A novel probe of Einstein-Hilbert action: Dynamic upgradation of metric parameters

TL;DR

This paper explores the peculiar features of the Einstein-Hilbert action, especially how dynamic upgradation of metric parameters affects its decomposition, leading to insights on curvature and topological changes.

Contribution

It introduces a novel approach of promoting static metric parameters to time-dependent variables and analyzes the resulting effects on the Einstein-Hilbert action and spacetime topology.

Findings

Bulk term remains invariant under parameter promotion

Surface term changes by a total derivative

Curvature becomes singular when parameters revert to static values

Abstract

The Einstein-Hilbert (EH) action is peculiar in many ways. Some of the Peculiar features have already been highlighted in literature. In the present article, we have discussed some peculiar features of EH action which has not been discussed earlier. It is well-known that there are several ways of decomposing the EH action into the bulk and the surface part with different underlying motivations. We provide a review on all of these decompositions. Then, we attempt to study the static coordinate as a limiting case of a time-dependent coordinate via dynamic upgradation of the constant metric parameters. Firstly, we study the consequences when the constant parameters, present in a static and spherically symmetric (SSS) metric, are promoted to the time dependent variables, which allows us to incorporate the time-dependence in the static coordinate. We find that, in every sets of decomposition, the expression of the bulk term remains invariant, whereas the surface term changes by a total derivative term. Finally, when we obliterate the time dependence of the metric parameters, we find that the expression of the Ricci-scalar (or the EH action) does not go back to its original value. Instead, we find that the curvature becomes singular on the horizon, which implies a topological change from the original spacetime.