  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.
