Gravitational self-force in nonvacuum spacetimes

TL;DR

This paper extends the gravitational self-force formulation to nonvacuum spacetimes, including scalar and electromagnetic fields, providing a foundation for more general applications beyond vacuum solutions.

Contribution

It introduces a concrete formulation of the gravitational self-force in nonvacuum backgrounds with scalar and electromagnetic fields, including local and tail terms.

Findings

Formulation includes couplings with scalar and electromagnetic fields.

Provides covariant local expansions for singular potentials.

Facilitates regularization and computation of self-force in nonvacuum spacetimes.

Abstract

The gravitational self-force has thus far been formulated in background spacetimes for which the metric is a solution to the Einstein field equations in vacuum. While this formulation is sufficient to describe the motion of a small object around a black hole, other applications require a more general formulation that allows for a nonvacuum background spacetime. We provide a foundation for such extensions, and carry out a concrete formulation of the gravitational self-force in two specific cases. In the first we consider a particle of mass $m$ and scalar charge $q$ moving in a background spacetime that contains a background scalar field. In the second we consider a particle of mass $m$ and electric charge $e$ moving in an electrovac spacetime. The self-force incorporates all couplings between the gravitational perturbations and those of the scalar or electromagnetic fields. It is expressed as a sum of local terms involving tensors defined in the background spacetime and evaluated at the current position of the particle, as well as tail integrals that depend on the past history of the particle. Because such an expression is rarely a useful starting point for an explicit evaluation of the self-force, we also provide covariant expressions for the singular potentials, expressed as local expansions near the world line; these can be involved in the construction of effective extended sources for the regular potentials, or in the computation of regularization parameters when the self-force is computed as a sum over spherical-harmonic modes.