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Event Number 1613
Thursday, November 5th, 2009
NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The Baryon Resonance Spectrum and the 1/Nc Expansion
- Time: 4:00 pm
- Place: 5310 Chamberlin
- Speaker: Richard Lebed, Arizona State University
- Abstract: Why do baryon resonance multiplets exist, and what controls their formation and decays? It is natural to consider them as merely excited states of some three-quark or meson-nucleon potential. But these are just simplistic quantum-mechanical pictures that recognize neither the full field-theoretical complexities of QCD nor the extremely brief lifetimes of resonances due to quark pair production. Both of these issues are addressed by the 1/Nc expansion of QCD, where Nc is the number of color charges. Constraints arising at large Nc on meson-baryon scattering amplitudes not only create linear relationships between them, thus linking distinct partial waves and their embedded resonances, but also restrict the possible resonant decay channels. I present strong experimental evidence in favor of this approach, describe the multiplet structure that it predicts, and show how to perform the analysis beyond the strict large Nc limit by incorporating 1/Nc-suppressed effects. This program has been developed to the point that now one possesses a full effective field theory formalism for physics in the baryon resonance region.
- Host: Michael Ramsey-Musolf
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