Gauge invariance and the choice of gauge for one-gluon-exchange corrections to quarkonium mass spectra

Abstract
The gauge invariance of the bound-state energy correction due to one-gluon exchange between a quark and antiquark is demonstrated under the assumption that, in zeroth order, the bound state is described by a Bethe-Salpeter equation with an instantaneous and local interaction kernel, which does not include one-gluon exchange. It is argued that the most convenient choice of gauge for the gluon propagator is the radiation gauge.