How to assess the primordial origin of single gravitational-wave events with mass, spin, eccentricity, and deformability measurements

TL;DR

This paper reviews methods to distinguish primordial black hole mergers from astrophysical ones using gravitational-wave data, emphasizing future detector capabilities and applying the approach to existing catalogs.

Contribution

It provides a comprehensive set of discriminators and estimates their effectiveness with current and future gravitational-wave detectors.

Findings

Current data cannot definitively identify primordial black holes.

Next-generation detectors will improve discrimination capabilities.

Applying the method to GWTC-3 shows limited current constraints.

Abstract

A population of primordial black holes formed in the early Universe could contribute to at least a fraction of the black-hole merger events detectable by current and future gravitational-wave interferometers. With the ever-increasing number of detections, an important open problem is how to discriminate whether a given event is of primordial or astrophysical origin. We systematically present a comprehensive and interconnected list of discriminators that would allow us to rule out, or potentially claim, the primordial origin of a binary by measuring different parameters, including redshift, masses, spins, eccentricity, and tidal deformability. We estimate how accurately future detectors (such as the Einstein Telescope and LISA) could measure these quantities, and we quantify the constraining power of each discriminator for current interferometers. We apply this strategy to the GWTC-3 catalog of compact binary mergers. We show that current measurement uncertainties do not allow us to draw solid conclusions on the primordial origin of individual events, but this may become possible with next-generation ground-based detectors.