Are $R^2$- and Higgs-inflations really unlikely?

TL;DR

This paper investigates the initial conditions of $R^2$- and Higgs-inflation models, showing they are not less likely than other inflation models when analyzed in the Jourdan frame, despite their flat potentials.

Contribution

It demonstrates that $R^2$- and Higgs-inflation models are not inherently unlikely when initial conditions are properly considered in the Jourdan frame.

Findings

Initial conditions in the Jourdan frame show models are not worse than others

Terms in Einstein frame are of the same order, just smaller

Models with flat potentials are not less probable than others

Abstract

We address the question of unlikeness of $R^2$- and Higgs inflations exhibiting exponentially flat potentials and hence apparently violating the inherent in a chaotic inflation initial condition when kinetic, gradient and potential terms are all of order one in Planck units. Placing the initial conditions in the Jourdan frame we find both models not worse than any other models with unbounded from above potentials: the terms in the Einstein frame are all of the same order, though appropriately smaller.