Karlsruhe 2011 – scientific programme

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T: Fachverband Teilchenphysik

T 9: Eingeladene Vorträge IV

T 9.3: Eingeladener Vortrag

Thursday, March 31, 2011, 15:00–15:30, 30.22: 130

Leptogenesis from First Principles: Finite Density Effects and Flavour Decoherence — •Björn Garbrecht — RWTH Aachen University

Leptogenesis is among the most plausible explanations for the dynamical emergence of the matter-antimatter asymmetry in the early Universe. The conventional description through Boltzmann equations, that heuristically combine elements of kinetic theory with vacuum S-matrix elements, leads to the problem of overcounting certain CP (charge parity) violating processes. Usually, this is resolved through the method of real intermediate state (RIS) subtraction. A first principle approach (i.e. starting from a path integral formulation) is given by the Closed-Time-Path (CTP) formalism. We show that this avoids the ad hoc subtraction of RIS and additionally gives rise to new corrections due to the finite density of particles in the early Universe. Since the basic dynamical quantities within the CTP framework are two-point Green functions, we can endow these with two flavour indices and address the problem of "flavoured leptogenesis," when the basis of the lepton asymmetry does not coincide with the flavour basis of the Standard Model, which distinguishes between the tauon, the muon and the electron. We show that due to fast gauge interactions, the flavour oscillations of these particles are overdamped at the time of leptogenesis and present a quantitative description of the decay of coherence between the different Standard Model flavours. Finally, we comment on potential phenomenological consequences of these results.