  We consider a class of cosmological models in which the universe is filled
with a (non-electric) charge density that repels itself by means of a force
carried by a vector boson with a tiny mass. When the vector's mass depends upon
other fields, the repulsive interaction gives rise to an electromagnetic
barrier which prevents these fields from driving the mass to zero. This can
modify the cosmology dramatically. We present a very simple realization of this
idea in which the vector's mass arises from a scalar field. The electromagnetic
barrier prevents this field from rolling down its potential and thereby leads
to accelerated expansion.
