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, $\kappa$, 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 Planck measurement of $n_s$ constrains the inflaton coupling to light fermions in the Einstein frame; $y<4.5\times {10}^{-4}$, corresponding to an upper limit on the reheating temperature $T_{\mathrm{RH}}<2\times {10}^{11}\mathrm{GeV}$, whereas the ACT DR6 measurement of $n_s$ corresponds to $3.8\times {10}^{-4}<y<5.6\times {10}^{-4}$ and $1.7\times {10}^{11}\mathrm{GeV}<T_{\mathrm{RH}}<2.8\times {10}^{11}\mathrm{GeV}$, while the upper limits on $r$ provide weaker constraints. Planck data also imply a constraint on a trilinear inflaton coupling to light scalars in the Einstein frame: $\kappa \le 4\times {10}^{12}\mathrm{GeV}$, corresponding to $T_{\mathrm{RH}}\le 4.2\times {10}^{13}\mathrm{GeV}$. We further present constraints on inflaton couplings to massive fermions and scalars, and analyze constraints on couplings in the Jordan frame.

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• Evolution of the Universe
• Inflation
• Particle interactions