1998 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/2980
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Item Classical essence of black hole radiation(2015-03-14) Nouri-Zonoz, M.; Padmanabhan, T.Item 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.Item Comparisons of various model fits to the iron line profile in MCG-30-15(2015-03-11) Misra, R.; Sutaria, F.K.Item Conformal transformations in classical gravitational theories and in cosmology(2015-03-11) Faraoni, Valerio; Gunzing , Edgard; Nardone, PasqualeIn 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.Item Do the central engines of quasars evolve by accretion(2015-03-11) Srianand, R.; Krishna-GopalItem Does inflationary particle production suggest Ωm< 1 ?(2015-03-13) Sahni, Varun; Habib, SalmanItem Does the non-minimal coupling of the scalar field improve or destroy inflation ?(2015-03-11) Faraoni, ValerioItem Doing it with mirrors : Classical analogues for black hole radiation(2015-03-14) Srinivasan, K.; Padmanabhan, T.Item A duality relation for fluid spacetime(2015-03-11) Dadhich, Naresh; Patel, L.K.; Tikekar, R.Item 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.Item Event horizon: Magnifying glass for planck length physics(2015-03-11) Padmanabhan, T.Item Evolution of multipolar magnetic field in isolated neutron stars(2015-03-13) Mitra, Dipanjan; Konar, Sushan; Bhattacharya, DipankarItem Facets of tunneling: Particle production in external fields(2015-03-11) Srinivasan, K.; Padmanabhan, T.Item Filaments and pancakes in the IRAS 1.2 jy redshift catalogue(2015-03-13) Sathyaprakash, B.S.; Sahni, Varun; Shandarian, Sergei; Fisher, K.B.Item Formal analysis of two dimensional gravity(2015-03-11) Engineer, Sunu; Srinivasan, K.; Padmanabhan, T.Several investigations in the study of cosmological structure formation use numerical simulations in both two and three dimensions. In this paper we address the subtle question of ambiguities in the nature of two dimensional gravity in an expanding background. We take a detailed and formal approach by deriving the equations describing gravity in (D + 1) dimensions using the action principle of Einstein. We then consider the Newtonian limit of these equations and finally obtain the necessary fluid equations required to describe structure formation. These equations are solved for the density perturbation in both the linearised form and in the spherical top hat model of nonlinear growth. We find that, when the special case of D = 2 is considered, no structures can grow. We therefore conclude that, within the frame work of Einstein's theory of gravity in (2 + 1) dimensions, formation of structures cannot take place. Finally, we indicate the different possible ways of getting around this difficulty so that growing structures can be obtained in two dimensional cosmological gravitational simulations and discuss their implications.Item Global anomalies in canonical gravity(2015-03-11) Surya, Sumati; Vaidya, SachindeoItem Hierarchial search strategy for inspiraling compact binaries(2015-03-11) Dhurandhar, S.V.Item The inflationary universe- from theory to observations(2015-03-11) Sahni, VarunItem 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.Item Lensing by gravitational waves in scalar – tensor gravity: Einstein frame analysis(2015-03-11) Faraoni, Valerio; Gunzing , EdgardThe 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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