Muon capture on A = 2 and 3 nuclei

We present the results of a recent simultaneous study of the muon capture reactions 2H(μ-,vμ)nn and 3He(μ-,vμ)3H. The initial and final A = 2 and 3 nuclear wave functions are obtained from the Argonne v18 or chiral N3LO twonucleon 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 e_ective field theory (xEFT) framework. In the first case, the only parameter is in the axial-vector current and is fixed by reproducing the experimental Gamow-Teller matrix element in tritium _-decay (GTEXP). 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 GTEXP. 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 to cuto_ sensitivity in the xEFT currents. These values are compared with available experimental data and results of previous calculations.