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 $\omega>1$ (Ekpyrotic matter) and a dark energy with positive pressure.Comment: 11 pages, no figure

Equivalence Principle (EP) and Solar System Constraints on R(1±ϵln⁡(RRc))R(1\pm \epsilon \ln({R \over R_c})) 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 $f(R)$ gravity as $f(R) = R(1\pm \epsilon \ln({R \over R_c}))$. 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 $\gamma_{PPN} = 1 \pm 1.13 \times10^{-5}$ which is agreement with experiment results. At last, we show that for $R_c \thickapprox \rho_c$ this model is consistent with EP, thin shell condition and fifth force of chameleon mechanism for $\epsilon \backsimeq 10^{-14}$.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, $\omega$, 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 $P(\lambda_{1}, \lambda_{2}, ..., \lambda_{N})$ 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 $\rho$ temperature $T$ and scale factor $a$ 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