3,729 research outputs found
News on Leptogenesis
The possibility to explain the CMB measurement of the baryon asymmetry with
leptogenesis results in a stringent bound on the neutrino masses such that
[(m_1)^2+(m_2)^2+(m_3)^2]^(1/2) < 0.30 eV. We discuss the implications of such
a bound for future experiments on the absolute neutrino mass scale.Comment: 12 pages, 4 figures included. Talk given at the Third Tropical
Workshop: Neutrinos, Branes and Cosmology, 19-23 August 2002, San Juan,
Puerto Rico. v2 references adde
The cosmological information on neutrino mixing
Cosmology provides interesting information on neutrino mixing models with
sterile neutrinos. In this case non standard BBN effects can be relevant. We
show how the recent measurement of the baryon content from the observations of
CMB anisotropies together with the primordial nuclear abundances measurements
can be used to constrain them. In particular four neutrino mixing models are
potentially at variance with the cosmological observations. We also discuss the
possible scenarios from future experiments.Comment: 5 pages, LaTeX, JHEP style, talk given at EPS HEP 2001, Budapest,
Hungary, 12 - 18 July 200
Flavoured leptogenesis: a successful thermal leptogenesis with N_1 mass below 10^8 GeV
We prove that taking correctly into account the lepton flavour dependence of
the CP asymmetries and washout processes, it is possible to obtain successful
thermal leptogenesis from the decays of the second right-handed neutrino. The
asymmetries in the muon and tau-flavour channels are then not erased by the
inverse decays of the lightest right-handed neutrino, N_1. In this way, we
reopen the possibility of ``thermal leptogenesis'' in models with a strong
hierarchy in the right-handed Majorana masses that is typically the case in
models with up-quark--neutrino Yukawa unification.Comment: 5 pages, no figures. References added, referencing correcte
The Neutrino Mass Window for Baryogenesis
Interactions of heavy Majorana neutrinos in the thermal phase of the early
universe may be the origin of the cosmological matter-antimatter asymmetry.
This mechanism of baryogenesis implies stringent constraints on light and heavy
Majorana neutrino masses. We derive an improved upper bound on the CP asymmetry
in heavy neutrino decays which, together with the kinetic equations, yields an
upper bound on all light neutrino masses of 0.1 eV. Lepton number changing
processes at temperatures above the temperature T_B of baryogenesis can erase
other, pre-existing contributions to the baryon asymmetry. We find that these
washout processes become very efficient if the effective neutrino mass
\tilde{m}_1 is larger than m_* \simeq 10^{-3} eV. All memory of the initial
conditions is then erased. Hence, for neutrino masses in the range from (\Delta
m^2_sol)^{1/2} \simeq 8*10^{-3} eV to (\Delta m^2_atm)^{1/2} \simeq 5*10^{-2}
eV, which is suggested by neutrino oscillations, leptogenesis emerges as the
unique source of the cosmological matter-antimatter asymmetry.Comment: 29 pages, 12 figures include
Some Aspects of Thermal Leptogenesis
Properties of neutrinos may be the origin of the matter-antimatter asymmetry
of the universe. In the seesaw model for neutrino masses this leads to
important constraints on the properties of light and heavy neutrinos. In
particular, an upper bound on the light neutrino masses of 0.1 eV can be
derived. We review the present status of thermal leptogenesis with emphasis on
the theoretical uncertainties and discuss some implications for lepton and
quark mass hierarchies, CP violation and dark matter. We also comment on the
`leptogenesis conspiracy', the remarkable fact that neutrino masses may lie in
the range where leptogenesis works best.Comment: 23 pages, 5 figures, submitted to the Focus on Neutrino Physics issue
of the New Journal of Physics, edited by F. Halzen, M. Lindner and A. Suzuk
Cosmic Microwave Background, Matter-Antimatter Asymmetry and Neutrino Masses
We study the implications of thermal leptogenesis for neutrino parameters.
Assuming that decays of N_1, the lightest of the heavy Majorana neutrinos,
initiate baryogenesis, we show that the final baryon asymmetry is determined by
only four parameters: the CP asymmetry epsilon_1, the heavy neutrino mass M_1,
the effective light neutrino mass \tilde{m}_1, and the quadratic mean \bar{m}
of the light neutrino masses. Imposing the CMB measurement of the baryon
asymmetry as constraint on the neutrino parameters, we show, in a model
independent way, that quasi-degenerate neutrinos are incompatible with thermal
leptogenesis. For maximal CP asymmetry epsilon_1, and neutrino masses in the
range from (\Delta m^2_{sol})^{1/2} to (\Delta m^2_{atm})^{1/2}, the
baryogenesis temperature is T_B = O(10^{10}) GeV.Comment: 28 pages, 14 figures included; v2: erratum added, M_1 lower bound in
the strong wash-out regime (see Eq. (63)) relaxed by a factor 2/
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