UV-Protected Inflation

TL;DR

This paper proposes a novel coupling of the inflaton to Einstein tensor that allows for natural inflation with a decay constant smaller than the Planck scale, maintaining perturbativity and shift symmetry.

Contribution

It introduces a unique kinetic coupling to Einstein tensor in Natural Inflation, enabling sub-Planckian decay constants while preserving key symmetries and perturbative control.

Findings

Allows f<<M_p in Natural Inflation models

Maintains perturbative regime throughout inflation

Preserves shift symmetry and avoids extra degrees of freedom

Abstract

In Natural Inflation, the Inflaton is a pseudo-Nambu-Goldstone boson which acquires a mass by explicit breaking of a global shift symmetry at scale f. In this case, for small field values, the potential is flat and stable under radiative corrections. Nevertheless, slow roll conditions enforce f>>M_p making the validity of the whole scenario questionable. In this letter, we show that a coupling of the Inflaton kinetic term to the Einstein tensor allows f<<M_p by enhancing the gravitational friction acting on the Inflaton during inflation. This new unique interaction, a) keeps the theory perturbative in the whole inflationary trajectory, b) preserves the tree-level shift invariance of the pseudo-Nambu-Goldstone Boson and c) avoids the introduction of any new degrees of freedom with respect the standard Natural Inflation.