Grand Unification and Subcritical Hybrid Inflation

TL;DR

This paper explores a hybrid inflation model with small inflaton-matter couplings, predicting inflationary parameters consistent with Planck data and linking the inflation energy scale to gauge unification.

Contribution

It introduces a subcritical hybrid inflation model where the inflaton potential smoothly transitions from quadratic to plateau, aligning predictions with observational constraints.

Findings

Predicted scalar spectral index n_s compatible with Planck data.

Tensor-to-scalar ratio r has a lower bound of 0.049.

Inflation energy scale aligns with gauge coupling unification in supersymmetry.

Abstract

We consider hybrid inflation for small couplings of the inflaton to matter such that the critical value of the inflaton field exceeds the Planck mass. It has recently been shown that inflation then continues at subcritical inflaton field values where quantum fluctuations generate an effective inflaton mass. The effective inflaton potential interpolates between a quadratic potential at small field values and a plateau at large field values. An analysis of the allowed parameter space leads to predictions for the scalar spectral index n_s and the tensor-to-scalar ratio r similar to those of natural inflation. Using the range for n_s and r favoured by the Planck data, we find that the energy scale of the plateau is constrained to the interval (1.6 - 2.4) * 10^16 GeV which includes the energy scale of gauge coupling unification in the supersymmetric standard model. The tensor-to-scalar ratio is predicted to have the lower bound r > 0.049 for 60 e-folds before the end of inflation.