55961336
Observational constraints on variable equation of state parameters of dark matter and dark energy after Planck
Note: This version of the paper matches the version published in Physics Letters B. The definitive ver- sion is available at Phys. Lett. B 737 (2014) 244-247. Abstract. In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann-Robertson-Walker space-time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier-Polarski-Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck+WMAP9+WiggleZ mea- surements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch.
119296892
STRING COSMOLOGY IN ANISOTROPIC BIANCHI-II SPACETIME
The present study deals with a spatially homogeneous and anisotropic Bianchi-II cosmological model representing massive strings. The energy–momentum tensor, as formulated by Letelier,10 has been used to construct a massive string cosmological model for which the expansion scalar is proportional to one of the components of shear tensor. The Einstein's field equations have been solved by applying a variation law for generalized Hubble's parameter that yields a constant value of deceleration parameter in Bianchi-II spacetime. A comparative study of accelerating and decelerating modes of the evolution of universe has been carried out in the presence of string scenario. The study reveals that massive strings dominate the early Universe. The strings eventually disappear from the Universe for sufficiently large times, which is in agreement with the current astronomical observations.
122510459
Exact Bianchi Type-I Cosmological Models in a Scalar-Tensor Theory
Abstract
In this paper, a spatially homogeneous and anisotropic Bianchi type-I space-time filled with perfect fluid is investigated within the framework of a scalar-tensor theory proposed by Saez and Ballester. Two different physically viable models of the universe are obtained by using a special law of variation for Hubble’s parameter that yields a constant value of deceleration parameter. One of the models is found to generalize a model recently investigated by Reddy et al. (Astrophys. Space Sci. 306:171, 2006). The Einstein’s field equations are solved exactly and the solutions are found to be consistent with the recent observations of type Ia supernovae. A detailed study of physical and kinematical properties of the models is carried out.

123666710
Early viscous universe with variable gravitational and cosmological ‘constants’
Einstein's field equations with variable gravitational and cosmological 'constants' are considered in the presence of bulk viscosity for a spatially flat homogeneous and isotropic universe. Solutions are obtained by using a 'gamma-law' equation of state p = (? ? 1)?, where the adiabatic parameter ? varies continuously as the universe expands. A unified description of the early evolution of universe is presented with a number of possible assumptions on the bulk viscous term and gravitational constant in which an inflationary phase is followed by radiation-dominated phase. We investigate the cosmological model with constant and time-dependent bulk viscosity (proportional to power function of energy density and to Hubble parameter) along with constant and variable gravitational constant. The effect of viscosity is shown to affect the past and future of the universe. In all cases, the cosmological constant ? is found to be positive and a decreasing function of time, which supports the results obtained from recent supernovae Ia observations. The possibility that the present acceleration of the universe is driven by a kind of viscous fluid is explained. At the background level this model is similar to the generalized Chaplygin gas model. The physical and geometrical significance of the early cosmological models has also been discussed.
118453863
SOME BIANCHI TYPE-V MODELS OF ACCELERATING UNIVERSE WITH DARK ENERGY
The paper deals with a spatially homogeneous and anisotropic universe filled with perfect fluid and dark energy components. The two sources are assumed to interact minimally together with a special law of variation for the average Hubble's parameter in order to solve the Einstein's field equations. The law yields two explicit forms of the scale factor governing the Bianchi-V spacetime and constant values of deceleration parameter. The role of dark energy with variable equation of state parameter has been studied in detail in the evolution of Bianchi-V universe. It has been found that dark energy dominates the universe at the present epoch, which is consistent with the observations. The universe achieves flatness after the dominance of dark energy. The physical behavior of the universe has been discussed in detail.
120039457
Viscous fluid cosmology with a cosmological constant
Exact solutions of the field equations for a Bianchi type-I space-time, filled with a viscous fluid and cosmological constant, are obtained. We utilize the constancy of deceleration parameter to get singular and non-singular solutions. We investigate a number of solutions with constant and time-varying cosmological constant together with a linear relation between shear viscosity and expansion scalar. Due to dissipative processes, the mean anisotropy and shear of the model tend to zero at a faster rate.
18426911
Two-Zero Symmetric Neutrino Mass Matrices in Minimal Supersymmetric SO(10)
The phenomenological neutrino mass matrix for two-zero symmetric texture has been obtained and used to rule out all possible two-zero symmetric neutrino mass matrices obtained from Yukawa couplings to $\mathbf{10}$ and $\mathbf{126}$ Higgs representations within the framework of minimal supersymmetric SO(10).
118516198
Cosmology with axionic-quintessence coupled with dark matter
We study the possibility of explaining the late time acceleration with an axion field which is coupled with the dark matter sector of the energy budget of the Universe. The axion field arises from the Ramond–Ramond sector of the Type-IIB string theory. We study the background evolution of the Universe as well as the growth of the matter perturbation in the linear regime. We subsequently use the observational data from Sn-Ia, BAO measurements, measurements of the Hubble parameter as well as the observational data for the growth of the matter perturbation to constrain our model. Our results show that coupled axion models are allowed to have larger deviation from the cosmological constant by the present observational data. Communicated by P R L V Moniz
116891254
Production of light and intermediate mass fragments using various clusterization algorithms
For the present analysis we simulate the reaction 129Xe 54+197Au79 at E=50 MeV/nucleon respectively[3]. This reaction is simulated at different impact parameters using hard equation of state. The stored phase space is then analyzed by using MST, MSTP and MSTB algorithms. MSTB and MSTP identifies the free nucleons as early as possible. In the two cases, a check in the form of binding energy and momentum cut helps to identify the fragments quite early. The normal MST takes quite a long time to identify the stable fragments which are residual of excited fragments.
119096687
Inflationary generalized Chaplygin gas and dark energy in light of the Planck and BICEP2 experiments
In this work, we study an inflationary scenario in the presence of Generalized Chaplygin Gas (GCG). We show that in Einstein gravity, GCG is not a suitable candidate for inflation; but in a five dimensional brane world scenario, it can work as a viable inflationary model. We calculate the relevant quantities such as $n_{s}$, $r$ and $A_{s}$ related to the primordial scalar and tensor fluctuations, and using their recent bounds from Planck and BICEP2, we constrain the model parameters as well as the five-dimensional Planck mass. But as a slow-roll inflationary model with a power-law type scalar primordial power spectrum, GCG as an inflationary model can not resolve the tension between results from BICEP2 and Planck with a concordance $\Lambda$CDM Universe. We show that going beyond the concordance $\Lambda$CDM model and incorporating more general dark energy behaviour, this tension may be eased. We also obtain the constraints on the $n_{s}$ and $r$ and the GCG model parameters using Planck+WP+BICEP2 data considering the CPL dark energy behaviour.
118469770
Probing the effect of different cross-sections in asymmetric collisions
We present a complete systematic theoretical study of multifragmentation for asymmetric colliding nuclei for heavy-ion reactions in the energy range between 50 MeV/nucleon and 1000 MeV/nucleon by using isospin dependent quantum molecular dynamics (IQMD) model. We have observed an interesting outcome for asymmetric colliding nuclei. The comparison between the symmetric and asymmetric colliding nuclei for the isospin independent cross section and isospin dependent cross section has been studied. We have found the pronounced effect of different cross section and mass asymmetry on the nuclear reaction dynamics.