High accuracy simulations of black hole binaries: Spins anti-aligned with the orbital angular momentum

High-accuracy binary black hole simulations are presented for black holes with spins anti-aligned with the orbital angular momentum. The particular case studied represents an equal-mass binary with spins of equal magnitude S/m²=0.437 57±0.000 01. The system has initial orbital eccentricity ~4×10^-5, and is evolved through 10.6 orbits plus merger and ringdown. The remnant mass and spin are Mf=(0.961 109±0.000 003)M and Sf/Mf²=0.547 81±0.000 01, respectively, where M is the mass during early inspiral. The gravitational waveforms have accumulated numerical phase errors of 0.1 radians without any time or phase shifts, and 0.01 radians when the waveforms are aligned with suitable time and phase shifts. The waveform is extrapolated to infinity using a procedure accurate to 0.01 radians in phase, and the extrapolated waveform differs by up to 0.13 radians in phase and about 1% in amplitude from the waveform extracted at finite radius $r=350M$. The simulations employ different choices for the constraint damping parameters in the wave zone; this greatly reduces the effects of junk radiation, allowing the extraction of a clean gravitational wave signal even very early in the simulation.