2001 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/628
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Item Non-conformally flat bulk spacetime and the 3-brane world(2001-01-05) Singh, Parampreet; Dadhich, NareshWe show that for non-conformally flat bulk spacetime, there exist no bound modes for zero mass graviton on the 3-brane. The brane world model is therefore unstable for the bulk spacetime being different from the conformally flat anti - de Sitter space.Item New stationary vacuum solution dual to the kerr solution(2001-05-01) Turakulov, Z . Ya.; Dadhich, NareshWe present a stationary axially symmetric two parameter vacuum solution which could be considered as “dual” to the Kerr solution. It is obtained by removing the mass parameter from the function of the radial coordinate and introducing a dimensionless parameter in the function of the angle coordinate in the metric functions. It turns out that it is in fact the massless limit of the Kerr - NUT solution.Item R=O spacetimes and self-dual lorentzian wormholes(2001-04-02) Dadhich, Naresh; Kar, Sayan; Mukherjee, Sailajananda; et al.A two–parameter family of spherically symmetric, static Lorentzian wormholes is obtained as the general solution of the equation ρ = ρt = 0, where ρ = Tij ui uj , ρt = (Tij − 1 2T gij ) ui uj , and ui ui = −1. This equation characterizes a class of spacetimes which are “self dual” (in the sense of electrogravity duality). The class includes the Schwarzschild black hole, a family of naked singularities, and a disjoint family of Lorentzian wormholes, all of which have vanishing scalar curvature (R = 0). Properties of these spacetimes are discussed. Using isotropic coordinates we delineate clearly the domains of parameter space for which wormholes, nakedly singular spacetimes and the Schwarzschild black hole can be obtained. A model for the required “exotic” stress–energy is discussed, and the notion of traversability for the wormholes is also examined.Item Nariai metric is the first example of the singularity free model(2001-07-01) Dadhich, NareshThis is just to point out that the Nariai metric is the first example of the singularity free expanding perfect fluid cosmological model satisfying the weak energy condition, ρ > 0, ρ + p = 0. It is a conformally non-flat Einstein space.Item On naked singularities in higher dimensional Vaidya space-times(2001-04-03) Ghosh, S. G.; Dadhich, NareshWe investigate the end state of gravitational collapse of null fluid in higher di- mensional space-times. Both naked singularities and black holes are shown to be developing as final outcome of the collapse. The naked singularity spectrum in col- lapsing Vaidya region (4D) gets covered with increase in dimensions and hence higher dimensions favor black hole in comparison to naked singularity. The Cosmic Censor- ship Conjecture will be fully respected for a space of infinite dimensionItem Subtle is the gravity(2001-07-05) Dadhich, NareshIn this lecture I build up the motivation for relativity and grav- itation based on general principles and common sense considera- tions which should fall in the sphere of appreciation of a general reader. There is a novel way of looking at things and understanding them in a more direct physical terms which should be of interest to fellow relativists as well as physicists in general.Item Field theories from the relativistic law of motion(2001-06-02) Singh, Parampreet; Dadhich, NareshFrom the relativistic law of motion we attempt to deduce the field theories corresponding to the force law being linear and quadratic in 4-velocity of the particle. The linear law leads to the vector gauge theory which could be the abelian Maxwell electrodynamics or the non-abelian Yang-Mills theory. On the other hand the quadratic law demands spacetime metric as its potential which is equivalent to de- manding the Principle of Equivalence. It leads to the tensor theory of gravitational field - General Relativity. It is remarkable that a purely dynamical property of the force law leads uniquely to the correspond- ing field theories