The double-soft limit in cosmological correlation functions and graviton exchange effects

TL;DR

This paper investigates the impact of graviton exchange on cosmological correlation functions using the double-soft limit technique, revealing that graviton effects dominate and could be observable in the trispectrum.

Contribution

It derives a new relation among correlation functions incorporating graviton exchange effects and compares different contributions, emphasizing the dominance of graviton effects in certain limits.

Findings

Graviton exchange effects are more dominant than scalar exchange and contact interactions.

These effects could be observed in the trispectrum in the double-soft limit.

The results support previous findings on graviton dominance in specific inflationary limits.

Abstract

The graviton exchange effect on cosmological correlation functions is examined by employing the double-soft limit technique. A new relation among correlation functions that contain the effects due to graviton exchange diagrams in addition to those due to scalar-exchange and scalar-contact-interaction, is derived by using the background field method and independently by the method of Ward identities associated with dilatation symmetry. We compare these three terms, putting small values for the slow-roll parameters and $(1-n_{s}) = 0.042$, where $n_{s}$ is the scalar spectral index. It is argued that the graviton exchange effects are more dominant than the other two and could be observed in the trispectrum in the double-soft limit. Our observation strengthens the previous work by Seery, Sloth and Vernizzi, in which it has been argued that the graviton exchange dominates in the counter-collinear limit for single field slow-roll inflation.