Jim Friar (T-16, LANL)
Isopin 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.