Boundary terms of the Einstein-Hilbert action

TL;DR

This paper introduces new variables for general relativity that lead to a well-posed Einstein-Hilbert action, analyzes boundary terms including null surfaces, and connects these findings to existing literature.

Contribution

It proposes two novel dynamical variables for general relativity, resulting in a well-posed action principle and provides a detailed analysis of boundary terms, including null surfaces.

Findings

New variables yield a well-posed Einstein-Hilbert action.

Boundary terms for null surfaces are systematically analyzed.

Connections to existing boundary term proposals are established.

Abstract

The Einstein-Hilbert action for general relativity is not well posed in terms of the metric $g_{ab}$ as a dynamical variable. There have been many proposals to obtain an well posed action principle for general relativity, e.g., addition of the Gibbons-Hawking-York boundary term to the Einstein-Hilbert action. These boundary terms are dependent on what one fixes on the boundary and in particular on spacetime dimensions as well. Following recent works of Padmanabhan we will introduce two new variables to describe general relativity and the action principle with these new dynamical variables will turn out to be well posed. Then we will connect these dynamical variables and boundary term obtained thereof to existing literature and shall comment on a few properties of Einstein-Hilbert action which might have been unnoticed earlier in the literature. Before concluding with future prospects and discussions, we will perform a general analysis of the boundary term of Einstein-Hilbert action for null surfaces as well.