CMB μT cross correlations as a probe of primordial black hole scenarios

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 toward 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 nonlinearities associated with PBH formation and evolution.

Automated summary

This study proposes a new method to probe inflationary models of primordial black hole (PBH) production by analyzing the characteristics of the primordial power spectrum profile, specifically focusing on the dip and surrounding scales. The research shows that the properties of PBH scenarios can be quantitatively studied by cross correlating CMB mu-distortions and temperature fluctuations, which may be tested in the next generation of CMB experiments.