46 research outputs found
Oscillating non-singular relativistic spherical model
A particular choice of the time function in the recently presented spherical
solution by Dadhich [1] leads to a singularity free cosmological model which
oscillates between two regular states. The energy-stress tensor involves
anisotropic pressure and a heat flux term but is consistent with the usual
energy conditions (strong, weak and dominant). By choosing the parameters
suitably one can make the model consistent with observational data. An
interesting feature of the model is that it involves blue shifts as in the
quasi steady state model [2] but without violating general relativity.Comment: 6 pages, REVTEX versio
Global monopole as dual-vacuum solution in Kaluza-Klein spacetime
By application of the duality transformation, which implies interchange of
active and passive electric parts of the Riemann curvature (equivalent to
interchange of Ricci and Einstein tensors) it is shown that the global monopole
solution in the Kaluza-Klein spacetime is dual to the corresponding vacuum
solution. Further we also obtain solution dual to flat space which would in
general describe a massive global monopole in 4-dimensional Euclidean space and
would have massless limit analogus to the 4-dimensional dual-flat solution.Comment: 8 pages, LaTEX versio
On the third law of black hole dynamics
The third law of black hole dynamics states that the surface gravity
(temperature) of black hole cannot be reduced to zero in finite sequence of
physical interactions. We argue that the same is true when surface gravity is
replaced by gravitational charge. We demonstrate that the prescribed window for
infalling energy and radiation pinches off as extremality ()
is approached.Comment: 9 pages, LaTeX version, Accepted in Physics Letters
Electromagnetic duality in general relativity
By 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.Comment: 18 pages, LaTEX versio