Rectifying Power-law $F(R)$ Gravity and Starobinsky Inflation Deformations in View of ACT

Abstract: In this work we aim to provide a consistent theoretical framework that revives the power-law $F(R)$ gravity inflation framework in the Jordan frame. It is known in the literature that the power-law $F(R)$ gravity inflation of the form $F(R)=R+\beta R^n$ is non-viable and produces a power-law evolution. We demonstrate that the standard approach in power-law $F(R)$ gravity inflation is flawed for many reasons and we introduce a new framework which elevates the role of power-law $F(R)$ gravity inflation, making it viable and compatible with both the Planck and ACT data. In our framework the power-law $F(R)$ gravity inflation is disentangled from a power-law evolution.