Leptogenesis
The leptogenesis (also Fukugita-Yanagida scenario ) is a theory for the dynamic creation of the baryon asymmetry in the early universe , which in 1986 by the Japanese physicists Masataka Fukugita and Tsutomu Yanagida was proposed.
It is a special model of baryogenesis , but does not assume a direct generation of the asymmetry between baryons and anti- baryons. Instead, the asymmetry is first created between leptons and antileptons ( lepton asymmetry ). Usually one introduces additional, right-handed neutrinos , which have a very large mass and form a singlet under the gauge group of the electroweak interaction (normal neutrinos are left-handed and have a very low mass). The decay of these additional neutrinos into leptons and Higgs bosons violates the CP symmetry , and therefore you get different numbers of leptons and antileptons. This asymmetry is then converted into baryon asymmetry by Sphaleron processes.
Extensions
There are now numerous extensions to the original scenario.
In the mid-1990s, for example, a research group at the University of Dortmund discovered a way of realizing the scenario with energies that can be investigated with particle accelerators in the near future . In the usual scenarios, the leptogenesis would have to have taken place at extremely high energies, so that an experimental verification of the model would be almost impossible. The new scenario, usually referred to as resonant leptogenesis , assumes that two of the heavy right-handed neutrinos have almost identical mass, which leads to an increase in resonance in the decay width .
Other popular extensions of the Fukugita-Yanagida scenario are the inclusion of supersymmetry (e.g. in the work of M. Plümacher), the consideration of thermal effects in the early universe or effects that are related to the fact that the lepton asymmetry is not evenly distributed over the three fermion generations distributed.
Due to the numerous extensions, leptogenesis has meanwhile become an extensive and demanding theory. Due to the many free and experimentally (so far) not verifiable parameters, however, it is not possible to say unequivocally whether one of the numerous variants is able to precisely predict the measured baryon asymmetry of the universe. So far, the attraction of the theory lies more in its theoretical beauty, since it combines processes at very high energies, such as those that prevailed shortly after the Big Bang , with physics at low energies, namely the physics of neutrinos. So the same model can also be used to provide a dynamic explanation of why the neutrinos have a very small but non-zero mass .
literature
- Fukugita, M., Yanagida, T., Baryogenesis without grand unification , Phys. Lat . B174, 45-47 (1986)
- M.Flanz, EAPaschos, U.Sarkar, J.Weiss, Baryogenesis through mixing of heavy Majorana neutrinos , Phys. Lat . B389, 693-699 (1996)
- A. Pilaftsis, TEJUnderwood, Resonant Leptogenesis , Nucl.Phys. B692, 303-345 (2004)
- M.Dine, A.Kusenko, Origin of the matter-antimatter asymmetry , Rev.Mod.Phys. 76, 1-30 (2004) (current review article on various theories of baryogenesis )
- W.Buchmüller, RDPeccei, T.Yanagida, Leptogenesis as the origin of matter , Ann.Rev.Nucl.Part.Sci. 55, 311-355 (2005) (current review article on leptogenesis)