# Bonn 2010 – wissenschaftliches Programm

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# T: Fachverband Teilchenphysik

## T 13: QCD (Theorie) IV / Quantenfeldtheorie II

### T 13.7: Vortrag

### Donnerstag, 18. März 2010, 18:25–18:40, HG XVI

**Systematic approach to leptogenesis in nonequilibrium quantum field theory** — Mathias Garny^{2}, Andreas Hohenegger^{1}, •Alexander Kartavtsev^{1}, and Manfred Lindner^{1} — ^{1}Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Deutschland — ^{2}Technische Universität München, James-Franck-Straß e, 85748 Garching, Deutschland

The generation of a baryon asymmetry via leptogenesis is usually studied by means of classical kinetic equations whose applicability to processes in the hot and expanding early universe is questionable. The approximations implied by the state of the art description can be tested in a first-principle approach based on nonequilibrium field theory techniques. We apply the Kadanoff-Baym formalism to a simple toy model of leptogenesis. We find that, within the toy model, medium effects increase the vertex contribution to the CP-violating parameter. At high temperatures it is a few times larger than in vacuum and asymptotically reaches the vacuum value as the temperature decreases. Contrary to the results obtained earlier in the framework of thermal field theory, the corrections are only linear in the particle number densities. An important feature of the Kadanoff-Baym formalism is that it is free of the double-counting problem, i.e. no need for Real Intermediate State subtraction arises. We show that in the resonant regime quantum corrections to the effective masses and decay widths lead to a modified expression for the self-energy CP-violating parameter. Most notably, in the maximal resonant regime the Boltzmann picture breaks down and an analysis in the full Kadanoff-Baym formalism is required.