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.

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