• B C Paul

      Articles written in Pramana – Journal of Physics

    • Wormholes in higher dimensions with Gauss-Bonnet terms

      B C Paul A Beesham S Mukherjee

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      A class of wormhole solutions permitted in a theory with Gauss-Bonnet terms in the gravitational action in higher dimensions have been studied. The case of de-Sitter type instantons, with a compact inner space, are of particular interest here. Some of the configurations, when continued analytically to the Lorentzian metric lead to the standard inflationary universe. Some multiple-sphere configurations of the type studied by Myers have also been noted. The Euclidean action for the solutions has been calculated and the relevance of the solutions in the quantum creation of the universe has been considered.

    • Observational constraints on extended Chaplygin gas cosmologies


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      We investigate cosmological models with extended Chaplygin gas (ECG) as a candidate for dark energy and determine the equation of state parameters using observed data namely, observed Hubble data, baryon acousticoscillation data and cosmic microwave background shift data. Cosmological models are investigated considering cosmic fluid which is an extension of Chaplygin gas, however, it reduces to modified Chaplygin gas (MCG) andalso to generalized Chaplygin gas (GCG) in special cases. It is found that in the case of MCG and GCG, the best-fit values of all the parameters are positive. The distance modulus agrees quite well with the experimental Union2data. The speed of sound obtained in the model is small, necessary for structure formation. We also determine the observational constraints on the constants of the ECG equation.

    • Skyrme fluid in anisotropic Universe


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      Cosmological solutions are obtained in anisotropic Kantowski–Sachs (KS) and Bianchi Type-I Universes considering a cosmological constant with Skyrme fluid. Interestingly, the solutions obtained here in both the KS and Bianchi-I anisotropic Universes are found to isotropise at late time due to the presence of the Skyrmefluid, even in the absence of ʌ term or any inflationary mechanism involving the inflaton field. A comparative study of both the anisotropic cosmological models are carried out here and it is found that the Bianchi-I Universe admits oscillatory solutions for a given matter configuration.We also note that the emergent Universe model can be obtained with the Skyrme fluid. The anisotropy, deceleration and jerk parameters have been studied along with the linear perturbative stability to explore the efficacy of the models. Both cosmological models are stable in the absenceof cosmological constant. Besides, their predictions are compatible with the observational data. Thus, wemay claim that Skyrme fluid is a possible source of isotropization of an anisotropic Universe via accelerated expansion, whichis capable of reproducing some features that can be observed in the Universe.

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