A generalized precession parameter χp to interpret gravitational-wave data

Davide Gerosa, Matthew Mould, Daria Gangardt, Patricia Schmidt, Geraint Pratten, Lucy Thomas

Research output: Contribution to journalArticlepeer-review


Originally designed for waveform approximants, the effective precession parameter  χp  is the most commonly used quantity to characterize spin-precession effects in gravitational-wave observations of black-hole binary coalescences. We point out that the current definition of  χp  retains some, but not all, variations taking place on the precession timescale. We rectify this inconsistency and propose more general definitions that either fully consider or fully average those oscillations. Our generalized parameter  χp ∈ [ 0 , 2 ]  presents an exclusive region  χp > 1  that can only be populated by binaries with two precessing spins. We apply our prescriptions to current LIGO/Virgo events and find that posterior distributions of  χp  tend to show longer tails at larger values. This appears to be a generic feature, implying that (i) current  χp  measurement errors might be underestimated, but also that (ii) evidence for spin precession in current data might be stronger than previously inferred. Among the gravitational-wave events released to date, that which shows the most striking behavior is GW190521. 
Original languageEnglish
Article number064067
Number of pages12
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Issue number6
Publication statusPublished - 15 Mar 2021


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