A covariant model for the nucleon and the Delta

作者：Ramalho G^*; Pena M T; Gross F

来源：European Physical Journal A, 2008, 36(3): 329-348.

DOI：10.1140/epja/i2008-10599-0

The covariant spectator formalism is used to model the nucleon and the Delta(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, G(M)*, for the gamma N -> Delta transition, can be described using manifestly covariant nucleon and Delta wave functions with zero orbital angular momentum L, but a successful description of G(M)* near Q(2) = 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

• 出版日期2008-6