Diresonance in production and scattering of heavy mesons
  We consider the production and scattering amplitudes of heavy mesons in a situation, where there are two closely spaced narrow resonances, which structure we refer to as a diresonance. Assuming strong overlapping of the resonances coupled to common channels, it is found, using the unitarity and analyticity constraints, that the production amplitudes in different channels should have similar behavior with energy. In particular the ratio of the coefficients for each pole contribution to the production amplitude is fixed at -1. 
S. Dubynskiy, M.B. Voloshin