Binary black hole spectroscopy: a no-hair test of GW190814 and GW190412

Gravitational waves provide a window to probe general relativity (GR) under extreme conditions. The recent observations of GW190412 and GW190814 are unique high-mass-ratio mergers that enable the observation of gravitational-wave harmonics beyond the dominant $(\mathrm{\ell },m)=(2,2)$ mode. Using these events, we search for physics beyond GR by allowing the source parameters measured from the sub-dominant harmonics to deviate from that of the dominant mode. All results are consistent with GR. We constrain the chirp mass as measured by the $(\mathrm{\ell },m)=(3,3)$ mode to be within $0_{-3}^{+5}\mathrm{\%}$ of the dominant mode when we allow both the masses and spins of the sub-dominant modes to deviate. If we allow only the mass parameters to deviate, we constrain the chirp mass of the $(3,3)$ mode to be within $\pm 1\mathrm{\%}$ of the expected value from GR.