Nucleon - Light Dark Matter Annihilation through Baryon Number Violation

Dark matter that participates in baryon-number violating interactions can annihilate with baryons if the dark matter particle is not protected under discrete symmetries. In this paper we investigate the dark matter - baryon annihilation in color-triplet extensions of the Standard Model, in which a fermionic dark matter can be kinematically stable within a small mass range near the proton mass. We demonstrate that the DM's annihilation with nucleons can be probed to stringent limits at large-volume water Cherenkov detectors like the Super-Kamionkonde experiment, with the mediator scale $m_\Phi$ constrained up to $10^{7}$ GeV. In case of a Majorana light dark matter, this constraint is weaker yet close in magnitude to that from neutron-antineutron oscillation. In the Dirac DM case, the dark matter- nucleon annihilation gives much stronger bounds than that from the uncertainties of the neutron decay lifetime. In a limited range of the DM mass above $m_p+m_e$, the DM-nucleon annihilation bound can be higher than the requirement from the DM's stability in the Universe. Given the strong limits from Super-Kamionkonde, we find it below the current experimental capabilities to indirectly detecting the dark matter- nucleon annihilation signal in diffuse Galactic gamma rays and neutron star heating.