Probing Dark Matter Isocurvature with Primordial Non-Gaussianity

TL;DR

This paper explores how primordial non-Gaussianity from isocurvature fluctuations during inflation can provide new insights into dark matter, especially the QCD axion, by identifying unique signatures that improve current detection methods.

Contribution

It introduces a novel form of mixed adiabatic-isocurvature non-Gaussianity with distinct kinematic dependence, enhancing search strategies for dark matter isocurvature signals.

Findings

Distinct kinematic dependence of non-Gaussianity compared to local shape

Parameter space where NG searches outperform Planck sensitivity

Potential to improve constraints on axion dark matter models

Abstract

Multiple fields can become dynamical during the inflationary epoch. We consider an example where a light field acquires isocurvature fluctuations during inflation and contributes to the dark matter abundance at late times. Interactions between the light field and the adiabatic sector contribute to mixed adiabatic-isocurvature non-Gaussianity (NG). We show the resulting form of NG has a different kinematic dependence than the 'local shape' commonly considered, and highlight the parameter space where a dedicated search is expected to significantly improve the current $\textit{Planck}$ sensitivity. We interpret our results in the context of the QCD axion and illustrate how the proposed NG searches can improve upon the existing searches for isocurvature power spectrum and bispectrum.