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M R Setare

Publications and source records attributed to M R Setare.

At least 37 records · Page 2Linked to original sources
arXiv2006

The holographic dark energy in non-flat Brans-Dicke cosmology

In this paper we study cosmological application of holographic dark energy density in the Brans-Dicke framework. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named $L$. Our calculation show, taking $Ω_Λ=0.73$ for the present time, the lower bound of $w_{\rm Λ}$ is -0.9. Therefore it is impossible to have $w_{\rm Λ}$ crossing -1. This implies that one can not generate phantom-like equation of state from a holographic dark energy model in non-flat universe in the Brans-Dicke cosmology framework. In the other hand, we suggest a correspondence between the holographic dark energy scenario in flat universe and the phantom dark energy model in framework of Brans-Dicke theory with potential.

hep-th↗
arXiv2006

Casimir stress on parallel plates in de Sitter space with signature change

The Casimir stress on two parallel plates in a de Sitter background corresponding to different metric signatures and cosmological constants is calculated for massless scalar fields satisfying Robin boundary conditions on the plates. Our calculation shows that for the parallel plates with false vacuum between and true vacuum outside, the total Casimir pressure leads to an attraction of the plates at very early universe.

gr-qc↗
arXiv2006

Generalized Second Law of Thermodynamics in Quintom Dominated Universe

In this paper we will investigate the validity of the Generalized Second Law of thermodynamics for the Quintom model of dark energy. Reviewing briefly the quintom scenario of dark energy, we will study the conditions of validity of the generalized second law of thermodynamics in three cases: quintessence dominated, phantom dominated and transition from quintessence to phantom will be discussed.

hep-th↗
arXiv2006

Bouncing cosmological solutions due to the self-gravitational corrections and their stability

In this paper we consider the bouncing braneworld scenario, in which the bulk is given by a five-dimensional AdS black hole spacetime with matter field confined in a $D_3$ brane. Exploiting the CFT/FRW-cosmology relation, we consider the self-gravitational corrections to the first Friedmann-like equation which is the equation of the brane motion. The self-gravitational corrections act as a source of stiff matter contrary to standard FRW cosmology where the charge of the black hole plays this role. Then, we study the stability of solutions with respect to homogeneous and isotropic perturbations. Specifically, if we do not consider the self-gravitational corrections, the AdS black hole with zero ADM mass, and open horizon is an attractor, while, if we consider the self-gravitational corrections, the AdS black hole with zero ADM mass and flat horizon, is a repeller

hep-th↗
arXiv2006

Casimir energy-momentum tensor for the Robin Surfaces in de Sitter Spacetime

The energy-momentum tensor for a massless conformally coupled scalar field in de Sitter spacetime in the presence of a couple curved branes is investigated. We assume that the scalar field satisfies the Robin boundary condition on the surfaces. Static de Sitter space is conformally related to the Rindler space, as a result we can obtain vacuum expectation values of energy-momentum tensor for conformally invariant field in static de Sitter space from the corresponding Rindler counterpart by the conformal transformation.

hep-th↗
arXiv2006

Space Noncommutativity Corrections to the Cardy-Verlinde Formula

In this letter we compute the corrections to the Cardy-Verlinde formula of Schwarzschild black holes. These corrections stem from the space noncommutativity. Because the Schwarzschild black holes are non rotating, to the first order of perturbative calculations, there is no any effect on the properties of black hole due to the noncommutativity of space.

gr-qc↗
arXiv2006

Large-N limit of the two-dimensinal Non-Local Yang-Mills theory on arbitrary surfaces with boundary

The large-N limit of the two-dimensional non-local U$(N)$ Yang-Mills theory on an orientable and non-orientable surface with boundaries is studied. For the case which the holonomies of the gauge group on the boundaries are near the identity, $U\simeq I$, it is shown that the phase structure of these theories is the same as that obtain for these theories on orientable and non-orientable surface without boundaries, with same genus but with a modified area $V+\hat{A}$.

hep-th↗
arXiv2005

Quasinormal Modes, Reduced Phase Space and Area Spectrum of Black Holes

Motivated by the recent interest in quantization of black hole area spectrum, we consider the area spectrum of Schwarzschild, BTZ, extremal Reissner-Nordström, near extremal Schwarzschild-de Sitter, and Kerr black holes. Based on the proposal by Bekenstein and others that the black hole area spectrum is discrete and equally spaced, we implement Kunstatter's method to derive the area spectrum for these black holes. We show that although as Schwarzschild black hole the spectrum is discrete, it is non equispaced in general. In the other hand the reduced phase space quantization is another technique which we discuss here. However there is a discrepancy between the result of the reduced phase space methodology and quasinormal modes approach for area spectrum of some black holes.

hep-th↗
arXiv2005

Surface vacuum energy and stresses for a brane in de Sitter spacetime

Vacuum expectation values of the surface energy-momentum tensor is investigated for a massless scalar field obeying mixed boundary condition on a brane in de Sitter bulk. To generate the corresponding vacuum surface densities we use the conformal relation between de Sitter and Rindler spacetimes.

hep-th↗
arXiv2005

The Generalized Uncertainty Principle and Corrections to the Cardy-Verlinde Formula in $SAdS_5$ Black Holes

In this letter, we investigate a possible modification to the temperature and entropy of $5-$dimensional Schwarzschild anti de Sitter black holes due to incorporating stringy corrections to the modified uncertainty principle. Then we subsequently argue for corrections to the Cardy-Verlinde formula in order to account for the corrected entropy. Then we show, one can taking into account the generalized uncertainty principle corrections of the Cardy-Verlinde entropy formula by just redefining the Virasoro operator $L_0$ and the central charge $c$.

hep-th↗
arXiv2005

The Self-Gravitational Corrections as the Source for Stiff Matter on the Brane in $SAdS_5$ Bulk

A $D3-$ brane with non-zero energy density is considered as the boundary of a five dimensional Schwarzschild anti de Sitter bulk background. Taking into account the semi-classical corrections to the black hole entropy that arise as a result of the self-gravitational effect, and employing the AdS/CFT correspondence, we obtain the self-gravitational correction to the first Friedmann-like equation. The additional term in the Hubble equation due to the self-gravitational effect goes as $a^{-6}$. Thus, the self-gravitational corrections act as a source of stiff matter contrary to standard FRW cosmology where the charge of the black hole plays this role.

hep-th↗
arXiv2005

Area Spectrum of Near Extremal Black Branes from Quasi-normal Modes

Motivated by the recent interest in quantization of black hole area spectrum, we consider the area spectrum of near extremal black $3-$branes. Based on the proposal by Bekenstein and others that the black hole area spectrum is discrete and equally spaced, we implement Kunstatter's method to derive the area spectrum for the near extremal black $3-$branes. The result for the area of event horizon although discrete, is not equally spaced.

hep-th↗
arXiv2004

Vacuum Quantum Effects for Parallel Plates Moving by Uniform Acceleration in Static de Sitter Space

The Casimir forces on two parallel plates moving by uniform proper acceleration in static de Sitter background due to conformally coupled massless scalar field satisfying Dirichlet boundary conditions on the plates is investigated. Static de Sitter space is conformally related to the Rindler space, as a result we can obtain vacuum expectation values of energy-momentum tensor for conformally invariant field in static de Sitter space from the corresponding Rindler counterpart by the conformal transformation.

hep-th↗
arXiv2004

Logarithmic correction to the Brane equation in Topological Reissner-Nordström de Sitter Space

In this paper we study braneworld cosmology when the bulk space is a charged black hole in de Sitter space (Topological Reissner-Nordström de Sitter Space) in general dimension, then we compute leading order correction to the Friedmann equation that arise from logarithmic corrections to the entropy in the holographic-branworld cosmological framwork. Finally we consider the holographic entropy bounds in this senario, we show the entropy bounds are also modified by logarithmic term.

hep-th↗
arXiv2004

Casimir Effect for Moving Branes in Static dS$_{4+1}$ Bulk

In this paper we study the Casimir effect for conformally coupled massless scalar fields on background of Static dS$_{4+1}$ spacetime. We will consider the general plane--symmetric solutions of the gravitational field equations and boundary conditions of the Dirichlet type on the branes. Then we calculate the vacuum energy-momentum tensor in a configuration in which the boundary branes are moving by uniform proper acceleration in static de Sitter background. Static de Sitter space is conformally related to the Rindler space, as a result we can obtain vacuum expectation values of energy-momentum tensor for conformally invariant field in static de Sitter space from the corresponding Rindler counterpart by the conformal transformation.

hep-th↗
arXiv2004

The Cardy-Verlinde formula and entropy of black holes in de Sitter spaces

In this paper we show that the entropy of a cosmological horizon in topological Reissner-Nordström- de Sitter and Kerr-Newman-de Sitter spaces can be described by the Cardy-Verlinde formula, which is supposed to be an entropy formula of conformal field theory in any number of dimension. Furthermore, we find that the entropy of a black hole horizon can also be rewritten in terms of the Cardy-Verlinde formula for these black holes in de Sitter spaces, if we use the definition due to Abbott and Deser for conserved charges in asymptotically de Sitter spaces. Such result presume a well-defined dS/CFT correspondence, which has not yet attained the credibility of its AdS analogue.

hep-th↗