A cavity experiment to search for hidden sector photons

We propose a cavity experiment to search for low mass extra U(1) gauge bosons with gauge-kinetic mixing with the ordinary photon, so-called paraphotons. The setup consists of two microwave cavities shielded from each other. In one cavity, paraphotons are produced via photon–paraphoton oscillations. The second, resonant, cavity is then driven by the paraphotons that permeate the shielding and reconvert into photons. This setup resembles the classic “light shining through a wall” setup. However, the high quality factors achievable for microwave cavities and the good sensitivity of microwave detectors allow for a projected sensitivity for photon–paraphoton mixing of the order of χ∼¹⁰⁻¹²–¹⁰⁻⁸$\chi \sim {10}^{\mathrm{-12}}\text{–}{10}^{\mathrm{-8}}$, for paraphotons with masses in the μeV to meV range—exceeding the current laboratory and astrophysics-based limits by several orders of magnitude. Therefore, this experiment bears significant discovery potential for hidden sector physics.