Stranger Still: Kaon Loops and Strange Quark Matrix Elements of the Nucleon

Abstract

Intrinsic strangeness contributions to low-energy strange quark matrix elements of the nucleon are modelled using kaon loops and meson-nucleon vertex functions taken from nucleon-nucleon and nucleon-hyperon scattering. A comparison with pion loop contributions to the nucleon electromagnetic (EM) form factors indicates the presence of significant SU(3)-breaking in the mean-square charge radii. As a numerical consequence, the kaon loop contribution to the mean square Dirac strangeness radius is significantly smaller than could be observed with parity-violating elastic ep experiments planned for CEBAF, while the contribution to the Sachs radius is large enough to be observed with PV electron scattering from (0^+,0) nuclei. Kaon loops generate a strange magnetic moment of the same scale as the isoscalar EM magnetic moment and a strange axial vector form factor having roughly one-third magnitude extracted from nu p/nubar p elastic scattering. In the chiral limit, the loop contribution to the fraction of the nucleon's scalar density arising from strange quarks has roughly the same magnitude as the value extracted from analyses of Sigma_{πN}. The importance of satisfying the Ward-Takahashi Identity, not obeyed by previous calculations, is also illustrated, and the sensitivity of results to input parameters is analyzed.