Numerical-Relativity-Informed Effective-One-Body model for Black-Hole-Neutron-Star Mergers with Higher Modes and Spin Precession

TL;DR

This paper introduces a new effective-one-body model for black-hole-neutron-star mergers that incorporates higher modes and spin precession, improving waveform accuracy and aiding gravitational wave data analysis.

Contribution

The paper presents the first NR-informed EOB model for generic-spins BHNS inspirals with higher modes and precession, validated against numerical relativity data and applied to GW event analysis.

Findings

Model reproduces NR waveforms with phase agreement within 0.5-1 rad.

Higher modes improve parameter estimation and evidence for their presence.

No evidence found for tidal effects in GW200105 and GW200115.

Abstract

We present the first effective-one-body (EOB) model for generic-spins quasi-circular black-hole--neutron-star (BHNS) inspiral-merger-ringdown gravitational waveforms (GWs). Our model is based on a new numerical-relativity (NR) informed expression of the BH remnant and its ringdown. It reproduces the NR $(\ell,m)=(2,2)$ waveform with typical phase agreement of ${\lesssim0.5}\,$rad (${\lesssim1}\,$rad) to merger (ringdown). The maximum (minimum) mismatch between the $(2,2)$ and the NR data is 4% (0.6%). Higher modes (HMs) $(2,1)$, $(3,2)$, $(3,3)$, $(4,4)$ and $(5,5)$ are included and their mismatch with the available NR waveforms are up to (down to) a 60% (1%) depending on the inclination. Phase comparison with a 16 orbit precessing simulation shows differences within the NR uncertainties. We demonstrate the applicability of the model in GW parameter estimation by perfoming the first BHNS Bayesian analysis with HMs (and non-precessing spins) of the event GW190814, together with new $(2,2)$-mode analysis of GW200105 and GW200115. For the GW190814 study, the inclusion of HMs gives tighter parameter posteriors. The Bayes factors of our analyses on this event show decisive evidence for the presence of HMs, but no clear preference for a BHNS or a binary black hole (BBH) source. Similarly, we confirm GW200105 and GW200115 show no evidence for tidal effects.