High scale inflation, model-independent string axion, and QCD axion with
  domain wall number one
  The recent BICEP2 result shows that the Universe once has gone through the
vacuum with the GUT scale energy density. The implied high scale inflation
nullifies the dilution idea of topological defects, strings and domain walls,
of the axionic system. In particular, domain walls are disastrous if the domain
wall problem with domain-wall number greater than 1 is present. We argue that
the model-independent axion in string compactification with the anomalous U(1)
gauge symmetry resolves the domain wall problem naturally with a symmetry
principle.
