Minimal Plateau Inflation in light of ACT DR6 Observations

Abstract

We explore a class of minimal plateau inflationary models constrained by the latest cosmological observations from ACT DR6, Planck 2018, BICEP/Keck 2018, and DESI, collectively referred to as P-ACT-LB-BK18. These models, characterized by a non-polynomial potential, are analyzed using both inflationary and post-inflationary reheating dynamics, and the limits on the viable model parameter space are obtained. Our results show that the minimal model with matter-like post inflationary reheating phase remains consistent with current data at both $1\sigma$ and $2\sigma$ levels. The inflaton potential's exponent $n$ and reheating epoch are intertwined in that upon its increase, corresponding to the stiffer reheating equation of state, the viable model parameter space in accordance with ACT shrinks, which is further facilitated by the primordial gravitational waves (PGWs) overproduction. We further explored a supergravity-inspired extension of the model under study with similar results, but with tighter constraints on the model parameters. These results emphasize the importance of jointly analyzing CMB data and reheating physics to test inflationary models.