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Reconciling Classical and Quantum Analyses of Radiation by an Accelerated Charge

Classical bremsstrahlung obviously has some affinity with Unruh radiation from an accelerated detector, although the latter involves both quantum theory and a distinction between inertial and accelerated vacuum states that has no obvious meaning in the classical context. In the case of uniform acceleration, the classical theory was the subject of many controversies that appeared to be settled in the 1960s but periodically reemerge. Around 1992 G. Matsas et al. investigated the process by QED perturbation theory and concluded that, from the point of view of the accelerated frame, inclusion of the Unruh thermal bath was essential to reproduce the known correct result. They also looked for traces of field quantization and Unruh temperature in the classical field theory of acceleration radiation. These two papers have been subject to criticism recently and are admittedly incomplete in some respects. In particular, it is unclear what happens when the initial state is the Rindler vacuum, and how such a scenario is consistent with any classical description. Recently Andre Landulfo, working with Matsas and me, has launched a reconstruction of the quantum and classical analyses that makes their conceptual consistency much clearer. His primary tool is the "Unruh modes" that occupy the middle position in the Bogolubov transformation between Minkowski and Rindler modes.