DR. BIBHAS MAJHI

We provide a simple and straightforward procedure for defining a Virasoro algebra basedon the diffeomorphisms near a null surface in a spacetime and obtain the entropy density of the null surface from its central charge. We use the o¿-shell Noether current corresponding to the diffeomorphism invariance of a gravitational Lagrangian and define the Virasoro algebra from its variation. This allows us to identify the central charge and the zero mode eigenvalue using which we obtain the entropy density of the Killing horizon. The entire analysis is done off-shell without using the field equations. Here the Noether current corresponding to the surface term of gravitational action and diffeomorphisms which leave the horizon structure unaltered are used. In this approach there are no ambiguities in the calculation of the central charge.