Pragmatic mode-sum regularization method for semiclassical black-hole spacetimes

TL;DR

The paper introduces a new numerical method for regularizing the stress-energy tensor in 4D semiclassical black-hole spacetimes, enabling more accurate calculations of quantum effects during black hole evaporation.

Contribution

A novel mode-sum regularization technique for the renormalized stress-energy tensor in 4D, with two variants for stationary and spherically-symmetric backgrounds, demonstrated on Schwarzschild spacetime.

Findings

Successfully computed ⟨φ²⟩_ren in Schwarzschild spacetime

Results agree with previous methods, validating the new approach

Lays groundwork for analyzing black hole evaporation dynamics

Abstract

Computation of the renormalized stress-energy tensor is the most serious obstacle in studying the dynamical, self-consistent, semiclassical evaporation of a black hole in 4D. The difficulty arises from the delicate regularization procedure for the stress-energy tensor, combined with the fact that in practice the modes of the field need be computed numerically. We have developed a new method for numerical implementation of the point-splitting regularization in 4D, applicable to the renormalized stress-energy tensor as well as to $\left\langle \phi^{2}\right\rangle _{ren}$, namely the renormalized $\left\langle \phi^{2}\right\rangle$. So far we have formulated two variants of this method: t-splitting (aimed for stationary backgrounds) and angular splitting (for spherically-symmetric backgrounds). In this paper we introduce our basic approach, and then focus on the t-splitting variant, which is the simplest of the two (deferring the angular-splitting variant to a forthcoming paper). We then use this variant, as a first stage, to calculate $\left\langle \phi^{2}\right\rangle _{ren}$ in Schwarzschild spacetime, for a massless scalar field in the Boulware state. We compare our results to previous ones, obtained by a different method, and find full agreement. We discuss how this approach can be applied (using the angular-splitting variant) to analyze the dynamical self-consistent evaporation of black holes.