Domain wall and isocurvature perturbation problems in a supersymmetric
  axion model
  The axion causes two serious cosmological problems, domain wall and
isocurvature perturbation problems. Linde pointed that the isocurvature
perturbations are suppressed when the Peccei-Quinn (PQ) scalar field takes a
large value $\sim M_{\text{pl}}$ (Planck scale) during inflation. In this case,
however, the PQ field with large amplitude starts to oscillate after inflation
and large fluctuations of the PQ field are produced through parametric
resonance, which leads to the formation of domain walls. We consider a
supersymmetric axion model and examine whether domain walls are formed by using
lattice simulation. It is found that the domain wall problem does not appear in
the SUSY axion model when the initial value of the PQ field is less than
$10^{3}\times v$ where $v$ is the PQ symmetry breaking scale.
