Hybrid inflation followed by modular inflation

TL;DR

This paper explores a two-stage inflationary model combining hybrid inflation at a superheavy scale with subsequent modular inflation driven by a string axion, aligning with recent cosmological data and GUT scale predictions.

Contribution

It introduces a hybrid-plus-modular inflation framework that satisfies observational constraints and connects inflationary parameters with grand unification scale predictions.

Findings

Hybrid inflation can produce the required curvature perturbations within observational bounds.

The model's parameters align the GUT scale with theoretical expectations.

Additional e-foldings from modular inflation solve horizon and flatness problems.

Abstract

Inflationary models with a superheavy scale F-term hybrid inflation followed by an intermediate scale modular inflation are considered. The restrictions on the power spectrum P_R of curvature perturbation and the spectral index n_s from the recent data within the power-law cosmological model with cold dark matter and a cosmological constant can be met provided that the number of e-foldings N_HI* suffered by the pivot scale k_*=0.002/Mpc during hybrid inflation is suitably restricted. The additional e-foldings needed for solving the horizon and flatness problems are generated by modular inflation with a string axion as inflaton. For central values of P_R and n_s, the grand unification scale comes out, in the case of standard hybrid inflation, close to its supersymmetric value M_GUT=2.86 x 10^16 GeV, the relevant coupling constant is relatively large (0.005-0.14), and N_HI* is between 10 and 21.7. In the shifted [smooth] hybrid inflation case, the grand unification scale can be identified with M_GUT for N_HI*=21 [N_HI*=18].