We study Abrikosov-Nielsen-Olesen (ANO) flux tubes on the Higgs branch of N = 2 QCD with SU(2) gauge group and Nf = 2 flavors of fundamental matter. In particular, we consider this theory near Argyres-Douglas (AD) point where the mass of monopoles connected by these ANO strings become small. In this regime the effective QED which describes the theory on the Higgs branch becomes strongly coupled. We argue that the appropriate description of the theory is in terms of long and thin flux tubes (strings) with small tension. We interpret this as another example of duality between field theory in strong coupling and string theory in weak coupling. Then we consider the non-critical string theory for these flux tubes which includes fifth (Liouville) dimension. We identify CFT at the AD point as UV fix point corresponding to AdS metric on the 5d "gravity" side. The perturbation associated with the monopole mass term creates a kink separating UV and IR behavior. We estimate the renormalized string tension and show that it is determined by the small monopole mass. In particular, it goes to zero at the AD point.
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The author is grateful to Alexandr Gorsky, Gennady Danilov, Andrei Marshakov, Erich Poppitz, Mikhail Shifman, Arkady Vainshtein and, in particular, to Alexei Morozov for helpful discussions. The author also would like to thank the Theoretical Physics Institute at the University of Minnesota for hospitality and support. This work is also supported by Russian Foundation for Basic Research under grant No. 99-02-16576, by the US Civilian Research and Development Foundation under grant No. RP1-2108 and by INTAS grant No. 2000-334.