Color coherence and parton-hadron duality in a model of effective string amplitudes

We derive and discuss a model of effective string amplitudes exhibiting the properties of color coherence and parton-hadron duality. The parameters on which this model depends, the running coupling and the running slope, are constrained by the compatibility with QCD and by the consistency of string quantization. This approach could provide a better theoretical foundation to the phenomenologically successful color dipole model and some hints about the effective string theory of QCD.