Inflationary observables in $F(R)$ gravity

TL;DR

This paper explores modified gravity models with polynomial terms and their inflationary signatures, showing compatibility with current observational bounds and suggesting some models predict very low tensor-to-scalar ratios.

Contribution

It introduces specific polynomial $f(R)$ gravity models and analyzes their inflationary signatures, highlighting models that predict lower tensor-to-scalar ratios than current bounds.

Findings

Models satisfy current phenomenological bounds from PLANCK and BICEP3.

Certain solutions predict very low tensor-to-scalar ratios ($<0.0015$).

Results are similar to previous $R^3$ model studies.

Abstract

We present phenomenological signatures for a modified gravity model f(R), constructed with linear, quadratic, cubic and quartic terms. The obtained signatures satisfy current phenomenological bounds reported by PLANCK and BICEP3. Furthermore, two of the model solutions $\sigma_1$ and $\sigma_2$ seem to favor a much lower value for the tensor-to-scalar ratio $0.0005<r_{\sigma_1}<0.0015$ and $r_{\sigma_2}<0.00015$ than the current reported experimental bounds. The results we obtained are quantitatively similar to those presented in previous studies for $R^3$ models.