Saving Natural Inflation

TL;DR

This paper proposes new models of Natural Inflation that avoid trans-Planckian field excursions by using extra-dimensional and composite Higgs inspired frameworks, enhancing the model's consistency with quantum gravity constraints.

Contribution

It introduces realistic Natural Inflation models with sub-Planckian field excursions using extra-natural and composite Higgs inspired approaches.

Findings

Achieves inflation without trans-Planckian field values.

Demonstrates models compatible with Planck data.

Provides four-dimensional dual descriptions.

Abstract

Slow-roll inflation requires the inflaton field to have an exceptionally flat potential, which combined with measurements of the scale of inflation demands some degree of fine-tuning. Alternatively, the flatness of the potential could be due to the inflaton's origin as a pseudo-Goldstone boson, as in Natural Inflation. Alas, consistency with Planck data places the original proposal of Natural Inflation in a tight spot, as it requires a trans-Planckian excursion of the inflaton. Although one can still tune the renormalizable potential to sub-Planckian values, higher order corrections from quantum gravity or sources of breaking of the Goldstone symmetry would ruin the predictivity of the model. In this paper we show how in more realistic models of Natural Inflation one could achieve inflation without a trans-Planckian excursion of the field. We show how a variant of Extra-natural inflation with bulk fermions can achieve the desired goal and discuss its four-dimensional duals. We also present a new type of four dimensional models inspired in Little Higgs and Composite Higgs models which can lead to sub-Planckian values of the inflaton field.