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High Energy Physics - Phenomenology, hep-ph
Abstract:
Refractive processes in strong-field QED are pure quantum processes, which
involve only external photons and the background electromagnetic field. We show
analytically that such processes occurring in a plane-wave field are all
characterized by a surprisingly modest net exchange of laser photons even at
ultrarelativistic laser intensities. We obtain this result by a direct
calculation of the transition matrix element of an arbitrary refractive QED
process and accounting exactly for the background plane-wave field. A simple
physical explanation of this modest net exchange of laser photons is provided,
based on the fact that the laser field couples with the external photons only
indirectly through virtual electron-positron pairs. For stronger and stronger
laser fields, the pairs cover a shorter and shorter distance before they
annihilate again, such that the laser can transfer to them an energy
corresponding to only a few photons. These results apply to both optical and
x-free electron lasers, and are relevant for upcoming experiments aiming to
test strong-field QED at present and next-generation facilities.
