Nonequilibrium QFT approach to leptogenesis

The observed baryon asymmetry of the Universe can be smartly explained in the leptogenesis scenario, where a net lepton asymmetry produced by the decay of heavy right-handed neutrinos is then transfered to the baryon number through the Standard Model sphalerons. Being an intrinsically quantum effect the generation of such an asymmetry in the hot early Universe can be described systematically only using nonequilibrium quantum field theory tools. Starting from first principles one derives a quantum Boltzmann-like equation for the lepton asymmetry which is free of the double counting problem and which incorporates consistently the medium corrections to the masses and decay widths. Medium corrections are particularly large for the CP-violating parameters. The total decay widths are affected to a lesser extent. We also investigate the Higgs decay, which becomes kinematically allowed at high temperature due to thermal mass. We find that the CP-violating parameters for the Higgs decay are larger that the one for the Majorana decay by several orders of magnitude.