1998 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/2980

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    Quantum structure of spacetime and blackhole entropy
    (2015-02-11) Padmanabhan, T.
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    Shapefinders: a new shape diagnostic for large scale structure
    (2015-03-11) Sahni, Varun; Sathyaprakash, B.S.; Shandarian, Sergei
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    Global anomalies in canonical gravity
    (2015-03-11) Surya, Sumati; Vaidya, Sachindeo
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    On electrogravity duality
    (2015-03-11) Dadhich, Naresh
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    A duality relation for fluid spacetime
    (2015-03-11) Dadhich, Naresh; Patel, L.K.; Tikekar, R.
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    Event horizon: Magnifying glass for planck length physics
    (2015-03-11) Padmanabhan, T.
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    Conformal transformations in classical gravitational theories and in cosmology
    (2015-03-11) Faraoni, Valerio; Gunzing , Edgard; Nardone, Pasquale
    In recent years, the use of conformal transformation techniques has become widespread in the literature on gravitational theories alternative to general relativity, on cosmology, and on nonminimally coupled scalar fields. Tipically, the transformation to the Einstein frame is generated by a fundamental scalar field already present in the theory. In this context, the problem of which conformal frame is the physical one has to be dealt with and, in the general case, it has been clarified only recently; the formulation of a theory in the "new" conformal frame leads to departures from canonical Einstein gravity. In this article, we review the literature on conformal transformations in classical gravitational theories and in cosmology, seen both as purely mathematical tools and as maps with physically relevant aspects. It appears particularly urgent to refer the analysis of experimental tests of Brans-Dicke and scalar-tensor theories of gravity, as well as the predictions of cosmological inflationary scenarios, to the physical conformal frame, in order to have a meaningful comparison with the observations.
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    Topology change and causal continuity
    (2015-03-11) Dowker, Fay; Surya, Sumati
    The result that, for a scalar quantum field propagating on a "trousers" topology in 1 + 1 dimensions, the crotch singularity is a source for an infinite burst of energy has been used to argue against the occurrence of topology change in quantum gravity. We draw attention to a conjecture due to Sorkin that it may be the particular type of topology change involved in the trousers transition that is problematic and that other topology changes may not cause the same difficulties. The conjecture links the singular behaviour to the existence of "causal discontinuities" in the spacetime and relies on a classification of topology changes using Morse theory. We investigate various topology changing transitions, including the pair production of black holes and of topological geons, in the light of these ideas.
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    Possible Newtonian interpretation of relativistic cosmological perturbation theory
    (2015-03-11) Nayeri, Ali; Padmanabhan, T.
    Cosmological perturbations with wavelengths smaller than Hubble radius can be handled in the context of Newtonian theory with very high accuracy. The application of this Newtonian approximation, however, is restricted to nonrelativistic matter and cannot be used for relativistic matter. Recently, by modifying the continuity equation, Lima, et. a!., extended the domain of applicability of Newtonian cosmology to radiation dominated phase. We adopted this continuity equation to re-examine linear cosmological perturbation theory for a two fluid universe with uniform pressure. We study the evolution equations for density contrasts and their validity in different epochs and on scales larger than Hubble radius and compare the results with the full relativistic approach. The comparison shows the high accuracy of this approximation.
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    Tales of tails in cosmology
    (2015-03-11) Faraoni, Valerio; Gunzing , Edgard
    Late time mild inflation (LTMI) proposes to solve the age of the universe problem and the discrepancy between locally and globally measured values of the Hubble parameter. However, the mechanism proposed to achieve LTMI is found to be physically pathological by applying the theory of tails for the solutions of wave equations in curved spaces. Alternative mechanisms for LTMI are discussed, and the relevance of scalar wave tails for cosmology is emphasized.
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    Localized branes and black holes
    (2015-03-11) Surya, Sumati; Marolf , Donald
    We address the delocalization of low dimensional D-branes and NS-branes when they are a part of a higher dimensional BPS black brane, and the homogeneity of the resulting horizon. We show that the effective delocalization of such branes is a classical effect that occurs when localized branes are brought together. Thus, the fact that the ~ew known solutions with inhomogeneous horizons are highly singular need not indicate a singularity of generic D- and NS-brane states. Rather, these singular solutions are likely to be unphysical as they cannot be constructed from localized branes which are brought together from a finite separation.
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    Site characterization for the IUCAA telescope
    (2015-03-11) Das, H.K.; Menon, S.M.; Paranjpye, A.; Tandon, S.N.
    We present the report on characterisation of the site for IUCAA telescope, which was conducted during October '96 to April '97. The main points highlighted are the results on: seeing, contribution of atmospheric turbulence neai• the surface to seeing , extinction and sky brightness, cloud coverage and surface weather data. In addition the key design features of the instruments developed for these observations are presented.
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    Rotation, closed timelike curves and a singularity theorem
    (2015-03-11) Raychaudhuri, A. K.
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    Lensing by gravitational waves in scalar – tensor gravity: Einstein frame analysis
    (2015-03-11) Faraoni, Valerio; Gunzing , Edgard
    The amplification of a light beam due to intervening gravitational waves is studied. The previous Jordan frame result according to which the amplification is many orders of magnitude larger in scalar-tensor gravity than in general relativity does not hold in the Einstein conformal frame. Lensing by gravitational waves is discussed in relation to the ongoing and proposed VLBI observations aimed at detecting the scintillation effect.
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    Molecules in the Zabc = 2.8112 damped system toward PKS 0528-250
    (2015-03-11) Srianand, R.; Petitjean, Patrick
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    Search for gravitational waves from the millisecond pulsar PSR 0437-471
    (2015-03-11) Mohanty, S.D.; Heng, I.S.; Blair, D.G; Dhurandhar, S.V.; Tobar, M.; Ivanov, E.
    A search for gravitational waves from the millisecond pulsar PSR 0437-471has been initiated using the bar detector NIOBE which is located at the University of Western Australia. This search involves a very long coherent integration of the bar output which may stretch over a few years. We present a detailed report on the data analysis algorithm, called phase plane rotation,which will be used in this search. A discussion of the actual implementation of the algorithm is presented.