Gravitational modulated reheating and non-Gaussianity in Supergravity
  R^2 inflation
  Reheating after R^2 inflation proceeds through gravitational particle
production of conformally noninvariant fields. We argue that the nonvanishing
expectation value of flat directions generic in supersymmetric theories break
conformal invariance of the fields coupled to them in a position-dependent
manner due to quantum fluctuations. As a result modulated reheating can occur
after the supergravity R^2-inflation. The resultant curvature fluctuation is a
mixture of the one produced during inflation and that produced by modulated
reheating. The spectral index takes a value between n_s=0.960 and 0.983, the
nonlinearity parameter of the local-type non-Gaussianity can be f_nl\sim \pm
10, and the tensor-to-scalar ratio is r \le 4\times 10^{-3}.
