Inflation in non-local hybrid metric-Palatini gravity

TL;DR

This paper explores how non-local modifications in hybrid metric-Palatini gravity can support inflation, analyzing stability and dynamics in a multi-field framework with non-minimal kinetic couplings.

Contribution

It introduces a non-local extension of hybrid metric-Palatini gravity and studies its inflationary dynamics and stability in a multi-field scalar-tensor setup.

Findings

Non-localities influence the number of e-folds and field trajectories.

The theory can be stable and free of ghost instabilities.

Analogies with single-field inflation help interpret results.

Abstract

Within the framework of hybrid metric-Palatini gravity, we incorporate non-localities introduced via the inverse of the d'Alembert operators acting on the scalar curvature. We analyse the dynamical structure of the theory and, adopting a scalar-tensor perspective, assess the stability conditions to ensure the absence of ghost instabilities. Focusing on a special class of well-defined hybrid actions -- where local and non-local contributions are carried by distinct types of curvature -- we investigate the feasibility of inflation within the resulting Einstein-frame multi-field scenario. We examine how the non-minimal kinetic couplings between the fields, reflecting the non-local structure of the original frame, influence the number of e-folds and the field trajectories. To clarify the physical interpretation of our results, we draw analogies with benchmark single-field inflation scenarios that include spectator fields.