Analysis of spin precession in binary black hole systems including quadrupole-monopole interaction

TL;DR

This paper derives new analytical solutions for spin precession in binary black hole systems including quadrupole-monopole interactions, improving understanding of precession dynamics and aiding gravitational wave data analysis.

Contribution

It introduces an exact solution for equal-mass binaries and accurate approximations for unequal masses, incorporating radiation reaction effects into precession modeling.

Findings

Conserved quantity at 2PN order with quadrupole-monopole coupling.

Analytic solutions match numerical results within 1.8% over many orbits.

Potential applications in gravitational wave template development and recoil analysis.

Abstract

We analyze in detail the spin precession equations in binary black hole systems, when the tidal torque on a Kerr black hole due to quadrupole-monopole coupling is taken into account. We show that completing the precession equations with this term reveals the existence of a conserved quantity at 2PN order when averaging over orbital motion. This quantity allows one to solve the (orbit-averaged) precession equations exactly in the case of equal masses and arbitrary spins, neglecting radiation reaction. For unequal masses, an exact solution does not exist in closed form, but we are still able to derive accurate approximate analytic solutions. We also show how to incorporate radiation reaction effects into our analytic solutions adiabatically, and compare the results to solutions obtained numerically. For various configurations of the binary, the relative difference in the accumulated orbital phase computed using our analytic solutions versus a full numerical solution vary from about 0.3% to 1.8% over the 80 - 140 orbital cycles accumulated while sweeping over the orbital frequency range 20 - 300 Hz. This typically corresponds to a discrepancy of order 5-6 radians. While this may not be accurate enough for implementation in LIGO template banks, we still believe that our new solutions are potentially quite useful for comparing numerical relativity simulations of spinning binary black hole systems with post-Newtonian theory. They can also be used to gain more understanding of precession effects, with potential application to the gravitational recoil problem, and to provide semi-analytical templates for spinning, precessing binaries.