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)(0), 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 cartful 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(o) magnetic moment. This hitherto unforeseen result leads to the value G(M)(s)(0)=-0.16+/-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)(0) towards small positive values.