119270955
Anisotropic model of a dark energy dominated universe with hybrid expansion law
The dynamics of the Universe is studied in the framework of a spatially homogeneous Bianchi-V space-time filled with a perfect fluid composed of non-interacting matter and dynamical dark energy components. We determine the Bianchi-V space-time by considering a hybrid expansion law (HEL) for the average scale factor that yields power-law and exponential-law cosmologies in its special cases. In the HEL cosmology, the Universe exhibits a transition from deceleration to acceleration. We find that the HEL Universe in the framework of Bianchi-V space-time is anisotropic at early stages of evolution and becomes isotropic at late times. The dynamic dark energy in this Universe does not show a departure from the usual cosmological constant at later times.
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.
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.

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.
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.
2063566
Phenomenology of Two-Texture Zero Neutrino Mass Matrices
The generic predictions of two-texture zero neutrino mass matrices in the flavor basis have been examined especially in relation to the degeneracies between mass matrices within a class and interesting constraints on the neutrino parameters have been obtained. It is shown that the knowledge of the octant of ${\ensuremath{\theta}}_{23}$, the sign of $\mathrm{cos}﻿\ensuremath{\delta}$, and neutrino mass hierarchy can be used to lift these degeneracies.
118511593
Influence of density-dependent symmetry energy on elliptical flow
Abstract.The effect of density-dependent symmetry energy on elliptical flow is studied using the isospin-dependent quantum molecular dynamics model (IQMD). We have used the reduced isospin-dependent cross-section with hard (H) equation of state to study the sensitivity of the elliptical flow to symmetry energy in the energy range 50-1000MeV/nucleon. The elliptical flow becomes zero at a particular energy termed as transition energy. A systematic effort has been made to pin down the transition energy for the density-dependent symmetry energy.
16460683
MODEL INDEPENDENT CONSTRAINTS ON NON-ELECTRONIC FLAVORS IN THE SOLAR BORON NEUTRINO FLUX
We perform the most general model-independent analysis of the latest 391-Day Salt Phase SNO Data Set incorporating the super-Kamiokande ES flux measurement and obtain bounds on the antineutrino and sterile neutrino flux in the solar 8B neutrino flux reaching the detectors on the earth. The muon/tauon antineutrino flux is found to be disallowed at 1.4σ C.L. The sterile flux is found to be nonzero at about 1.26 standard deviations.
116623275
Experimental study of nuclei in the vicinity of the 'island of inversion' through the fusion-evaporation reaction
We report the observation of high-spin states in nuclei in the vicinity of the 'island of inversion', populated via the {sup 18}O+{sup 18}O fusion reaction at an incident beam energy of 34 MeV. The fusion reaction mechanism circumvents the limitations of other reactions used so far to populate excited states in these nuclei. The level structures of {sup 33,34}P and {sup 33}S have been investigated and their level schemes were substantially extended. The intensities and branching ratios of the {gamma} transitions were measured. The observed {gamma} coincidence intensity anisotropy and polarization asymmetry were analyzed for a consistent assignment of the spins and parities of the nuclear levels. The 1876-keV transition in {sup 34}P that had an ambiguous multipolarity assignment has been confirmed to be a mixed transition. Truncated (1p-1h) shell model calculations within the 'sdpf' valence space were performed. These calculations reproduce the experimental excitation energies of {sup 34}P but fail to explain the observed mixing ratio for the 1876-keV transition.
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