Asymptotic freedom in a string model of high temperature QCD

Recently we have shown that a phase transition occurs in the leading and sub-leading approximation of the large N limit in rigid strings coupled to long range Kalb-Ramond interactions. The disordered phase is essentially the Nambu-Goto-Polyakov string theory while the ordered phase is a new theory. In this letter we compute the free energy per unit length of the interacting rigid string at finite temperature. We show that the mass of the winding states solves that of QCD strings in the limit of high temperature. We obtain a precise identification of the QCD coupling constant and those of the interacting rigid string. The relation we obtain is Ngqcd2 = (4π2(d−2)/3)21/3κ where κ = Dtαπμc is the ratio of the extrinsic curvature coupling constant t, the Kalb-Ramond coupling constant α, and the critical string tension μc. The running beta function of κ reproduces correctly the asymptotic behaviour of QCD.