Chiral gravitational waves and primordial black holes in UV-protected Natural Inflation

Abstract

We consider an UV-protected Natural Inflation scenario involving Chern-Simons-like interactions between the inflaton and some beyond the Standard Model gauge fields. The accelerated expansion of the Universe is supported by a combination of a gravitationally-enhanced friction sensitive to the scale of inflation and quantum friction effects associated with the explosive production of gauge fluctuations. The synergy of these two velocity-restraining mechanisms allows for: $i)$ Natural Inflation potentials involving only sub-Planckian coupling constants, $ii)$ the generation of a dark matter component in the form of primordial black holes, and $iii)$ a potentially observable background of chiral gravitational waves at small scales.