Pade Approximants and Borel Summation for QCD Perturbation Expansions

We study the applicability of Pade Approximants (PA) to estimate a ”sum” of asymptotic series of the type appearing in QCD. We indicate that one should not expect PA to converge for positive values of the coupling constant and propose to use PA for the Borel transform of the series. If the latter has poles on the positive semiaxis, the Borel integral does not exist, but we point out that the Cauchy pricipal value integral can exist and that it represents one of the possible ”sums” of the original series, the one that is real on the positive semiaxis. We mention how this method works for Bjorken sum rule, and study in detail its application to series appearing for the running coupling constant for the Richardson static QCD potential. We also indicate that the same method should work if the Borel transform has branchpoints on the positive semiaxis and support this claim by a simple numerical experiment. PACS numbers: 12.38 Bx, 12.38 Cy;