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An effective sigma model describing behavior of the 3d rigid string with a$\theta$-term at $\theta=\pi$ is proposed. It contains non-perturbativecorrections resulting from summation over different genera of the 2d surfaces.The effective theory is the SU(2) WZW model coupled to the Nambu-Goto action.RG analysis shows the existence of a IR fixed point at which the normal to thesurface has long range correlations. A similar model can describe criticalbehaviour of the 3d Y-M fields or the Ising model.Comment: 7 pages, Late

AN EFFECTIVE 3-D RIGID STRING AT θ=π