A covariant model for the nucleon and the Δ

Regular Article - Theoretical Physics

DOI: 10.1140/epja/i2008-10599-0

Cite this article as:
Ramalho, G., Peña, M.T. & Gross, F. Eur. Phys. J. A (2008) 36: 329. doi:10.1140/epja/i2008-10599-0


The covariant spectator formalism is used to model the nucleon and the Δ(1232) as a system of three constituent quarks with their own electromagnetic structure. The definition of the “fixed-axis” polarization states for the diquark emitted from the initial-state vertex and absorbed into the final-state vertex is discussed. The helicity sum over those states is evaluated and seen to be covariant. Using this approach, all four electromagnetic form factors of the nucleon, together with the magnetic form factor, GM * , for the γN → Δ transition, can be described using manifestly covariant nucleon and Δ wave functions with zero orbital angular momentum L , but a successful description of GM * near Q2 = 0 requires the addition of a pion cloud term not included in the class of valence quark models considered here. We also show that the pure S -wave model gives electric, GE * , and Coulomb, G * C , transition form factors that are identically zero, showing that these form factors are sensitive to wave function components with L > 0 .


12.39.Ki Relativistic quark model 11.30.Cp Lorentz and Poincaré invariance 13.40.Gp Electromagnetic form factors 14.20.Gk Baryon resonances with S = 0  

Copyright information

© Società Italiana di Fisica and Springer-Verlag 2008

Authors and Affiliations

  1. 1.Thomas Jefferson National Accelerator FacilityNewport NewsUSA
  2. 2.Centro de Fısica Teórica de PartıculasLisboaPortugal
  3. 3.Department of PhysicsInstituto Superior TécnicoLisboaPortugal
  4. 4.College of William and MaryWilliamsburgUSA

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