Mesonic exchange currents in 3-nucleon systems

Nuclear Physics has undergone a major breakthrough during the seventies for the development of Mesonic Exchange Currents (MEC) domain and of availability of three-nucleon systems wave functions. On one side, the use of principles based on chiral invariance has drastically improved our grasp of the role of MEC in weak and electromagnetic exchange current operators, allowing a better quantititave agreement between calculations and experimental data in several cases; some of those cases precisely concern three nucleon systems. The author discusses how, with the development of Fadeev techniques (and of high speed computers) it is now possible to get three-nucleons wave functions exactly (at least in principle) once the nucleon-nucleon interaction is given. This interrelation between the wave function and the nucleon-nucleon interaction, itself correlated with exchange current operators, makes the 3-nucleon system a good framework for more consistent calculations of nuclear transition matrix elements