ANALYTIC PERTURBATION-THEORY - A NEW APPROACH TO THE ANALYTIC CONTINUATION OF THE STRONG-COUPLING CONSTANT ALPHA(S) INTO THE TIME-LIKE REGION

The renormalization group applied to perturbation theory is ordinarily used to define the running coupling constant in the spacelike region. However, to describe processes with timelike momenta transfers, it is important to have a self-consistent determination of the running coup ling constant in the timelike region. The technique called analytic pe rturbation theory (APT) allows a consistent determination of this runn ing coupling constant. The results are found to disagree significantly with those obtained in the standard perturbative approach. Comparison between the standard approach and APT is carried out to two loops, an d threshold matching in APT is applied in the timelike region.