Multi-Natural Inflation in Supergravity
  We show that the recently proposed multi-natural inflation can be realized
within the framework of 4D ${\cal N}=1$ supergravity. The inflaton potential
mainly consists of two sinusoidal potentials that are comparable in size, but
have different periodicity with a possible non-zero relative phase. For a
sub-Planckian decay constant, the multi-natural inflation model is reduced to
axion hilltop inflation. We show that, taking into account the effect of the
relative phase, the spectral index can be increased to give a better fit to the
Planck results, with respect to the hilltop quartic inflation. We also consider
a possible UV completion based on a string-inspired model. Interestingly, the
Hubble parameter during inflation is necessarily smaller than the gravitino
mass, avoiding possible moduli destabilization. Reheating processes as well as
non-thermal leptogenesis are also discussed.
