Improved initial Lapse and Shift for Binary Black Hole Simulations

We present a new set of initial lapse and shift for binary black hole (BBH) evolutions by constructing analytic formulas that mimic the settled behavior of those metric components in the moving puncture gauge. These initial values allow for substantial improvements in the initial shape of both the lapse and the shift. Current simulations set initial shift β=0 and lapse α to be isotropic asymptotically. Our new initial construction sets these initial values to be closer to the settled shape of α and β for boosted, spinning black holes. To evaluate the effects of the initial lapse and shift on evolutions, we monitor both the Hamiltonian and Momentum constraint violations. This method shows explicit improvements in a simulation of a 1:3 mass ratio, nonspinning BBH system and also in an equal-mass system with spins a=0.8. We explore the extent in the binary’s parameter space where this method reduces the amount of time required for the settling of the lapse and shift, while improving the satisfaction of the constraints and thus making simulations of both high mass-ratio and near extremally spinning systems computationally more efficient.