61 research outputs found
On the Anisotropic Big Bang Cosmology With A General Non-Linear EoS
We study the anisotropic Big Bang cosmology for a general non-linear equation
of state (EoS) in standard general relativity cosmology in early times.
According to brane world cosmology and loop quantum gravity which introduce a
quadratic term in the energy density, we study a non-linear EoS with a general
nonlinear term in the energy density. We show that this general non-linear term
isotropize the universe at early times. And also, we find out this model has a
phantom like behavior for special case.Comment: 10 pages, no figure
Bouncing cosmology without anisotropy
Using non-linear equation of state for pressure and density energy, we show
that the universe is began with a smooth and isotropic bounce. We use a
non-linear equation of state which is a binary mixture of perfect fluid and
dark energy. We show that in order to preserve a smooth and isotropic bounce,
the source for contraction before the bounce, must have an equation of state
with (Ekpyrotic matter) and a dark energy with positive pressure.Comment: 11 pages, no figure
Equivalence Principle (EP) and Solar System Constraints on model of Gravity
Experiments on the violation of equivalence principle (EP) and solar system
give a number of constraints in which any modified gravity model must satisfy
them. We study these constraints on a kind of gravity as . For this investigation we use of chameleon
mechanism and show that a spherically body has thin-shell in this model. So
that we obtain an effective coupling of the fifth force which is suppressed
through a chameleon mechanism. Also, we obtain which is agreement with experiment results. At last, we show
that for this model is consistent with EP, thin shell
condition and fifth force of chameleon mechanism for .Comment: 6 pages, no figure, Accepted for publication in Astrophysics & Space
Scienc
Gravitational Baryogenesis in Anisotropic Universe
The interaction between Ricci scalar curvature and the baryon number current,
dynamically breaks CPT in an expanding universe and leads to baryon asymmetry.
Using this kind of interaction and study the gravitational baryogenesis in the
Bianchi type I universe. We find out the effect of anisotropy of the universe
on the baryon asymmetry for the case which the equation of state parameter,
, is dependent to time.Comment: 12 pages, no figur
Analysis of Poisson Networks and Their Relation with Random Cellular Structures
We perform a detailed analysis of the statistical properties of Poisson
networks and show that the metric and topological properties of random cellular
structures, can not be derived from simple models of random networks based on a
poisson point distribution [1]. In particular we show that Lewis and
Aboav-Wieare laws are not obeyed in these network.Comment: 17 pages , Latex , 3 Figures available upon reques
Inhomogenous Poisson Networks and Random Cellular Structures
we study the statistical properties of inhomogenous Poisson networks. we
perform a detailed analysis of the statistical properties of Poisson networks
and show that the topological properties of random cellular structures, can be
derived from these models of random networks. we study both two and three
dimensional networks with non uniform density and show that with a class of
symmetric distribution Lewis
and Aboav-Weaire laws are obeyed in these networks.Comment: 15 pages, 3 figure
Chameleon mechanism with a new potential
Chameleon scalar field is a new model, which introduced to provide a
mechanism for exhibiting accelerating universe. Chameleon field has several
interesting aspects, such as field dependence on the local matter density. For
this model we introduce a new kind of potential which has run away form and
satisfies chameleon constraints. The results are acceptable in comparison with
the other potentials which studied up to now.Comment: 5 pages, 3 figure
Quark-Hadron Phase Transition in DGP Brane Gravity with Bulk Scalar Field
A DGP brane-world framework is picked out to study quark-hadron phase
transition problem. The model also includes a bulk scalar field in agreement
with string theory prediction. The work is performed utilizing two formalisms
as: smooth crossover approach and first order approach, and the results are
plotted for both branches of DGP model. General behavior of temperature is the
same in these two approaches and it decrease by passing time and expanding
Universe. Phase transition occurs at about micro-second after the big bang. The
results show that transition time depends on brane tension value in which
larger brane tension comes to earlier transition time.Comment: 14 pages, 13 figure
QCD phase transition with a power law chameleon scalar field in the bulk
In this work, a brane world model with a perfect fluid on brane and a scalar
field on bulk has been used to study quark-hadron phase transition. The bulk
scalar field has an interaction with brane matter. This interaction comes into
non-conservation relation which describe an energy transfer between bulk and
brane. Since quark-hadron transition curly depends on the form of evolution
equations therefore modification of energy conservation equation and Friedmann
equation comes into some interesting results about the time of transition. The
evolution of physical quantities relevant to quantitative of early times namely
energy density temperature and scale factor have been considered
utilizing two formalisms as crossover formalism and first order phase
transition formalism. The results show that the quark-hadron phase transition
in occurred about nanosecond after big bang and the general behavior
temperature is similar in both of two formalism.Comment: 22 pages, 8 figure
Tachyon constant-roll inflation
The constant-roll inflation is studied where the inflaton is taken as a
tachyon field. Since in this approach the second slow-roll parameter is assumed
to be of order one instead of being small, then the perturbation parameters
will be considered again. The results are compared with observational data, and
it is confirmed that the model could stand as a proper candidate for inflation.Comment: 16 pages, 8 figures, Typos corrected, references adde
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