Exponential plateaus and inflation in metric-affine gravity

TL;DR

The paper addresses how to realize robust inflation in metric-affine gravity by coupling the inflaton to the Holst invariant with a coupling that vanishes at some phi0 and has a large slope. This leads to an exponential plateau in the canonically normalized potential, yielding Starobinsky-like predictions with r ≈ 12/N^2 and n_s ≈ 1 - 2/N, largely independent of the original potential V(phi). The mechanism is shown to be universal within a strong-coupling regime and is extendable to generalizations V_m(χ) and to non-minimal coupling to the Ricci scalar. This provides a flexible MAG-based framework for inflation with potentially favorable phenomenology for addressing cosmological data tensions.

Abstract

We propose a new mechanism for inflationary model building in the framework of metric-affine gravity. Such a mechanism involves an inflaton non-minimally coupled with the Holst invariant. If the non-minimal coupling function has a zero point and it is very steep at that same point, then the canonically normalized inflaton potential always features an exponential plateau, regardless of the shape of the original inflaton potential. The inflationary predictions in such a region are equivalent to the ones of Starobinsky inflation.