Effective Lagrangian Models for gauge theories of fundamental interactions (original) (raw)
In this thesis we show that the effective Lagrangian models, encoding the relevant symmetries of the underlying fundamental gauge theory for strong interactions (QCD), provide a reasonable understanding of the interactions among light mesons at intermediate energies as well as of the properties of Heavy baryons. In the first part of the thesis we show that it is possible to build a chiral and crossing symmetric model for light meson interactions at intermediate energies, which we have called the Chiral Resonance Model (ChRM). Using the previous scheme we can understand ππ−scattering up to the 1 GeV region by considering the resonance exchange together with the contact term contributions. We also observe that to fully describe low energy ππ−scattering in the Chiral Resonance framework a broad scalar σ(550) particle is needed. In the second part of the thesis we investigate the heavy baryon spectra in the bound state picture. In this picture the heavy baryon is treated as a heavy spin multiplet of mesons (Qq) bound in the background field of the nucleon (qqq), which in turn arises as a soliton configuration of light meson fields. We show that a relativistic model with light vectors gives a very satisfactory account of the Σ * c − Σ c hyperfine splitting in contrast to the model without light vectors. In the last chapter we also present a generalization of the bound state model. Indeed by binding heavy spin excited multiplets to the background Skyrmion field we can describe the spectrum of excited heavy baryons of arbitrary spin.
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