Inflation in theories with broken diffeomorphisms

TL;DR

This paper explores how breaking diffeomorphism invariance in the inflaton sector affects inflationary dynamics, primordial perturbations, and post-inflationary behavior, with implications for CMB observations.

Contribution

It introduces models invariant under transverse diffeomorphisms, derives key inflationary parameters, and analyzes their observational and dynamical consequences.

Findings

Modified scalar spectral index consistent with CMB data

Distinct post-inflationary regimes due to broken diffeomorphisms

Quadratic potential models exhibit novel dynamical behavior

Abstract

We analyze the impact of breaking diffeomorphism invariance in the inflaton sector. In particular, we consider inflaton models which are invariant under the subgroup of transverse diffeomorphisms and address the possibility of implementing a slow-roll phase. We obtain the corresponding expressions for relevant quantities such as the slow-roll parameters and the number of $e$-folds, and derive the primordial power-spectrum of curvature perturbations. The scalar spectral index features modifications which are confronted with CMB data from Planck and ACT. We study in detail the quadratic potential model, combining asymptotic and numerical analysis. We show that the post-inflationary behavior can be drastically different from the diffeomorphism-invariant case, exhibiting novel dynamical regimes.