Gravity waves and proton decay in a flipped SU(5) hybrid inflation model

We revisit supersymmetric hybrid inflation in the context of the flipped SU(5) model. With minimal superpotential and minimal Kähler potential, and soft supersymmetry (SUSY) masses of order (1–100) TeV, compatibility with the Planck data yields a symmetry breaking scale M of flipped SU(5) close to (2–4)×1015 GeV. This disagrees with the lower limit M≳7×1015 GeV set from proton decay searches by the Super-Kamiokande collaboration. We show how M close to the unification scale 2×1016 GeV can be reconciled with SUSY hybrid inflation by employing a nonminimal Kähler potential. Proton decays into e+π0 with an estimated lifetime of order 1036 years. The tensor to scalar ratio r in this case can approach observable values ∼10−4–10−3.