190 research outputs found
Neutrino masses and the baryon asymmetry
Due to sphaleron processes in the high-temperature symmetric phase of the
standard model the cosmological baryon asymmetry is related to neutrino
properties. For hierarchical neutrino masses, with broken at the
unification scale GeV, the observed baryon
asymmetry can be naturally explained by the decay of
heavy Majorana neutrinos. We illustrate this mechanism with two models of
neutrino masses, consistent with the solar and atmospheric neutrino anomalies,
which are based on the two symmetry groups and
.
We also review related cosmological bounds on Majorana neutrino masses and
the use of Boltzmann equations.Comment: 45 pages, 12 figure
Baryogenesis and lepton number violation
The cosmological baryon asymmetry can be explained by the nonperturbative electroweak reprocessing of a lepton asymmetry generated in the out-of-equilibrium decay of heavy right-handed Majorana neutrinos. We analyze this mechanism in detail in the framework of a SO(10)-subgroup. We take three right-handed neutrinos into account and discuss physical neutrino mass matrices
CP Asymmetry in Majorana Neutrino Decays
We study CP asymmetries in lepton-number violating two-body scattering
processes and show how they are related to CP asymmetries in the decays of
intermediate massive Majorana neutrinos. Self-energy corrections, which do not
contribute to CP asymmetries in two-body processes, induce CP violating
couplings of the intermediate Majorana neutrinos to lepton-Higgs states. We
briefly comment on the implications of these results for applications at finite
temperature.Comment: latex2e, 14 pages, 4 figures, extended version, conclusion change
Remarks on the high-energy behaviour of cross-sections in weak-scale string theories
We consider the high-energy behaviour of processes involving Kaluza-Klein (KK) gravitons of weak-scale string theories. We discuss how form-factors derived within string theory modify the couplings of KK gravitons and thereby lead to an exponential fall-off of cross sections in the high-energy limit. Further, we point out that the assumption of Regge behaviour for a scattering amplitude in the high energy limit, , combined with a linear growth of the total cross-section, , violates elastic unitarity. Regge behaviour leads to a stringent bound on the growth of the total cross-section, \stot (s) \leq 32\pi \alpha' \ln(s/s_0)
Matter Antimatter Asymmetry and Neutrino Properties
The cosmological baryon asymmetry can be explained as remnant of heavy
Majorana neutrino decays in the early universe. We study this mechanism for two
models of neutrino masses with a large \nu_\mu-\nu_\tau mixing angle which are
based on the symmetries SU(5) x U(1)_F and SU(3)_c x SU(3)_L x SU(3)_R x
U(1)_F, respectively. In both cases B-L is broken at the unification scale
\Lambda_{GUT}. The models make different predictions for the baryogenesis
temperature and the gravitino abundance.Comment: latex2e, 14 pages, 2 figures, Contribution to the Festschrift for L.
B. Okun, to appear in a special issue of Physics Reports, eds. V. L. Telegdi
and K. Winte
Spectator processes and baryogenesis
Spectator processes which are in thermal equilibrium during the period of baryogenesis influence the final baryon asymmetry. We study this effect quantitatively for thermal leptogenesis where we find a suppression by a factor O(1)
Leptogenesis for Pedestrians
During the process of thermal leptogenesis temperature decreases by about one
order of magnitude while the baryon asymmetry is generated. We present an
analytical description of this process so that the dependence on the neutrino
mass parameters becomes transparent. In the case of maximal CP asymmetry all
decay and scattering rates in the plasma are determined by the mass M_1 of the
decaying heavy Majorana neutrino, the effective light neutrino mass tilde{m}_1
and the absolute mass scale bar{m} of the light neutrinos. In the mass range
suggested by neutrino oscillations, m_{sol} \simeq 8*10^{-3} eV \lesssim
\tilde{m}_1 \lesssim m_{atm} \simeq 5*10^{-2} eV, leptogenesis is dominated
just by decays and inverse decays. The effect of all other scattering processes
lies within the theoretical uncertainty of present calculations. The final
baryon asymmetry is dominantly produced at a temperature T_B which can be about
one order of magnitude below the heavy neutrino mass M_1. We also derive an
analytical expression for the upper bound on the light neutrino masses implied
by successful leptogenesis.Comment: 55 pages, 14 figures include
- …