PUB - Publikationen an der Universität Bielefeld

The current status of baryogenesis is reviewed, with an emphasis on electroweak baryogenesis and leptogenesis. The first detailed studies were carried out for SU(5) grand unified theory (GUT) models where CP-violating decays of leptoquarks generate a baryon asymmetry. These GUT models were excluded by the discovery of unsuppressed, (B+L)-violating sphaleron processes at high temperatures. Yet a new possibility emerged: electroweak baryogenesis. Here sphaleron processes generate a baryon asymmetry during a strongly first-order phase transition. This mechanism has been studied in detail in many extensions of the standard model. However, constraints from the LHC and from low-energy precision experiments exclude most of the known models, leaving composite Higgs models of electroweak symmetry breaking as an interesting possibility. Sphaleron processes are also the basis of leptogenesis, where CP-violating decays of heavy right-handed neutrinos generate a lepton asymmetry that is partially converted to a baryon asymmetry. This mechanism is closely related to that of GUT baryogenesis, and simple estimates based on GUT models can explain the order of magnitude of the observed baryon-to-photon ratio. In the one-flavor approximation an upper bound on the light-neutrino masses has been derived that is consistent with the cosmological upper bound on the sum of neutrino masses. For quasidegenerate right-handed neutrinos the leptogenesis temperature can be lowered from the GUT scale down to the weak scale, and CP-violating oscillations of GeV sterile neutinos can also lead to successful leptogenesis. Significant progress has been made in developing a full field-theoretical description of thermal leptogenesis, which demonstrated that interactions with gauge bosons of the thermal plasma play a crucial role. Finally, recent ideas on how the seesaw mechanism and B−L breaking at the GUT scale can be probed by gravitational waves are discussed.