Prospects of Future CMB Anisotropy Probes for Primordial Black Holes

TL;DR

Future CMB experiments like CMB-S4 and PICO could significantly tighten constraints on primordial black holes in the mass range of 10^{15} to 10^{17} grams, surpassing current bounds and potentially excluding all currently allowed parameter space.

Contribution

This study evaluates the sensitivity of upcoming CMB experiments to constrain primordial black holes across various mass functions, improving upon current bounds by two orders of magnitude.

Findings

Future experiments can exclude PBHs heavier than 4×10^{16} grams.

Upcoming missions will improve current bounds by about 100 times.

All currently allowed PBH parameter space can be ruled out with high significance.

Abstract

Cascade of particles injected as Hawking Radiation from Primordial Black Holes (PBH) can potentially change the cosmic recombination history by ionizing and heating the intergalactic medium, which results in altering the anisotropy spectra of the Cosmic Microwave Background (CMB). In this paper, we study the expected sensitivity of several future CMB experiments in constraining the abundance of PBHs distributed in $10^{15}\sim10^{17}$ g mass window according to four mass functions: the monochromatic, log-normal, power-law and critical collapse models. Our result shows that future experiments, such as CMB-S4 and PICO, can improve current {\it{Planck}} bounds by about two orders of magnitudes. All regions in PBH parameter space that are allowed by current CMB data, including monochromatically distributed PBHs with mass heavier than $4 \times 10^{16}$ grams, can be excluded by upcoming missions with high significance.