A new branch of inflationary speed limits

TL;DR

This paper introduces a novel inflationary mechanism that imposes a speed limit on scalar field motion, enabling accelerated expansion on steep potentials through integrating out coupled fields, with observational constraints discussed.

Contribution

It presents a new inflation model with a speed limit derived from integrating out additional fields, leading to a nontrivial effective action with a logarithmic function of the scalar derivative.

Findings

The model exhibits a speed limit at the branch cut of a logarithmic function.

It generates accelerated expansion on steep potentials.

Observational constraints on model parameters are analyzed.

Abstract

We present a new mechanism for inflation which exhibits a speed limit on scalar motion, generating accelerated expansion even on a steep potential. This arises from explicitly integrating out the short modes of additional fields coupled to the inflaton $\phi$ via a dimension six operator, yielding an expression for the effective action which includes a nontrivial (logarithmic) function of $(\partial\phi)^2$. The speed limit appears at the branch cut of this logarithm arising in a large flavor expansion, similarly to the square root branch cut in DBI inflation arising in a large color expansion. Finally, we describe observational constraints on the parameters of this model.