Chiral electromagnetic meson exchange currents

Properties of electromagnetic isovector meson exchange currents are discussed starting from the concept of chiral symmetry and vector meson dominance. The 4-currents are constructed in the framework of theS-matrix method and satisfy the current conservation also at the relativistic level. The comparison with the standard approach is made in detail. The case when only current conservation and Lorentz invariance are taken into account is also considered. Cross sections are compared with the new data.Lectures held at the Indian Summer School on Electromagnetic and Weak Interactions of Particles with Nuclei, Sázava, Czechoslovakia, 6–11 September 1992I am indebted to the organizers for inviting me to the school.