Status Report on the Instanton Counting

The non-perturbative behavior of the $\mathcal N=2$ supersymmetric Yang–Mills theories is both highly non-trivial and tractable. In the last three years the valuable progress was achieved in the instanton counting, the direct evaluation of the low-energy effective Wilsonian action of the theory. The localization technique together with the Lorentz deformation of the action provides an elegant way to reduce functional integrals, representing the effective action, to some finite dimensional contour integrals. These integrals, in their turn, can be converted into some difference equations which define the Seiberg–Witten curves, the main ingredient of another approach to the non-perturbative computations in the $\mathcal N=2$ super Yang–Mills theories. Almost all models with classical gauge groups, allowed by the asymptotic freedom condition can be treated in such a way. In my talk I explain the localization approach to the problem, its relation to the Seiberg–Witten approach and finally I give a review of some interesting results.