Isospin Violation in the Nuclear Force
Isospin symmetry in nuclei was one of the first dynamical symmetries to be
incorporated into a quantum mechanical framework. Beginning with the work of
Heisenberg, this symmetry has played an exceptional role in our understanding of
nuclear energies and spectra. Violation of this symmetry in the nuclear force
occurs at a level of about 1%. Until very recently there was no comprehensive
picture of the mechanisms behind this isospin violation. Chiral Perturbation
Theory has provided that picture and links isospin violation in nuclei to
fundamental elements of QCD, such as the mass difference of up and down quarks
and hard electromagnetic interactions at the quark level. The power counting (or
dimensional analysis) associated with Chiral Perturbation Theory allows an
ordering of sizes of various isospin-violating mechanisms. Isospin violation in
few-nucleon systems (including a comparison of theory and experiment) will be
discussed.