Induced-Gravity Inflation in no-Scale Supergravity and Beyond

Supersymmetric versions of induced-gravity inflation are formulated within Supergravity (SUGRA) employing two gauge singlet chiral superfields. The proposed superpotential is uniquely determined by applying a continuous R and a discrete Z_n symmetry. We select two types of logarithmic Kahler potentials, one associated with a no-scale-type SU(2,1) / SU(2) x U(1)_R x Z_n Kahler manifold and one more generic. In both cases, imposing a lower bound on the parameter cR involved in the coupling between the inflaton and the Ricci scalar curvature - e.g. cR > 76, 105, 310 for n=2,3 and 6 respectively -, inflation can be attained even for subplanckian values of the inflaton while the corresponding effective theory respects the perturbative unitarity. In the case of no-scale SUGRA we show that, for every n, the inflationary observables remain unchanged and in agreement with the current data while the inflaton mass is predicted to be 3x10^13 GeV. Beyond no-scale SUGRA the inflationary observables depend mildly on n and crucially on the coefficient involved in the fourth order term of the Kahler potential which mixes the inflaton with the accompanying non-inflaton field.