121 research outputs found
Validity of the Generalized Second Law of Thermodynamics of the Universe Bounded by the Event Horizon in Holographic Dark Energy Model
In this letter, we investigate the validity of the generalized second law of
thermodynamics of the universe bounded by the event horizon in the holographic
dark energy model. The universe is chosen to be homogeneous and isotropic and
the validity of the first law has been assumed here. The matter in the universe
is taken in the form of non-interacting two fluid system- one component is the
holographic dark energy model and the other component is in the form of dust.Comment: 8 page
Interacting Three Fluid System and Thermodynamics of the Universe Bounded by the Event Horizon
The work deals with the thermodynamics of the universe bounded by the event
horizon. The matter in the universe has three constituents namely dark energy,
dark matter and radiation in nature and interaction between then is assumed.
The variation of entropy of the surface of the horizon is obtained from unified
first law while matter entropy variation is calculated from the Gibbss' law.
Finally, validity of the generalized second law of thermodynamics is examined
and conclusions are written point wise.Comment: 7 page
Braneworld models with a non-minimally coupled phantom bulk field: a simple way to obtain the -1-crossing at late times
We investigate general braneworld models, with a non-minimally coupled
phantom bulk field and arbitrary brane and bulk matter contents. We show that
the effective dark energy of the brane-universe acquires a dynamical nature, as
a result of the non-minimal coupling which provides a mechanism for an indirect
"bulk-brane interaction" through gravity. For late-time cosmological evolution
and without resorting to special ansatzes or to specific areas of the parameter
space, we show that the -1-crossing of its equation-of-state parameter is
general and can be easily achieved. As an example we provide a simple, but
sufficiently general, approximate analytical solution, that presents the
crossing behavior.Comment: 11 pages, 2 figure
Cyclic Universes from General Collisionless Braneworld Models
We investigate the full 5D dynamics of general braneworld models. Without
making any further assumptions we show that cyclic behavior can arise naturally
in a fraction of physically accepted solutions. The model does not require
brane collisions, which in the stationary case remain fixed, and cyclicity
takes place on the branes. We indicate that the cosmological constants play the
central role for the realization of cyclic solutions and we show that its
extremely small value on the observable universe makes the period of the cycles
and the maximum scale factor astronomically large.Comment: 17 pages, 1 figure, version published in Nucl. Phys.
Scalar-Tensor Theory of Gravity and Generalized Second Law of Thermodynamics on the Event Horizon
In blackhole physics, the second law of thermodynamics is generally valid
whether the blackhole is a static or a non-static one. Considering the universe
as a thermodynamical system the second law of blackhole dynamics extends to the
non-negativity of the sum of the entropy of the matter and the horizon, known
as generalized second law of thermodynamics(GSLT). Here, we have assumed the
universe to be bounded by the event-horizon or filled with perfect fluid and
holographic dark energy in two cases. Thus considering entropy to be an
arbitrary function of the area of the event-horizon, we have tried to find the
conditions and the restrictions over the scalar field and equation of state for
the validity of the GSLT and both in quintessence-era and in phantom-era in
scalar tensor theory.Comment: 8 page
An efficient algorithm simulating a macroscopic system at the critical point
It is well known that conventional simulation algorithms are inefficient for
the statistical description of macroscopic systems exactly at the critical
point due to the divergence of the corresponding relaxation time (critical
slowing down). On the other hand the dynamics in the order parameter space is
simplified significantly in this case due to the onset of self-similarity in
the associated fluctuation patterns. As a consequence the effective action at
the critical point obtains a very simple form. In the present work we show that
this simplified action can be used in order to simulate efficiently the
statistical properties of a macroscopic system exactly at the critical point.
Using the proposed algorithm we generate an ensemble of configurations
resembling the characteristic fractal geometry of the critical system related
to the self-similar order parameter fluctuations. As an example we simulate the
one-component real scalar field theory at the transition point as a
representative system belonging to the Ising universality class.Comment: 10 pages, 6 figures, submitted for publication to Journal of
Computational Physic
Phase-space analysis of interacting phantom cosmology
We perform a detailed phase-space analysis of various phantom cosmological
models, where the dark energy sector interacts with the dark matter one. We
examine whether there exist late-time scaling attractors, corresponding to an
accelerating universe and possessing dark energy and dark matter densities of
the same order. We find that all the examined models, although accepting stable
late-time accelerated solutions, cannot alleviate the coincidence problem,
unless one imposes a form of fine-tuning in the model parameters. It seems that
interacting phantom cosmology cannot fulfill the basic requirement that led to
its construction.Comment: 6 figures, use revtex, v2: minor corrections, references added,
accepted for publication in JCA
Restoring New Agegraphic Dark Energy in RS II Braneworld
Motivated by recent works [1,2], we investigate new agegraphic model of dark
energy in the framework of RS II braneworld. We also include the case of
variable gravitational constant in our model. Furthermore, we establish
correspondence between the new agegraphic dark energy with other dark energy
candidates based on scalar fields.Comment: 13 pages, accepted for publication in IJT
Non-minimally coupled canonical, phantom and quintom models of holographic dark energy
We investigate canonical, phantom and quintom models, with the various fields
being non-minimally coupled to gravity, in the framework of holographic dark
energy. We classify them and we discuss their cosmological implications. In
particular, we examine the present value of the dark energy equation-of-state
parameter and the crossing through the phantom divide, and we extract the
conditions for a future cosmological singularity. The combined scenarios are in
agreement with observations and reveal interesting cosmological behaviors.Comment: 9 pages, 5 figures, version published in Phys. Lett.
Constraints on massive gravity theory from big bang nucleosynthesis
The massive gravity cosmology is studied in the scenario of big bang
nucleosynthesis. By making use of current bounds on the deviation from the
fractional mass, we derive the constraints on the free parameters of the
theory. The cosmological consequences of the model are also discussed in the
framework of the PAMELA experiment.Comment: 5 page
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