2006 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/335

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Subject: search.filters.subject.Cosmological constant

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    Five dimensional dust collaspe with cosmological constant
    (2006-07-31) Ghosh, S. G.; Deshkar, D. W.; Saste, N. N.
    We study five dimensional spherical collapse of a inhomogeneous dust in presence of a positive cosmological constant. The general interior solutions, in the closed form, of the Einstein field equations, i.e., the 5D Tolman-Bondi-de Sitter, is obtained which in turn is matched to exterior 5D Scwarschild-de Sitter. It turns out that the collapse proceed in the same way as in the Minkowski background, i.e., the strong curvature naked singularities form and thus violate the cosmic censorship conjecture. A brief discussion on the causal structure singularities and horizons is also given.
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    Dark energy
    (2006-01-10) Sahni, Varun
    The cosmological constant problem as well as the case for dark energy are briefly reviewed and some theoretical models of dark energy are discussed in detail. These include: the cosmological constant, quintessence, the Chaplygin gas and Braneworld models. I also discuss model independent measures of dark energy and conclude by mentioning some properties of the Statefinder diagnostic which can successfully differentiate between different families of dark energy models.
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    Casimir effect confronts cosmological constant
    (2006-04-02) Mahajan, Gaurang; Sarkar, Sudipta; Padmanabhan, T.
    It has been speculated that the zero-point energy of the vacuum, regularized due to the existence of a suitable ultraviolet cut-off scale, could be the source of the non-vanishing cosmological constant that is driving the present acceleration of the universe. We show that the presence of such a cut-off can significantly alter the results for the Casimir force between parallel conducting plates and even lead to repulsive Casimir force when the plate separation is smaller than the cut-off scale length. Using the current experimental data we rule out the possibility that the observed osmological constant arises from the zero-point energy which is made finite by a suitable cut-off. Any such cut-off which is consistent with the observed Casimir effect will lead to an energy density which is about 1012 times larger than the observed one, if gravity couples to these modes. The implications are discussed.