Should the Strange Magnetic Moment of the Nucleon be Positive?

The strange magnetic moment of the nucleon (µ s) is examined as part of the nucleon's isoscalar anomalous moment. The dominant up and down quark effects in the anomalous moment may actually tend to favor µ s > 0, which is contrary to the negative values that generally result from model calculations. The possible origins of this apparent discrepancy are considered. Several years ago, Kaplan and Manohar 1 pointed out that the neutral weak current could be used to determine the strange quark-antiquark (¯ ss) contributions to nucleon form factors. These ¯ ss effects are very interesting in that they represent low energy properties of the nucleon which must be due to the quark-antiquark sea. Determining such quantities can thus provide deeper insight into the origins of nucleon properties in terms of QCD. The magnetic moment is an excellent example of a nucleon property that can be studied in this fashion. Electromagnetic couplings probe only the charged constituents of the nucleon: the quarks and antiquarks. The anomalous components of the nucleon magnetic moments are known to be large, but we still do not have a satisfactory explanation of their magnitudes in the context of QCD. While many models do give reasonable values, none are firmly based (without additional assumptions) on QCD. Thus, the real origin of the nucleon's anomalous magnetic moment in terms of QCD (rather than ad hoc models like constituent quarks) has been elusive. After the suggestion of Kaplan and Manohar, it was proposed that the neutral weak magnetic moment of the proton could be measured in parity violating electron scattering. 2 Indeed, such an experiment (the SAMPLE experiment 3) is currently in progress and results are expected soon. In this Letter I examine the role of µ s , the strange quark-antiquark contribution to the nucleon's isoscalar anomalous moment. In particular, it will be suggested that it may be very natural to expect that the value of µ s is positive, rather than the generally negative values obtained in model calculations.