arXiv subjects

J Sadeghi

Publications and source records attributed to J Sadeghi.

6 recordsLinked to original sources

arXiv2009

Vacuum quantum effect for curved boundaries in static Robertson--Walker spacetime

The energy-momentum tensor for a massless conformally coupled scalar field in the region between two curved boundaries in $k=-1$ static Robertson--Walker spacetime is investigated. We assume that the scalar field satisfies the Dirichlet boundary condition on the boundaries. $k=-1$ Robertson--Walker 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 Robertson--Walker space from the corresponding Rindler counterpart by the conformal transformation.

hep-th↗

arXiv2009

Non-minimal Maxwell-Modified Gauss-Bonnet Cosmologies: Inflation and Dark Energy

In this paper we show that power-law inflation can be realized in non-minimal gravitational coupling of electromagnetic field with a general function of Gauss-Bonnet invariant. Such a non-minimal coupling may appear due to quantum corrections. We also consider modified Maxwell-$F(G)$ gravity in which non-minimal coupling between electromagnetic field and $f(G)$ occur in the framework of modified Gauss-Bonnet gravity. It is shown that inflationary cosmology and late-time accelerated expansion of the universe are possible in such a theory.

hep-th↗

arXiv2009

Cosmic acceleration and crossing of $ω=-1$ in non-minimal modified Gauss-Bonnet gravity

Modified Gauss-Bonnet, i.e, $f(G)$ gravity is a possible explanation of dark energy. Late time cosmology for the $f(G)$ gravity non-minimally coupled with a free massless scalar field have been investigated in Ref. [32]. In this paper we generalize the work of Ref. [32] by including scalar potential in the matter Lagrangian which is non-minimally coupled with modified Gauss-Bonnet gravity. Also we obtain the conditions for having a much more amazing problem than the acceleration of the universe, i.e: crossing of $ω=-1$, in $f(G)$ non-minimally coupled with tachyonic Lagrangian.

hep-th↗

arXiv2009

String Inspired Quintom Model with Non-minimally Coupled Modified Gravity

In this paper we consider a quintom model of dark energy with non-minimal coupling between scalar field and modified gravity which is known $f(R)$ gravity. The Lagrangian for scalar field has been inspired by tachyonic Lagrangian in string theory. Then we obtain the equation of state (EoS), and the condition required for the model parameters when $ω$ crosses over -1. This model shows that for having $ω$ across over -1, one doesn't need to add some higher derivative operator in the tachyonic part of action (the way that usually used to obtain crossing of the phantom divide line for EoS parameter).

hep-th↗

arXiv2009

Interacting tachyon dark energy in non-flat universe

In this paper we study the tachyon cosmology in non-interacting and interacting cases in non-flat FRW universe. Then we reconstruct the potential and the dynamics of the tachyon field which describe tachyon cosmology.

gr-qc↗

arXiv2008

Reconstructing a String-Inspired Non-minimally Coupled Quintom Model

Motivated by the recent work of Zhang and Chen \cite{bin}, we generalize their work to the non-minimally coupled case. We consider a quintom model of dark energy with a single scalar field $T$ given by a Lagrangian which inspired by tachyonic Lagrangian in string theory. We consider non-minimal coupling of tachyon field to the scalar curvature, then we reconstruct this model in the light of three forms of parametrization for dynamical dark energy.

hep-th↗