Prof. Wolfgang Lucha (HEPHY Vienna Austria)
We show that the effective continuum threshold - one of the key parameters of the method of Borel sum rules for the calculation of properties of an isolated bound-state - is a complicated quantity. Although a constant approximation for the effective threshold is commonly used in the analysis of hadron observables within sum rules in QCD, the effective threshold in fact depends on the Borel parameter and for the case of the three-point function also on the momentum transfer. Moreover, the effective threshold which isolates the contribution of the ground state to a specific correlator turns out to vary from one correlator to another. We discuss an algorithm for fixing these thresholds which leads to a considerable improvement of the accuracy of the method of sum rules for the bound-state properties.