Gluon condensate and non-perturbative quark-photon vertex 1 Supported by BMBF, GSI Darmstadt, DFG, a

We evaluate the quark-photon vertex non-perturbatively taking into account the gluon condensate at finite temperature. This vertex is related to the previously derived effective quark propagator by a QED like Ward-Takahashi identity. The importance of the effective vertex for the dilepton production rate from a quark-gluon plasma is stressed.