Enhanced Sensitivity to Ultralight Bosonic Dark Matter in the Spectra of the Linear Radical SrOH

TL;DR

This paper explores how ultracold polyatomic molecules like SrOH can significantly enhance the detection sensitivity for ultralight bosonic dark matter by measuring variations in fundamental constants with high precision.

Contribution

It demonstrates the potential of laser-cooled SrOH molecules to improve sensitivity to ultralight dark matter effects through amplified spectral shifts and long coherence times.

Findings

High enhancement factors (~10^3) in molecular spectra for UDM detection.

Potential fractional uncertainty of ~10^-17 in measuring variations of μ with one day of measurement.

Ultracold SrOH offers a promising platform for high-precision dark matter searches.

Abstract

Coupling between Standard Model particles and theoretically well-motivated ultralight dark matter (UDM) candidates can lead to time variation of fundamental constants including the proton-to-electron mass ratio $\mu\equiv m_{p}/m_{e}\approx1836$. The presence of nearly-degenerate vibrational energy levels of different character in polyatomic molecules can result in significantly enhanced relative energy shifts in molecular spectra originating from $\partial_{t}\mu$, relaxing experimental complexity required for high-sensitivity measurements. We analyze the amplification of UDM effects in the spectrum of laser-cooled strontium monohydroxide (SrOH). SrOH is the first and, so far, the only polyatomic molecule to be directly laser cooled to sub-millikelvin temperatures, opening the possibility of long experimental coherence times. Because of the high enhancement factors ($\left|Q_{\mu}\right|\approx10^{3}$), measurements of the $\tilde{X}\left(200\right)\leftrightarrow\tilde{X}\left(03^{1}0\right)$ rovibrational transitions of SrOH in the microwave regime can result in $\sim10^{-17}$ fractional uncertainty in $\delta\mu/\mu$ with one day of integration. Furthermore, ultracold SrOH provides a promising platform for suppressing systematic errors. More complex SrOR radicals with additional vibrational modes arising from larger ligands R could lead to even greater enhancement factors.