Pair production, vacuum birefringence and radiation reaction in strong field QED

Doctoral thesis, 2016

In this thesis we consider three QED phenomena in strong electromagnetic fields: Schwinger pair production, vacuum birefringence and radiation reaction. We study electron-positron pair production in a variety of field configurations and, using complex worldline instantons, reveal new insights into the case of fields with lightlike inhomogeneities. We also find universal scaling for the pair production probability near critical points. Vacuum birefringence is the change in polarisation of a probe laser beam induced by interaction with a second electromagnetic field. We relate this macroscopic phenomena to the microscopic physics of individual photons in the probe flipping polarisation or helicity in a strong background field, and use this to make predictions for upcoming birefringence experiments, by considering the impact of realistic field geometry. Radiation reaction is the recoil effect on the motion of a radiating particle as it is accelerated by a background field. Due to the existence of unphysical solutions to the equation of motion derived in classical electrodynamics, several alternative classical equations have been proposed. We derive radiation reaction from QED and take the classical limit to test the validity of a number of these classical equations. Choosing a plane wave background allows us to treat the background field exactly and also to make general predictions about the form of a classical equation. We treat both vacuum birefringence and radiation reaction in a field theory formalism that naturally lends itself to systems with plane wave backgrounds - namely lightfront quantisation.