Measuring the Energy Scale of Inflation with Large Scale Structures

TL;DR

This paper explores how large-scale structure observations can be used to measure the inflationary energy scale by detecting specific non-Gaussian signatures from graviton exchange, offering an alternative to CMB B-mode polarization.

Contribution

It calculates the graviton exchange contribution to halo correlation functions, revealing a detectable signature at large scales that can probe tensor fluctuations independently of CMB methods.

Findings

Graviton exchange impacts halo clustering at large scales.

The signal magnitude is comparable or larger than other non-Gaussian effects.

Provides a new observational route to detect tensor fluctuations.

Abstract

The determination of the inflationary energy scale represents one of the first step towards the understanding of the early Universe physics. The (very mild) non-Gaussian signals that arise from any inflation model carry information about the energy scale of inflation and may leave an imprint in some cosmological observables, for instance on the clustering of high-redshift, rare and massive collapsed structures. In particular, the graviton exchange contribution due to interactions between scalar and tensor fluctuations leaves a specific signature in the four-point function of curvature perturbations, thus on clustering properties of collapsed structures. We compute the contribution of graviton exchange on two- and three-point function of halos, showing that at large scales $k\sim 10^{-3}\ \mathrm{Mpc}^{-1}$ its magnitude is comparable or larger to that of other primordial non-Gaussian signals discussed in the literature. This provides a potential route to probe the existence of tensor fluctuations which is alternative and highly complementary to B-mode polarisation measurements of the cosmic microwave background radiation.