A central issue in any relativistic quantum theory is how to introduce interactions without spoiling relativistic invariance. This volume shows that interactions can be incorporated in a mass operator, in such a way that relativistic invariance is maintained. Surprisingly for a relativistic theory, such a construction allows for instantaneous interactions.

A central issue in any relativistic quantum theory is how to introduce interactions without spoiling relativistic invariance. This volume shows that interactions can be incorporated in a mass operator, in such a way that relativistic invariance is maintained. Surprisingly for a relativistic theory, such a construction allows for instantaneous interactions.