  The operator product expansion (OPE) for heavy-light-quark pseudoscalar
mesons (D-mesons and B-mesons) in medium is determined, both for a moving meson
with respect to the surrounding medium as well as for a meson at rest. First of
all, the OPE is given in terms of normal-ordered operators up to mass dimension
5, and the mass of the heavy-quark and the mass of the light-quark are kept
finite. The Wilson coefficients of such an expansion are infrared (IR)
divergent in the limit of a vanishing light-quark mass. A consistent separation
of scales necessitates an OPE in terms of non-normal-ordered operators, which
implies operator mixing, where the IR-divergences are absorbed into the
operators. It is shown that the Wilson coefficients of such an expansion are
IR-stable, and the limit of a vanishing light-quark mass is perfomed. Details
of the major steps for the calculation of the Wilson coefficients are
presented. By a comparison with previous results obtained by other theoretical
groups we have found serious disagreements.
