IUCAA Preprints
Permanent URI for this communityhttp://localhost:4000/handle/11007/149
Browse
80 results
Search Results
Item LRS bianchi-type I models with a time dependent cosmological “constant”(2015-03-14) Vishwakarma, R.G.; Abdussattar; Beesham, A.Plane symmetric homogeneous models of the universe with a perfect fluid distribution of matter and a variable cosmological "constant" representing the energy density of vacuum have been presented. The models are highly anisotropic in the early stages of evolution and ultimately evolve to the standard model at the present epoch. Of the three models obtained in this paper, one has an increasing vacuum energy density with time in the early universe. Though highly negative in the very early universe, the vacuum density soon becomes positive, and meets the observational limits at the present epoch. The negative vacuum in the early universe in this model, which decays numerically, adds up to anisotropy and at the same time contributes to the isotropization process. The second model is found to admit matter creation from the decaying vacuum energy whereas the third one, in which the vacuum density is always one third of the corresponding radiation density, is devoid of any such creation.Item Morphology of clusters and superclusters in N-body simulations of cosmological gravitational clustering(2015-03-13) Sathyaprakash, B.S.; Sahni, Varun; Shandarian, SergeiItem 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 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.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 Tales of tails in cosmology(2015-03-11) Faraoni, Valerio; Gunzing , EdgardLate 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.Item 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 Shapefinders: a new shape diagnostic for large scale structure(2015-03-11) Sahni, Varun; Sathyaprakash, B.S.; Shandarian, SergeiItem Reconstructing the cosmic equation of state from supernova distances(2015-03-01) Saini, Tarun Deep; Raychaudhuri, Somak; Sahni, Varun; Strarobinsky, A.A.Item A new class of LRS Bianchi Type –I cosmological models in lyra geometry(2015-03-01) Pradhan, Anirudh; Vishwakarma, Anil KumarLRS Bianchi type-1 models have been studied in the cosmological theory based on Lyra's geometry. A new class of exact solutions has been obtained by considering a time dependent and constant displacement field for constant deceleration parameter models of the universe. The physical behaviour of the models is examined in vacuum and in the presence of perfect fluids.