ABSTRACT
In this chapter we will discuss in detail some applications of the concepts developed so far. We shall consider first the scattering in an external field, and the associated issues arising from the emission of low-energy photons—bremsstrahlung—and the occurrence of the infrared divergence. We will then analyse the calculation of order α $ \alpha $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315369723/48d43afe-85b0-4e2b-a932-df2bd1af07be/content/inline-math12_1235.tif"/> corrections to the energy levels of atomic electrons obtained from solving the Dirac equation [1], to the photon propagator and to the magnetic moment of the electron. The agreement between the results of these calculations and the experimental data has confirmed unequivocally the validity of QED and, more generally, the concepts which are at the foundations of quantum field theory.
