  We investigate the propagation of electromagnetic fields and potentials in
the plasma of the early Universe, assuming a Friedmann-Robertson-Walker
background with negative curvature. Taking over results from classical plasma
physics, we show that charged particles will acquire an effective mass that has
not only the expected thermal component but also a non-thermal component due to
the influence of distant matter. Although this is a direct effect of the vector
potential, we show the theory is nevertheless gauge invariant. This phenomenon
is therefore in the same category as the Aharonov-Bohm effect. The non-thermal
component becomes increasingly important with time, and in some cosmological
models can prove to be of decisive importance in bringing about the phase
transition that generates normal masses.
