A classical view of the quantum vacuum

  • Alexander MacLeod

Student thesis: Doctoral Thesis


In the coming years, a previously unexplored regime of quantum electrodynamics will be opened up to experimental study for the first time: the strong-field 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 energy-momentum tensor of light. In the context of light interacting with a medium two rival forms exist of the energy-momentum 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 Poincaré symmetry group. In general, nonlinear electrodynamics is invariant under Poincaré 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 strong-field 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 strong-field 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 high-energy 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 high-energy photons in astrophysical observations.
Date of Award12 Apr 2019
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorDino Jaroszynski (Supervisor) & Adam Noble (Supervisor)

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