Finite density aspects of leptogenesis

Abstract

Leptogenese ist ein Modell zur dynamischen Erklärung der Materie-Antimaterie Asymmetrie. Dieser Prozess findet im frühen Universum bei hohen Temperaturen statt und eine Abweichung vom Gleichgewicht ist fundamentale Voraussetzung für die Erzeugung der Asymmetrie. Die Beschreibung dieses Prozesses basiert auf klassischen Boltzmann Gleichungen (BGn). Diese wurden durch die Verwendung thermaler Propagatoren verfeinert. In Anbetracht der grundlegenden Beschränkungen dieser Gleichungen erscheint es wünschenswert einen systematischen Ansatz zu entwickeln der auf Nicht-Gleichgewichts QFT beruht. In dieser Arbeit werden modifizierte BGn verwendet die aus ersten Prinzipien innerhalb des Kadanoff-Baym Formalismus hergeleitet werden. Dies wird für ein einfaches Toy-Modell durchgeführt welches ausreichend komplex ist um populäre Szenarien wie das der thermalen Leptogenese in Analogie untersuchen zu können. Dieser Ansatz legt die Struktur der korrigierten BGn offen und führt zu einem neuen Ergebnis für die thermalen Beiträge zum CP-verletzenden Parameter, sodass die gängige Form überdacht werden muss. Es stellt sich heraus, dass die verschiedenen Ansätze in Einklang gebracht werden können. Die neuen Ergebnisse sagen eine Verstärkung der Asymmetrie vorher. Die Grösse der Korrekturen innerhalb des Toy-Modells wird durch numerische Lösung der vollen BGn bestimmt. Finite Density Aspects of LeptogenesisLeptogenesis is a model for the dynamical generation of the matter-antimatter asymmetry. This process takes place in the early universe at very high temperatures and a deviation from equilibrium is a fundamental requirement for the formation of the asymmetry. The equations used for its description originate from classical Boltzmann equations (BEs), which were refined using thermal propagators. In view of the basic restrictions of BEs, it is desirable to develop a systematic approach which uses non-equilibrium QFT as starting point. In this thesis modified BEs are used which are derived from first principles in the Kadanoff-Baym formalism. This is done for a simple toy model which is sufficiently intricate to study popular scenarios such as thermal leptogenesis in analogy to the phenomenological theory. This approach uncovers the structure of the corrected BEs and leads to a new result for the form of the thermal contributions to the CP-violating parameter, so that the established one must be reconsidered. It turns out that the different approaches can be reconciled. The new form predicts an enhancement of the asymmetry. The quantitative implications of the medium corrections within the toy model are studied numerically in terms of the full BEs.

Cutting rules on a cylinder: a simplified diagrammatic approach to quantum kinetic theory

“…[14,15] pointed out that using a finitetemperature generalization of Cutkosky cutting rules [38,39] leads to the wrong statistical factors with incorrect additional −2 f eq l f eq H term [40][41][42]. Instead, the causal n-point functions [37] or direct closed-time-path derivation should be used [14][15][16][17][18][19][20][21][22][23][24]. Remarkably, our result is in exact agreement with the latter, which seems to be the first time the correct form of Eq.…”

“…In Sects. 2 and 3, these features will be demonstrated within the seesaw type-I leptogenesis, where the results are easily comparable to the broad literature on the subject [14][15][16][17][18][19][20][21][22][23][24]. However, we would like to emphasize that the present work is not about leptogenesis in particular.…”

Cutting rules on a cylinder: a bottom-up approach to quantum kinetic theory for the early universe

“…[13,14] pointed out that using a finite-temperature generalization of Cutkosky cutting rules [33,34] leads to the wrong statistical factors with incorrect additional −2f eq l f eq H term [35][36][37]. Instead, the causal n-point functions [32] or direct closed-time-path derivation should be used [13][14][15][16][17][18][19][20][21][22][23]. It is remarkable that our result is in exact agreement with the latter, which seems to be the first time the correct form of Eq.…”

“…These features of our general framework will be demonstrated within the seesaw type-I leptogenesis, such that the results are easily comparable to broad literature on the subject [13][14][15][16][17][18][19][20][21][22][23].…”