Beyond general relativity: Designing a template-based search for exotic gravitational wave signals

Accurate waveform models describing the complete evolution of compact binaries are crucial for the maximum likelihood detection framework, testing the predictions of general relativity (GR) and investigating the possibility of an alternative theory of gravity. Deviations from general relativity could manifest in subtle variations of the numerical value of the gravitational wave signal's phasing coefficients. Once the search pipelines confirm an unambiguous signal detection, deviations of the signal phasing coefficients at various post-Newtonian orders are routinely measured and reported. As the search templates themselves do not incorporate any deviations from general relativity, they may miss astrophysical signals carrying a significant departure from GR. We present a parametrized template-based search for exotic gravitational-wave signals beyond general relativity by incorporating deviations to the signal's phasing coefficients at different post-Newtonian orders in the search templates. We present critical aspects of the new search, such as improvements in search volume and its effect on various parts of the parameter space. In particular, we demonstrate a twofold increase in search sensitivity (at a fixed false-alarm rate) to beyond-GR exotic signals by using search templates that admit a range of departures from general relativity. We also present the results from a reanalysis of ten days long duration of LIGO data from the first science run that includes the epoch of the GW150914 event.