The μ−d capture rate in effective field theory

Muon capture on the deuteron is studied in a framework that essentially incorporates heavy baryon chiral perturbation theory (HBχPT). It is found that by far the dominant contribution to μd capture comes from a region of the final three-body phase-space in which the energy of the two neutrons is sufficiently small for HBχPT to be applicable. The single unknown low-energy constant having been fixed from the tritium beta decay rate, our calculation contains no free parameter. Our estimate of the μd capture rate is consistent with the existing data. The relation between μd capture and the νd reactions, which are important for the SNO experiments, is briefly discussed.