Spectral index and non-Gaussianity in supersymmetric hybrid inflation

We consider a supersymmetric hybrid inflation model with two inflaton fields. The superpotential during inflation is dominated by W=(κS+κ'S')M 2, where S, S' are inflatons carrying the same U(1)R charge, κ, κ' are dimensionless couplings, and M (∝10 15-16 GeV) is a dimensionful parameter associated with a symmetry breaking scale. One light mass eigenstate drives inflation, while the other heavier mass eigenstate is stuck to the origin. The smallness of the lighter inflaton mass for the scalar spectral index ns∼0.96, which is the center value of WMAP7, can be controlled by the ratio κ'/κ through the supergravity corrections. We also discuss the possibility of the two field inflation and large non-Gaussianity in this setup. (orig.)