Magnetic Moment and Isospin Symmetry Breaking ∗

The small mass difference m n − m p = 1.3 MeV between the proton and neutron leads to an excess of n = π − p over p = π + n fluctuations which can be calculated by using a light-cone meson-baryon fluctuation model of intrinsic quark-antiquark pairs of the nucleon sea. The Gottfried sum rule violation may partially be explained by isospin symmetry breaking between the proton and neutron and the same effect introduces correction terms to the anomalous magnetic moments and the anomalous weak magnetic moments of the proton and neutron. We also evaluated the strange magnetic moment of the nucleon from the lowest strangeness KΛ fluctuation and found a non-trivial influence due to isospin symmetry breaking in the experimental measurements of the strange magnetic moment of the nucleon.