Lattice QCD analysis of the strangeness magnetic moment of the nucleon

The outcome of the SAMPLE experiment suggests that the strange-quark contribution to the nucleon magnetic moment, $G_M^s\mathrm{}\left(0\right),$ may be greater than zero. This result is very difficult to reconcile with expectations based on the successful baryon magnetic-moment phenomenology of the constituent quark model. We show that careful consideration of chiral symmetry reveals some rather unexpected properties of QCD. In particular, it is found that the valence u-quark contribution to the magnetic moment of the neutron can differ by more than 50% from its contribution to the ${\Xi }^0$ magnetic moment. This hitherto unforeseen result leads to the value $G_M^s\mathrm{}\left(0\right)=-0.16\pm 0.18$ with a systematic error, arising from the relatively large strange quark mass used in existing lattice calculations, that would tend to shift $G_M^s\mathrm{}\left(0\right)\mathrm{}$ towards small positive values.