Nucleon Decay into a Dark Sector

A sub-GeV dark sector fermion X can have baryon-number-violating interactions induced by high-scale physics, leading to nucleon decay into X + meson and neutron -> X + photon. Such processes can mimic standard search modes containing a neutrino, but have different kinematics and may have escaped detection. If a dark force mediated by a light vector Z(d) acts on X, depending on parameters, neutron -> X + Z(d) can be important. In typical scenarios, Z(d) decays into l(+)l(-) where l = e, mu, with an order unity branching fraction. Nucleon decay searches can potentially uncover new dark states that are otherwise inaccessible, due to their negligible coupling to ordinary matter or cosmological abundance.