72 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
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)
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
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
Baryon Asymmetry and Dark Matter
We study the implications of a large baryogenesis temperature, GeV), on the mass spectrum of superparticles in supersymmetric
extensions of the standard model. Models with a neutralino as lightest
superparticle (LSP) are excluded. A consistent picture is obtained with the
gravitino as LSP, followed by a higgsino-like neutralino (NSP). Gravitinos with
masses from 10 to 100 GeV may be the dominant component of dark matter.Comment: 10 pages, 2 figures included, eq. (13) replaced by leading order
approximatio
A bound on neutrino masses from baryogenesis
Properties of neutrinos, the lightest of all elementary particles, may be the
origin of the entire matter-antimatter asymmetry of the universe. This requires
that neutrinos are Majorana particles, which are equal to their antiparticles,
and that their masses are sufficiently small. Leptogenesis, the theory
explaining the cosmic matter-antimatter asymmetry, predicts that all neutrino
masses are smaller than 0.2 eV, which will be tested by forthcoming laboratory
experiments and by cosmology.Comment: 8 pages, 2 figure
Hard-Thermal-Loop Corrections in Leptogenesis I: CP-Asymmetries
We investigate hard-thermal-loop (HTL) corrections to the CP-asymmetries in
neutrino and, at high temperature, Higgs boson decays in leptogenesis. We pay
special attention to the two leptonic quasiparticles that arise at non-zero
temperature and find that there are four contributions to the CP-asymmetries,
which correspond to the four combinations of the two leptonic quasiparticles in
the loop and in the final states. In two additional cases, we approximate the
full HTL-lepton propagator with a zero-temperature propagator that employs the
thermal lepton mass m_l(T), or the asymptotic thermal lepton mass sqrt{2}
m_l(T). We find that the CP-asymmetries in the one-mode approaches differ by up
to one order of magnitude from the full two-mode treatment in the interesting
temperature regime T \sim M_1. The asymmetry in Higgs boson decays turns out to
be two orders of magnitude larger than the asymmetry in neutrino decays in the
zero-temperature treatment. The effect of HTL corrections on the final lepton
asymmetry are investigated in paper II of this series.Comment: 38 pages, 14 figure
Predictions of the most minimal see-saw model
We derive the most minimal see-saw texture from an extra-dimensional
dynamics. It predicts theta_13 = 0.078 \pm 0.015 and m_ee = 2.6 \pm 0.4 meV.
Assuming thermal leptogenesis, the sign of the CP-phase measurable in neutrino
oscillations, together with the sign of baryon asymmetry, determines the order
of heavy neutrino masses. Unless heavy neutrinos are almost degenerate,
successful leptogenesis fixes the lightest mass. Depending on the sign of the
neutrino CP-phase, the supersymmetric version of the model with universal soft
terms at high scale predicts BR(mu --> e gamma) or BR(tau --> mu gamma), and
gives a lower bound on the other process.Comment: 6 pages, 5 figures. Version 2: inclusion of new KamLAND data makes
predictions more precise and within reach of future experiments. New fig. 2
added with solar and KamLAND fits. Final version, to appear on Phys. Lett.
Decay of a Yukawa fermion at finite temperature and applications to leptogenesis
We calculate the decay rate of a Yukawa fermion in a thermal bath using
finite temperature cutting rules and effective Green's functions according to
the hard thermal loop resummation technique. We apply this result to the decay
of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach
where thermal masses are inserted into the kinematics of final states, we find
that deviations arise through two different leptonic dispersion relations. The
decay rate differs from the usual approach by more than one order of magnitude
in the temperature range which is interesting for the weak washout regime. We
discuss how to arrive at consistent finite temperature treatments of
leptogenesis.Comment: 16 pages, 5 figure
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