Pseudonatural Inflation

TL;DR

This paper explores how to construct natural, flat inflaton potentials compatible with particle physics, emphasizing non-linearly realized symmetries, extra-dimensional models, and mechanisms like little-Higgs or supersymmetry to ensure validity.

Contribution

It proposes new models of inflation with flat potentials using non-linear symmetries, extra dimensions, and symmetry mechanisms to address quantum gravity and naturalness issues.

Findings

Single pseudo Nambu Goldstone boson models require super-Planckian scales.

Extra-dimensional models can achieve large field values consistently.

Minimal 4D models need approximate symmetries plus little-Higgs or supersymmetry.

Abstract

We study how to obtain a sufficiently flat inflaton potential that is natural from the particle physics point of view. Supersymmetry, which is broken during inflation, cannot protect the potential against non-renormalizable operators violating slow-roll. We are therefore led to consider models based on non-linearly realized symmetries. The basic scenario with a single four-dimensional pseudo Nambu Goldstone boson requires the spontaneous breaking scale to be above the Planck scale, which is beyond the range of validity of the field theory description, so that quantum gravity corrections are not under control. A nice way to obtain consistent models with large field values is to consider simple extensions in extra-dimensional setups. We also consider the minimal structures necessary to obtain purely four-dimensional models with spontaneous breaking scale below M_P; we show that they require an approximate symmetry that is supplemented by either the little-Higgs mechanism or supersymmetry to give trustworthy scenarios.