Natural and Multi-Natural Inflation in Axion Landscape
  We propose a landscape of many axions, where the axion potential receives
various contributions from shift symmetry breaking effects. We show that the
existence of the axion with a super-Planckian decay constant is very common in
the axion landscape for a wide range of numbers of axions and shift symmetry
breaking terms, because of the accidental alignment of axions. The effective
inflation model is either natural or multi-natural inflation in the axion
landscape, depending on the number of axions and the shift symmetry breaking
terms. The tension between BICEP2 and Planck could be due to small modulations
to the inflaton potential or steepening of the potential along the heavy axions
after the tunneling. The total duration of the slow-roll inflation our universe
experienced is not significantly larger than $60$ if the typical height of the
axion potentials is of order $(10^{16-17}{\rm \,GeV})^4$.
