  There exists a puzzling disagreement between the results for the neutron
lifetime obtained in experiments using the beam technique versus those relying
on the bottle method. A possible explanation of this discrepancy postulates the
existence of a beyond-Standard-Model decay channel of the neutron involving new
particles in the final state, some of which can be dark matter candidates. We
review the current theoretical status of this proposal and discuss the particle
physics models accommodating such a dark decay. We then elaborate on the
efforts undertaken to test this hypothesis, summarizing the prospects for
probing neutron dark decay channels in future experiments.
