IUCAA Preprints
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Item Time in a quantum gravity(2015-03-13) Biswas, S.; Shaw, A.; Modak, B.Item On the brown-york quasilocal energy, gravitational charge, and black hole event horizons(2015-03-13) Bose, Sukanta; Dadhich, NareshWe prove the recently proposed identity for certain black hole spacetimes that relates the difference of the Brown-York quasilocal energy and the Komar charge at the event horizon of the hole to the total energy of the spacetime. We prove this identity for the Kerr-Newman family of black hole spacetimes and for non-static (cosmological) spherically symmetric shear-free perfect fluid solutions of general relativity that contain black hole event horizons. We explicitly demonstrate its validity by applying it to several asymptotically fiat as well as non-fiat black hole solutions, including the case of a black hole with a global monopole charge.Item Global anomalies in canonical gravity(2015-03-11) Surya, Sumati; Vaidya, SachindeoItem 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 Aspects of gravitational clustering(2015-03-01) Padmanabhan, T.Several issues related to the gravitational clustering of collisionless dark matter in an expanding universe is discussed. The discussion is pedagogical but the emphasis is on semianalytic methods and open questions-rather than on well established results.Item New classes of black hole spacetime in 2+1 gravity(2015-03-01) Bose, Sukanta; Dadhich, Naresh; Kar, SyanNew multi-parameter families of black holes in three-dimensional (3D) gravity are obtained. We apply the electrogravity transformation (which implies an exchange of the Ricci and Einstein tensors) to the 3D field equations to obtain these solutions. Several properties of these geometries, including the nature of the matter that threads them, are discussed. Some of these properties are found to be strikingly different from known black holes in (2+1) dimensions.Item Gravoelectric-dual of the kerr solution(2015-03-01) Dadhich, Naresh; Patel, L.K.By decomposing the Riemann curvature into electric and magnetic parts, we define the gravoelectric duality transformation by interchange of active and passive electric parts which amounts to interchange of the Ricci and Einstein tensors. It turns out that the vacuum equation is duality-invariant. We obtain solutions dual to the Kerr solution by writing an effective vacuum equation in such a way that it still admits the Kerr solution but is not duality invariant. The dual equation is then solved to obtain the dual-Kerr solution which can be interpreted as the Kerr black hole sitting in a string dust universe.Item Detection of gravitational waves using a network of detectors(2015-03-01) Bose, Sukanta; Dhurandhar, S.V.; Pai, ArchanaWe formulate the data analysis problem for the detection of the Newtonian coalescing-binary signal by a network of laser interferometric gravitational wave detectors that have arbitrary orientations, but are located at the same site. We use the maximum likelihood method for optimizing the detection problem. We show that for networks comprising of up to three detectors, the optimal statistic is just the matched network-filter. Alternatively, it is simply a linear combination of the signal-to-noise ratios of the individual detectors. This statistic, therefore, can be interpreted as the signal-to-noise ratio of the network. The overall sensitivity of the network is shown to increase roughly as the square-root of the number of detectors in the network. We further show that these results continue to hold even for the restricted post Newtonian filters. Finally, our formalism is general enough to be extended, in a straightforward way, to address the problem of detection of such waves from other sources by some other types of detectors, eg., bars or spheres, or even by networks of spatially well-separated detectors.Item Gravoelectromagnetic approach to the gravitational faraday rotation in stationary spacetimes(2015-03-01) Nouri- Zonoz, MohammadUsing the 1 + 3 formulation of stationary spacetimes we show, in the context of gravoelectromagnetism, that the plane of the polarization of light rays passing close to a black hole undergoes a rotation. We show that this rotation has the same integral form as the usual Faraday effect, i.e. it is proportional to the integral of the component of the gravomagnetic field along the propagation path. We apply this integral formula to calculate the Faraday rotation induced by the Kerr and NUT spaces using the quasi-Maxwell form of the vacuum Einstein equations.Item Gravitational instability in the strongly nonlinear regime: A study of various approximations(2015-02-18) Sathyaprakash, B.S.; Sahni, Varun; Munshi, Dipak; Pogosysn, D.; Melott, A.L.