ABSTRACT
In this chapter, we first describe radiation in terms of the Tamm-Frank theory, closely following the detailed exposition given by Zrelov in his book on radiation in high-energy physics. We then introduce the relativistic transform of the electromagnetic inductions and perform a detailed analysis of the radiation condition based on the relativistic transform of the refractive index. This approach provides a powerful
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example of the application of the principle of relativity and illustrates in a clear manner the crucial difference between scalars, as defined within the context of special relativity, and pseudoscalars, such as the refractive index, which behave in a very complex manner under Lorentz transform. It also provides a different insight into the physics of radiation and clearly exemplifies the importance and usefulness of complementary approaches to the description of a given physical phenomenon. Finally,
radiation, just like transition radiation, is an interesting form of production of light by a charged particle because it first seems that a particle moving with constant velocity can actually radiate, apparently violating the principle of relativity. The detailed analyses presented in this chapter resolve this apparent contradiction by showing that the particle is in fact subjected to an image current which gives it a small transverse acceleration. This electromagnetic image is induced by boundary conditions in the case of transition radiation or by the polarization of the medium traversed by the charge in the case of radiation.
