A modification of minimal analytic QCD at low energies
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We present an approach which allows for modifications of the (minimal) analytic QCD model of Shirkov, Solovtsov et al. The discontinuity function of the (minimal) analytic QCD coupling parameter is changed at the low time-like momenta by a simple ansatz motivated by the vector meson dominance for the vector channel of the e+e- hadronic decay ratio R_v(s). In this way, the additional low energy parameters introduced in the coupling parameter make it possible to obtain the correct value of the semihadronic tau decay ratio without having to introduce the unusually heavy quark masses of u, d and s quarks, in contrast to the minimal analytic QCD. Some numerical results are presented in the leading skeleton approximation for a simple version of such a model. We hope that a more systematic analysis of such models leads to an approximately universal coupling parameter.
5 pages, 1 figure (presented at QCD05, Montpellier, 4-8 July 2005); a typo in Eq.(15) corrected
5 pages, 1 figure (presented at QCD05, Montpellier, 4-8 July 2005); a typo in Eq.(15) corrected