The merger rate of primordial black hole binaries as a probe of Hubble parameter

TL;DR

This paper proposes using the merger rate of primordial black hole binaries observed via gravitational waves as a method to constrain the Hubble parameter, linking cosmology with black hole merger observations.

Contribution

It introduces a novel approach to determine the Hubble parameter by analyzing the redshifted mass distribution of PBH binaries and their merger rates.

Findings

Method to invert PBH mass function using gradient descent.

Hubble parameter constraints derived from PBH merger rate comparison.

Potential to measure Hubble parameter with future GW detector data.

Abstract

We propose that the merger rate of primordial black hole (PBH) binaries can be a probe of Hubble parameter by constraining PBH mass function in the redshifted mass distribution of PBH binaries. In next-generation gravitational wave (GW) detectors, the GWs from PBH binaries would be detected at high redshifts, which gives their redshifted mass and luminosity distances. From a number of detected events, the redshifted mass distribution of PBH binaries can be statistically obtained, and it depends on PBH mass function and redshift distribution of detected PBH binaries. The PBH mass function can be inversely solved by applying the gradient descent method in the relation between redshifted mass distribution and redshift distribution. However, the construction of redshift distribution requires an assumed Hubble parameter in a background cosmology to extract redshift from luminosity distances, which causes solved PBH mass function also depends on assumed Hubble parameter. To determine the Hubble parameter, the merger rate of PBH binaries constrains on this Hubble parameter-dependent PBH mass function by comparing calculated merger rate distribution with observed one, and the best-fit result produces an approximate mass distribution of the physical PBH mass function and pins down the Hubble parameter.