Electroweak radiative corrections to muon capture on nuclei are computed and found to be sizable. They enhance the capture rates for hydrogen and helium by 2.8% and 3.0%, respectively. As a result, the value of the induced pseudoscalar coupling, $g_P^{\exp }$, extracted from a recent hydrogen $1S$ singlet capture experiment is increased by about 21% to $g_P^{\exp }=7.3\pm 1.2$ and brought into good agreement with the prediction of chiral perturbation theory, $g_P^{\mathrm{theory}}=8.2\pm 0.2$. Implications for helium capture rate predictions are also discussed.

• Received 26 April 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.032003