Inflationary Slow-Roll Parameters in the Jordan Frame for Cosmological F(R) Gravity Models

TL;DR

This paper analyzes $F(R)$ inflationary models directly in the Jordan frame, providing conditions for inflationary attractors and a method to compute observables, applied to a new model consistent with recent observational data.

Contribution

It introduces a procedure to analyze $F(R)$ inflationary models in the Jordan frame and applies it to a novel model aligned with current observations.

Findings

Established conditions for global inflationary attractors in $F(R)$ models

Developed a method to calculate inflationary observables in the Jordan frame

A new $F(R)$ model matches recent ACT data predictions

Abstract

$F(R)$ inflationary models are analyzed without the Weyl transformation to the Einstein frame. Sufficient conditions for existence of global inflationary attractors in $F(R)$ models are provided. Following that, the procedure for calculating inflationary observables completely in the original, Jordan, frame is given. The described procedure is used to analyze a new $F(R)$ inflationary model (a one-parameter deformation of the Starobinsky model), which is shown to provide predictions in good agreement with the recent ACT data.