SU(6) breaking in a relativistic quark model

Abstract

Consideration of the relativistic motion of quarks within a composite baryon is shown to lead to an unambiguous procedure for calculating SU(6)-breaking effects. Matrix elements of the weak and electromagnetic currents between low-lying baryon states are calculated. The symmetry breaking is appreciable, and for neutron $\beta$ decay, $\frac{g_A}{g_V}=-1.265\mathrm{}$ for $m_{\mathrm{quark}}=300\mathrm{}$ MeV. Small deviations from the conserved-vector-current hypothesis are calculated, and the symmetry breaking induces small second-class current terms between physical states. These weak form factors are in agreement with the available data. Symmetry breaking of the correct order of magnitude is predicted for the magnetic moments of the baryon octet, but the agreement with experiment is not as good in this case.