We calculate the proton's magnetic moment µ p and its axial-vector coupling g A as a function of its Dirac radius R 1 using a relativisitic three-quark model formulated on the light-cone. The relationship between µ p and g A is found to be independent of the assumed form of the light-cone wavefunction. At the physical radius R 1 = 0.76 fm, one obtains the experimental values for both µ p and g A , and the helicity carried by the valence u and d quarks are each reduced by a factor ≃ 0.75 relative to their non-relativistic values. At large proton radius, µ p and g A are given by the usual non-relativistic formulae. At small radius, µ p becomes equal to the Dirac moment, as demanded by the Drell-Hearn-Gerasimov sum rule. In addition, as R 1 → 0, the constituent quark helicities become completely disoriented and g A → 0.Typeset using REVT E X LC for three-quarks, we shall have to proceed by making an ansatz for the momentum space structure of the wavefunction Ψ.This may seem quite arbitrary, but as we will show below, for a given size of the proton, the predictions and interrelations between observables at Q 2 = 0, such as the proton magnetic moment µ p and its axial coupling g A , turn out to be essentially independent of the shape of the wavefunction.

We calculate the electroweak properties of nucleons and hyperons in a relativistic constituent quark model using the light-front formalism. The parameters of the model, namely the constituent quark mass and the confinement scale, can be uniquely chosen for both the electromagnetic and weak experimental data. A consistent physical picture of the qqq system appears in this work with a symmetric nucleon wave function and an asymmetric hyperon wave function. Only for the strangeness-changing weak decays do we need nontrivial form factors of the constituent quark.11.10. St, 12.40.Aa, 13.30.Ce, 13.40.Fn