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