NUCLEON GENERALIZED POLARIZABILITIES WITHIN A RELATIVISTIC CONSTITUENT QUARK-MODEL

Nucleon generalized polarizabilities are investigated within a relativ istic framework, defining such quantities through a Lorentz covariant multipole expansion of the amplitude for virtual Compton scattering. T he key physical ingredients in the calculation of the nucleon polariza bilities are the Lorentz invariant reduced matrix elements of the elec tromagnetic transition current, which can be evaluated from off-energy -shell helicity amplitudes. The evolution of the proton paramagnetic p olarizability beta(para)(q) as a function of the virtual-photon three- momentum transfer q is explicitly evaluated within a relativistic cons tituent quark model by adopting transition form factors obtained in th e light-front formalism. The discussion is focused on the role played by the effects due to the relativistic approach and to the transition form factors, derived within different models. [S0556-2813(98)06505-4] .