The case for dynamical dark energy revisited

Alam, Ujjaini; Sahni, Varun; Starobinsky, Alexei A.

doi:10.1088/1475-7516/2004/06/008

Cited by 417 publications

(413 citation statements)

References 50 publications

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“…For c < 1, we adopt the constrained value c = 0.815 from the observational data (Alam et al 2004). In this case (reddashed line) the phantom regime can be crossed in the near past in agreement with observations (Alam et al 2004;Gong 2005;Gong & Zhang 2005;Huterer & Cooray 2005;Wang & Tegmark 2005).…”

Section: Cosmology With Holographic Dark Energysupporting

confidence: 71%

Evolution of spherical overdensities in holographic dark energy models

Naderi¹,

Malekjani²,

Pace³

2015

Monthly Notices of the Royal Astronomical Society

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In this work we investigate the spherical collapse model in flat 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 (EoS) parameter w de 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 behavior of the HDE model and compare the results with standard Einstein-de Sitter (EdS) and ΛCDM models. We then calculate the evolution of two characterizing parameters in the spherical collapse model, i.e., the linear density threshold δ c and the virial overdensity parameter ∆ vir . We show that in HDE cosmologies the growth factor g(a) and the linear overdensity parameter δ c fall behind the values for a ΛCDM universe while the virial overdensity ∆ vir is larger in HDE models than in the ΛCDM 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 ΛCDM universe. Hence the growth of structures starts earlier in HDE models than in ΛCDM 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 halos in HDE cosmologies and find out that in general this value is smaller than for ΛCDM models at higher redshifts and we compare different mass function prescriptions. Finally, we compare the results of the HDE models with observations.

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Section: Cosmology With Holographic Dark Energysupporting

confidence: 71%

Evolution of spherical overdensities in holographic dark energy models

Naderi¹,

Malekjani²,

Pace³

2015

Monthly Notices of the Royal Astronomical Society

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“…One of the most interesting aspects of these discussions is the possibility to have a slowly varying DE density of the Universe [16]. This option cannot be ruled out by the analysis of the present data [17,18]. In case that the new generation of cosmic observational experiments will indeed detect a variable DE, the natural question to ask is: would this fact really mean the manifestation of a qualitatively new physical reality such as quintessence [19], Chaplygin gas [20], extra dimensions [21] or of low-energy quantum gravity [22,23,24,25]?…”

Section: Introductionmentioning

confidence: 73%

Density perturbations for a running cosmological constant

Fabris

Shapiro

Solà

2007

J. Cosmol. Astropart. Phys.

152

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The dynamics of density and metric perturbations is investigated for the previously developed model where the decay of the vacuum energy into matter (or vice versa) is due to the renormalization group (RG) running of the cosmological constant (CC) term. The evolution of the CC depends on the single parameter ν, which characterizes the running of the CC produced by the quantum effects of matter fields of the unknown high energy theory below the Planck scale. The sign of ν indicates whether bosons or fermions dominate in the running. The spectrum of perturbations is computed assuming an adiabatic regime and an isotropic stress tensor. Moreover, the perturbations of the CC term are generated from the simplest covariant form suggested by the RG model under consideration. The corresponding numerical analysis shows that for ν > 0 there is a depletion of the matter power spectrum at low scales (large wave numbers) as compared to the standard ΛCDM model, whereas for ν < 0 there is an excess of power at low scales. We find that the LSS data rule out the range |ν| > 10 −4 while the values |ν| ≤ 10 −6 look perfectly acceptable. For ν < 0 the excess of power at low scales grows rapidly and the bound is more severe. From the particle physics viewpoint, the values |ν| ≃ 10 −6 correspond to the "desert" in the mass spectrum above the GUT scale M X ∼ 10 16 GeV . Our results are consistent with those obtained in other dynamical models admitting an interaction between dark matter and dark energy. We find that the matter power spectrum analysis is a highly efficient method to discover a possible scale dependence of the vacuum energy.

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“…In the analysis of dark energy the main attraction should be on the state parameter w = p ρ where p and ρ are the pressure and energy density of the dark energy. In Cosmological constant model w = −1 around present epoch [8] from w > −1 in the near past [9]. There are various kinds of models of dark energy and among all of them, the simplest case is the ΛCDM model which has ρ = Λ = constant and the equation of state as p = −ρ.…”

Section: Pacs Numbersmentioning

confidence: 99%

Holographic dark energy interacting with two fluids and validity of generalized second law of thermodynamics

Debnath

2011

Astrophys Space Sci

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We have considered a cosmological model of holographic dark energy interacting with dark matter and another unknown component of dark energy of the universe. We have assumed two interaction terms Q and Q ′ in order to include the scenario in which the mutual interaction between the two principal components (i.e., holographic dark energy and dark matter) of the universe leads to some loss in other forms of cosmic constituents. Our model is valid for any sign of Q and Q ′ . If Q < Q ′ , then part of the dark energy density decays into dark matter and the rest in the other unknown energy density component. But if Q > Q ′ , then dark matter energy receives from dark energy and from the unknown component of dark energy. Observation suggests that dark energy decays into dark matter. Here we have presented a general prescription of a cosmological model of dark energy which imposes mutual interaction between holographic dark energy, dark matter and another fluid. We have obtained the equation of state for the holographic dark energy density which is interacting with dark matter and other unknown component of dark energy. Using first law of thermodynamics, we have obtained the entropies for holographic dark energy, dark matter and other component of dark energy, when holographic dark energy interacting with two fluids (i.e., dark matter and other component of dark energy). Also we have found the entropy at the horizon when the radius (L) of the event horizon measured on the sphere of the horizon. We have investigated the GSL of thermodynamics at the present time for the universe enveloped by this horizon. Finally, it has been obtained validity of GSL which implies some bounds on deceleration parameter q.

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The case for dynamical dark energy revisited

Cited by 417 publications

References 50 publications

Evolution of spherical overdensities in holographic dark energy models

Evolution of spherical overdensities in holographic dark energy models

Density perturbations for a running cosmological constant

Holographic dark energy interacting with two fluids and validity of generalized second law of thermodynamics

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