  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.
