Hierarchical Axion Inflation
  We propose a new field theory mechanism for generating an effective
trans-Planckian decay constant from sub-Planckian ones. Using the minimal two
axions and a hierarchy between two axion decay constants is sufficient for
realizing inflation through non-perturbative effects only and with minimal
tuning. The inflationary motion is kept entirely within a sub-Planckian domain.
We outline possible strategies of embedding the model in a string theory setup.
