The problem of exotic states: view from complex angular momenta

Having in mind present uncertainty of the experimental situation in respect to exotic hadrons, it is important to discuss any possible theoretical arguments, pro and contra. Up to now, there are no theoretical ideas which could forbid existence of the exotic states. Theoretical proofs for their existence are also absent. However, there are some indirect arguments for the latter case. It will be shown here, by using the complex angular momenta approach, that the standard assumptions of analyticity and unitarity for hadronic amplitudes lead to a non-trivial conclusion: the S-matrix has infinitely many poles in the energy plane (accounting for all its Riemann sheets). This is true for any arbitrary quantum numbers of the poles, exotic or non-exotic. Whether some of the poles may provide physical (stable or resonance) states, should be determined by some more detailed dynamics.Comment: 6 pages, Latex; based on talks at HSQCD2005 (St.Petersburg, Russia, September 20 - 24, 2005), NSTAR2005 (Tallahassee, FA, USA, October 12 - 15. 2005), Scientific session of the Nuclear Physics Section of RAS (Moscow, Russia, December 5 - 9, 2005

Mixing and decays of rho- and omega-mesons

Isospin violating mixing of \rho- and \omega-mesons is reconsidered in terms of propagators. Its influence on various pairs of (\rho^0,\omega)-decays to the same final states is demonstrated. Some of them, (\rho^0,\omega)\to\pi^+\pi^- and (\rho^0,\omega)\to\pi^0\gamma, have been earlier discussed in the literature, others (e.g., (\rho^0,\omega)\to\eta\gamma and (\rho^0,\omega)\to e^+e^-) are new in this context. Changes in partial widths for all the decay pairs are shown to be correlated. The set of present experimental data, though yet inconclusive, provides some limits for the direct (\rho\omega)-coupling and indirectly supports enhancement of \rho^0\to\pi^0\gamma in comparison with \rho^{\pm}\to\pi^{\pm}\gamma, though not so large as in some previous estimates.Comment: 22 pages, 1 eps fi