Effective Field Theories for Heavy Majorana Neutrinos in a Thermal Bath

This thesis discusses the construction of an effective field theory (EFT) for non-relativistic Majorana fermions, shows how to use it to calculate observables in a thermal medium, and derives the effects of these thermal particles on the CP asymmetry. The methods described in this thesis are the only ones to date that allow a systematic and effective description of the non-relativistic dynamics of a heavy Majorana fermion at finite temperature. The CP asymmetry is studied for hierarchical and nearly degenerate heavy-neutrino masses and the analysis includes the treatment of lepton-flavor effects.

Heavy Majorana neutrinos are involved in many scenarios of physics beyond the standard model and, in the leptogenesis framework, they are at the root of the baryon asymmetry in the Universe. Besides simplifying existing results, the EFT approach provides useful tools for addressing even more involved observables. Indeed, taken together, the approach and the material pres

ented here represent an important step toward a systematic improvement of our knowledge of the CP asymmetry in heavy-neutrino decays at finite temperature.

Auteur

After completing the Bachelor and Master in Physics at the University of Perugia in Italy, the author joined the international research program of the Max Planck Institute for Physics in Munich to carry out his Ph.D. He worked in the group led by Prof. Nora Brambilla at the Technische Universitaet Muenchen. Currently the author is a postdoc at the Albert Einstein Center at the University of Bern, where he continues his research on the physics of the early universe including dark matter, leptogenesis and quark-gluon plasma.

Résumé

In this thesis we discuss the construction of an effective field theory (EFT) for non-relativistic Majorana fermions, show how to use it to calculate observables in a thermal medium, and derive the effects of these thermal particles on the CP asymmetry.

The methods described in this thesis allow a systematic and effective description of the non-relativistic dynamics of a heavy Majorana fermion at finite temperature. The CP asymmetry is studied for hierarchical and nearly degenerate heavy-neutrino masses and the analysis includes the treatment of lepton-flavor effects.

Heavy Majorana neutrinos are involved in many scenarios of physics beyond the standard model and, in the leptogenesis framework, they are at the root of the baryon asymmetry in the Universe. Besides simplifying exist in

g results, the EFT approach provides useful tools for addressing even more involved observables. Indeed, taken together, the approach and the material presented here represent an important step toward a systematic improvement of our knowledge of the CP asymmetry in heavy-neutrino decays at finite temperature.

Contenu
Baryon Asymmetry in the Early Universe.- Baryogenesis via Leptogenesis.- Eective Field Theories.- Thermal Field Theory in a Nutshell.- EFT Approach for Right-handed Neutrinos in a Thermal Bath.- CP Asymmetries at Finite Temperature: the Nearly Degenerate Case.- CP Asymmetries at Finite Temperature: the Hierarchical Case.- Flavoured CP Asymmetries.