On Soft Limits of Inflationary Correlation Functions

TL;DR

This paper revisits and unifies the theoretical understanding of soft limits in inflationary correlation functions, highlighting their importance in probing light fields during inflation and illustrating with a case study.

Contribution

It provides a universal derivation of key theorems about soft limits, clarifying their significance in inflationary models and light field spectra.

Findings

Re-derivation of soft limit theorems in a universal framework

Demonstration of soft limits as probes of light fields during inflation

Application to quasi-single-field inflation case study

Abstract

Soft limits of inflationary correlation functions are both observationally relevant and theoretically robust. Various theorems can be proven about them that are insensitive to detailed model-building assumptions. In this paper, we re-derive several of these theorems in a universal way. Our method makes manifest why soft limits are such an interesting probe of the spectrum of additional light fields during inflation. We illustrate these abstract results with a detailed case study of the soft limits of quasi-single-field inflation.