Coalescing black-hole–black-hole and neutron-star–black-hole binaries are among the most promising sources for second-generation ground-based interferometers, but to detect them efficiently and extract their parameters accurately we need to model their gravitational waveforms very faithfully: GW searches work by systematically correlating the detector output with families of theoretical signal templates, and selecting the best-matching candidates.
Gravitational waves from a coalescing neutron-star binary (credit: NASA).
Together with CMU's Ira Rothstein and my JPL postdoc Chad Galley, I have been leading an effort to develop spinning-binary templates that are consistently accurate to 3.5PN order, as high as currently available nonspinning models, using techniques from effective field theory.
This approach maps the complex integrals of post-Newtonian theory into the computation of Feynman diagrams, which can rely on 50 years of experience in quantum field theory. The biggest difficulties lie in bookkeeping a large number of Feynman diagrams, and calculating the hardest sub-diagram integrals using strategies from multi-loop calculations in particle physics.
The five diagrams that generate individual terms in the 1PN Einstein–Infeld–Hoffmann potential.
Between 2001 and 2005 I worked with Alessandra Buonanno, Yanbei Chen, and Yi Pan to devise robust families of signal templates for the inspiraling binaries sought by LIGO.
We first developed a phenomenological template family, BCV, that could embed all credible (but discordant) post-Newtonian resummations at the late stage of inspiral.
We then tackled the effects of spins, which can induce strong precession-induced modulations in the signals, requiring a prohibitively large number of parameters to describe them. We developed a family of modulated detection templates, BCV2, which are functions of very few physical and phenomenological parameters, but model spin effects remarkably well.
We also created a separate template family for spinning binaries, PBCV, which consists of essentially exact waveforms written directly in terms of the physical parameters of the binary, and which can be used in a fast matched-filtering scheme. The crucial insight was a new decomposition of detector response into a time-dependent component that encodes the binary evolution, and a constant component that represents the relative position and orientation of detector and binary.
Our template families were used in the LIGO searches for inspiraling binaries in data from science runs S2, S3, and S4.
I also participated directly in the analysis of the LIGO data from science run S5, and in the development of the ihope detection pipeline.
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