Final State Interactions in Decays of the Exotic $\pi_{1}$ Meson
  We analyze the role of final state interactions in decay of the lighest exotic meson, $pi_1$ with $J^{PC}=1^{-+}. We use the relativistic Lippmann-Schwinger equation for two coupled $\pi b_{1}$ and $\pi\rho$ channels. The first one is the predicted dominant decay mode of the $\pi_{1}$, whereas in the other a narrow $\pi_1(1600)$ exotic signal has been reported by the E852 collaboration. The FSI potential is constructed, based on the $\omega$ meson exchange between the two channels. We find that this process introduces corrections to the $\pi_{1}$ widths of the order of only a few MeV. Therefore, we conclude that a substantial $\pi\rho$ mode cannot be generated through level mixing. 
Nikodem J. Poplawski, Adam P. Szczepaniak, J.T.Londergan