In this thesis we discuss the quantum field-theoretical techniques that allow a consistent, complete and unified description of the generation of the observed matter/antimatter asymmetry in the Early Universe, through the Resonant Leptogenesis mechanism. After reviewing the basic formalism of thermal field theory at equilibrium, we present the paradigm of leptogenesis, with particular emphasis on the resonant case, in which the presence of quasi-degenerate heavy Majorana neutrinos can enhance significantly the CP asymmetry generated by their decays in the Early Universe.After these introductory discussions, we develop a fully flavour-covariant formalism for transport phenomena, capable of describing the time-evolution of particle number-densities in a statistical ensemble with arbitrary flavour content. By using this formalism for a semi-classical analysis of Resonant Leptogenesis, in which the resummation of resonant heavy-neutrino absorptive transitions is performed effectively at zero temperature, we obtain the flavour-covariant rate equations, that provide a complete and unified description of this phenomenon, capturing three relevant physical effects: (i) the resonant mixing between the heavy-neutrino states, (ii) coherent oscillations between heavy-neutrino flavours, and (iii) quantum decoherence effects in the charged-lepton sector.Subsequently, we discuss the consistent field-theoretical formulation of non-equilibrium phenomena and use it to develop a flavour-covariant analysis of Resonant Leptogenesis in a fully thermal-field-theoretical framework. This formalism allows us to confirm the results of the semi-classical analysis in a more first-principles approach, and provides the consistent thermal description of the resonant enhancement of the asymmetry due to heavy-neutrino mixing. Finally, we present an explicit model of Resonant Leptogenesis, with electroweak-scale Majorana neutrinos and observable signatures in current and near-future experiments. We study the predictions of this model by means of the flavour-covariant rate equations, and demonstrate the numerical significance of the formalism developed in this thesis for an accurate prediction of the baryon asymmetry generated in the Early Universe.
|Date of Award||31 Dec 2015|
- The University of Manchester
|Supervisor||Apostolos Pilaftsis (Supervisor)|