Muon Capture on Deuteron and (3)He

We present the results of a recent simultaneous study of the muon capture reactions (2)H(mu (-), nu (mu) )nn and (3)He(mu (-), nu (mu) )(3)H. The initial and final A = 2 and 3 nuclear wave functions are obtained from the Argonne v (18) or chiral N3LO two-nucleon potential, in combination with, respectively, the Urbana IX or chiral N2LO three-nucleon potential in the case of A = 3. The weak current consists of polar- and axial-vector components. The former are related to the isovector piece of the electromagnetic current via the conserved-vector-current hypothesis. These and the axial currents are derived either in a meson-exchange or in a chiral effective field theory (chi EFT) framework. In the first case, there is one parameter which is fixed by reproducing the Gamow-Teller matrix element in tritium beta-decay (GT(EXP)). In the second case, the low-energy constants, two in the polar and one in the axial-vector current, are fixed, respectively, by reproducing the A = 3 magnetic moments and GT(EXP). The total rates are found to be 392.0 +/- 2.3 s(-1) for A = 2, and 1484 +/- 13 s(-1) for A = 3, where the spread accounts for the model dependence relative to the adopted interactions and currents (and cutoff sensitivity in the chi EFT currents)