Constraints on the cosmic string loop collapse fraction from Primordial Black Holes

TL;DR

This paper refines constraints on the fraction of cosmic string loops collapsing into primordial black holes, tightening bounds by two orders of magnitude through updated calculations considering the PBH mass function.

Contribution

It provides a more precise upper limit on the cosmic string loop collapse fraction by incorporating the extended PBH mass function and updated formation rate calculations.

Findings

Upper limit on loop collapse fraction: f < 10^{-31} (Gμ/c^2)^{-3/2}

Constraints are roughly 100 times tighter than previous bounds

Refinements in formation rate calculations offset some improvements

Abstract

A small fraction, $f$, of cosmic string loops can collapse to form Primordial Black Holes (PBHs). Constraints on the abundance of PBHs can therefore be used to constrain $f$. We update these calculations, taking into account the PBH extended mass function, and find $f < 10^{-31} (G \mu/ c^2)^{-3/2}$. This is roughly two orders of magnitude tighter than previous constraints. The improvement from the tighter constraints on the abundance of PBHs is partly off-set by refinements to the theoretical calculation of the cosmic string loop formation rate.