Infrared behavior and running couplings in interpolating gauges in QCD

We consider the class of gauges that interpolates between Landau- and Coulomb-gauge QCD, and show the nonrenormalization of the two independent ghost-gluon vertices. This implies the existence of two renormalization group (RG)-invariant running couplings, one of which is interpreted as an RG-invariant gauge parameter. We also present the asymptotic infrared limit of solutions of the Dyson-Schwinger equations in interpolating gauges. The infrared critical exponents of these solutions as well as the resulting infrared fixed point of one of the couplings are independent of the gauge parameter. This coupling also has a fixed point in the Coulomb-gauge limit and constitutes a second invariant charge besides the well known color-Coulomb potential