Smooth hybrid inflation with low reheat temperature and observable gravity waves in SU(5) x U(1)chi super-GUT

We realize smooth hybrid inflation in the framework of supersymmetric SU(5) x U(1)x c SO(10) model which provides a natural solution to the monopole problem appearing in the spontaneous symmetry breaking of SU(5). The breaking of U(1)x symmetry leaves a residual discrete Z2 symmetry, that serves as the MSSM matter parity, realizing the possi-bility of the lightest supersymmetric particle as a cold dark matter candidate. The d = 5 proton lifetime for the decay p -> K+(nu) over bar, mediated by color-triplet Higgsinos is found to satisfy current experimental bounds if split-high scale SUSY scenario is employed. We show that with minimal Kahler potential, the soft supersymmetry breaking terms play a vital role in bringing the scalar spectral index ns within the Planck's latest bounds. In a minimal Kahler potential setup, small values of tensor-to-scalar ratio r less than or similar to 3.5 x 10(-7) are obtained, whereas the gravitino mass turns out to be in the range that favors PeV scale SUSY but is not suf-ficiently high to avoid the d = 5 proton decay. A non-minimal Kahler potential including higher order corrections is required to realize successful inflation with central value of scalar spectral index n(s) = 0.9655, large tensor modes r < 0.056 and a low reheat temperature (3 x 10(6) less than or similar to T-r less than or similar to 6.5 x 10(7)) GeV consistent with leptogenesis and baryogenesis.