Observable r, gravitino dark matter, and non-thermal leptogenesis in no-scale supergravity

Abstract

We analyse the shifted hybrid inflation in a no-scale supersymmetric SU(5) GUT model which naturally circumvents the monopole problem. The no-scale framework is derivable as the effective field theory of the supersymmetric (SUSY) compactifications of string theory, and yields a flat potential with no anti-de Sitter vacua, resolving the η problem. The model predicts a scalar spectral tilt n_s compatible with the most recent measurements by the Planck satellite, while also accommodating large values of the tensor-to-scalar ratio r (~ 0.0015), potentially measurable by the near-future experiments. Moreover, the proton decay lifetime in the presence of the dimension-5 operators is found to lie above the current limit imposed by the Super-Kamiokande experiment. A realistic scenario of reheating and non-thermal leptogenesis is employed, wherein the reheating temperature T_r lies in the (2 × 10⁶ ≲ T_r ≲ 2 × 10⁹) GeV range, and at the same time realizing gravitino as a viable dark matter (DM) candidate.