Isospin violation in the two-nucleon system

Abstract

I discuss isospin violation in an effective field theory appraoch of the nucleon-nucleon interaction. The observed leading order charge independence breaking is explained in terms of one-pion exchange together with a four-nucleon contact term. A general classification scheme of corrections to this leading order results is presented and an explanation is offered why charge-dependent pion-nucleon coupling constants can not play a role in the observed isospin violation in the NN scattering lengths. Charge symmetry breaking, the size of $πγ$-exchange graphs and the pionless theory are also discussed.

16 pp, LaTeX, uses epsfig and sprocl.sty, invited talk, Workshop on Nuclear Physics with Effective Field Theory: 1999, INT Seattle, Feb. 25-26, 1999, to appear in the proceedings; discussion about two-pion and pi-gamma graphs extended, more references