CMB $\mu T$ cross-correlations as a probe of PBH scenarios

TL;DR

This paper introduces a novel approach to test primordial black hole formation models by analyzing CMB $d$-distortion and temperature cross-correlations, focusing on large-scale features of the primordial power spectrum.

Contribution

It presents an analytical framework for using CMB $d$-distortions and temperature correlations to probe inflationary PBH scenarios without relying on non-linear PBH formation effects.

Findings

Enhanced squeezed bispectrum at the dip scale.

Characteristic scale dependence of cross-correlations.

Potential detectability with next-generation CMB experiments.

Abstract

We propose a new method for probing inflationary models of primordial black hole (PBH) production, using only CMB physics at relatively large scales. In PBH scenarios, the primordial power spectrum profile for curvature perturbations is characterized by a pronounced dip, followed by a rapid growth towards small scales, leading to a peak responsible for PBH formation. We focus on scales around the dip that are well separated from the peak to analytically compute expressions for the curvature power spectrum and bispectrum. The size of the squeezed bispectrum is enhanced at the position of the dip, and it acquires a characteristic scale dependence that can be probed by cross-correlating CMB $\mu$-distortions and temperature fluctuations. We quantitatively study the properties of such cross-correlations and how they depend on the underlying model, discussing how they can be tested by the next generation of CMB $\mu$-distortion experiments. This method allows one to experimentally probe inflationary PBH scenarios using well-understood CMB physics, without considering non-linearities associated with PBH formation and evolution.