Adiabatic suppression of the axion abundance and isocurvature due to
  coupling to hidden monopoles
  The string theory predicts many light fields called moduli and axions, which
cause a cosmological problem due to the overproduction of their coherent
oscillation after inflation. One of the prominent solutions is an adiabatic
suppression mechanism, which, however, is non-trivial to achieve in the case of
axions because it necessitates a large effective mass term which decreases as a
function of time. The purpose of this paper is twofold. First, we provide an
analytic method to calculate the cosmological abundance of coherent oscillation
in a general situation under the adiabatic suppression mechanism. Secondly, we
apply our method to some concrete examples, including the one where a string
axion acquires a large effective mass due to the Witten effect in the presence
of hidden monopoles.
