Mass change and motion of a scalar charge in cosmological spacetimes

TL;DR

This paper calculates the self-force on a scalar charge in various cosmological spacetimes, revealing effects on mass variation and motion deviation, with implications for electromagnetic forces and flat spacetime scenarios.

Contribution

It provides exact calculations of mass change and motion deviation due to self-force in cosmological models, extending previous work and including electromagnetic analogs.

Findings

Mass decreases and recovers in certain cosmologies

Self-force causes a net push on the particle

Effects are consistent with electromagnetic self-force

Abstract

Continuing previous work reported in an earlier paper [L.M. Burko, A.I. Harte, and E. Poisson, Phys. Rev. D 65, 124006 (2002)] we calculate the self-force acting on a point scalar charge in a wide class of cosmological spacetimes. The self-force produces two types of effect. The first is a time-changing inertial mass, and this is calculated exactly for a particle at rest relative to the cosmological fluid. We show that for certain cosmological models, the mass decreases and then increases back to its original value. For all other models except de Sitter spacetime, the mass is restored only to a fraction of its original value. For de Sitter spacetime the mass steadily decreases. The second effect is a deviation relative to geodesic motion, and we calculate this for a charge that moves slowly relative to the dust in a matter-dominated cosmology. We show that the net effect of the self-force is to push on the particle. We show that this is not an artifact of the scalar theory: The electromagnetic self-force acting on an electrically charged particle also pushes on the particle. The paper concludes with a demonstration that the pushing effect can also occur in the context of slow-motion electrodynamics in flat spacetime.