Enhanced sensitivity to ultralight bosonic dark matter in the spectra of SrOH

The rich spectra of polyatomic molecules offer the possibility of enhanced sensitivity to variations in fundamental constants such as the proton-to-electron mass ratio, $\mu$, arising from coupling between Standard Model particles and theoretically well-motivated ultralight dark matter (UDM) candidates. Recent extension of direct laser cooling techniques to a few linear triatomic metal hydroxide radicals has potential to enable long measurement coherence times and high spectroscopic precision. We show that in SrOH, a near-degeneracy between rotational states in the $X(200)$ and $X(03^10)$ vibrational manifolds of different character leads to $~10^3\times$ enhanced sensitivity to $\mu$: a time-dependent change $\delta\mu$ in $\mu$ would lead to a change $\delta\nu$ in the resonance frequency $\nu$ according to $\delta\nu/\nu~10^3\delta\mu/\mu$. We propose to use laser cooling and trapping of SrOH molecules and an experimental approach to enable measurements of $\delta\mu/\mu$ with as low as $10^{-17}$ fractional uncertainty [1]. A preliminary investigation of potential systematic errors will be discussed as well as possible implications for UDM searches. [1] Kozyryev et al., arXiv:1805.08185