ABSTRACT
DIVERGENT SECOND-ORDER PROCESSES
The more success the quantum theory has, the sillier it looks.
Albert Einstein
The study of some second-order processes is very difficult, since they lead to divergent integrals. The divergences are of several kinds. In this chapter we shall focus on the so-called ”ultraviolet divergences”, which arrise at very high energies, due to the fact that the product of two integrable singular functions does not lead - in general - to an integrable singular function. In principle, these kinds of divergences can be eliminated by subtracting from the matrix elements some finite quantities, well-justified from the physical point of view. As we shall see, the physical interpretation of eliminating divergences leads to mass and charge renormalization.
