Detecting a fifth-force gauge boson via superconducting Josephson junctions

A new fifth force between particles carrying B − L charges is well-motivated by the intriguing U ( 1 ) B − L extension of the standard model. The gauge boson mediator, Féeton, also serves as a dark matter candidate. In this letter, we propose a novel experimental design to detect the quantum phase difference caused by this fifth force using a superconducting Josephson junction. We find that the experiment has the best sensitivity to the gauge coupling when the gauge boson is within the mass range of 0.01 eV to 10 eV, which is an interesting mass region for the Féeton dark matter. This opens up a new avenue for the measurement of new physics at small scale below millimeter.