MR. KRISHNA MOHAN PARATTU

It is common knowledge that the Einstein-Hilbert action for general relativity does not furnish a consistent variational principle when the spacetime manifold under consideration has a boundary. One way to remedy this is to add an extra term, called a counter-term, to the action. The most commonly used counter-term is the Gibbons-Hawking-York counter-term constructed using the unit normal to the boundary. This prescription, however, cannot be used for a null boundary as the normal to a null surface has zero norm and cannot be normalized to unity. The speaker will show how one can construct an appropriate counter-term for a null boundary. He will also show how the metric degrees of freedom whose variations appear in the boundary term can be naturally separated into gauge degrees and physical degrees.