  We study a new mechanism to discover dark photon fields, by resonantly
triggering two photon transitions in cold gas preparations. Using coherently
prepared cold parahydrogen, coupling sensitivity for sub-meV mass dark photon
fields can be advanced by orders of magnitude, with a modified
light-shining-through-wall setup. We calculate the effect of a background dark
photon field on the dipole moment and corresponding transition rate of cold
parahydrogen pumped into its first vibrational excited state by
counter-propagating laser beams. The nonlinear amplification of two photon
emission triggered by dark photons in a cold parahydrogen sample is numerically
simulated to obtain the expected dark photon coupling sensitivity.

High Energy Physics - Phenomenology;High Energy Physics - Experiment