Baryon form factors of relativistic constituent-quark models

Abstract

The electromagnetic and axial form factors of the nucleon and its lowest positive parity excitations, the Delta(1232) and the N*(1440), are calculated with constituent-quark models that are specified by simple algebraic representations of the mass-operator eigenstates. Poincar\'e covariant current operators are generated by the dynamics from single-quark currents that are covariant under a kinematic subgroup. The dependence of the calculated form factors on the choice of kinematics and on the gross features of the wave functions is illustrated for instant-form, point-form, and front-form kinematics. A simple algebraic form of the orbital ground state wave function, which depends on two parameters, allows a fair description of all the form factors over the empirically accessible range, although with widely different choices of the parameters, which determine the range and shape of the orbital wave function. The neutron electric form factor requires additional features, for instance the presence of mixed symmetry S-state component with 1 -- 2 % probability in the ground state wave function. Instant and front form kinematics demand a spatially extended wave function, whereas in point form kinematics the form factors may be described with a quite compact wave function.