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HK: Physik der Hadronen und Kerne
HK 46: Theory VII
HK 46.3: Talk
Thursday, March 11, 2004, 17:30–17:45, D
Two-photon decays of π0, η and η′ — •Robin Nißler and Buḡra Borasoy — Institute for Theoretical Physics (T39), TU München, Germany
The anomalous decays of π0, η and η′ into two photons are investigated in an effective U(3) chiral Lagrangian approach without employing large Nc arguments [1].
Unitarity corrections beyond one-loop play an important role for the decays with off-shell photons and are included by utilizing a coupled channel Bethe-Salpeter equation which satisfies unitarity constraints and generates vector-mesons from composed states of two pseudoscalar mesons without including them explicitly. In this framework the phase shifts of meson-meson scattering, particularly in the important ρ-resonance channel, are precisely reproduced. We compare our method with the common picture of Vector Meson Dominance, where vector mesons are included explicitly and mediate all couplings between Goldstone bosons and external photons. The importance of double vector meson exchange which is crucial for the anomalous magnetic moment of the muon and kaon matrix elements is critically re-examined within our approach. We present our results and predictions for the decays with one, both or none of the photons being off-shell. Financial support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.
- [1] B. Borasoy and R. Nißler, Eur. Phys. J. A (in print), hep-ph/0309011