Naresh Dadhich
Articles written in Pramana – Journal of Physics
Volume 8 Issue 1 January 1977 pp 14-21 Astronomy And Astrophysics
Spectral features of radiation from Nordström and Kerr-Newman white holes
Unlike the Schwarzschild white hole, Nordström and Kerr-Newman white holes cannot explode right down from the space time singularity
Here the explosion is decelerated by the presence of charge and rotation and hence the radiation emitted would be not as energetic as in the Schwarzschild case where its energy is infinitely large for emission from
Volume 9 Issue 1 July 1977 pp 71-77 General Relativity
Timelike and null geodesics in the Nordström field
The timelike and null geodesics are investigated in the Nordström geometry and it is found that incoming geodesics always encounter a turning point at a finite radial distance. The limits for escape, bound and stable orbits are obtained and they are closer to the source as compared to their counterparts in the Schwarzschild’s field.
Volume 44 Issue 4 April 1995 pp 303-316
On singularity-free spacetimes
Naresh Dadhich L K Patel R Tikekar
We consider here the metric for the singularity-free family of fluid models. The metric is unique for cylindrically symmetric space-time with metric potentials being separable functions of radial and time coordinates in the comoving coordinates. It turns out that fluid models separate out into two classes, with
Volume 47 Issue 5 November 1996 pp 387-392
A class of stationary rotating string cosmological models
We obtain a one parameter class of stationary rotating string cosmological models of which the well-known Gödel universe is a particular case. By suitably choosing the free parameter function, it is always possible to satisfy the energy conditions. The rotation of the model hinges on the cosmological constant which turns out to be negative. String-dust distribution in Gödel-type universes is also briefly discussed.
Volume 49 Issue 2 August 1997 pp 213-224 Research Articles
Inhomogeneous cosmological models with heat flux
L K Patel Ramesh Tikekar Naresh Dadhich
We present a general class of inhomogeneous cosmological models filled with non-thermalized perfect fluid by assuming that the background spacetime admits two space-like commuting Killing vectors and has separable metric coefficients. The singularity structure of these models depends on the choice of the parameters and the metric functions. A number of previously known perfect fluid models follow as particular cases of this general class. Physical and geometrical features of these models are studied and the general expression for temperature distribution is given.
Volume 49 Issue 4 October 1997 pp 417-420 Research Articles
Isothermal fluid sphere: Uniqueness and conformal mapping
We prove the theorem: A necessary and sufficient condition for a spacetime to represent an isothermal fluid sphere (linear equation of state with density falling off as inverse square of the curvature radius) without boundary is that it is conformal to a spacetime of zero gravitational mass (‘minimally’ curved).
Volume 50 Issue 4 April 1998 pp 307-314
Schwarzschild black hole with global monopole charge
Naresh Dadhich K Narayan U A Yajnik
We derive the metric for a Schwarzschild black hole with global monopole charge by relaxing asymptotic flatness of the Schwarzschild field. We then study the effect of global monopole charge on particle orbits and the Hawking radiation. It turns out that existence, boundedness and stability of circular orbits scale up by (1−8
Volume 52 Issue 4 April 1999 pp 359-367
On spacetimes dual to spherically symmetric solutions
By defining a duality transformation which implies interchange of active and passive electric parts of gravitational field, it is possible to construct spacetimes dual to solutions of the Einstein equation. Under the duality transformation a fluid spacetime maps into a fluid spacetime with density and pressure transforming as ρ
Volume 63 Issue 4 October 2004 pp 859-864
Quantifying energy condition violations in traversable wormholes
Sayan Kar Naresh Dadhich Matt Visser
The ‘theoretical’ existence of traversable Lorentzian wormholes in the classical, macroscopic world is plagued by the violation of the well-known energy conditions of general relativity. In this brief article we show: (i) how the extent of violation can be quantified using certain volume integrals and (ii) whether this ‘amount of violation’ can be minimised for some specific cut-and-paste geometric constructions. Examples and possibilities are also outlined.
Volume 63 Issue 4 October 2004 pp 887-889
Summary of classical general relativity workshop
Naresh Dadhich Narayan Banerjee
This is a summary of the presentations at the parallel session in the classical general relativity workshop of the ICGC-2004.
Volume 69 Issue 1 July 2007 pp 1-2
Naresh Dadhich Pankaj Joshi Probir Roy
Volume 69 Issue 1 July 2007 pp 23-29
Singularity: Raychaudhuri equation once again
I first recount Raychaudhuri's deep involvement with the singularity problem in general relativity. I then argue that precisely the same situation has arisen today in loop quantum cosmology as obtained when Raychaudhuri discovered his celebrated equation. We thus need a new analogue of the Raychaudhuri equation in quantum gravity.
Volume 74 Issue 6 June 2010 pp 875-882 Research Articles
Characterization of the Lovelock gravity by Bianchi derivative
We prove the theorem: The second-order quasilinear differential operator as a second-rank divergence-free tensor in the equation of motion for gravitation could always be derived from the trace of the Bianchi derivative of the fourth-rank tensor, which is a homogeneous polynomial in curvatures. The existence of such a tensor for each term in the polynomial Lagrangian is a new characterization of the Lovelock gravity.
Volume 77 Issue 3 September 2011 pp 433-437
On the enigmatic 𝛬 – A true constant of spacetime
Had Einstein followed the Bianchi differential identity for the derivation of his equation of motion for gravitation, 𝛬 would have emerged as a true new constant of spacetime on the same footing as the velocity of light? It is then conceivable that he could have perhaps made the most profound prediction that the Universe may suffer accelerated expansion some time in the future! Further we argue that its identiﬁcation with the quantum vacuum energy is not valid as it should have to be accounted for like the gravitational ﬁeld energy by enlarging the basic framework of spacetime and not through a stress tensor. The acceleration of the expansion of the Universe may indeed be measuring its value for the ﬁrst time observationally.
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