OPE, charm-quark mass, and decay constants of D and Ds mesons from QCD sum rules

We present a sum-rule extraction of the decay constants of the charmed mesons D and D-s from the two-point correlator of pseudoscalar currents. First, we compare the perturbative expansion for the correlator and the decay constant performed in terms of the pole and the running (MS) over bar masses of the charm quark. The perturbative expansion in terms of the pole mass shows no signs of convergence whereas reorganizing this very expansion in terms of the (MS) over bar mass leads to a distinct hierarchy of the perturbative expansion. Furthermore, the decay constants extracted from the pole-mass correlator turn out to be considerably smaller than those obtained by means of the (MS) over bar -mass correlator. Second, making use of the OPE in terms of the (MS) over bar mass, we determine the decay constants of both D and D-s mesons with an emphasis on the uncertainties in these quantities related both to the input QCD parameters and to the limited accuracy of the method of sum rules. (C) 2011 Elsevier B.V. All rights reserved.