IUCAA Preprints
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Item Electromagnetic duality in general relativity(2015-03-01) Dadhich, NareshBy resolving the Riemann curvature relative to a unit timelike vector into electric and magnetic parts, we consider duality relations analogous to the electromagnetic theory. It turns out that the duality symmetry of the Einstein action implies the Einstein vacuum equation without the cosmological term. The vacuum equation is invariant under interchange of active and passive electric parts giving rise to the same vacuum solutions but the gravitational constant changes sign. Further by modifying the equation it is possible to construct interesting dual solutions to vacuum as well as to flat spacetimes.Item General relativity, collapse of rotating star and emission of gravity wave(2015-02-18) Parui, Ramen KumarItem A New Solution of Einstein’s Vacuum Field Equations(IUCAA, 2015-02) Vishwakarma, R. G.Item Cylindrically symmetric viscous universes(2014-11-26) Patel, L.K.; Dadhich, NareshWe have considered here cylindrically symmetric cosmological models with viscous fluid having the Kasnerian time evolution. It turns out that the ‘‘no‐matter’’ limit of our geodetic viscous universes, which can as well be looked upon as string dust universes, is the non-flat empty Kasner spacetime. We thus propose that the universe may be born with the Kasner geometry at t = 0 with matter in the form of viscous fluid, then it may follow the path: geodetic to non-geodetic and finally to the radiation phase when viscosity is fully worn out. We have solutions to describe each phase separately.Item Cylindrical universes with heat and null radiation flow(2014-11-25) Patel, L.K.; Dadhich, NareshIn paper-I(Patel and Dadhich ,1992) we have discussed cylindrically symmetric viscous fluid models with the Kasnerian time evolution. In this paper we incorporate heat flow and null radiation flow with the perfect fluid. Here again, in the case of heat flow the Kasner spacetime is the matter-free limit of the model. We establish a general result that a static perfect fluid distribution will on Kasnerization (introduce t4/3, t4/3, and t−2/3 in the coefficients of dr2, dΦ2, and dz2) yield a time-dependent distribution with the same equation of state and with or without heat flow.Item On some transonic aspects of general relativistic spherical accretion onto schwarzschild black holes(2001-01-02) Das, Tapas K.The equations governing general relativistic, spherically symmetric, hydrodynamic accretion of polytropic fluid onto black holes are solved in Schwarzschild metric to investigate some of the transonic properties of the flow. Only stationary solutions are discussed. For such accretion, it has been shown that real physical sonic points may form even for flow with γ < 4 3 or γ > 5 3 . Behaviour of some flow variables in the close vicinity of the event horizon are studied as a function of specific energy and polytropic index of the flow.Item Heat flow in general relativity(2001-02) Banerjee, A.A few models of bounded sphere containing heat flux in the radial direction are constructed. These models satisfy the conditions of fit at their boundaries with vaidya's radiating metric. further the casual heat transport equation is considered in the background of one of the above metrics and it is found to be consistent with the inflationary expansion. Our case is more general than that discussed previously by maartens et al.Item Relativistic world : A common sense perspective(2002-03-01) Dadhich, NareshItem Combining general relativity and quantum theory : points of conflict and contact(2001-09-12) Padmanabhan, T.The issues related to bringing together the principles of general relativity and quantum theory are discussed. After briefly summarising the points of conflict between the two formalisms I focus on four specific themes in which some contact has been established in the past between GR and quantum field theory: (i) The role of planck length in the microstructure of spacetime (ii) The role of quantum effects in cosmology and origin of the universe (iii) The thermodynamics of spacetimes with horizons and especially the concept of entropy related to spacetime geometry (iv) The problem of the cosmological constant.Item Accretion powered spherical wind in general relativity(2001-04-14) Das, Tapas K.Using full general relativistic calculations, we investigate the possibility of generation of mass outflow from spherical accretion onto non-rotating black holes. Introducing a relativistic hadronic-pressure-supported steady, standing, spherically-symmetric shock surface around a Schwarzschild black hole as the effective physical barrier that may be responsible for the generation of spherical wind, we calculate the mass outflow rate R ˙ m in terms of three accretion parameters and one outflow parameter by simultaneously solving the set of general relativistic hydrodynamic equations describing spherically symmetric, transonic, polytropic accretion and wind around a Schwarzschild black hole. Not only do we provide a sufficiently plausible estimation of R ˙ m, we also successfully study the dependence and variation of this rate on various physical parameters governing the flow. Our calculation indicates that independent of initial boundary conditions, the baryonic matter content of this shock-generated wind always correlates with post-shock flow temperature.