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Search for oscillations of fundamental constants using molecular spectroscopy

A possible implication of an ultralight dark matter (UDM) field interacting wibeginth the Standard Model (SM) degrees of freedom is oscillations of fundamental constants. Here, we establish direct experimental bounds on the coupling of an oscillating UDM field to the up, down, and strange quarks and to the gluons, for oscillation frequencies between 10 Hz and 10^8 Hz. We employ spectroscopic experiments that take advantage of the dependence of molecular transition frequencies on the nuclear masses. Our results apply to previously unexplored frequency bands, and improve on existing bounds at frequencies > 5 MHz. We identify a sector of UDM - SM coupling space where the bounds from Equivalence Principle tests may be challenged by next-generation experiments of the present kind.