UV-protected (Natural) Inflation: Primordial Fluctuations and non-Gaussian Features

TL;DR

This paper introduces UV-protected inflation, where quantum symmetry breaking and gravitationally enhanced friction enable sub-Planckian couplings, resulting in a single-field inflation model with potential for detectable gravitational waves and non-Gaussian features.

Contribution

It proposes a novel UV-protected inflation model with enhanced gravitational friction, maintaining perturbative unitarity and predicting observable non-Gaussianities and gravitational waves.

Findings

The model yields a red tilted spectrum consistent with observations.

Non-Gaussianity is dominated by gauge transformation effects and parity-violating interactions.

Potentially detectable non-Gaussian signals from parity violation in inflaton interactions.

Abstract

We consider the UV-protected inflation, where the inflaton potential is obtained by quantum (one-loop) breaking of a global symmetry into a discrete symmetry. In this model, all coupling scales are sub-Planckian. This is achieved by coupling the inflaton kinetic term to the Einstein tensor such that the friction is enhanced gravitationally at high energies. In this respect, this new interaction makes virtually any potential adequate for inflation while keeping the system perturbative unitary. We show that even if the gravitationally enhanced friction intrinsically contains new nonlinearities, the UV-protected inflation (and any similar models) behaves as a single field scenario with red tilted spectrum and potentially detectable gravitational waves. Interestingly enough, we find that non-Gaussianity of the curvature perturbations in the local form are completely dominated by the nonlinear gauge transformation from the spatially flat to uniform-field gauge and/or by parity violating interactions of the inflaton and gauge bosons. In particular, the parity violating interactions may produce detectable non-Gaussianity.