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First principles approach to leptogenesis


Frossard,  Tibor
Division Prof. Dr. Manfred Lindner, MPI for Nuclear Physics, Max Planck Society;

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Frossard, T. (2013). First principles approach to leptogenesis. PhD Thesis, Ruprecht-Karls-Universität, Heidelberg.

Baryogenesis via leptogenesis offers an elegant explanation of the origin of the baryon asymmetry of the universe by means of the CP-violating decay of heavy right-handed neutrinos in the early universe. This scenario has become very popular over the past decades due to its connection with neutrino physics. A precise computation of the baryon asymmetry produced in the leptogenesis scenario is difficult since it requires to follow the out-of-equilibrium evolution of the hot early universe. We present here a nonequilibrium quantum field theory approach to leptogenesis. This method is free of many problems inherent to the conventional approach based on the classical Boltzmann equation. Starting from first principles we derive a quantum-corrected Boltzmann equation for the asymmetry. The obtained equation is free of the double counting problem and incorporates consistently thermal corrections to the quasiparticles properties, in particular thermal masses and thermal widths. Finite width effects are taken into account through the extended quasiparticle approximation. We compare numerically the reaction densities obtained from the conventional and nonequilibrium quantum field theory approaches. We find that the enhancement due to thermal effects is partially compensated by the suppression due to thermal masses.