Vacuum decay, gravitational waves and magnetic fields in the early universe

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

If a quantum field gets stuck in a meta-stable false vacua it can decay via a first order phase transition to a lower energy vacuum, either by thermally jumping over the potential barrier or tunnelling through it. Bubbles of true vacuum nucleate and if the nucleation rate is large enough expand to engulf the universe. In this thesis we study the underlying tunnelling process by which this can happen as well as the observational consequences of first order transitions in the early universe.
With regard to the tunnelling process we numerically investigate false vacuum decay to a non-adjacent minima of a potential with numerous meta-stable vacua, as motivated by modern conceptions of the string theory landscape. Our code finds stable tunnelling solutions to non-adjacent minima for certain single and two field toy-model landscapes.
With regard to observational consequences we study the characteristic frequency spectrum of gravitational waves produced by a first order phase transition in a very cold SU(2) hidden sector, polarisation of the stochastic gravitational wave background generated by a period of helical MHD plasma turbulence that can follow a generic transition and finally, primordial magnetic fields generated from a first order transition in two Standard Model extensions (SM+H6 and SMB−L) which can evolve to intergalactic scales if helicity is initially seeded in the gauge field or kinetically in the plasma.
Date of Award1 Sept 2021
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorMalcolm Fairbairn (Supervisor)

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