Non-metric chaotic inflation

TL;DR

This paper explores how a simple non-metric extension of Einstein gravity, characterized by a graviscalar field, impacts chaotic inflation dynamics, leading to significant modifications at high field values and small corrections to observable parameters.

Contribution

It introduces a non-metric gravity framework with a graviscalar field affecting inflation, revealing new dynamics and constraints on e-folds and inflationary observables.

Findings

Non-metricity alters inflaton dynamics for large field values.

Imposes an upper bound on the number of e-folds in certain potentials.

Small corrections to spectral index and tensor-to-scalar ratio.

Abstract

We consider inflation within the context of what is arguably the simplest non-metric extension of Einstein gravity. There non-metricity is described by a single graviscalar field with a non-minimal kinetic coupling to the inflaton field $\Psi$, parameterized by a single parameter $\gamma$. We discuss the implications of non-metricity for chaotic inflation and find that it significantly alters the inflaton dynamics for field values $\Psi \gtrsim M_P/\gamma$, dramatically changing the qualitative behaviour in this regime. For potentials with a positive slope non-metricity imposes an upper bound on the possible number of e-folds. For chaotic inflation with a monomial potential, the spectral index and the tensor-to-scalar ratio receive small corrections dependent on the non-metricity parameter. We also argue that significant post-inflationary non-metricity may be generated.