Accelerating gravitational-wave parametrized tests of general relativity using a multiband decomposition of likelihood

The detection of gravitational waves from compact binary coalescence (CBC) has allowed us to probe the strong-field dynamics of general relativity (GR). Among various tests performed by the LIGO-Virgo-KAGRA Collaboration are parametrized tests, where parametrized modifications to GR waveforms are introduced and constrained. This analysis typically requires the generation of more than millions of computationally expensive waveforms. The computational cost is higher for a longer signal, and current analyses take weeks to years to complete for a binary neutron star (BNS) signal. We present a technique to accelerate the parametrized tests using a multiband decomposition of likelihood, which was originally proposed by one of the authors to accelerate parameter estimation analyses of CBC signals assuming GR. We show that our technique speeds up the parametrized tests of a 1.4 M_⊙- 1.4 M_⊙ BNS signal by a factor of O (10 ) for a low-frequency cutoff of 20 Hz. We also verify the accuracy of our method using simulated signals and real data.