Exotics and PWA for piN scattering

Our talk is intended for the session in memory of Mitya Diakonov. The problem is considered of existence of flavor multiplets consisting of multi-quark baryons. We have argued that the Smatrix should have poles, at least Regge ones, with any quantum numbers, including exotic. This is a novel argument for possible reality of hadrons with arbitrary exotic structure. Though it does not provide a proof, yet there are no theoretical arguments to forbid exotics. Then we apply the partial-wave analysis (PWA) with addressing mainly to the non-strange exotic members of the anti-decuplet or even of higher multiplets. It suggested new N(1680) as a possible partner of Θ + . Later independent measurements of several collaborations seem to support our finding for N(1680), though its quantum numbers still wait for investigation. Similar approach to π + -proton scattering, in combination with K + -proton scattering, suggests a number of candidates for 27-plets. Their interesting feature is possible existence of both very wide and very narrow baryon states. This phenomenon may be analogous to recent Weinberg’s suggestion for tetra-quark mesons. The situation is worth of further theoretical and experimental studies.