On cosmological Inflation In Palatini $F(R,\phi)$ Gravity

TL;DR

This paper explores various inflationary models within Palatini $F(R,)$ gravity, analyzing their predictions for observable parameters like $n_s$ and $r$ and comparing them with recent and upcoming observational data.

Contribution

It provides a comprehensive analysis of inflation in Palatini quadratic gravity with non-minimal couplings, including new forecasts for observational constraints on inflationary parameters.

Findings

Different inflationary regimes yield distinct $n_s$ and $r$ predictions.

Models are consistent with Planck 2018 and BICEP/Keck data within certain parameter ranges.

Forecasts show future observations can tightly constrain inflationary model parameters.

Abstract

Single field inflationary models are investigated within Palatini quadratic gravity represented by $R+\alpha R^2$ along with a non-minimal coupling of the form $f(\phi) R$ between the inflaton field $\phi$ and the gravity. The treatment is performed in the Einstein frame, where the minimal coupling to gravity is recovered through conformal transformation. We consider various limits of the model with different inflationary scenarios characterized as canonical slow-roll inflation in the limit $\alpha \dot{\phi}^2\ll (1+f(\phi)) $, constant-roll k-inflation for $\alpha \ll 1$, and slow-roll K-inflation for$ \alpha \gg 1$ . A cosine and exponential potential are examined with the limits mentioned above and different well-motivated non-minimal couplings to gravity. We compare the theoretical results, exemplified by the tensor-to-scalar $r$ ratio and spectral index $n_s$, with the recent observational results of Planck 2018 $\&$ BICEP/Keck . Furthermore, we include the results of a new study forecast precision with which $n_s$ and $r$ can be constrained by currently envisaged observations, including CMB (Simons Observatory, CMB-S4, and LiteBIRD)