The connection between Unruh radiation and quantum electrodynamics (QED) lies in the fact that Unruh radiation is a consequence of the principles of QED. In QED, particles and fields are described by quantum mechanical equations, and the theory also includes the effects of special relativity. Unruh radiation arises when a particle undergoes acceleration in a vacuum, which is a situation that can be described within the framework of QED.
In QED, Unruh radiation is hidden in the mathematical formalism of the theory. It is not explicitly included in the equations, but can be derived from them using mathematical techniques. Specifically, Unruh radiation arises from the concept of virtual particles, which are particles that are allowed to exist for a very short time according to the uncertainty principle. These virtual particles can be thought of as fluctuations in the vacuum, and when a particle is accelerated, it interacts with these fluctuations, leading to the emission of real particles (Unruh radiation).
Feynman diagrams, which are graphical representations of particle interactions in QED, do not explicitly assign Unruh radiation. However, they do show the interactions between particles and virtual particles, which ultimately lead to the emission of Unruh radiation.
Nonlinear QED, which takes into account the effects of strong electric fields, is not necessary for the existence of Unruh radiation. However, it may play a role in the strength and behavior of the radiation in certain scenarios.
In conclusion, Unruh radiation is a consequence of the principles of QED and is hidden in the mathematical formalism of the theory. It can be derived from the concept of virtual particles and is not explicitly included in Feynman diagrams. While nonlinear QED may play a role in certain scenarios, it is not necessary for the existence of Unruh radiation.