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. 
Ido Ben-Dayan, Francisco Gil Pedro, Alexander Westphal
hep-th astro-ph.CO hep-ph