Viable Chaotic Inflation as a Source of Neutrino Masses and Leptogenesis
  We show that the seesaw mechanism as well as leptogenesis are natural
outcomes of a viable chaotic inflation in supergravity. The inflation model
contains two superfields, the inflaton and stabilizer fields, which, being
singlets under the standard model gauge symmetry, naturally couple to the
lepton and Higgs doublets. The inflaton decays into leptons and Higgs fields,
and the reheating temperature is predicted to be of O(10^{13}) GeV, for which
thermal leptogenesis is possible. On the other hand, gravitinos are copiously
produced, and various solutions to the gravitino problem are discussed. We also
argue that, if the shift symmetry of the inflaton is explicitly broken down to
a discrete one, neutrino Yukawa couplings are periodic in the inflaton field,
and masses of leptons and Higgs do not blow up even if the inflaton takes
super-Planckian field values. The inflaton potential is given by a sum of
sinusoidal functions with different height and periodicity, the so-called
multi-natural inflation. We show that the predicted scalar spectral index and
tensor-to-scalar ratio lie in the region favored by the Planck data.
