New Inflation in Supersymmetric SU(5) and Flipped SU(5) GUT Models

TL;DR

This paper explores implementing supersymmetric new inflation within SU(5) and flipped SU(5) GUT models, ensuring compatibility with observational data, gauge unification, and proton decay suppression, while addressing monopole dilution and reheating.

Contribution

It introduces a specific inflationary scenario in SU(5) models using GUT Higgs fields, incorporating additional symmetries and addressing key cosmological and particle physics constraints.

Findings

Predictions align with Planck data for spectral index n_s

Tensor-to-scalar ratio r is negligibly small, between 10^{-12} and 10^{-8}

Reheat temperature range is consistent with gravitino constraints

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 $U(1)_R \times Z_{n}$ symmetry for its successful implementation. The standard model (SM) gauge singlet scalar components of $24_H$ and $10_H$ 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, $n_s$, for $n \geq 5$ in $SU(5)$ model and for $n \geq 6$ in flipped $SU(5)$ model. In particular, the tensor to scalar ratio $r$ and the running of spectral index $d n_s/ d\ln k$ are negligibly small and lie in the range, $10^{-12} \lesssim r \lesssim 10^{-8}$ and $10^{-9} \lesssim dn_s/d\ln k \lesssim 10^{-3}$, for realistic values of $n$. In numerical estimation of the various predictions, we fix the gauge symmetry breaking scale, $M$, around $2 \times 10^{16}$ 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, $3 \times 10^{7}\text{ GeV }\lesssim T_r \lesssim 2 \times 10^{9}$ GeV, is safe from the gravitino problem for the gravitino mass, $m_{3/2} \gtrsim 10$ TeV. Finally, the $U(1)_R \times Z_{n}$ symmetry is also observed to play a crucial role in suppressing the various fast proton decay operators.