Continuum limit of hyperon vector coupling f1 (0) from 2+1 flavor domain wall QCD

We determine the hyperon vector couplings f1(0) for Σ-→nl-νl and Ξ0→Σ+l-νl semileptonic decays in the continuum limit with (2+1)-flavors of dynamical domain-wall fermions, using the Iwasaki gauge action at two different lattice spacings of a=0.114(2) and 0.086(2) fm. A theoretical estimation of flavor SU(3)-breaking effect on the vector coupling is required to extract Vus from the experimental rate of hyperon beta decays. We obtain the vector couplings f1(0) for Σ→N and Ξ→Σ beta-decays with an accuracy of less than one percent. We then find that lattice results of f1(0) combined with the best estimate of |Vus| with imposing Cabibbo-Kobayashi-Maskawa (CKM) unitarity are slightly deviated from the experimental result of |Vusf1(0)| for the Σ→N beta-decay. This discrepancy can be attributed to an assumption made in the experimental analysis on |Vusf1(0)|, where the induced second-class form factor g2 is set to be zero regardless of broken SU(3) symmetry. We report on this matter and then estimate the possible value of g2(0), which is evaluated from the experimental decay rate with our lattice result of f1(0) under the first-row CKM-unitarity condition.