  We consider the transfer of a U(1) charge density between Bose-Einstein
condensates of complex scalar fields coupled to a thermal bath, focusing on the
case of a homogeneous Affleck-Dine field transmitting the charge stored in its
angular motion to an axion field. We demonstrate that in the absence of
additional symmetries this charge transfer, aided by cosmic expansion as well
as the thermal effective potential of the Affleck-Dine field, can be very
efficient. The charge redistribution between the scalar fields becomes possible
if the interactions with the thermal bath break the original U(1) x U(1)
symmetry down to a single U(1) symmetry; the charge distribution between the
two fields is then determined by minimizing the free energy. We discuss
implications for cosmological setups involving complex scalars, with
applications to axion dark matter, baryogenesis, kination domination, and
gravitational wave production.
