IUCAA Preprints

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    Comments on ''remarks on a decrumpling model of the universe''
    (2015-03-14) Vishwakarma, R.G.
    A recent paper by Lima and Mohazzab has been examined and it is found that their results, that the Einstein field equations are consistent only for a dust and a turning point in the dynamics of the evolution is possible, are erroneous. This is due to their ignorance of the fact that the field equations and the energy conservation equation are not independent.
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    Topology of the universe: Theory and observation
    (2015-03-01) Luminet, Jean-pierre; Roukema, B. F.
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    ISW effect as probe of features in the expansion history of the Universe
    (IUCAA, 2015-02) Das, Santanu; Shafieloo, Arman; Tarun, Sauradeep
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    String-dust in Einstein and godel universes
    (2015-01-27) Dadhich, Naresh; Patel, L.K.
    We consider the mixture of perfect fluid and string-dust and obtain string-dust generalization of the Einstein and godel universes.
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    Recycling the universe using scalar fields
    (2001-07-02) Kanekar, Nissim; Sahni, Varun; Shtanov, Yuri
    We examine the behaviour of a closed oscillating universe filled with a homogeneous scalar field and find that, contrary to naive expectations, such a universe expands to larger vol- umes during successive expansion epochs. This intriguing be- haviour introduces an arrow of time in a system which is time- reversible. The increase in the maximum size of the universe s closely related to the work done on/by the scalar field dur- ng one complete oscillatory cycle which, in turn, is related to the asymmetry in the scalar field equation of state dur- ng expansion and collapse. Our analysis shows that scalar fields with polynomial potentials V (φ) = λφq , q > 1 lead to a growing oscillation amplitude for the universe: the increase n amplitude between successive oscillations is more signifi- cant for smaller values of q. Such behaviour allows for the effective recycling of the universe. A recycled universe can be quite old and can resolve the flatness problem. These results have strong bearing on cosmological models in which the role of dark matter is played by a scalar field. They are also rele- vant for chaotic inflationary models of the early universe since they demonstrate that, even if the universe fails to inflate the first time around, it will eventually do so during future oscil- atory cycles. Thus, the space of initial conditions favourable or chaotic inflation increases significantly.
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    Phantom field and the fate of the Universe
    (2011-07-06) Sami, M.; Toporensky, A.
    In this paper we analyze the cosmological dynamics of phantom field in a variety of potentials unbounded from above. We demonstrate that the nature of future evolution generically depends upon the steepness of the phantom potential and discuss the fate of Universe accordingly.
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    Understanding Our Universe : Current Status and Open Issues
    (2005-03-01) Padmanabhan, T.
    Last couple of decades have been the golden age for cosmology. High quality data confirmed the broad paradigm of standard cosmology but have thrusted upon us a preposterous composition for the universe which defies any simple explanation, thereby posing probably the greatest challenge theoretical physics has ever faced. Several aspects of these developments are critically reviewed, concentrating on conceptual issues and open questions.
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    Quantum effects, soft singularities and the fate of the universe in a braneworld cosmology
    (2006-03-24) Tretjakov, P. V.; Toporensky, A.; Shtanov, Yuri; et al.
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    Fate of (phantom) dark energy universe with string curvature corrections
    (2005-01-01) Sami, M.; Tsujikawa, Shinji; Tretjakov, P. V.; et al.
    We study the evolution of (phantom) dark energy universe by taking into account the higher-order string corrections to Einstein-Hilbert action with fixed dilaton and modulus fields. While the presence of a cosmological constant gives stable de-Sitter fixed points in the cases of heterotic and bosonic strings, no stable de-Sitter solutions exist when a phantom fluid is present. We find that the universe can exhibit a Big Crunch singularity with a finite time for type II string, whereas it reaches a Big Rip singularity for heterotic and bosonic strings. Thus the fate of dark energy universe crucially depends upon the type of string theory under consideration.