Dark Matter interpretation of the neutron decay anomaly

Abstract: We add to the Standard Model a new fermion $\chi$ with minimal baryon number 1/3. Neutron decay $n \to \chi\chi\chi$ into non-relativistic $\chi$ can account for the neutron decay anomaly, compatibly with bounds from neutron stars. $\chi$ can be Dark Matter, and its cosmological abundance can be generated by freeze-in dominated at $T \sim m_n$. The associated processes $n \to \chi\chi\chi \gamma$, hydrogen decay ${\rm H}\to \chi\chi \chi\nu(\gamma)$ and DM-induced neutron disappearance $\bar\chi n \to \chi \chi (\gamma)$ have rates below experimental bounds and can be of interest for future experiments.