Effects of radiative corrections on Starobinsky inflation

We analyze radiative corrections to the predictions of Starobinsky-like models of inflation arising from self-interactions of the inflaton, and from its Yukawa couplings, y , to matter fermions, and dimensionful trilinear couplings, κ , to scalar fields, which could be responsible for reheating the Universe after inflation. The inflaton self-interactions are found to be of higher order in the Hubble expansion rate during inflation, and hence unimportant for CMB observations. In contrast, Einstein-frame matter couplings to an inflaton generating Starobinsky-like inflation can have significant effects on the spectral index of scalar CMB perturbations, n s , and on the tensor-to-scalar ratio, r . Using a renormalization-group improved analysis of the effective inflationary potential, we find that the measurement of n s constrains the inflaton coupling to light fermions in the Einstein frame; y < 4.5 × 10 − 4 , corresponding to an upper limit on the reheating temperature T RH < 2 × 10 11 GeV , whereas the ACT DR6 measurement of n s corresponds to 3.8 × 10 − 4 < y < 5.6 × 10 − 4 and 1.7 × 10 11 GeV < T RH < 2.8 × 10 11 GeV , while the upper limits on r provide weaker constraints. data also imply a constraint on a trilinear inflaton coupling to light scalars in the Einstein frame: κ ≤ 4 × 10 12 GeV , corresponding to T RH ≤ 4.2 × 10 13 GeV . We further present constraints on inflaton couplings to massive fermions and scalars, and analyze constraints on couplings in the Jordan frame.