We compute the quark couplings in flavor-changing semileptonic transitions induced by lowest-order gluon corrections. We investigate the consequences of these radiative corrections for the quark axial-vector coupling, the deviations from Cabibbo universality for the axial-vector relative to the vector current, and the induced couplings (first-class pseudoscalar and anomalous magnetic moment, and second-class scalar and pseudotensor). The correction lowers the axial-vector coupling and increases the magnetic moment. We study the dependence of the couplings on the quark mass difference. Some of these results, true to all orders in ${\alpha }_s$, generalize the theorem of Ademollo and Gatto. The effective current is pure $V-A$ to a very good approximation for transitions of heavy quarks ($m\gtrsim 5$ GeV).

• Received 7 April 1980

DOI:https://doi.org/10.1103/PhysRevD.22.2906