  Electric flux may be screened by pair nucleation of heavy charges, a process
that has a simple description in terms of a worldline instanton. When flux is
wrapped around a small compact spatial dimension, worldline instantons still
induce flux dissipation, but the leading process does not create real charged
pairs. Instead, dissipation can be described in effective field theory as the
production of long-wavelength scalar quanta via parametric resonance. The rate
is computed semiclassically, and comments are made on the related problem of
pair creation at finite temperature, for which differing results appear in the
literature. Flux dissipation and the weak gravity conjecture together imply
that the proper distance in field space a homogeneous axion field can traverse
is bounded.
