Constraining the Precession of Binary Black Hole Systems Using New Parameters

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Abstract:: The precession of Binary Black Holes (BBHs) can be informative of the formation channel of the system; weakly/non-precessing systems are likely to have formed through binary stellar evolution, while strongly precessing systems may have formed dynamically. Despite the growing number of LIGO sources, evidence of precession is strongly debated in the literature. The parameter χ_p is currently used to evaluate the precession of observed BBH systems. However, χ_p is difficult to constrain to a narrow range of values for most events and can yield vanishing prior probability density at the aligned-spin configuration. We present an alternative spin precession parameter, the cosine of the angle between the total spin and the orbital angular momentum cos(θ_LS), that provides better localization of a precession value and allows a non-zero probability of aligned spins. We begin by testing cos(θ_LS), χ_p, and other parameters against synthetic data with known values to determine the best statistical measurement of precession. We then use cos(θ_LS) to evaluate the precession in events from O3, the third observing run of LIGO and Virgo.

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LIGO Document T2400214-v1