Browsing by Author "Paul, B. C."

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    Core-envelope model of compact stars
    (2011-07-06) Paul, B. C.; Tikekar, R.
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    Inflation in bianchi models and the cosmic no hair theorem in brane world
    (2002-04-30) Paul, B. C.
    In this paper, the cosmic no hair theorem for anisotropic Bianchi models which admit inflation with a scalar field is studied in the framework of Brane world. It is found that all Bianchi models except Bianchi type IX, transit to an inflationary regime with vanishing anisotropy. In the Brane world, anisotropic universe approaches the inflationary era much faster than that in the general theory of relativity. The form of the potential does not affect the evolution in the inflationary epoch. However, the late time behaviour is controlled by a constant additive factor in the potential for the inflaton field.
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    Note on inflation the Tachyon rolling on the Gauss-Bonnet Brane
    (2011-07-06) Paul, B. C.; Sami, M.
    In this paper we study the tachyonic inflation in brane world cosmology with Gauss-Bonnet term in the bulk. We obtain the exact solution of slow roll equations in case of exponential potential. We attempt to implement the proposal of Lidsey and Nunes[1] for the tachyon condensate rolling on the Gauss-Bonnet brane and discuss the difficulties associated with the proposal.
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    On the mass of a uniform density star in higher dimensions
    (2001-01-14) Paul, B. C.
    Within the framework of higher dimensions the mass of a uniform density star is evaluated. The four-dimensional upper bound for the mass-to-radius ratio obtained by Schwarzschild is generalized within the framework of higher- dimensional spacetime. It is found that the analogue upper bound for the mass- to-radius ratio in higher dimensions tends to increase at first as the number of dimensions of spacetime increases, it attains amaximumat nine dimensions and thereafter decreases. It is found that D = 4 is the lowest number of spacetime dimensions for which the mass-to-radius ratio of a uniform density star can be derived.
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    Probabitlity for Primordial Black holes Pair in 1/R Gravity
    (2005-08-01) Paul, Dilip; Paul, B. C.
    The probability for quantum creation of an inflationary universe with a pair of black holes in 1/R - gravitational theory has been studied. Considering a gravitational action which includes a cosmological constant (Λ) in addition to δ R−1 term, the probability has been evaluated in a semiclassical approximation with Hartle-Hawking boundary condition. We obtain instanton solutions determined by the parameters δ and Λ satisfying the constraint δ ≤ 4Λ23 . However, we note that two different classes of instanton solutions exists in the region 0 < δ < 4Λ23 . The probabilities of creation of such configurations are evaluated. It is found that the probability of creation of a universe with a pair of black holes is strongly suppressed with a positive cosmological constant except in one case when 0 < δ < Λ2. It is also found that gravitational instanton solution is permitted even with Λ = 0 but one has to consider δ < 0. However, in the later case a universe with a pair of black holes is less probable.
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    Viscous cosmologies with extra dimensions
    (2001-07-05) Paul, B. C.
    We present an analysis of a n-dimensional vacuum Einstein field equations in which 4-dimensional space-time is described by a Friedmann Robertson- Walker (FRW) metric and that of the extra dimensions by a Kasner type Euclidean metric. The field equations are interpreted as four dimensional Einstein equations with effective matter properties. The effective matter is then treated as viscous fluid. We consider the theories of imperfect fluid given by Eckart, truncated Israel-Stewart and full Israel-Stewart theories and obtain cosmological solutions for a flat model of the universe. The imperfect fluid assumption admits here power law inflation for the 3-physical space in some cases.