Effectual gravitational-wave template banks for coalescing compact binaries using a hybrid placement algorithm

Abstract

Recent discoveries of gravitational wave (GW) signals from astrophysical compact binary systems of neutron stars and black holes have firmly established them as prime sources for advanced GW detectors. Accurate theoretical models of expected signals from such systems have been used to filter the detector data using the matched filtering technique. An efficient grid over the parameter space at a fixed minimal match has a direct impact on improving the computational efficiency of these searches. To this end, in a recent paper, we had introduced a new hybrid geometric-random template placement algorithm over three-dimensional parameter spaces having moderately varying curvature. In this paper, we extend the formalism to arbitrary dimensions using the A?n lattice. By an explicit construction of such hybrid template banks in idealized situations, we demonstrate the theoretical improvement possible over a stochastic template placement in 3 and 4 dimensions. Next, we construct template banks for binary black hole and neutron star-black hole searches in Advanced LIGO data, using the numerically evaluated metric on the space of IMRPhenomD waveforms. This technique is computationally efficient and can be applied to calculate the metric for any waveform family. We show that the template placement is robust and can automatically accommodate varying curvature and boundary effects with no explicit fine tuning in the design. By comparing these banks against existing stochastic template banks, we establish that while both are equally effectual in capturing sources modeled by IMRPhenomD and SEOBNRv4_ROM waveform families, the hybrid banks are significantly smaller in size. Further, we show that the hybrid banks can be generated much faster in comparison to the stochastic banks. The resulting template banks are ready to be used in future LIGO searches.