Comparison of Numerical and Post-Newtonian Waveforms for Generic Precessing Black-Hole Binaries

TL;DR

This paper compares numerical relativity waveforms with post-Newtonian predictions for a precessing black-hole binary, demonstrating high agreement and highlighting the importance of higher PN orders for accurate modeling.

Contribution

It provides the first long-term, fully non-linear simulation of a generic precessing black-hole binary and compares it with advanced post-Newtonian models, revealing insights into waveform accuracy and eccentricity.

Findings

High overlap (~99%) between numerical and 3.5PN waveforms for initial cycles.

3.5PN reduces eccentricity more effectively than 2.5PN.

Phase differences are small and consistent across modes for the first few orbits.

Abstract

We compare waveforms and orbital dynamics from the first long-term, fully non-linear, numerical simulations of a generic black-hole binary configuration with post-Newtonian predictions. The binary has mass ratio q~0.8 with arbitrarily oriented spins of magnitude S_1/m_1^2~0.6 and S_2/m_2^2~0.4 and orbits 9 times prior to merger. The numerical simulation starts with an initial separation of r~11M, with orbital parameters determined by initial 2.5PN and 3.5PN post-Newtonian evolutions of a quasi-circular binary with an initial separation of r=50M. The resulting binaries have very little eccentricity according to the 2.5PN and 3.5PN systems, but show significant eccentricities of e~0.01-0.02 and e~0.002-0.005 in the respective numerical simulations, thus demonstrating that 3.5PN significantly reduces the eccentricity of the binary compared to 2.5PN. We perform three numerical evolutions from r~11M with maximum resolutions of h=M/48,M/53.3,M/59.3, to verify numerical convergence. We observe a reasonably good agreement between the PN and numerical waveforms, with an overlap of nearly 99% for the first six cycles of the (l=2,m=+-2) modes, 91% for the (l=2,m=+-1) modes, and nearly 91% for the (l=3,m=+-3) modes. The phase differences between numerical and post-Newtonian approximations appear to be independent of the (l,m) modes considered and relatively small for the first 3-4 orbits. An advantage of the 3.5 PN model over the 2.5 PN one seems to be observed, which indicates that still higher PN order (perhaps even 4.0PN) may yield significantly better waveforms. In addition, we identify features in the waveforms likely related to precession and precession-induced eccentricity.