antimatter. Our basic assumption is that the Universe contains equal amounts of matter and antimatter, with antimatter possibly located in cosmic voids, as discussed in previous works. From this scenario we develop a simple cosmological model, from whose equations we derive the first results. While the existence of the elusive dark energy is completely replaced by gravitational repulsion, the presence of dark matter is not excluded, but not strictly required, as most of the related phenomena can also be ascribed to repulsive-gravity effects. With a matter energy density ranging from ˜5 % (baryonic matter alone, and as much antimatter) to ˜25 % of the so-called critical density, the present age of the Universe varies between about 13 and 15 Gyr. The SN Ia test is successfully passed, with residuals comparable with those of the ?CDM model in the observed redshift range, but with a clear prediction for fainter SNe at higher z. Moreover, this model has neither horizon nor coincidence problems, and no initial singularity is requested. In conclusion, we have replaced all the tough problems of the current standard cosmology (including the matter-antimatter asymmetry) with only one question: is the gravitational interaction between matter and antimatter really repulsive as predicted by the theory and as the observation of the Universe seems to suggest? We are awaiting experimental responses.

  15. A critical value for dark energy

    E-print Network

    Rowlands, Peter

    2013-01-01

    Experimental evidence over a number of recent years has shown the density parameter of the universe omega converging to the critical value of 1, which defines a flat, Euclidean universe. No such calculations have defined a critical value for the most significant component of omega, that for the dark energy, omega lambda, but the new data provided by the Planck probe open up the previously unconsidered possibility that a particular value with special physical significance occurs at omega lambda = 2/3. If future observations should converge on exactly this value, then we may have the first indication that the explanation for this phenomenon lies in necessary constraints provided by fundamental laws of physics on possible cosmologies for the universe.

  16. Neutrino dark energy in grand unified theories

    NASA Astrophysics Data System (ADS)

    Bhatt, Jitesh R.; Gu, Pei-Hong; Sarkar, Utpal; Singh, Santosh K.

    2009-10-01

    We studied a left-right symmetric model that can accommodate the neutrino dark energy (?DE) proposal. The type-III seesaw mechanism is implemented to give masses to the neutrinos. After explaining the model, we study the consistency of the model by minimizing the scalar potential and obtaining the conditions for the required vacuum expectation values of the different scalar fields. This model is then embedded in an SO(10) grand unified theory and the allowed symmetry breaking scales are determined by the condition of the gauge coupling unification. Although SU(2)R breaking is required to be high, its Abelian subgroup U(1)R is broken in the TeV range, which can then give the required neutrino masses and predicts new gauge bosons that could be detected at LHC. The neutrino masses are studied in detail in this model, which shows that at least 3 singlet fermions are required.

  17. Probing Dark Energy models with neutrons

    E-print Network

    Pignol, G

    2015-01-01

    There is a deep connection between cosmology -- the science of the infinitely large --and particle physics -- the science of the infinitely small. This connection is particularly manifest in neutron particle physics. Basic properties of the neutron -- its Electric Dipole Moment and its lifetime -- are intertwined with baryogenesis and nucleosynthesis in the early Universe. I will cover this topic in the first part, that will also serve as an introduction (or rather a quick recap) of neutron physics and Big Bang cosmology. Then, the rest of the manuscript will be devoted to a new idea: using neutrons to probe models of Dark Energy. In the second part, I will present the chameleon theory: a light scalar field accounting for the late accelerated expansion of the Universe, which interacts with matter in such a way that it does not mediate a fifth force between macroscopic bodies. However, neutrons can alleviate the chameleon mechanism and reveal the presence of the scalar field with properly designed experiments....

  18. A critical value for dark energy

    E-print Network

    Peter Rowlands

    2013-05-30

    Experimental evidence over a number of recent years has shown the density parameter of the universe omega converging to the critical value of 1, which defines a flat, Euclidean universe. No such calculations have defined a critical value for the most significant component of omega, that for the dark energy, omega lambda, but the new data provided by the Planck probe open up the previously unconsidered possibility that a particular value with special physical significance occurs at omega lambda = 2/3. If future observations should converge on exactly this value, then we may have the first indication that the explanation for this phenomenon lies in necessary constraints provided by fundamental laws of physics on possible cosmologies for the universe.

  19. A bound system in the expanding universe with modified holographic Ricci dark energy and dark matter

    E-print Network

    En-Kun Li; Yu Zhang; Jin-Ling Geng; Peng-Fei Duan

    2015-02-12

    The evolution of a bound system in the expanding background has been investigated in this paper. The background is described by a FRW universe with the modified holographic dark energy model, whose equation of state parameter changes with time and can cross the phantom boundary. To study the evolution of the bound system, an interpolating metric is considered, and on this basis the geodesics of a test particle are given. The equation of motion and the effective potential are also derived from the geodesics. By studying the the effective potential and the evolution of the radius of a test particle in the bound system of the Milky Way galaxy, we have found that the galaxy would go through three stages: expands from a singular point; stays in a discoid for a period of time; big rip in the future. With the help of analysing the critical angular momentum, we find that the test particle needs less angular momentum to escape from the center mass as time passes.

  20. Cosmic slowing down of acceleration for several dark energy parametrizations

    NASA Astrophysics Data System (ADS)

    Magaña, Juan; Cárdenas, Víctor H.; Motta, Verónica

    2014-10-01

    We further investigate slowing down of acceleration of the universe scenario for five parametrizations of the equation of state of dark energy using four sets of Type Ia supernovae data. In a maximal probability analysis we also use the baryon acoustic oscillation and cosmic microwave background observations. We found the low redshift transition of the deceleration parameter appears, independently of the parametrization, using supernovae data alone except for the Union 2.1 sample. This feature disappears once we combine the Type Ia supernovae data with high redshift data. We conclude that the rapid variation of the deceleration parameter is independent of the parametrization. We also found more evidence for a tension among the supernovae samples, as well as for the low and high redshift data.

  1. Cosmic slowing down of acceleration for several dark energy parametrizations

    E-print Network

    Juan Magaña; Víctor H. Cárdenas; V. Motta

    2014-09-08

    We further investigate slowing down of acceleration of the universe scenario for five parametrizations of the equation of state of dark energy using four sets of supernovae data. In a maximal probability analysis we also use the baryon acoustic oscillation and cosmic microwave background observations. We found the low redshift transition of the deceleration parameter appears, independently of the parametrization, using supernovae data alone except for the Union 2.1 sample. This feature disappears once we combine the supernova data with high redshift data. We conclude that the rapid variation of the deceleration parameter is independent of the parametrization. We also found more evidence for a tension among the supernovae samples, as well as for the low and high redshift data.

  2. Physical approximations for the nonlinear evolution of perturbations in inhomogeneous dark energy scenarios

    NASA Astrophysics Data System (ADS)

    Abramo, L. R.; Batista, R. C.; Liberato, L.; Rosenfeld, R.

    2009-01-01

    The abundance and distribution of collapsed objects such as galaxy clusters will become an important tool to investigate the nature of dark energy and dark matter. Number counts of very massive objects are sensitive not only to the equation of state of dark energy, which parametrizes the smooth component of its pressure, but also to the sound speed of dark energy, which determines the amount of pressure in inhomogeneous and collapsed structures. Since the evolution of these structures must be followed well into the nonlinear regime, and a fully relativistic framework for this regime does not exist yet, we compare two approximate schemes: the widely used spherical collapse model and the pseudo-Newtonian approach. We show that both approximation schemes convey identical equations for the density contrast, when the pressure perturbation of dark energy is parametrized in terms of an effective sound speed. We also make a comparison of these approximate approaches to general relativity in the linearized regime, which lends some support to the approximations.

  3. Holographic dark energy reconstruction in gravity

    NASA Astrophysics Data System (ADS)

    Salako, Ines G.; Jawad, Abdul; Chattopadhyay, Surajit

    2015-07-01

    The present paper reports a holographic reconstruction scheme for gravity proposed in Harko et al. (J. Cosmol. Astropart. Phys. 12:021, 2014), where is the torsion scalar and is the trace of the energy-momentum tensor considering future event horizon as the enveloping horizon of the universe. We consider and for reconstruction. We also extract the equation of state parameter for these models. We also give the comparison of the results with observational data and found the consistency of our results.

  4. arXiv:astro-ph/0401559v126Jan2004 Self-Calibration of Cluster Dark Energy Studies: Counts in Cells

    E-print Network

    Hu, Wayne

    arXiv:astro-ph/0401559v126Jan2004 Self-Calibration of Cluster Dark Energy Studies: Counts in Cells of Chicago, Chicago IL 60637 Cluster number counts can constrain the properties of dark energy if and only constraints on the dark energy equation of state by a factor of 2 or more to (w) = 0.06 for a deep 4000 deg2

  5. Interacting two-fluid viscous dark energy models in a non-flat universe

    NASA Astrophysics Data System (ADS)

    Amirhashchi, Hassan; Pradhan, Anirudh; Zainuddin, Hishamuddin

    2013-02-01

    We study the evolution of the dark energy parameter within the scope of a spatially non-flat and isotropic Friedmann-Robertson-Walker model filled with barotropic fluid and bulk viscous stresses. We have obtained cosmological solutions that do not have a Big Rip singularity, and concluded that in both non-interacting and interacting cases the non-flat open Universe crosses the phantom region. We find that during the evolution of the Universe, the equation of state for dark energy ?D changes from ?effD > -1 to ?effD < -1, which is consistent with recent observations.

  6. LSST Probes of Dark Energy: New Energy vs New Gravity

    NASA Astrophysics Data System (ADS)

    Bradshaw, Andrew; Tyson, A.; Jee, M. J.; Zhan, H.; Bard, D.; Bean, R.; Bosch, J.; Chang, C.; Clowe, D.; Dell'Antonio, I.; Gawiser, E.; Jain, B.; Jarvis, M.; Kahn, S.; Knox, L.; Newman, J.; Wittman, D.; Weak Lensing, LSST; LSS Science Collaborations

    2012-01-01

    Is the late time acceleration of the universe due to new physics in the form of stress-energy or a departure from General Relativity? LSST will measure the shape, magnitude, and color of 4x109 galaxies to high S/N over 18,000 square degrees. These data will be used to separately measure the gravitational growth of mass structure and distance vs redshift to unprecedented precision by combining multiple probes in a joint analysis. Of the five LSST probes of dark energy, weak gravitational lensing (WL) and baryon acoustic oscillation (BAO) probes are particularly effective in combination. By measuring the 2-D BAO scale in ugrizy-band photometric redshift-selected samples, LSST will determine the angular diameter distance to a dozen redshifts with sub percent-level errors. Reconstruction of the WL shear power spectrum on linear and weakly non-linear scales, and of the cross-correlation of shear measured in different photometric redshift bins provides a constraint on the evolution of dark energy that is complementary to the purely geometric measures provided by supernovae and BAO. Cross-correlation of the WL shear and BAO signal within redshift shells minimizes the sensitivity to systematics. LSST will also detect shear peaks, providing independent constraints. Tomographic study of the shear of background galaxies as a function of redshift allows a geometric test of dark energy. To extract the dark energy signal and distinguish between the two forms of new physics, LSST will rely on accurate stellar point-spread functions (PSF) and unbiased reconstruction of galaxy image shapes from hundreds of exposures. Although a weighted co-added deep image has high S/N, it is a form of lossy compression. Bayesian forward modeling algorithms can in principle use all the information. We explore systematic effects on shape measurements and present tests of an algorithm called Multi-Fit, which appears to avoid PSF-induced shear systematics in a computationally efficient way.

  7. Modified Friedmann model in Randers-Finsler space of approximate Berwald type as a possible alternative to dark energy hypothesis

    E-print Network

    Zhe Chang; Xin Li

    2009-01-08

    Gravitational field equations in Randers-Finsler space of approximate Berwald type are investigated. A modified Friedmann model is proposed. It is showed that the accelerated expanding universe is guaranteed by a constrained Randers-Finsler structure without invoking dark energy. The geodesic in Randers-Finsler space is studied. The additional term in the geodesic equation acts as repulsive force against the gravity.

  8. A Possible Solution to the Smallness Problem of Dark Energy

    SciTech Connect

    Chen, Pisin; /SLAC; Gu, Je-An; /Taiwan, Natl. Taiwan U.

    2005-07-08

    The smallness of the dark energy density has been recognized as the most crucial difficulty in understanding dark energy and also one of the most important questions in the new century. In a recent paper[1], we proposed a new dark energy model in which the smallness of the cosmological constant is naturally achieved by invoking the Casimir energy in a supersymmetry-breaking brane-world. In this paper we review the basic notions of this model. Various implications, perspectives, and subtleties of this model are briefly discussed.

  9. Interaction between Tachyon and Hessence (or Hantom) dark energies

    E-print Network

    Surajit Chattopadhyay; Ujjal Debnath

    2010-10-07

    In this paper, we have considered that the universe is filled with tachyon, hessence (or hantom) dark energies. Subsequently we have investigated the interactions between tachyon and hessence (hantom) dark energies and calculated the potentials considering the power law form of the scale factor. It has been revealed that the tachyonic potential always decreases and hessence (or hantom) potential increases with corresponding fields. Furthermore, we have considered a correspondence between the hessence (or hantom) dark energy density and new variable modified Chaplygin gas energy density. From this, we have found the expressions of the arbitrary positive constants B0 and C of new variable modified Chaplygin gas.

  10. Effects of Electromagnetic Field on the Dynamics of Bianchi type $VI_0$ Universe with Anisotropic Dark Energy

    E-print Network

    M. Sharif; M. Zubair

    2010-08-04

    Spatially homogeneous and anisotropic Bianchi type $VI_0$ cosmological models with cosmological constant are investigated in the presence of anisotropic dark energy. We examine the effects of electromagnetic field on the dynamics of the universe and anisotropic behavior of dark energy. The law of variation of the mean Hubble parameter is used to find exact solutions of the Einstein field equations. We find that electromagnetic field promotes anisotropic behavior of dark energy which becomes isotropic for future evolution. It is concluded that the isotropic behavior of the universe model is seen even in the presence of electromagnetic field and anisotropic fluid.

  11. Studying the Nature of Dark Energy with Galaxy Clusters

    E-print Network

    Sarazin, Craig

    Studying the Nature of Dark Energy with Galaxy Clusters Thomas H. Reiprich 1 , Daniel S. Hudson 1, 53121 Bonn, Germany thomas@reiprich.net 2 Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903­0818, USA Summary. We report on the status of our e#ort to constrain the nature of dark

  12. Testing a DBI model for the unification of dark matter and dark energy with gamma-ray bursts

    NASA Astrophysics Data System (ADS)

    Montiel, Ariadna; Bretón, Nora

    2012-07-01

    We study the range of consistency of a model based on a nonlinear scalar field Dirac-Born-Infeld action for the unification of dark matter and dark energy using Gamma-Ray Bursts at high-redshifts. We use the sample of 59 high-redshift GRBs reported by Wei (2010), calibrated at low redshifts with the Union 2 sample of SNe Ia, thus avoiding the circularity problem. In this analysis, we also include the CMB7-year data and the baryonic acoustic peak BAO. Besides, it is calculated the parameter of the equation of state w, the deceleration parameter q0 and the redshift of the transition to the decelerate-accelerated phase zt.

  13. Co-existence of Gravity and Antigravity: The Unification of Dark Matter and Dark Energy

    E-print Network

    Xiang-Song Chen

    2005-06-07

    Massive gravity with second and fourth derivatives is shown to give both attractive and repulsive gravities. In contrast to the attractive gravity correlated with the energy-momentum tensor, the repulsive gravity is related to a fixed mass $m_x$, which equals a spin-dependent factor $f_\\sigma$ times the graviton mass. Therefore, particles with energy below $m_x$ are both dark matter and dark energy: Their overall gravity is attractive with normal matter but repulsive among themselves. Detailed analyses reveal that this unified dark scenario can properly account for the observed dark matter/energy phenomena: galaxy rotation curves, transition from early cosmic deceleration to recent acceleration; and naturally overcome other dark scenarios' difficulties: the substructure and cuspy core problems, the difference of dark halo distributions in galaxies and clusters, and the cosmic coincidence. Very interestingly, Dirac particles have $f_\\sigma=1/\\sqrt 2$, all bosonic matter particles have $f_\\sigma=0$, and the only exceptional boson is the graviton itself, which may have $f_\\sigma>1$.

  14. Dark energy with non-adiabatic sound speed: initial conditions and detectability

    E-print Network

    Guillermo Ballesteros; Julien Lesgourgues

    2010-10-27

    Assuming that the universe contains a dark energy fluid with a constant linear equation of state and a constant sound speed, we study the prospects of detecting dark energy perturbations using CMB data from Planck, cross-correlated with galaxy distribution maps from a survey like LSST. We update previous estimates by carrying a full exploration of the mock data likelihood for key fiducial models. We find that it will only be possible to exclude values of the sound speed very close to zero, while Planck data alone is not powerful enough for achieving any detection, even with lensing extraction. We also discuss the issue of initial conditions for dark energy perturbations in the radiation and matter epochs, generalizing the usual adiabatic conditions to include the sound speed effect. However, for most purposes, the existence of attractor solutions renders the perturbation evolution nearly independent of these initial conditions.

  15. Dark energy with non-adiabatic sound speed: initial conditions and detectability

    SciTech Connect

    Ballesteros, Guillermo [Museo Storico della Fisica e Centro Studi e Ricerche ''Enrico Fermi'', Piazza del Viminale 1, I-00184, Rome (Italy); Lesgourgues, Julien, E-mail: ballesteros@pd.infn.it, E-mail: julien.lesgourgues@cern.ch [CERN, Theory Division, CH-1211 Geneva 23 (Switzerland)

    2010-10-01

    Assuming that the universe contains a dark energy fluid with a constant linear equation of state and a constant sound speed, we study the prospects of detecting dark energy perturbations using CMB data from Planck, cross-correlated with galaxy distribution maps from a survey like LSST. We update previous estimates by carrying a full exploration of the mock data likelihood for key fiducial models. We find that it will only be possible to exclude values of the sound speed very close to zero, while Planck data alone is not powerful enough for achieving any detection, even with lensing extraction. We also discuss the issue of initial conditions for dark energy perturbations in the radiation and matter epochs, generalizing the usual adiabatic conditions to include the sound speed effect. However, for most purposes, the existence of attractor solutions renders the perturbation evolution nearly independent of these initial conditions.

  16. Testing for dynamical dark energy models with redshift-space distortions

    SciTech Connect

    Tsujikawa, Shinji [Department of Physics, Faculty of Science, Tokyo University of Science, 1-3, Kagurazaka, Shinjuku-ku, Tokyo 162-8601 (Japan); Felice, Antonio De [ThEP's CRL, NEP, The Institute for Fundamental Study, Naresuan University, Phitsanulok 65000 (Thailand); Alcaniz, Jailson, E-mail: shinji@rs.kagu.tus.ac.jp, E-mail: antoniod@nu.ac.th, E-mail: alcaniz@on.br [Departamento de Astronomia, Observatório Nacional, 20921-400 Rio de Janeiro - RJ (Brazil)

    2013-01-01

    The red-shift space distortions in the galaxy power spectrum can be used to measure the growth rate of matter density perturbations ?{sub m}. For dynamical dark energy models in General Relativity we provide a convenient analytic formula of f(z)?{sub 8}(z) written as a function of the redshift z, where f = dln ?{sub m}/dln a (a is the cosmological scale factor) and ?{sub 8} is the rms amplitude of over-density at the scale 8 h{sup ?1} Mpc. Our formula can be applied to the models of imperfect fluids, quintessence, and k-essence, provided that the dark energy equation of state w does not vary significantly and that the sound speed is not much smaller than 1. We also place observational constraints on dark energy models of constant w and tracking quintessence from the recent data of red-shift space distortions.

  17. See-Change: an HST program to probe Dark Energy time variation

    NASA Astrophysics Data System (ADS)

    Hayden, Brian; Perlmutter, Saul; Nordin, Jakob; Rubin, David; Lidman, Chris; Deustua, Susana E.; Fruchter, Andrew S.; Aldering, Greg Scott; Brodwin, Mark; Cunha, Carlos E.; Eisenhardt, Peter R.; Gonzalez, Anthony H.; Jee, Myungkook J.; Hildebrandt, Hendrik; Hoekstra, Henk; Santos, Joana; Stanford, S. Adam; Stern, Daniel; Fassbender, Rene; Richard, Johan; Rosati, Piero; Wechsler, Risa H.; Muzzin, Adam; Willis, Jon; Boehringer, Hans; Gladders, Michael; Goobar, Ariel; Amanullah, Rahman; Hook, Isobel; Huterer, Dragan; Huang, Xiaosheng; Kim, Alex G.; Kowalski, Marek; Linder, Eric; Pain, Reynald; Saunders, Clare; Suzuki, Nao; Barbary, Kyle H.; Rykoff, Eli S.; Meyers, Joshua; Sofiatti, Caroline; Wilson, Gillian; Rozo, Eduardo; Hilton, Matt; Spadafora, Anthony L.

    2015-01-01

    Using the Hubble Space Telescope, the Supernova Cosmology Project is performing a type Ia supernova search in the highest-redshift, most massive clusters known to date. This program was awarded 174 orbits spanning HST cycles 22-23. It will improve the constraint by a factor of 3 on the Dark Energy equation of state above z ~ 1, allowing an unprecedented probe of Dark Energy time variation. When combined with the improved cluster mass calibration provided by the deep WFC3-IR observations of the clusters, the SNe + clusters observed also will triple the Dark Energy Task Force Figure of Merit. We present the supernova survey strategy and cluster selection criteria, and discuss the first few months of the program.

  18. Spectroscopic Needs for Imaging Dark Energy Experiments

    DOE PAGESBeta

    Newman, Jeffrey A.; Slosar, Anze; Abate, Alexandra; Abdalla, Filipe B.; Allam, Sahar; Allen, Steven W.; Ansari, Reza; Bailey, Stephen; Barkhouse, Wayne A.; Beers, Timothy C.; et al

    2015-03-01

    Ongoing and near-future imaging-based dark energy experiments are critically dependent upon photometric redshifts (a.k.a. photo-z’s): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-z’s will result in smaller random errors on cosmological parameters; while systematic errors in photometric redshift estimates, if not constrained, may dominate all other uncertainties from these experiments. The desired optimization and calibration is dependent upon spectroscopic measurements for secure redshift information; this is the key application of galaxy spectroscopy for imaging-based dark energy experiments. Hence, to achieve their full potential, imaging-based experiments will require large setsmore »of objects with spectroscopically-determined redshifts, for two purposes: Training: Objects with known redshift are needed to map out the relationship between object color and z (or, equivalently, to determine empirically-calibrated templates describing the rest-frame spectra of the full range of galaxies, which may be used to predict the color-z relation). The ultimate goal of training is to minimize each moment of the distribution of differences between photometric redshift estimates and the true redshifts of objects, making the relationship between them as tight as possible. The larger and more complete our “training set” of spectroscopic redshifts is, the smaller the RMS photo-z errors should be, increasing the constraining power of imaging experiments; Requirements: Spectroscopic redshift measurements for ~30,000 objects over >~15 widely-separated regions, each at least ~20 arcmin in diameter, and reaching the faintest objects used in a given experiment, will likely be necessary if photometric redshifts are to be trained and calibrated with conventional techniques. Larger, more complete samples (i.e., with longer exposure times) can improve photo-z algorithms and reduce scatter further, enhancing the science return from planned experiments greatly (increasing the Dark Energy Task Force figure of merit by up to ~50%); Options: This spectroscopy will most efficiently be done by covering as much of the optical and near-infrared spectrum as possible at modestly high spectral resolution (?/?? > ~3000), while maximizing the telescope collecting area, field of view on the sky, and multiplexing of simultaneous spectra. The most efficient instrument for this would likely be either the proposed GMACS/MANIFEST spectrograph for the Giant Magellan Telescope or the OPTIMOS spectrograph for the European Extremely Large Telescope, depending on actual properties when built. The PFS spectrograph at Subaru would be next best and available considerably earlier, c. 2018; the proposed ngCFHT and SSST telescopes would have similar capabilities but start later. Other key options, in order of increasing total time required, are the WFOS spectrograph at TMT, MOONS at the VLT, and DESI at the Mayall 4 m telescope (or the similar 4MOST and WEAVE projects); of these, only DESI, MOONS, and PFS are expected to be available before 2020. Table 2-3 of this white paper summarizes the observation time required at each facility for strawman training samples. To attain secure redshift measurements for a high fraction of targeted objects and cover the full redshift span of future experiments, additional near-infrared spectroscopy will also be required; this is best done from space, particularly with WFIRST-2.4 and JWST; Calibration: The first several moments of redshift distributions (the mean, RMS redshift dispersion, etc.), must be known to high accuracy for cosmological constraints not to be systematics-dominated (equivalently, the moments of the distribution of differences between photometric and true redshifts could be determined instead). The ultimate goal of calibration is to characterize these moments for every subsample used in analyses - i.e., to minimize the uncertainty in their mean redshift, RMS dispersion, etc. – rather than to make the m

  19. Spectroscopic Needs for Imaging Dark Energy Experiments

    DOE PAGESBeta

    Newman, Jeffrey A. [Univ. of Pittsburgh and PITT PACC, PA (United States). Dept of Physics and Astronomy; Slosar, Anze [Brookhaven National Laboratory (BNL), Upton, NY (United States); Abate, Alexandra [Univ. of Arizona, Tucson, AZ (United States); Abdalla, Filipe B. [Univ. College London (United Kingdom); Allam, Sahar [Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States); Allen, Steven W. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Ansari, Reza [LAL Univ. Paris-Sud, Orsay (France); Bailey, Stephen [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Barkhouse, Wayne A. [Univ. of North Dakota, Grand Forks, ND (United States); Beers, Timothy C. [National Optical Astronomy Observations, Tucson, AZ (United States); Blanton, Michael R. [New York Univ., NY (United States); Brodwin, Mark [Univ. of Missouri at Kansas City, Kansas City, MO (United States); Brownstein, Joel R. [Univ. of Utah, Salt Lake City, UT (United States); Brunner, Robert J. [Illinois Univ., Urbana, IL (United States); Carrasco-Kind, Matias [Illinois Univ., Urbana, IL (United States); Cervantes-Cota, Jorge [Inst. Nacional de Investigaciones Nucleares (ININ), Escandon (Mexico); Chisari, Nora Elisa [Princeton Univ., Princeton, NJ (United States); Colless, Matthew [Australian National Univ., Canberra (Australia). Research School of Astronomy and Astrophysics; Comparat, Johan [Campus of International Excellence UAM and CSIC, Madrid (Spain); Coupon, Jean [Univ. of Geneva (Switzerland). Astronomical Observatory; Cheu, Elliott [Univ. of Arizona, Tucson, AZ (United States); Cunha, Carlos E. [Stanford Univ., Stanford, CA (United States). Kavli Inst. for Particle Astrophysics and Cosmology; de la Macorra, Alex [UNAM, Mexico City (Mexico). Dept. de Fisica Teorica and Inst. Avanzado de Cosmologia; Dell’Antonio, Ian P. [Brown Univ., Providence, RI (United States); Frye, Brenda L. [Univ. of Arizona, Tucson, AZ (United States); Gawiser, Eric J. [State Univ. of New Jersey, Piscataway, NJ (United States); Gehrels, Neil [NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Grady, Kevin [NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Hagen, Alex [Penn State Univ., University Park, PA (United States); Hall, Patrick B. [York Univ., Toronto, ON (Canada); Hearin, Andrew P. [Yale Univ., New Haven, CT (United States); Hildebrandt, Hendrik [Argelander-Inst. fuer Astronomie, Bonn (Germany); Hirata, Christopher M. [Ohio State Univ., Columbus, OH (United States); Ho, Shirley [Carnegie Mellon Univ., Pittsburgh, PA (United States). McWilliams Center for Cosmology; Honscheid, Klaus [Ohio State Univ., Columbus, OH (United States); Huterer, Dragan [Univ. of Michigan, Ann Arbor, MI (United States); Ivezic, Zeljko [Univ. of Washington, Seattle, WA (United States); Kneib, Jean -Paul [Laboratoire d'Astrophysique, Ecole Polytechnique Federale de Lausanne (EPFL) (Swizerland); Laboratoire d'Astrophysique de Marseille (France); Kruk, Jeffrey W. [NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Lahav, Ofer [Univ. College London, Bloomsbury (United Kingdom); Mandelbaum, Rachel [Carnegie Mellon Univ., Pittsburgh, PA (United States). McWilliams Center for Cosmology; Marshall, Jennifer L. [Texas A and M Univ., College Station, TX (United States); Matthews, Daniel J. [Univ. of Pittsburgh and PITT PACC, PA (United States). Dept of Physics and Astronomy; Menard, Brice [Johns Hopkins Univ., Baltimore, MD (United States); Miquel, Ramon [Univ. Autonoma de Barcelona (Spain). Inst. de Fisica d'Altes Energies (IFAE); Moniez, Marc [Univ. Paris-Sud, Orsay (France); Moos, H. W. [Johns Hopkins Univ., Baltimore, MD (United States); Moustakas, John [Siena College, Loudonville, NY (United States); Papovich, Casey [Texas A and M Univ., College Station, TX (United States); Peacock, John A. [Univ. of Edinburgh (United Kingdom). Inst. for Astronomy, Royal Observatory; Park, Changbom [Korea Inst. for Advanced Study, Seoul (Korea, Republic of); Rhodes, Jason [Jet Propulsion Lab./Caltech, Pasadena, CA (United States)

    2015-03-01

    Ongoing and near-future imaging-based dark energy experiments are critically dependent upon photometric redshifts (a.k.a. photo-z’s): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-z’s will result in smaller random errors on cosmological parameters; while systematic errors in photometric redshift estimates, if not constrained, may dominate all other uncertainties from these experiments. The desired optimization and calibration is dependent upon spectroscopic measurements for secure redshift information; this is the key application of galaxy spectroscopy for imaging-based dark energy experiments. Hence, to achieve their full potential, imaging-based experiments will require large sets of objects with spectroscopically-determined redshifts, for two purposes: Training: Objects with known redshift are needed to map out the relationship between object color and z (or, equivalently, to determine empirically-calibrated templates describing the rest-frame spectra of the full range of galaxies, which may be used to predict the color-z relation). The ultimate goal of training is to minimize each moment of the distribution of differences between photometric redshift estimates and the true redshifts of objects, making the relationship between them as tight as possible. The larger and more complete our “training set” of spectroscopic redshifts is, the smaller the RMS photo-z errors should be, increasing the constraining power of imaging experiments; Requirements: Spectroscopic redshift measurements for ~30,000 objects over >~15 widely-separated regions, each at least ~20 arcmin in diameter, and reaching the faintest objects used in a given experiment, will likely be necessary if photometric redshifts are to be trained and calibrated with conventional techniques. Larger, more complete samples (i.e., with longer exposure times) can improve photo-z algorithms and reduce scatter further, enhancing the science return from planned experiments greatly (increasing the Dark Energy Task Force figure of merit by up to ~50%); Options: This spectroscopy will most efficiently be done by covering as much of the optical and near-infrared spectrum as possible at modestly high spectral resolution (?/?? > ~3000), while maximizing the telescope collecting area, field of view on the sky, and multiplexing of simultaneous spectra. The most efficient instrument for this would likely be either the proposed GMACS/MANIFEST spectrograph for the Giant Magellan Telescope or the OPTIMOS spectrograph for the European Extremely Large Telescope, depending on actual properties when built. The PFS spectrograph at Subaru would be next best and available considerably earlier, c. 2018; the proposed ngCFHT and SSST telescopes would have similar capabilities but start later. Other key options, in order of increasing total time required, are the WFOS spectrograph at TMT, MOONS at the VLT, and DESI at the Mayall 4 m telescope (or the similar 4MOST and WEAVE projects); of these, only DESI, MOONS, and PFS are expected to be available before 2020. Table 2-3 of this white paper summarizes the observation time required at each facility for strawman training samples. To attain secure redshift measurements for a high fraction of targeted objects and cover the full redshift span of future experiments, additional near-infrared spectroscopy will also be required; this is best done from space, particularly with WFIRST-2.4 and JWST; Calibration: The first several moments of redshift distributions (the mean, RMS redshift dispersion, etc.), must be known to high accuracy for cosmological constraints not to be systematics-dominated (equivalently, the moments of the distribution of differences between photometric and true redshifts could be determined instead). The ultimate goal of calibration is to characterize these moments for every subsample used in analyses - i.e., to minimize the uncertainty in their mean redshift, RMS dispersion, etc. – rather than to make the moments themselve

  20. $f(T)$ theories from holographic dark energy models

    E-print Network

    Peng Huang; Yong-chang Huang

    2013-03-25

    We reconstruct $f(T)$ theories from three different holographic dark energy models in different time durations. For the HDE model, the dark energy dominated era with new setting up is chosen for reconstruction, and the radiation dominated era is chosen when the involved model changes into NADE. For the RDE model, radiation, matter and dark energy dominated time durations are all investigated. We also investigate the limitation which prevents an arbitrary choice of the time duration for reconstruction in HDE and NADE, and find that an improved boundary condition is needed for a more precise reconstruction of $f(T)$ theory.

  1. The Chaplygin dark star

    E-print Network

    O. Bertolami; J. Paramos

    2005-12-14

    We study the general properties of a spherically symmetric body described through the generalized Chaplygin equation of state. We conclude that such object, dubbed generalized Chaplygin dark star, should exist within the context of the generalized Chaplygin gas model of unification of dark energy and dark matter, and derive expressions for its size and expansion velocity. A criteria for the survival of the perturbations in the GCG background that give origin to the dark star are developed, and its main features are analyzed.

  2. Modified Gravitational Theory as an Alternative to Dark Energy and Dark Matter

    Microsoft Academic Search

    J. W. Moffat

    2004-01-01

    The problem of explaining the acceleration of the expansion of the universe\\u000aand the observational and theoretical difficulties associated with dark matter\\u000aand dark energy are discussed. The possibility that Einstein gravity does not\\u000acorrectly describe the large-scale structure of the universe is considered and\\u000aan alternative gravity theory is proposed as a possible resolution to the\\u000aproblems.

  3. Evolution of dark-matter haloes in a variety of dark-energy cosmologies

    Microsoft Academic Search

    Matthias Bartelmann; Klaus Dolag; Francesca Perrotta; Carlo Baccigalupi; Lauro Moscardini; Massimo Meneghetti; Giuseppe Tormen

    2005-01-01

    High resolution, numerical simulations of 17 cluster-sized dark-matter haloes in eight different cosmologies with and without dynamical dark-energy confirm the picture that core halo densities are imprinted early during their formation by the mean cosmological density. Quite independent of cosmology, halo concentrations have a log-normal distribution with a scatter of ?0.2 about the mean. We propose a simple scaling relation

  4. Smoothly evolving Supercritical-String Dark Energy relaxes Supersymmetric-Dark-Matter Constraints

    E-print Network

    A. B. Lahanas; N. E. Mavromatos; D. V. Nanopoulos

    2007-04-28

    We show that Supercritical-String-Cosmology (SSC) off-equilibrium and time-dependent-dilaton effects lead to a smoothly evolving dark energy for the last 10 billion years in concordance with all presently available astrophysical data. Such effects dilute by a factor O (10) the supersymmetric dark matter density (neutralinos), relaxing severe WMAP 1,3 constraints on the SUSY parameter space. Thus, LHC anticipated searches/discoveries may discriminate between conventional and Supercritical-String Cosmology.

  5. Separating Dark Physics from Physical Darkness: Minimalist Modified Gravity vs. Dark Energy

    SciTech Connect

    Huterer, Dragan; Linder, Eric V.

    2007-01-31

    The acceleration of the cosmic expansion may be due to a new component of physical energy density or a modification of physics itself. Mapping the expansion of cosmic scales and the growth of large scale structure in tandem can provide insights to distinguish between the two origins. Using Minimal Modified Gravity (MMG) - a single parameter gravitational growth index formalism to parameterize modified gravity theories - we examine the constraints that cosmological data can place on the nature of the new physics. For next generation measurements combining weak lensing, supernovae distances, and the cosmic microwave background we can extend the reach of physics to allow for fitting gravity simultaneously with the expansion equation of state, diluting the equation of state estimation by less than 25percent relative to when general relativity is assumed, and determining the growth index to 8percent. For weak lensing we examine the level of understanding needed of quasi- and nonlinear structure formation in modified gravity theories, and the trade off between stronger precision but greater susceptibility to bias as progressively more nonlinear information is used.

  6. Interacting entropy-corrected new agegraphic tachyon, K-essence and dilaton scalar field models of dark energy in non-flat universe

    E-print Network

    M. Umar Farooq; Muneer A. Rashid; Mubasher Jamil

    2010-04-06

    We present the new agegraphic dark energy model by introducing the quantum corrections to the entropy-area relation in the setup of loop quantum gravity. Employing this new form of dark energy, we investigate the model of interacting dark energy and derive its equation of state. We study the correspondence between the tachyon, K-essence and dilaton scalar field models with the interacting entropy-corrected new agegraphic dark energy model in the non-flat FRW universe. Moreover, we reconstruct the corresponding scalar potentials which describe the dynamics of the scalar field models.

  7. Cooling the dark energy camera instrument

    SciTech Connect

    Schmitt, R.L.; Cease, H.; /Fermilab; DePoy, D.; /Ohio State U.; Diehl, H.T.; Estrada, J.; Flaugher, B.; /Fermilab; Kuhlmann, S.; /Ohio State U.; Onal, Birce; Stefanik, A.; /Fermilab

    2008-06-01

    DECam, camera for the Dark Energy Survey (DES), is undergoing general design and component testing. For an overview see DePoy, et al in these proceedings. For a description of the imager, see Cease, et al in these proceedings. The CCD instrument will be mounted at the prime focus of the CTIO Blanco 4m telescope. The instrument temperature will be 173K with a heat load of 113W. In similar applications, cooling CCD instruments at the prime focus has been accomplished by three general methods. Liquid nitrogen reservoirs have been constructed to operate in any orientation, pulse tube cryocoolers have been used when tilt angles are limited and Joule-Thompson or Stirling cryocoolers have been used with smaller heat loads. Gifford-MacMahon cooling has been used at the Cassegrain but not at the prime focus. For DES, the combined requirements of high heat load, temperature stability, low vibration, operation in any orientation, liquid nitrogen cost and limited space available led to the design of a pumped, closed loop, circulating nitrogen system. At zenith the instrument will be twelve meters above the pump/cryocooler station. This cooling system expected to have a 10,000 hour maintenance interval. This paper will describe the engineering basis including the thermal model, unbalanced forces, cooldown time, the single and two-phase flow model.

  8. Graviweak Unification, Invisible Universe and Dark Energy

    NASA Astrophysics Data System (ADS)

    Das, C. R.; Laperashvili, L. V.; Tureanu, A.

    2013-07-01

    We consider a graviweak unification model with the assumption of the existence of a hidden (invisible) sector of our Universe, parallel to the visible world. This Hidden World (HW) is assumed to be a Mirror World (MW) with broken mirror parity. We start with a diffeomorphism invariant theory of a gauge field valued in a Lie algebra g, which is broken spontaneously to the direct sum of the space-time Lorentz algebra and the Yang-Mills algebra: ˜ {g} = {{su}}(2) (grav)L ? {{su}}(2)L — in the ordinary world, and ˜ {g}' = {{su}}(2){' (grav)}R ? {{su}}(2)'R — in the hidden world. Using an extension of the Plebanski action for general relativity, we recover the actions for gravity, SU(2) Yang-Mills and Higgs fields in both (visible and invisible) sectors of the Universe, and also the total action. After symmetry breaking, all physical constants, including the Newton's constants, cosmological constants, Yang-Mills couplings, and other parameters, are determined by a single parameter g present in the initial action, and by the Higgs VEVs. The dark energy problem of this model predicts a too large supersymmetric breaking scale (MSUSY 1010GeV), which is not within the reach of the LHC experiments.

  9. Decaying Dark Energy in Higher-Dimensional Gravity

    Microsoft Academic Search

    J. M. Overduin; P. S. Wesson; B. Mashhoon

    2007-01-01

    We use data from observational cosmology to put constraints on\\u000ahigher-dimensional extensions of general relativity in which the effective\\u000afour-dimensional dark-energy density (or cosmological \\

  10. Model selection as a science driver for dark energy surveys

    E-print Network

    Mukherjee, P; Corasaniti, P S; Liddle, A R; Kunz, M; Mukherjee, Pia; Parkinson, David; Corasaniti, Pier Stefano; Liddle, Andrew R.; Kunz, Martin

    2005-01-01

    A key science goal of upcoming dark energy surveys is to seek time evolution of the dark energy. This problem is one of {\\em model selection}, where the aim is to differentiate between cosmological models with different numbers of parameters. However, the power of these surveys is traditionally assessed by estimating their ability to constrain parameters, which is a different statistical problem. In this paper we use Bayesian model selection techniques, specifically forecasting of the Bayes factors, to compare the abilities of different proposed surveys in discovering dark energy evolution. We consider six experiments -- supernova luminosity measurements by the Supernova Legacy Survey, SNAP, JEDI, and ALPACA, and baryon acoustic oscillation measurements by WFMOS and JEDI -- and use Bayes factor plots to compare their statistical constraining power. The concept of Bayes factor forecasting has much broader applicability than dark energy surveys.

  11. Model selection as a science driver for dark energy surveys

    E-print Network

    Pia Mukherjee; David Parkinson; Pier Stefano Corasaniti; Andrew R. Liddle; Martin Kunz

    2006-05-04

    A key science goal of upcoming dark energy surveys is to seek time evolution of the dark energy. This problem is one of {\\em model selection}, where the aim is to differentiate between cosmological models with different numbers of parameters. However, the power of these surveys is traditionally assessed by estimating their ability to constrain parameters, which is a different statistical problem. In this paper we use Bayesian model selection techniques, specifically forecasting of the Bayes factors, to compare the abilities of different proposed surveys in discovering dark energy evolution. We consider six experiments -- supernova luminosity measurements by the Supernova Legacy Survey, SNAP, JEDI, and ALPACA, and baryon acoustic oscillation measurements by WFMOS and JEDI -- and use Bayes factor plots to compare their statistical constraining power. The concept of Bayes factor forecasting has much broader applicability than dark energy surveys.

  12. Model selection as a science driver for dark energy surveys

    NASA Astrophysics Data System (ADS)

    Mukherjee, Pia; Parkinson, David; Corasaniti, Pier Stefano; Liddle, Andrew R.; Kunz, Martin

    2006-07-01

    A key science goal of upcoming dark energy surveys is to seek time-evolution of the dark energy. This problem is one of model selection, where the aim is to differentiate between cosmological models with different numbers of parameters. However, the power of these surveys is traditionally assessed by estimating their ability to constrain parameters, which is a different statistical problem. In this paper, we use Bayesian model selection techniques, specifically forecasting of the Bayes factors, to compare the abilities of different proposed surveys in discovering dark energy evolution. We consider six experiments - supernova luminosity measurements by the Supernova Legacy Survey, SNAP, JEDI and ALPACA, and baryon acoustic oscillation measurements by WFMOS and JEDI - and use Bayes factor plots to compare their statistical constraining power. The concept of Bayes factor forecasting has much broader applicability than dark energy surveys.

  13. Reconstructing the properties of dark energy from recent observations

    E-print Network

    Puxun Wu; Hongwei Yu

    2007-10-10

    We explore the properties of dark energy from recent observational data, including the Gold Sne Ia, the baryonic acoustic oscillation peak from SDSS, the CMB shift parameter from WMAP3, the X-ray gas mass fraction in cluster and the Hubble parameter versus redshift. The $\\Lambda CDM$ model with curvature and two parameterized dark energy models are studied. For the $\\Lambda CDM$ model, we find that the flat universe is consistent with observations at the $1\\sigma$ confidence level and a closed universe is slightly favored by these data. For two parameterized dark energy models, with the prior given on the present matter density, $\\Omega_{m0}$, with $\\Omega_{m0}=0.24$, $\\Omega_{m0}=0.28$ and $\\Omega_{m0}=0.32$, our result seems to suggest that the trend of $\\Omega_{m0}$ dependence for an evolving dark energy from a combination of the observational data sets is model-dependent.

  14. Variable $G$ Correction for Dark Energy Model in Higher Dimensional Cosmology

    E-print Network

    Shuvendu Chakraborty; Ujjal Debnath; Mubasher Jamil

    2012-04-04

    In this work, we have considered $N (=4+d)$-dimensional Einstein field equations in which 4-dimensional space-time which is described by a FRW metric and that of the extra $d$-dimensions by an Euclidean metric. We have calculated the corrections to statefinder parameters due to variable gravitational constant $G$ in higher dimensional Cosmology. We have considered two special cases whether dark energy and dark matter interact or not. In a universe where gravitational constant is dynamic, the variable $G$-correction to statefinder parameters is inevitable. The statefinder parameters are also obtained for generalized Chaplygin gas in the effect of the variation of $G$ correction.

  15. Topics in cosmology: Structure formation, dark energy and recombination

    NASA Astrophysics Data System (ADS)

    Alizadeh, Esfandiar

    The field of theoretical cosmology consists of numerous, inter-related branches, whose ambitious goal is to uncover the history of the universe from its beginning to its future. Achieving this, no doubt, requires a deep understanding of many areas of physics. In this thesis I touch upon a few of these areas in which I worked during my PhD studies. Chapter (2) describes our work in finding the accretion and merger history of dark matter halos. Dark matter halos are the collapsed dark matter structures in the late time evolution of the universe, whose existence is vital for the formation of galaxies in the Universe as they act as the potential wells where normal matter (collectively called Baryons) can accumulate, cool, and form stars. It is then no surprise that the properties of galaxies depends on the properties of the dark matter halo in which it resides, including its merger history, i.e. the number of times it merged with other halos. Even though these merger rates can be calculated theoretically for infinitesimal time steps, in order to find the merger history over an extended period of time one had to use either Monte-Carlo simulations to build up the total rates of merging and accreting from the infinitesimal rates or use N-body simulations. In chapter (2) we show how we used random walk formalism to write down an analytical (integral) equation for the merger history of halos. We have solved this equation numerically and find very good agreement with Monte-Carlo simulations. This work can be used in theories of galaxy formation and evolution. We then switch from the overdense regions of the Universe, halos, to the underdense ones, voids. These structures have not attracted as much attention from cosmologists as their overdense counterparts in probing the cosmological models. We show here that the shapes of voids as a probe can be of use for future surveys to pin down the equation of state of the dark energy, i.e. the ratio of its pressure to its energy density. As first approximation, voids can be considered to be ellipsoids whose axis ratio evolution depends on the cosmological parameters. This, together with the fact that the initial distribution of the axis ratios is known (because the intial density field is Gaussian) can be used to infer the equation of state of the dark energy statistically from the observation of voids at different redshifts and with different sizes. The standard method of Fisher matrices is then used to forecast how well a future survey can measure the equation of state. We find promising results with constraints coming from void ellipticity measurements comparable to those of other standard methods. Chapter (4) goes farther back in the history of the Universe. During the recombination era, when the Universe was around a thousandth of its present size, it became cool enough that free electrons got captured by free protons to make hydrogen atoms. Consequently, the Thompson scattering of photons off of free electrons dropped dramatically and the Universe became transparent to photon propagation. The Cosmic Microwave Background (CMB) is a remnant from this epoch, consisting of photons last scattered off of a free electron. A wealth of information is contained in the statistical properties of the CMB field. However, in order to take full advantage of this probe one needs to know the recombination history, i.e. the evolution of the number density of free electrons as a function of time, to sub-percent level accuracy during this era. There are a plethora of phenomena, from radiative transfer effects to atomic and molecular ones, that have the potential to change the recombination history to this level. Our work was to calculate the effect that the formation of hydrogen molecules will have on the recombination history. Even though the abundance of hydrogen molecules is very small, they still have the potential to change the recombination history by reshuffling photons from the blue side of the Ly-alpha line to its red side and vise-versa. To find the magnitude of the effect, we solve the appropri

  16. Model independent early expansion history and dark energy

    NASA Astrophysics Data System (ADS)

    Samsing, Johan; Linder, Eric V.; Smith, Tristan L.

    2012-12-01

    We examine model independent constraints on the high redshift and prerecombination expansion history from upcoming cosmic microwave background observations, using a combination of principal component analysis and other techniques. This can be translated to model independent limits on early dark energy and the number of relativistic species Neff. Models such as scaling (Doran-Robbers), dark radiation (?Neff), and barotropic aether fall into distinct regions of eigenspace and can be easily distinguished from each other. Incoming CMB data will map the expansion history from z=0-105, achieving subpercent precision around recombination, and enable determination of the amount of early dark energy and valuable guidance to its nature.

  17. Dark Energy, Anthropic Selection Effects, Entropy and Life

    Microsoft Academic Search

    Chas Astro Egan

    2010-01-01

    According to the standard LCDM model, the matter and dark energy densities (rho_m and rho_DE) are only comparable for a brief time. We address the cosmic coincidence problem under LCDM and generalized dark energy models by considering the temporal distribution of terrestrial planets. We compare the Sun to representative stellar samples in 11 properties plausibly related to life.

  18. Decaying dark energy in higher-dimensional gravity

    Microsoft Academic Search

    J. M. Overduin; P. S. Wesson; B. Mashhoon

    2007-01-01

    Aims:We use data from observational cosmology to put constraints on higher-dimensional extensions of general relativity in which the effective four-dimensional dark-energy density (or cosmological ``constant'') decays with time. Methods: In particular we study the implications of this decaying dark energy for the age of the universe, large-scale structure formation, big-bang nucleosynthesis and the magnitude-redshift relation for type Ia supernovae. Results:

  19. New Light on Dark Energy (LBNL Science at the Theater)

    ScienceCinema

    Linder, Eric; Ho, Shirly; Aldering, Greg; Fraiknoi, Andrew

    2011-06-08

    A panel of Lab scientists ? including Eric Linder, Shirly Ho, and Greg Aldering ? along with Andrew Fraiknoi, the Bay Area's most popular astronomy explainer, gathered at the Berkeley Repertory Theatre on Monday, April 25, 2011, for a discussion about "New Light on Dark Energy." Topics will include hunting down Type 1a supernovae, measuring the universe using baryon oscillation, and whether dark energy is the true driver of the universe.

  20. Power Spectra to 1% Accuracy between Dynamical Dark Energy Cosmologies

    E-print Network

    Matthew J. Francis; Geraint F. Lewis; Eric V. Linder

    2007-04-03

    For dynamical dark energy cosmologies we carry out a series of N-body gravitational simulations, achieving percent level accuracy in the relative mass power spectra at any redshift. Such accuracy in the power spectrum is necessary for next generation cosmological mass probes. Our matching procedure reproduces the CMB distance to last scattering and delivers subpercent level power spectra at z=0 and z~3. We discuss the physical implications for probing dark energy with surveys of large scale structure.

  1. Large Synoptic Survey Telescope: Dark Energy Science Collaboration

    E-print Network

    LSST Dark Energy Science Collaboration

    2012-11-01

    This white paper describes the LSST Dark Energy Science Collaboration (DESC), whose goal is the study of dark energy and related topics in fundamental physics with data from the Large Synoptic Survey Telescope (LSST). It provides an overview of dark energy science and describes the current and anticipated state of the field. It makes the case for the DESC by laying out a robust analytical framework for dark energy science that has been defined by its members and the comprehensive three-year work plan they have developed for implementing that framework. The analysis working groups cover five key probes of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia supernovae, and strong lensing. The computing working groups span cosmological simulations, galaxy catalogs, photon simulations and a systematic software and computational framework for LSST dark energy data analysis. The technical working groups make the connection between dark energy science and the LSST system. The working groups have close linkages, especially through the use of the photon simulations to study the impact of instrument design and survey strategy on analysis methodology and cosmological parameter estimation. The white paper describes several high priority tasks identified by each of the 16 working groups. Over the next three years these tasks will help prepare for LSST analysis, make synergistic connections with ongoing cosmological surveys and provide the dark energy community with state of the art analysis tools. Members of the community are invited to join the LSST DESC, according to the membership policies described in the white paper. Applications to sign up for associate membership may be made by submitting the Web form at http://www.slac.stanford.edu/exp/lsst/desc/signup.html with a short statement of the work they wish to pursue that is relevant to the LSST DESC.

  2. Can the time arrow be influenced by the dark energy?

    E-print Network

    A. E. Allahverdyan; V. G. Gurzadyan

    2015-05-25

    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 meta-stable states under generic perturbations. These states will not be meta-stable without dark energy. The latter also ensures a hyperbolic motion leading to dynamic entropy production with the rate determined by the cosmological constant.

  3. Can the time arrow be influenced by the dark energy?

    E-print Network

    Allahverdyan, A E

    2015-01-01

    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 meta-stable states under generic perturbations. These states will not be meta-stable without dark energy. The latter also ensures a hyperbolic motion leading to dynamic entropy production with the rate determined by the cosmological constant.

  4. What do we really know about dark energy?

    PubMed

    Durrer, Ruth

    2011-12-28

    In this paper, we discuss what we truly know about dark energy. I shall argue that, to date, our single indication for the existence of dark energy comes from distance measurements and their relation to redshift. Supernovae, cosmic microwave background anisotropies and observations of baryon acoustic oscillations simply tell us that the observed distance to a given redshift z is larger than the one expected from a Friedmann-Lemaître universe with matter only and the locally measured Hubble parameter. PMID:22084297

  5. On the Growth of Perturbations as a Test of Dark Energy and Gravity

    NASA Astrophysics Data System (ADS)

    Bertschinger, Edmund

    2006-09-01

    The strongest evidence for dark energy at present comes from geometric techniques such as the supernova distance-redshift relation. By combining the measured expansion history with the Friedmann equation, one determines the energy density and its time evolution and hence the equation of state of dark energy. Because these methods rely on the Friedmann equation, which has not been independently tested, it is desirable to find alternative methods that work for both general relativity and other theories of gravity. Assuming that sufficiently large patches of a perturbed Robertson-Walker spacetime evolve like separate Robertson-Walker universes, that shear stress is unimportant on large scales, and that energy and momentum are locally conserved, we derive several relations between long-wavelength metric and matter perturbations. These relations include generalizations of the initial-value constraints of general relativity. For a class of theories including general relativity we reduce the long-wavelength metric, density, and velocity potential perturbations to quadratures including curvature perturbations, entropy perturbations, and the effects of nonzero background curvature. When combined with the expansion history measured geometrically, the long-wavelength solution provides a test that could distinguish modified gravity from other explanations of dark energy.

  6. WIMP Dark Matter and the QCD Equation of State

    E-print Network

    Mark Hindmarsh; Owe Philipsen

    2005-01-25

    Weakly Interacting Massive Particles (WIMPs) of mass m freeze out at a temperature T_f ~ m/25, i.e. in the range 400 MeV -- 40 GeV for a particle in the typical mass range 10 -- 1000 GeV. The WIMP relic density, which depends on the effective number of relativistic degrees of freedom at T_f, may be measured to better than 1% by Planck, warranting comparable theoretical precision. Recent theoretical and experimental advances in the understanding of high temperature QCD show that the quark gluon plasma departs significantly from ideal behaviour up to temperatures of several GeV, necessitating an improvement of the cosmological equation of state over those currently used. We discuss how this increases the relic density by approximately 1.5 -- 3.5% in benchmark mSUGRA models, with an uncertainly in the QCD corrections of 0.5 -- 1 %. We point out what further work is required to achieve a theoretical accuracy comparable with the expected observational precision, and speculate that the effective number of degrees of freedom at T_f may become measurable in the foreseeable future.

  7. Interacting New Agegraphic Dark Energy in a Cyclic Universe

    E-print Network

    Kh. Saaidi; H. Sheikhahmadi; A. H. Mohammadi

    2014-01-16

    The main goal of this work is investigation of NADE in the cyclic universe scenario. Since, cyclic universe is explained by a phantom phase ($\\omega<-1$), it is shown when there is no interaction between matter and dark energy, ADE and NADE do not produce a phantom phase, then can not describe cyclic universe. Therefore, we study interacting models of ADE and NADE in the modified Friedmann equation. We find out that, in the high energy regime, which it is a necessary part of cyclic universe evolution, only NADE can describe this phantom phase era for cyclic universe. Considering deceleration parameter tells us that the universe has a deceleration phase after an acceleration phase, and NADE is able to produce a cyclic universe. Also it is found valuable to study generalized second law of thermodynamics. Since the loop quantum correction is taken account in high energy regime, it may not be suitable to use standard treatment of thermodynamics, so we turn our attention to the result of \\citep{29}, which the authors have studied thermodynamics in loop quantum gravity, and we show that which condition can satisfy generalized second law of thermodynamics.

  8. DGP cosmological model with generalized Ricci dark energy

    NASA Astrophysics Data System (ADS)

    Aguilera, Yeremy; Avelino, Arturo; Cruz, Norman; Lepe, Samuel; Peña, Francisco

    2014-11-01

    The brane-world model proposed by Dvali, Gabadadze and Porrati (DGP) leads to an accelerated universe without cosmological constant or other form of dark energy for the positive branch . For the negative branch we have investigated the behavior of a model with an holographic Ricci-like dark energy and dark matter, where the IR cutoff takes the form , being the Hubble parameter and , positive constants of the model. We perform an analytical study of the model in the late-time dark energy dominated epoch, where we obtain a solution for , where is the leakage scale of gravity into the bulk, and conditions for the negative branch on the holographic parameters and , in order to hold the conditions of weak energy and accelerated universe. On the other hand, we compare the model versus the late-time cosmological data using the latest type Ia supernova sample of the Joint Light-curve Analysis (JLA), in order to constrain the holographic parameters in the negative branch, as well as in the positive branch, where is the Hubble constant. We find that the model has a good fit to the data and that the most likely values for lie in the permitted region found from an analytical solution in a dark energy dominated universe. We give a justification to use a holographic cutoff in 4D for the dark energy in the 5-dimensional DGP model. Finally, using the Bayesian Information Criterion we find that this model is disfavored compared with the flat CDM model.

  9. Gravitational Collapse with Dark Energy and Dark Matter in Ho?ava-Lifshitz Gravity

    NASA Astrophysics Data System (ADS)

    Rudra, Prabir; Debnath, Ujjal

    2014-08-01

    In this work, the collapsing process of a spherically symmetric star, made of dust cloud, is studied in Ho?ava Lifshitz gravity in the background of Chaplygin gas dark energy. Two different classes of Chaplygin gas, namely, New variable modified Chaplygin gas and generalized cosmic Chaplygin gas are considered for the collapse study. Graphs are drawn to characterize the nature and to determine the possible outcome of gravitational collapse. A comparative study is done between the collapsing process in the two different dark energy models. It is found that for open and closed universe, collapse proceeds with an increase in black hole mass, the only constraint being that, relatively smaller values of ? has to be considered in comparison to ?. But in case of flat universe, possibility of the star undergoing a collapse in highly unlikely. Moreover it is seen that the most favourable environment for collapse is achieved when a combination of dark energy and dark matter is considered, both in the presence and absence of interaction. Finally, it is to be seen that, contrary to our expectations, the presence of dark energy does not really hinder the collapsing process in case of Ho?ava-Lifshitz gravity.

  10. Early dark energy at high redshifts: status and perspectives

    SciTech Connect

    Xia, Jun-Qing [Scuola Internazionale Superiore di Studi Avanzati, Via Beirut 2-4, I-34014 Trieste (Italy)] [Scuola Internazionale Superiore di Studi Avanzati, Via Beirut 2-4, I-34014 Trieste (Italy); Viel, Matteo, E-mail: xia@sissa.it, E-mail: viel@oats.inaf.it [INAF-Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste (Italy)] [INAF-Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste (Italy)

    2009-04-15

    Early dark energy models, for which the contribution to the dark energy density at high redshifts is not negligible, influence the growth of cosmic structures and could leave observable signatures that are different from the standard cosmological constant cold dark matter ({Lambda}CDM) model. In this paper, we present updated constraints on early dark energy using geometrical and dynamical probes. From WMAP five-year data, baryon acoustic oscillations and type Ia supernovae luminosity distances, we obtain an upper limit of the dark energy density at the last scattering surface (lss), {Omega}{sub EDE}(z{sub lss}) < 2.3 Multiplication-Sign 10{sup -2} (95% C.L.). When we include higher redshift observational probes, such as measurements of the linear growth factors, Gamma-Ray Bursts (GRBs) and Lyman-{alpha} forest (Ly{alpha}), this limit improves significantly and becomes {Omega}{sub EDE}(z{sub lss}) < 1.4 Multiplication-Sign 10{sup -3} (95% C.L.). Furthermore, we find that future measurements, based on the Alcock-Paczynski test using the 21cm neutral hydrogen line, on GRBs and on the Ly{alpha} forest, could constrain the behavior of the dark energy component and distinguish at a high confidence level between early dark energy models and pure {Lambda}CDM. In this case, the constraints on the amount of early dark energy at the last scattering surface improve by a factor ten, when compared to present constraints. We also discuss the impact on the parameter {gamma}, the growth rate index, which describes the growth of structures in standard and in modified gravity models.

  11. Bistability and instability of dark-antidark solitons in the cubic-quintic nonlinear Schroedinger equation

    SciTech Connect

    Crosta, M. [Dept. of Physics, Sapienza University of Rome, I-00185, Rome (Italy); Fratalocchi, A. [PRIMALIGHT, Faculty of Electrical Engineering, Applied Mathematics and Computational Science, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia); Trillo, S. [Dipartimento di Ingegneria, Universita di Ferrara, Via Saragat 1, I-44122 Ferrara (Italy)

    2011-12-15

    We characterize the full family of soliton solutions sitting over a background plane wave and ruled by the cubic-quintic nonlinear Schroedinger equation in the regime where a quintic focusing term represents a saturation of the cubic defocusing nonlinearity. We discuss the existence and properties of solitons in terms of catastrophe theory and fully characterize bistability and instabilities of the dark-antidark pairs, revealing mechanisms of decay of antidark solitons into dispersive shock waves.

  12. Numerical Solutions to the Continuity Equation in the Negative-Glow-Faraday-Dark-Space Transition

    Microsoft Academic Search

    W. B. Hurt

    1971-01-01

    The one-dimensional charged-particle continuity equation with recombination-volume loss terms has been solved in a negative-glow-Faraday-dark-space environment without the usual assumptions neglecting the dependence of electron transport and recombination coefficients on the electric field. It is concluded that such assumptions are in serious error in the one-dimensional case and this raises the question of their effect on a three-dimensional model.

  13. Bifurcating bright and dark solitary waves of the nearly nonlinear cubic-quintic Schrodinger equation

    Microsoft Academic Search

    Todd Kapitula

    1996-01-01

    The existence of bright and dark multi-bump solitary waves for Ginzburg-Landau type perturbations of the cubic-quintic Schrodinger equation is considered. The waves in question are not perturbations of known analytic solitary waves, but instead arise as a bifurcation from a heteroclinic cycle in a three dimensional ODE phase space. Using geometric singular perturbation techniques, regions in parameter space for which

  14. Reconstruction of the dark matter-vacuum energy interaction

    E-print Network

    Wang, Yuting; Wands, David; Pogosian, Levon; Crittenden, Robert G

    2015-01-01

    An interaction between the vacuum energy and dark matter is an intriguing possibility which may offer a way of solving the cosmological constant problem. Adopting a general prescription for momentum exchange between the two dark components, we reconstruct the temporal evolution of the coupling strength between dark matter and vacuum energy, $\\alpha(a)$ in a non-parametric Bayesian approach using the combined observational datasets from the cosmic microwave background, supernovae and large scale structure. An evolving interaction between the vacuum energy and dark matter removes some of the tensions between different types of datasets, and is favoured at $\\sim95\\%$ CL if we include the baryon acoustic oscillations measurements of the BOSS Lyman-$\\alpha$ forest sample.

  15. A new mechanism for dark energy: the adaptive screening

    E-print Network

    Andi Hektor; Luca Marzola; Martti Raidal; Hardi Veermäe

    2015-01-22

    We describe how known matter effects within a well-motivated particle physics framework can explain the dark energy component of the Universe. By considering a cold gas of particles which interact via a vector mediator, we show that there exists a regime where the gas reproduces the dynamics of dark energy. In this regime the screening mass of the mediator is proportional to the number density of the gas, hence we refer to this phenomenon as "the adaptive screening mechanism". As an example, we argue that such screening mass can result from strong localization of the vector mediators. The proposed dark energy mechanism could be experimentally verified through cosmological observations by the Euclid experiment, as well as by studying properties of dark photons and sterile neutrinos.

  16. Interacting new agegraphic dark energy model and generalized second law of thermodynamics in non-flat universe

    E-print Network

    Karami, K

    2009-01-01

    We consider the interacting new agegraphic dark energy model to investigate the validity of the generalized second law of thermodynamics in non-flat universe enclosed by the apparent horizon. We show that for this model in presence of interaction with the cold dark matter, the equation of state parameter can cross the phantom divide. We also present that for the selected model under thermal equilibrium with the Hawking radiation, the generalized second law is always satisfied for any spatial curvature.

  17. The Dark Energy Survey Data Management System

    SciTech Connect

    Mohr, Joseph J.; /Illinois U., Urbana, Astron. Dept. /Illinois U., Urbana; Barkhouse, Wayne; /North Dakota U.; Beldica, Cristina; /Illinois U., Urbana; Bertin, Emmanuel; /Paris, Inst. Astrophys.; Dora Cai, Y.; /NCSA, Urbana; Nicolaci da Costa, Luiz A.; /Rio de Janeiro Observ.; Darnell, J.Anthony; /Illinois U., Urbana, Astron. Dept.; Daues, Gregory E.; /NCSA, Urbana; Jarvis, Michael; /Pennsylvania U.; Gower, Michelle; /NCSA, Urbana; Lin, Huan; /Fermilab /Rio de Janeiro Observ.

    2008-07-01

    The Dark Energy Survey (DES) collaboration will study cosmic acceleration with a 5000 deg2 griZY survey in the southern sky over 525 nights from 2011-2016. The DES data management (DESDM) system will be used to process and archive these data and the resulting science ready data products. The DESDM system consists of an integrated archive, a processing framework, an ensemble of astronomy codes and a data access framework. We are developing the DESDM system for operation in the high performance computing (HPC) environments at the National Center for Supercomputing Applications (NCSA) and Fermilab. Operating the DESDM system in an HPC environment offers both speed and flexibility. We will employ it for our regular nightly processing needs, and for more compute-intensive tasks such as large scale image coaddition campaigns, extraction of weak lensing shear from the full survey dataset, and massive seasonal reprocessing of the DES data. Data products will be available to the Collaboration and later to the public through a virtual-observatory compatible web portal. Our approach leverages investments in publicly available HPC systems, greatly reducing hardware and maintenance costs to the project, which must deploy and maintain only the storage, database platforms and orchestration and web portal nodes that are specific to DESDM. In Fall 2007, we tested the current DESDM system on both simulated and real survey data. We used TeraGrid to process 10 simulated DES nights (3TB of raw data), ingesting and calibrating approximately 250 million objects into the DES Archive database. We also used DESDM to process and calibrate over 50 nights of survey data acquired with the Mosaic2 camera. Comparison to truth tables in the case of the simulated data and internal crosschecks in the case of the real data indicate that astrometric and photometric data quality is excellent.

  18. The Dark Energy Survey: Survey Strategy

    NASA Astrophysics Data System (ADS)

    Annis, James T.; Cunha, C.; Busha, M.; Ma, Z.; DES Collaboration

    2011-01-01

    The Dark Energy Survey uses 525 nights over 5 years of time on the CTIO Blanco 4m telescope to image 5000 sq-degrees of the South Galactic Cap in 5 filters while also performing a roughly 15 sq-degree time domain survey for supernovae. The survey strategy is designed to optimize three things: our ability to do cluster and LSS science early in the survey, our ability to do weak lensing, and our ability to collect an cosmologically interesting sample of supernovae. Thus we cover the entire survey area twice per year per bandpass (grizY, i > 24); we devote the best seeing time to the main survey; and we observe the SN fields at high cadence over 5-6 months while minimizing observation gaps of a week or more. We have chosen survey metrics which report survey area covered given a fiducial exposure time (the equivalent number of tilings), and an estimate of the total number of galaxies useful for weak lensing that is essentially a non-linear combination of signal to noise and seeing (the effective number of galaxies, n_eff). We have developed photo-z simulations given survey strategy parameters, and these along with the area covered, the depth achieved and n_eff allow us to estimate the figure of merit for our LSS, clusters, and weak lensing projects to judge the the ability of the each scenario to maximize the DETF FOM. We have developed a tool that uses the extensive weather and seeing data available for CTIO to simulate the survey. The poster will describe the current survey strategy and the results that support each choice.

  19. Existence of dark solitons in a class of stationary nonlinear Schroedinger equations with periodically modulated nonlinearity and periodic asymptotics

    SciTech Connect

    Belmonte-Beitia, J. [Departamento de Matematicas, E. T. S. de Ingenieros Industriales and Instituto de Matematica Aplicada a la Ciencia y la Ingenieria (IMACI), Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Cuevas, J. [Grupo de Fisica No Lineal, Departamento de Fisica Aplicada I, Escuela Politecnica Superior, Universidad de Sevilla, C/ Virgen de Africa, 7, 41011 Sevilla (Spain)

    2011-03-15

    In this paper, we give a proof of the existence of stationary dark soliton solutions or heteroclinic orbits of nonlinear equations of Schroedinger type with periodic inhomogeneous nonlinearity. The result is illustrated with examples of dark solitons for cubic and photorefractive nonlinearities.

  20. Dark energy from quantum uncertainty of distant clock

    NASA Astrophysics Data System (ADS)

    Luo, M. J.

    2015-06-01

    The observed cosmic acceleration was attributed to an exotic dark energy in the framework of classical general relativity. The dark energy behaves very similar with vacuum energy in quantum mechanics. However, once the quantum effects are seriously taken into account, it predicts a completely wrong result and leads to a severe fine-tuning. To solve the problem, the exact meaning of time in quantum mechanics is reexamined. We abandon the standard interpretation of time in quantum mechanics that time is just a global parameter, replace it by a quantum dynamical variable playing the role of physical clock. We find that synchronization of two spatially separated clocks can not be precisely realized at quantum level. There is an intrinsic quantum uncertainty of distant clock time, which implies an apparent vacuum energy fluctuation and gives an observed dark energy density at tree level approximation, where L P and L H are the Planck and Hubble scale cutoffs. The fraction of the dark energy is given by , which does not evolve with the internal clock time. The "dark energy" as a quantum cosmic variance is always seen comparable with the matter energy density by an observer using the internal clock time. The corrected distance-redshift relation of cosmic observations due to the distant clock effect are also discussed, which again gives a redshift independent fraction . The theory is consistent with current cosmic observations.