Searching for vector boson-star mergers within LIGO-Virgo intermediate-mass black-hole merger candidates

TL;DR

This study systematically searches for exotic compact object mergers, specifically Proca-star mergers, in LIGO-Virgo gravitational-wave data, finding some events weakly favoring the exotic hypothesis and estimating the potential population fraction.

Contribution

First systematic analysis comparing Proca-star merger models to LIGO-Virgo events, providing constraints on boson masses and potential population fractions of exotic mergers.

Findings

GW190521 and GW200220 favor Proca-star merger hypothesis with consistent boson masses.

Proca-star merger hypothesis is strongly rejected for GW190426.

Estimated fraction of Proca-star mergers in the population is around 27-39%.

Abstract

We present the first systematic search for exotic compact mergers in Advanced LIGO and Virgo events. We compare the short gravitational-wave signals GW190521, GW190426$\_$190642, GW200220$\_$061928 and the trigger 200114$\_$020818 (or S200114f) to a new catalogue of 759 numerical simulations of head-on mergers of horizonless exotic compact objects known as Proca stars, interpreted as self-gravitating lumps of (fuzzy) dark matter sourced by an ultralight (vector) bosonic particle. The Proca-star merger hypothesis is strongly rejected with respect to the black hole merger one by GW190426, weakly rejected by GW200220 and weakly favoured by GW190521 and S200114f. GW190521 and GW200220 yield highly consistent boson masses of $\mu_{\rm B} = 8.69^{+0.61}_{-0.75}\times10^{-13}$ eV and $\mu_{\rm B} = 9.13^{+1.18}_{-1.30}\times10^{-13}$ eV at the $90\%$ credible level. We conduct a preliminary population study of the compact binaries behind these events. Excluding (including) S200114f as a real event, and ignoring boson-mass consistencies across events, we estimate a fraction of Proca-star mergers of $\zeta = 0.27^{+0.43}_{-0.25} \ (0.39^{+0.38}_{-0.33})$. We discuss the impact of boson-mass consistency across events in such estimates. Our results maintain GW190521 as a Proca-star merger candidate and pave the way towards population studies considering exotic compact objects.