Some Simple Consequences ofSU(4)Symmetry

The electromagnetic properties of the nucleons and $N^{*}$, as well as the meson-baryon coupling constants, are examined within the framework of an $\mathrm{SU}\left(4\right)\mathrm{}$ symmetry combining spin and isospin. The motivation is to examine the consequences of such a symmetry at low energies without having to worry about the large mass differences within the $\mathrm{SU}\left(3\right)\mathrm{}$ multiplets in the corresponding $\mathrm{SU}\left(6\right)\mathrm{}$ theory. The coupling-constant ratios are in qualitative agreement with the experimental values. The arbitrariness in the proton-neutron magnetic-moment ratio is discussed. In the model where the electromagnetic interaction of the baryons is mediated by the vector mesons in the adjoint representation of $\mathrm{SU}\left(4\right)\mathrm{}$, the magnetic-moment ratios agree with the $\mathrm{SU}\left(6\right)\mathrm{}$ results.