Implications of the Present Bound on the Width of the Theta(1540)
  The recently reported Theta(1540) exotic baryon seems to be very narrow: Gamma(Theta)< 1 MeV according to some analyses. Using methods of low energy scattering theory, we develop expectations for the width of the Theta, an elastic resonance in KN scattering in a theory where the characteristic range of interactions is ~1 Fermi. If the Theta is a potential scattering resonance, generated by the forces in the KN channel, its width is hard to account for unless the KN-channel orbital angular momentum, l, is two or greater. If the Theta is a CDD pole, its coupling to the scattering channel is at least an order of magnitude less than the coupling of the Lambda(1520) unless l is two or greater. Either way, if the Theta proves to be in the KN s- or p-wave, new physics must be responsible for its narrow width. 
R. L. Jaffe and Ambar Jain