Evolution of CMB spectral distortion anisotropies and tests of primordial non-Gaussianity

TL;DR

This paper develops a systematic framework to describe and analyze anisotropies in CMB spectral distortions caused by early Universe processes, especially focusing on primordial non-Gaussianity and the importance of absolute measurements.

Contribution

It introduces a Fourier-space formulation for distortion anisotropies, generalizes previous approximations, and emphasizes the need for absolute measurements to constrain primordial non-Gaussianity.

Findings

Distortion anisotropies depend on both local heating and homogeneous distortions.

Absolute measurements are essential for model-independent non-Gaussianity constraints.

The framework can be extended to higher order correlations and polarization anisotropies.

Abstract

Anisotropies in distortions to the frequency spectrum of the cosmic microwave background (CMB) can be created through spatially varying heating processes in the early Universe. For instance, the dissipation of small-scale acoustic modes does create distortion anisotropies, in particular for non-Gaussian primordial perturbations. In this work, we derive approximations that allow describing the associated distortion field. We provide a systematic formulation of the problem using Fourier-space window functions, clarifying and generalizing previous approximations. Our expressions highlight the fact that the amplitudes of the spectral-distortion fluctuations induced by non-Gaussianity depend also on the homogeneous value of those distortions. Absolute measurements are thus required to obtain model-independent distortion constraints on primordial non-Gaussianity. We also include a simple description for the evolution of distortions through photon diffusion, showing that these corrections can usually be neglected. Our formulation provides a systematic framework for computing higher order correlation functions of distortions with CMB temperature anisotropies and can be extended to describe correlations with polarization anisotropies.