Tests of General Relativity with GW230529: a neutron star merging with a lower mass-gap compact object

Abstract: We performed tests of General Relativity on gravitational wave signal GW230529_181500, which comes from what is most likely a neutrons star merging with a black hole in the lower mass gap. We used two different frameworks to perform parameterized inspiral tests. We find that the signal is consistent with General Relativity for all deviation parameters and we obtain particularly tight constraints on dipole radiation. We discuss some challenges that arise when analyzing this signal, namely biases due to correlations with tidal effects and the degeneracy between the deviation parameter at Newtonian order and the chirp mass. We also performed a theory-specific test for Einstein-scalar-Gauss-Bonnet gravity where we obtain the best constraints on this theory to date.