Determination of s(p) from gluon and from ghost propagators

We present a numerical study of the running coupling constant in 4d pure-SU(2) lattice gauge theory. The running coupling is evaluated by fitting data for gluon and ghost propagators in minimal Landau gauge. The fitting formulae are obtained by a simultaneous integration of the function and of a function coinciding (in the momentum-subtraction scheme) with the anomalous dimension of the propagator. We use these formulae at two, three and four loops. In the ghost case, a careful analysis of finite-size and hypercubic effects reveals a smooth behavior of the data over the whole range of momenta considered (i.e. up to about 25 GeV). This allows a precise determination of [overline MS]{expression} and an investigation of possible anomalous running (power corrections) in the strength of the coupling.