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<tt>Theory Center Seminar<br>
Monday, Feb. 18, 2013<br>
CEBAF Center, Room L102<br>
1:00 p.m. (coffee at 12:45 p.m.)<br>
<br>
<br>
Bastian Kubis</tt> <tt><br>
University of Bonn<br>
<br>
<b>What Can We Learn From Hadronic and Radiative<br>
Decays of Light Mesons?" </b></tt> <tt><br>
<br>
Chiral perturbation theory offers a powerful tool for the<br>
investigation of light pseudoscalar mesons. It incorporates<br>
the fundamental symmetries of QCD, interrelates various <br>
processes, and allows to link these to the light quark masses.<br>
Its shortcomings lie in a limited energy range: the radius of<br>
convergence of the chiral expansion is confined to below <br>
resonance scales. Furthermore, the strongest consequences <br>
of chiral symmetry are manifest for pseudoscalars (pions, <br>
kaons, eta) only: vector mesons, e.g., have a severe impact<br>
in particular for reactions involving photons. In this talk,<br>
I advocate dispersions relations as another model-independent<br>
tool to extend the applicability range of chiral perturbation<br>
theory. They even allow to tackle the physics of vector mesons<br>
in a rigorous way. It will be shown how dispersive methods can <br>
be used to resum large rescattering effects, and to provide <br>
model-independent links between hadronic and radiative decay <br>
modes. Examples to be discussed will include Dalitz plot <br>
distributions of decays into 3 pions; and meson transition<br>
form factors, which have an important impact on the hadronic <br>
light-by-light-scattering contribution to the anomalous <br>
magnetic moment of the muon. </tt>
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