Abstract :
Using recent results of Avdeev et al. and an expansion for μtm̂t(Mt) (Mt is the pole mass and μt≡m̂t(μt)), it is shown that when Δϱ is expressed in terms of m̂t2(Mt), the QCD correction is only (2–3) × 10−3 in the NLO approximation. As a consequence, in terms of Mt2 the correction to Δϱ is almost entirely contained in m̂t2(Mt)Mt2, a pure QCD effect. The latter is studied using various optimization procedures, and the results compared with the expansion proposed by Avdeev et al.. Implications for electroweak physics are discussed. Threshold effects are analyzed on the basis of a simple sum rule.
