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We revisit supersymmetric hybrid inflation in the context of the flipped SUð5Þ 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 SUð5Þ close to ð2-4Þ × 10 15 GeV. This disagrees with the lower limit M ≳ 7 × 10 15 GeV set from proton decay searches by the Super-Kamiokande collaboration. We show how M close to the unification scale 2 × 10 16 GeV can be reconciled with SUSY hybrid inflation by employing a nonminimal Kähler potential. Proton decays into e þ π 0 with an estimated lifetime of order 10 36 years. The tensor to scalar ratio r in this case can approach observable values ∼10 −4 -10 −3 .

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A scheme of simplified smooth hybrid inflation is realized in the framework of supersymmetric SU (5). The smooth model of hybrid inflation provides a natural solution to the monopole problem that appears in the breaking of SU (5) gauge symmetry. The supergravity corrections with nonminimal Kähler potential are shown to play important role in realizing inflation with a red-tilted scalar spectral index n s < 1, within Planck's latest bounds. As compared to shifted model of hybrid inflation, relatively large values of the tensor-to-scalar ratio r 0.01 are achieved here, with nonminimal couplings −0.05 κ S 0.01 and −1 κ SS 1 and the gauge symmetry-breaking scale M ≃ (2.0 − 16.7) × 10 16 GeV.