184 research outputs found
Gravitational reheating in quintessential inflation
We provide a detailed study of gravitational reheating in quintessential
inflation generalizing previous analyses only available for the standard case
when inflation is followed by an era dominated by the energy density of
radiation. Quintessential inflation assumes a common origin for inflation and
the dark energy of the Universe. In this scenario reheating can occur through
gravitational particle production during the inflation-kination transition. We
calculate numerically the amount of the radiation energy density, and determine
the temperature at which radiation starts dominating over kination. The
value of is controlled by the Hubble parameter during inflation and
the transition time , scaling as
for and for . The model-dependent parameter is found to be around 0.5 in two
different parametrizations for the transition between inflation and kination.Comment: 12 pages, 5 figure
Validity of Generalized Second Law of Thermodynamics in the Logamediate and Intermediate scenarios of the Universe
In this work, we have investigated the validity of the generalized second law
of thermodynamics in logamediate and intermediate scenarios of the universe
bounded by the Hubble, apparent, particle and event horizons using and without
using first law of thermodynamics. We have observed that the GSL is valid for
Hubble, apparent, particle and event horizons of the universe in the
logamediate scenario of the universe using first law and without using first
law. Similarly the GSL is valid for all horizons in the intermediate scenario
of the universe using first law. Also in the intermediate scenario of the
universe, the GSL is valid for Hubble, apparent and particle horizons but it
breaks down whenever we consider the universe enveloped by the event horizon
Generalised second law of thermodynamics for interacting dark energy in the DGP brane world
In this paper, we investigate the validity of the generalized second law of
thermodynamics (GSLT) in the DGP brane world when universe is filled with
interacting two fluid system: one in the form of cold dark matter and other is
holographic dark energy. The boundary of the universe is assumed to be enclosed
by the dynamical apparent horizon or the event horizon. The universe is chosen
to be homogeneous and isotropic FRW model and the validity of the first law has
been assumed here
Cosmological evolution of interacting dark energy in Lorentz violation
The cosmological evolution of an interacting scalar field model in which the
scalar field interacts with dark matter, radiation, and baryon via Lorentz
violation is investigated. We propose a model of interaction through the
effective coupling . Using dynamical system analysis, we study the
linear dynamics of an interacting model and show that the dynamics of critical
points are completely controlled by two parameters. Some results can be
mentioned as follows. Firstly, the sequence of radiation, the dark matter, and
the scalar field dark energy exist and baryons are sub dominant. Secondly, the
model also allows the possibility of having a universe in the phantom phase
with constant potential. Thirdly, the effective gravitational constant varies
with respect to time through . In particular, we consider a simple
case where has a quadratic form and has a good agreement with the
modified CDM and quintessence models. Finally, we also calculate the
first post--Newtonian parameters for our model.Comment: 14 pages, published versio
Generalized Second Law of Thermodynamics on the Event Horizon for Interacting Dark Energy
Here we are trying to find the conditions for the validity of the generalized
second law of thermodynamics (GSLT) assuming the first law of thermodynamics on
the event horizon in both cases when the FRW universe is filled with
interacting two fluid system- one in the form of cold dark matter and the other
is either holographic dark energy or new age graphic dark energy. Using the
recent observational data we have found that GSLT holds both in quintessence
era as well as in phantom era for new age graphic model while for holographic
dark energy GSLT is valid only in phantom era.Comment: 8 pages, 2 figure
Observable Effects of Scalar Fields and Varying Constants
We show by using the method of matched asymptotic expansions that a
sufficient condition can be derived which determines when a local experiment
will detect the cosmological variation of a scalar field which is driving the
spacetime variation of a supposed constant of Nature. We extend our earlier
analyses of this problem by including the possibility that the local region is
undergoing collapse inside a virialised structure, like a galaxy or galaxy
cluster. We show by direct calculation that the sufficient condition is met to
high precision in our own local region and we can therefore legitimately use
local observations to place constraints upon the variation of "constants" of
Nature on cosmological scales.Comment: Invited Festscrift Articl
Modified f(G) gravity models with curvature-matter coupling
A modified f(G) gravity model with coupling between matter and geometry is
proposed, which is described by the product of the Lagrange density of the
matter and an arbitrary function of the Gauss-Bonnet term. The field equations
and the equations of motion corresponding to this model show the
non-conservation of the energy-momentum tensor, the presence of an extra-force
acting on test particles and the non-geodesic motion. Moreover, the energy
conditions and the stability criterion at de Sitter point in the modified f(G)
gravity models with curvature-matter coupling are derived, which can degenerate
to the well-known energy conditions in general relativity. Furthermore, in
order to get some insight on the meaning of these energy conditions, we apply
them to the specific models of f(G) gravity and the corresponding constraints
on the models are given. In addition, the conditions and the candidate for
late-time cosmic accelerated expansion in the modified f(G) gravity are studied
by means of conditions of power-law expansion and the equation of state of
matter less than -1/ 3 .Comment: 13 pages, 4 figure
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