  Cosmological solutions with a homogeneous Yang-Mills field which oscillates
and passes between topologically distinct vacua are discussed. These solutions
are used to model the collapsing Bartnik-McKinnon gravitational sphaleron and
the associated anomalous production of fermions. The Dirac equation is analyzed
in these backgrounds. It is shown explicitly that a fermion energy level
crosses from the negative to positive energy spectrum as the gauge field
evolves between the topologically distinct vacua. The cosmological solutions
are also generalized to include an axion field.
