SU(3)-symmetry breaking and configuration mixing in baryon semileptonic decays

We discuss small contributions to baryon semileptonic decays which provide corrections to the simplest SU(3)-symmetric formulas. In particular, we consider (1) SU(3)-symmetry breaking resulting from the wave-function deformations due to the $s-u$, $d$ quark mass difference and (2) the effects of the configuration mixing of ${}_{}{}^2{}_{}{}^{}S_M^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}S_S^{}{}_{}{}^{}$ states, originating from QCD hyperfine interactions. Both effects are treated in combination with the form-factor suppression effect which is operative if the three-momentum transfer between the initial and final hadron is nonzero. Our estimates are performed in the framework of the harmonic-oscillator quark model. While the inclusion of the $s-u$, $d$ quark mass difference leads to an unacceptable $\frac{g_A}{g_V}$ ratio for $\Lambda \to p{e}^{-}\nu$ semileptonic decay, the corrections due to configuration mixing do not lead to disagreement with the data. Better measurements of the $\Xi \to n{e}^{-}\nu$ and $\Xi \to \Lambda e^{-}\nu$ decays are needed if a choice is to be made between the standard SU(3)-symmetric parametrization and the pattern of SU(3) breaking resulting from configuration mixing.