CMB spectral distortions constraints on primordial black holes, cosmic strings and long lived unstable particles revisited

TL;DR

This paper revisits constraints on primordial black holes, cosmic strings, and unstable particles using detailed spectral distortion calculations, revealing stronger bounds and new insights into particle decay channels and cosmic string emissions.

Contribution

It provides more accurate spectral distortion constraints by including all standard model particle emissions from black holes and extends decay constraints to additional channels and cosmic string decay.

Findings

Stronger constraints on primordial black hole abundance.

Spectral distortions are sensitive to black hole mass and decay channels.

New bounds on cosmic string decay from spectral distortions.

Abstract

We calculate the spectral distortions from Hawking evaporation of primordial black holes before the epoch of recombination, taking into account emission of all standard model particles, including quark and gluons, and evolving the resulting particle cascades in the expanding Universe. We show that the constraints on the abundance of primordial black holes are stronger by more than an order of magnitude compared to the previous calculations which take only the primary photon emission into account. We also show that the shapes of the spectral distortions is different from the $y$ or $i$-type distortions and are sensitive to the mass of the primordial black holes. We also extend previous constraints on the decay of long lived unstable particles before recombination to additional decay channels. We show that for dark matter mass $\lesssim$ 1 GeV, the spectral distortion shape is a function of the dark matter mass as well as the decay channel to standard model particles. We also provide new spectral distortion constraints on superconducting cosmic string decay. We explicitly show that consideration of emitted photon spectrum from string decay is not only important for the future experiments but also for already available COBE-FIRAS data.