Pi from the sky -- A null test of general relativity from a population of gravitational wave observations

Abstract

Our understanding of observed Gravitational Waves (GWs) comes from matching data to known signal models describing General Relativity (GR). These models, expressed in the post-Newtonian formalism, contain the mathematical constant $\pi$. Allowing $\pi$ to vary thus enables a strong, universal and generalisable null test of GR. From a population of 22 GW observations, we make an astrophysical measurement of $\pi =3.115_{-0.088}^{+0.048}$, and prefer GR as the correct theory of gravity with a Bayes factor of 321. We find the variable $\pi$ test robust against simulated beyond-GR effects.

8 pages, 5 figures

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