We revisit higher order corrections to the Starobinsky inflationary model using the most recent P-ACT-LB-BK18 data, which exhibits a mild but definite tension with the predictions of the original model. Our results demonstrate how even small {higher order} deformations of the Ricci scalar (e.g. R3,R4,⋯) can bring the model into better agreement with current data and impose nontrivial constraints on the post-inflationary dynamics.
Cite
@article{arxiv.2509.04105,
title = {Beyond the Starobinsky model after ACT},
author = {Min Gi Park and Dhong Yeon Cheong and Seong Chan Park},
journal= {arXiv preprint arXiv:2509.04105},
year = {2026}
}