Curvature corrections to Starobinsky inflation can explain the ACT results

TL;DR

This paper explores how adding higher-order curvature corrections to the Starobinsky inflation model can better align its predictions with recent ACT observational data, potentially resolving previous discrepancies.

Contribution

It introduces specific curvature corrections to the Starobinsky model and demonstrates their impact on inflationary predictions, improving agreement with ACT results.

Findings

Curvature corrections shift inflationary predictions closer to ACT data.

Modified models can reconcile standard Starobinsky predictions with observations.

Measuring tensor modes can help distinguish these curvature corrections.

Abstract

We investigate the impact of curvature corrections to Starobinsky inflation in light of the latest observational results from the Atacama Cosmology Telescope (ACT). While the pure Starobinsky model remains a compelling candidate for cosmic inflation, we explore how the higher-order curvature terms $R^3$, $R^{4}$ and $R^{3/2}$ modify the inflationary predictions. Using the scalar-tensor formulation of $f(R)$ gravity, we derive the effective scalar potentials and compute the resulting scalar tilt $n_s$, its running index $\alpha_s$ and the tensor-to-scalar ratio $r$. We show that those curvature corrections can shift the predictions to align better with the ACT data, thus providing a possible resolution to a minor discrepancy between the standard Starobinsky model and ACT observations. Our findings suggest that the modified Starobinsky models with the higher-order curvature terms offer a viable pathway to reconciling inflationary predictions with precision cosmological measurements. At the same time, measuring or constraining primordial tensor modes can help to discriminate between these corrections.