Effective hadron dynamics: From meson masses to the proton spin puzzle

Abstract

We construct a three-flavor chiral Lagrangian of pseudoscalars and vectors with special emphasis on the symmetry-breaking terms. Comparing tree-level two- and three-point functions with experiment allows us to first fix the parameters of the model (including the light quark mass ratios) and, second, to predict $m({K}^{*+})\ensuremath{-}m({K}^{*0})$, $\ensuremath{\Gamma}({K}^{*}\ensuremath{\rightarrow}K\ensuremath{\pi})$, and $\ensuremath{\Gamma}(\ensuremath{\varphi}\ensuremath{\rightarrow}K\overline{K})$. The last mentioned quantities come out reasonably well, in contrast with an "ordinary" SU(3) treatment. For this purpose we need "second-order" symmetry breakers involving the vector fields analogous to those needed for the chiral perturbation theory program with only pseudoscalars. An improved description of the $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\eta}}^{\ensuremath{'}}$ system is also given. We then use the soliton sector of this improved chiral Lagrangian to investigate some aspects of baryon physics which are especially sensitive to symmetry breaking. For this purpose a fairly elaborate "cranking" technique is employed in connection with the collective Hamiltonian. In addition to the "strong" baryon mass spectrum a careful investigation is made of the nonelectromagnetic part of the neutron-proton mass difference. This work is needed to improve our previous estimates concerning the two-component approach to the "proton spin" puzzle. We find that both the "matter" and "glue" contributions are small but they do tend to cancel each other. It is noted that the "proton spin" matrix element measures "short distance" aspects of the model, in contrast with ${g}_{a}$, which is dominated by long distance effects.