Electroweak Processes in Few-Nucleon Systems

Abstract.

 After a brief introduction into the basic ingredients of electroweak theory as a spontaneously broken local, non-Abelian gauge symmetry, the general properties of the electromagnetic current and two-photon operators are discussed. In particular, the consequences of gauge invariance and the resulting low-energy theorems are reviewed. The multipole decomposition of the current operators and the general Siegert theorem are presented. The specific forms of vector and axial one-nucleon currents are given, together with lowest-order π- meson exchange and isobar currents as well as meson production currents. A brief overview is given on the most important one- and two-boson processes. Electron scattering in the one-boson approximation is then considered in greater detail. Formal expressions of the cross section for inclusive and exclusive processes are given, including parity-violating contributions from γ-Z interference as well as from parity-violating components in the hadronic wave function. Specific electromagnetic reactions on the deuteron are then discussed with respect to the influence of meson exchange currents, isobar configurations in the deuteron ground state, relativistic contributions and the role of π-meson retardation. Furthermore, recent results on coherent and incoherent π- and η-photoproduction are presented as well as a discussion of the Gerasimov-Drell-Hearn sum rule and the effect of a parity-violating deuteron component on inclusive electron scattering off the deuteron for quasifree kinematics. The review closes with a summary and a brief outlook.