Hyperon semileptonic decays and quark spin content of the proton

We investigate the hyperon semileptonic decays and the quark spin content of the proton ΔΣ, taking into account flavor SU(3) symmetry breaking. Symmetry breaking is implemented with the help of the chiral quark-soliton model in an approach in which the dynamical parameters are fixed by the experimental data for six hyperon semileptonic decay constants. As a result we predict the unmeasured decay constants, particularly for Ξ⁰→Σ⁺, which will be soon measured and examine the effect of SU(3) symmetry breaking on the spin content ΔΣ of the proton. Unfortunately large experimental errors of Ξ^- decays propagate in our analysis, making ΔΣ and Δs practically undetermined. We conclude that statements concerning the values of these two quantities, which are based on exact SU(3) symmetry, are premature. We stress that meaningful results can be obtained only if the experimental errors for the Ξ decays are reduced.