Strange-quark asymmetry in the proton in chiral effective theory

We perform a comprehensive analysis of the strange-antistrange parton distribution function (PDF) asymmetry in the proton in the framework of chiral effective theory, including the full set of lowest-order kaon loop diagrams with off-shell and contact interactions, in addition to the usual on-shell contributions previously discussed in the literature. We identify the presence of δ-function contributions to the s¯ PDF at x=0, with a corresponding valencelike component of the s-quark PDF at larger x, which allows greater flexibility for the shape of s−s¯. Expanding the moments of the PDFs in terms of the pseudoscalar kaon mass, we compute the leading nonanalytic behavior of the number and momentum integrals of the s and s¯ distributions, consistent with the chiral symmetry of QCD. We discuss the implications of our results for the understanding of the NuTeV anomaly and for the phenomenology of strange-quark PDFs in global QCD analysis.