CONSIDERATIONS CONCERNING THE QCD CORRECTIONS OF DELTA-RHO

Using recent results of Avdeev et al. and an expansion for mu(t)/(m) o ver cap(t)(M(t)) (M(t) is the pole mass and mu t = (m) over cap(t)(mu( t))), it is shown that when Delta rho is expressed in terms of (m) ove r cap(t)(2)(M(t)), the QCD correction is only (2-3) x 10(-3) in the NL O approximation. As a consequence, in terms of M(t)(2) the correction to Delta rho is almost entirely contained in (m) over cap(t)(2)(M(t))/ M(t)(2), a pure QCD effect. The latter is studied using various optimi zation procedures, and the results compared with the expansion propose d by Avdeev et al.. Implications for electroweak physics are discussed . Threshold effects are analyzed on the basis of a simple sum rule.