New inflation in supersymmetric SU(5) and flipped SU(5) GUT models

Abstract

We study the feasibility of realizing supersymmetric new inflation model, introduced by Senoguz and Shafi in [1], for SU(5) and flipped SU(5) models of grand unified theories (GUTs). This realization requires an additional U(1)R × Zn symmetry for its successful implementation. The standard model (SM) gauge singlet scalar components of 24H and 10H GUT Higgs superfields are respectively employed to realize successful inflation in SU(5) and flipped SU(5) models. The predictions of the various inflationary observables lie within the recent Planck bounds on the scalar spectral index, ns, for n ⩾ 5 in SU(5) model and for n ⩾ 6 in flipped SU(5) model. In particular, the tensor to scalar ratio r and the running of spectral index d ns/ d ln k are negligibly small and lie in the range, 10−12 ≲ r ≲ 10−8 and 10−9 ≲ dns/d ln k ≲ 10−3, for realistic values of n. In numerical estimation of the various predictions, we fix the gauge symmetry breaking scale, M, around 2 × 1016 GeV . The issue of gauge coupling unification in R-symmetric SU(5) is evaded by adding vectorlike families with mass splitting within their multiplets. The dilution of monopoles beyond the observable limit is naturally achieved in the breaking of SU(5) gauge symmetry during inflation. A realistic scenario of reheating with non-thermal leptogenesis is employed for both models. The predicted range of reheat temperature within Planck bounds, 3 × 107 GeV ≲ Tr ≲ 2 × 109 GeV, is safe from the gravitino problem for the gravitino mass, m3/2 ≳ 10 TeV . Finally, the U(1)R × Zn symmetry is also observed to play a crucial role in suppressing the various fast proton decay operators.