A New Window on Primordial non-Gaussianity

TL;DR

This paper proposes using mu-type spectral distortions of the CMB, especially mu-T and mu-mu correlations, to probe primordial non-Gaussianity on small scales from 50 to 10^4 Mpc^-1, a range previously unexplored.

Contribution

It introduces a novel method to test primordial non-Gaussianity on small scales using CMB spectral distortions and provides forecasts for observational constraints.

Findings

mu-T correlation measures fNL^loc in the squeezed limit

mu-mu correlation measures trispectrum parameter tauNL

Forecasts indicate potential for strong constraints on small-scale non-Gaussianity

Abstract

We know very little about primordial curvature perturbations on scales smaller than about a Mpc. Measurements of the mu-type distortion of the CMB spectrum provide the unique opportunity to probe these scales over the unexplored range from 50 to 10^4 Mpc^-1. This is a very clean probe, in that it relies only on well-understood linear evolution. We point out that correlations between mu-distortion and temperature anisotropies can be used to test Gaussianity at these very small scales. In particular the mu-T cross correlation is proportional to the very squeezed limit of the primordial bispectrum and hence measures fNL^loc, while mu-mu is proportional to the primordial trispectrum and measures tauNL. We present a Fisher matrix forecast of the observational constraints.