1998 (IPP)

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

Browse

Now showing 1 - 20 of 46

Quantum structure of spacetime and blackhole entropy
(2015-02-11) Padmanabhan, T.
Shapefinders: a new shape diagnostic for large scale structure
(2015-03-11) Sahni, Varun; Sathyaprakash, B.S.; Shandarian, Sergei
Naked singularities in low energy, effective string theory
(2015-03-11) Kar, Sayan
Hierarchial search strategy for inspiraling compact binaries
(2015-03-11) Dhurandhar, S.V.
Event horizon: Magnifying glass for planck length physics
(2015-03-11) Padmanabhan, T.
Turbulent transport of a tracer: An electromagnetic formulation
(2015-03-11) Sridhar, S.
Does the non-minimal coupling of the scalar field improve or destroy inflation ?
(2015-03-11) Faraoni, Valerio
Global anomalies in canonical gravity
(2015-03-11) Surya, Sumati; Vaidya, Sachindeo
A duality relation for fluid spacetime
(2015-03-11) Dadhich, Naresh; Patel, L.K.; Tikekar, R.
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.
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.
Effective radii and color gradients in radio galaxies
(2015-03-11) Mahabal, A.; Kembhavi, A. K.; Mccarthy, P.J.
We present de Vaucouleurs' effective radii in Band R bands for a sample of MRC radio galaxies and a control sample of normal galaxies. We use the ratio of the scale lengths in the two bands as an indicator to show that the radio galaxies tend to have excess of blue color in their inner region much more frequently than the control galaxies. We show that the scale length ratio is a useful indicator of radial color variation even when the conventional color gradient is too noisy to serve the purpose. We also discuss other interesting morphological features of radio galaxies including departures from de Vaucouleurs' law profiles in their central regions.
On electrogravity duality
(2015-03-11) Dadhich, Naresh
Facets of tunneling: Particle production in external fields
(2015-03-11) Srinivasan, K.; Padmanabhan, T.
Do the central engines of quasars evolve by accretion
(2015-03-11) Srianand, R.; Krishna-Gopal
Influence of the cosmological expansion on local systems
(2015-03-11) Cooperstock, F.I.; Faraoni, Valerio; Vollick, D.N.
Following renewed interest, the problem of whether the cosmological expansion affects the dynamics of local systems is reconsidered. The cosmological correction to the equations of motion in the locally inertial Fermi normal frame (the relevant frame for astronomical observations) is computed. The evolution equations for the cosmological perturbation of the two-body problem are solved in this frame. The effect on the orbit is insignificant as are the effects on the galactic and galactic cluster scales.
Comparisons of various model fits to the iron line profile in MCG-30-15
(2015-03-11) Misra, R.; Sutaria, F.K.
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.
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.
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.