Constant-roll $f(R)$ inflation compared with Cosmic Microwave Background anisotropies and swampland criteria

TL;DR

This paper investigates constant-roll $f(R)$ inflation models, compares their predictions with CMB data, and examines their compatibility with swampland criteria, revealing limitations in spectral index predictions.

Contribution

It introduces and analyzes specific constant-roll $f(R)$ inflation models, comparing their observational viability and theoretical consistency with swampland conjectures.

Findings

Models fit observational data for tensor-to-scalar ratio r

Spectral index n_s exceeds 1 in some models, indicating tension with observations

Logarithmic model predicts n_s between 0.996 and 0.999

Abstract

Inflationary models derived from $f(R)$ gravity, where the scalaron rolls down with a constant rate from the top to the minimum of the effective potential, are considered. Specifically, we take into account three $f(R)$ models \textit{i.e.}\,Starobinsky $R^{2}$, $R^{2p}$ and the logarithmic corrected models. We compare the inflationary parameters derived from the models with the observational data of CMB anisotropies \textit{i.e.} the Planck and Keck/array datasets in order to find observational constraints on the parameters space. We find that although our $f(R)$ constant-roll models for $\gamma=0$ show observationally acceptable values of $r$, they do not predict favoured values of the spectral index. In particular, we have $n_{s}>1$ for the Starobinsky $R^{2}$ and $R^{2p}$ models and $0.996<n_{s}<0.999$ for logarithmic model. Finally, we study the models from the point of view of Weak Gravity Conjecture adopting the swampland criteria.