Enhanced Sensitivity to Bosonic Ultralight Dark Matter from Acetylene Transitions between Near-Degenerate Vibrational Modes

The nature of dark matter is unknown despite the work performed in high energy physics toward its direct detection [1]. Couplings between ultralight dark matter candidates to the particles of the Standard Model can induce temporal variations of the fundamental constants that were probed through precision measurements with atoms and molecules [2]. Transitions between near-resonant energy levels of atoms or molecules were addressed in dark matter searches [3] to benefit from their enhanced sensitivity to the variations of the fundamental constants. Acetylene transitions were exploited as frequency references in the $1.5\ \mu\mathrm{m}$ domain. This work addresses the potential for dark matter searches from transitions between near-resonant energy levels of ¹²C2H2.