In the coming years, a previously unexplored regime of quantum electrodynamics will be opened up to experimental study for the first time: the strongfield regime. Under the influence of strong electromagnetic fields, virtual particles in the quantum vacuum become polarised, and wave propagation in regions of strong field becomes nonlinear.This Thesis explores this regime using nonlinear vacuum electrodynamics.The nonlinear nature of the vacuum imbues a region of strong field with an effective refractive index, such that wave propagation becomes analogous to propagation in a medium. This permits a novel view of an old problem concerning the energymomentum tensor of light. In the context of light interacting with a medium two rival forms exist of the energymomentum exist, each supposedly supported by theoretical and experimental evidence. By translating the problem to nonlinear electrodynamics, where the medium is replaced by a strong electromagnetic field, it is found that a much more precise statement can be made about which formulation should be adopted. Maxwellian electrodynamics is known to be invariant under the conformal group, an extension of the usual PoincarĂ© symmetry group. In general, nonlinear electrodynamics is invariant under PoincarĂ© symmetries, and not the extended conformal group.;The conformal group has been exploited in a wide range of areas of physics to simplify difficult problems. The possibility of using a conformally invariant, nonlinear theory of electrodynamics to describe strongfield physics is investigated. An entire class of conformally invariant nonlinear theories of electrodynamics is found, and their structure analysed. The role such theories may have in strongfield physics is then assessed,and it is found that in (3 + 1) spacetime dimensions, the only physically meaningful conformally invariant theory of electrodynamics is Maxwell's theory.A charged particle moving through a medium emits Cherenkov radiation when its velocity exceeds the phase velocity of light in that medium. Under the influence of a strong electromagnetic field the nonlinear nature of the vacuum allows for the possibility of highenergy particles to radiate via the Cherenkov process. The properties of this vacuum Cherenkov radiation are analysed from first principles, and applied to two physically relevant examples. It is found that this radiation process may be relevant to the excess signals of highenergy photons in astrophysical observations.
Date of Award  12 Apr 2019 

Original language  English 

Awarding Institution   University Of Strathclyde


Sponsors  EPSRC (Engineering and Physical Sciences Research Council) 

Supervisor  Dino Jaroszynski (Supervisor) & Adam Noble (Supervisor) 
