118430195
Clustering GCG: a viable option for unified dark matter-dark energy?
We study the clustering Generalized Chaplygin Gas (GCG) as a possible candidate for dark matter-dark energy unification. The vanishing speed of sound 0c{sub s}{sup 2} = ) for the GCG fluid can be obtained by incorporating higher derivative operator in the original K-essence Lagrangian. The evolution of the density fluctuations in the GCG+Baryon fluid is studied in the linear regime. The observational constraints on the model are obtained using latest data from SNIa, H(z), BAO and also for the fσ{sub 8} measurements. The matter power spectra for the allowed parameter values are well behaved without any unphysical features.
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
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.
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.
117283830
Isospin effects on fragment production
To understand the isospin effects in nearly symmetric nuclear matter we performed a complete systematical theoretical study within an Isospin dependent Quantum Molecular Dynamical Model (IQMD) and using Minimum Spanning Tree (MST) algorithm. Simulations are carried out for the reactions $_{124}Sn^{50}+_{124}Sn^{50}$ and $_{107}Sn^{50}+_{124}Sn^{50}$. The collision geometry is varied from central to peripheral. We find that neutron rich colliding nuclei are better candidate to study the isospin effects
123091744
Supercurrent Anomaly in the Framework of Analytic Regularization
122529836
Anisotropic dark energy models with constant deceleration parameter
We consider a spatially homogeneous and totally anisotropic Bianchi-I space-time with perfect fluid (dark matter and standard visible matter) and anisotropic dark energy, which has dynamical energy density. The two sources are assumed to interact minimally and therefore their energy momentum tensors are conserved separately. Using suitable physical assumptions, the field equations are solved exactly. Various dark energy models are studied and it is found that quintessence model is suitable for describing the present evolution of the universe. The geometrical and kinematical features of the models and the behavior of the anisotropy of the dark energy, are examined in detail.
118545653
Systematic study of multifragmentation in asymmetric colliding nuclei
We present a complete systematically theoretical study of multifragmentation for asymmetric colliding nuclei for heavy-ion reactions in the energy range between 50 MeV/nucleon and 600 MeV/nucleon by using soft and hard equations of state. This study is performed within an isospin-dependent quantum-molecular dynamics model. To see the effect of mass asymmetry, simulations are carried out in the absence of Coulomb interactions. Coulomb interactions enhance the production of fragments by about 20%. We envision an interesting outcome for large asymmetric colliding nuclei. Although nearly symmetric nuclei depict a well-known trend for rising and falling with a peak around E=100 MeV/nucleon, this trend, however, is completely missing for large asymmetric nuclei. Therefore, experiments are needed to verify this prediction.