The Strong Multifield Slowroll Condition and Spiral Inflation

TL;DR

This paper clarifies the correct slowroll conditions for multifield inflation, introduces the concept of spiral inflation that bypasses traditional slowroll constraints, and connects it to string theory structures.

Contribution

It identifies the proper slowroll condition for multifield inflation, introduces spiral inflation as a novel model, and links it to string theory monodromy structures.

Findings

Gradient flow requirement is stronger than slow change in quasi-de Sitter space.

Multifield slowroll models can exist without following gradient flow.

Spiral inflation relies on string theory monodromy loci.

Abstract

We point out the existing confusions about the slowroll parameters and conditions for multifield inflation. If one requires the fields to roll down the gradient flow, we find that only articles adopting the Hubble slowroll expansion are on the right track, and a correct condition can be found in a recent book by Liddle and Lyth. We further analyze this condition and show that the gradient flow requirement is stronger than just asking for a slowly changing, quasi-de Sitter solution. Therefore it is possible to have a multifield slowroll model that does not follow the gradient flow. Consequently, it no longer requires the gradient to be small. It even bypasses the first slowroll condition and some related no-go theorems from string theory. We provide the "spiral inflation" as a generic blueprint of such inflation model and show that it relies on a monodromy locus---a common structure in string theory effective potentials.