Neutrino masses and the origin of matter through leptogenesis

Abstract

The properties of particles and antiparticles are firmly established in collider physics. They appear to be on the same footing in the Standard Model, which naturally poses the question of why the observed Universe is composed nearly exclusively of matter, in contrast to little or no primordial antimatter.

Despite its remarkable success in describing many of the inner workings of Nature at its most fundamental level, the Standard Model struggles to explain the existence of a biased Universe. A compelling possibility is that the baryon asymmetry of the Universe is generated dynamically, a scenario that is known as baryogenesis, which implies the non-conservation of the baryon number B. In the past thirty to forty years, several mechanisms for baryogenesis have been put forth: grand unified theory baryogenesis, electroweak baryogenesis, Affleck-Dine mechanism, spontaneous baryogenesis.

Nonetheless, the most compelling one is the mechanism of baryogenesis via leptogenesis, first proposed by Fukugita and Yanagida, whose simplest and theoretically best motivated realization is within the seesaw mechanism of neutrino masses.

In this thesis, we discuss the mathematical implementation of leptogenesis in the context of type-I seesaw mechanism. Additionally, we consider the evolution of the baryonic asymmetry during the course of different temperature regimes, discriminating between the unflavoured and flavoured treatment of leptogenesis. Lastly, we take into consideration the importance of decoherence effects in transition regimes, which leads us to opt for an alternative description under the formalism of density matrix equations.