Classical Analysis of non-coherent Dark Matter to Photon Conversions in a Resonant Cavity

Both axion and dark photon dark matter are among the most promising candidates of dark matter. What we know with some confidence is that they exhibit a small velocity distribution $\delta v\lesssim v\sim 10^{-3}$c. In addition, their mass is small, resulting in a long de Broglie wavelength and a high particle number density. Their phase space distribution has many uncertainties; thus they could give rise to a coherent or noncoherent wave on the laboratory scale. In this paper, we demonstrated that a resonant cavity can enhance the noncoherent axion-to-photon or dark photon-to-photon transitions. The reason in a classical picture is that a cavity can resonantly respond to many different resonant sources at the same time. This is consistent with the quantum perspective. The induced signals, however, are noncoherent and therefore may need a single-photon readout.