This work investigates the muon capture reactions 2H(μ −, ν μ )nn and 3He(μ −, ν μ )3H and the contribution to their total capture rates arising from the axial two-body currents obtained imposing the partially-conserved-axial-current (PCAC) hypothesis. The initial and final A = 2 and 3 nuclear wave functions are obtained from the Argonne v 18 two-nucleon potential, in combination with the Urbana IX three-nucleon potential in the case of A = 3. The weak current consists of vector and axial components derived in chiral effective field theory. The low-energy constant entering the vector (axial) component is determined by reproducting the isovector combination of the trinucleon magnetic moment (Gamow-Teller matrix element of tritium beta-decay). The total capture rates are 393.1(8) s−1 for A = 2 and 1488(9) s−1 for A = 3, where the uncertainties arise from the adopted fitting procedure.
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