Speaker
Description
A cosmic or local abundance of millicharged particles may be produced by the early universe, stellar environments, dark matter, or dark energy. If such particles are light, these production channels result in a background of millicharged radiation. We show that light-shining-through-wall experiments employing superconducting RF cavities can also be used as “direct deflection” experiments to search for this relativistic background. The millicharged plasma is first subjected to an oscillating electromagnetic field of a driven cavity, which induces charge and current perturbations in the plasma. In turn, these perturbations can propagate outwards and resonantly excite electromagnetic fields in a shielded cavity placed nearby, enabling detection. We estimate that future versions of the existing Dark SRF experiment can probe orders of magnitude of currently unexplored parameter space, including millicharges produced from the Sun, the cosmic neutrino background, and other mechanisms that generate a thermal abundance with energy density down to $\sim 10^{-4}$ that of the cosmic microwave background.
