4 research outputs found
Flavour Issues in Leptogenesis
We study the impact of flavour in thermal leptogenesis, including the quantum
oscillations of the asymmetries in lepton flavour space. In the Boltzmann
equations we find different numerical factors and additional terms which can
affect the results significantly. The upper bound on the CP asymmetry in a
specific flavour is weaker than the bound on the sum. This suggests that --
when flavour dynamics is included -- there is no model-independent limit on the
light neutrino mass scale,and that the lower bound on the reheat temperature is
relaxed by a factor ~ (3 - 10).Comment: 19 pages, corrected equations for flavour oscillation
Supersymmetric Thermalization and Quasi-Thermal Universe: Consequences for Gravitinos and Leptogenesis
Motivated by our earlier paper \cite{am}, we discuss how the infamous
gravitino problem has a natural built in solution within supersymmetry.
Supersymmetry allows a large number of flat directions made up of {\it gauge
invariant} combinations of squarks and sleptons. Out of many at least {\it one}
generically obtains a large vacuum expectation value during inflation. Gauge
bosons and Gauginos then obtain large masses by virtue of the Higgs mechanism.
This makes the rate of thermalization after the end of inflation very small and
as a result the Universe enters a {\it quasi-thermal phase} after the inflaton
has completely decayed. A full thermal equilibrium is generically established
much later on when the flat direction expectation value has substantially
decareased. This results in low reheat temperatures, i.e., , which are compatible with the stringent bounds arising from the
big bang nucleosynthesis. There are two very important implications: the
production of gravitinos and generation of a baryonic asymmetry via
leptogenesis during the quasi-thermal phase. In both the cases the abundances
depend not only on an effective temperature of the quasi-thermal phase (which
could be higher, i.e., ), but also on the state of equilibrium
in the reheat plasma. We show that there is no ``thermal gravitino problem'' at
all within supersymmetry and we stress on a need of a new paradigm based on a
``quasi-thermal leptogenesis'', because in the bulk of the parameter space the
{\it old} thermal leptogenesis cannot account for the observed baryon
asymmetry.Comment: 53 pages. Final version published in JCA
Models of Neutrino Masses and Mixings
We review theoretical ideas, problems and implications of neutrino masses and
mixing angles. We give a general discussion of schemes with three light
neutrinos. Several specific examples are analyzed in some detail, particularly
those that can be embedded into grand unified theories.Comment: 44 pages, 2 figures, version accepted for publication on the Focus
Issue on 'Neutrino Physics' edited by F.Halzen, M.Lindner and A. Suzuki, to
be published in New Journal of Physics
Flavour Physics of Leptons and Dipole Moments.
This chapter of the report of the ``Flavour in the era of the LHC'' Workshop
discusses the theoretical, phenomenological and experimental issues related to
flavour phenomena in the charged lepton sector and in flavour-conserving
CP-violating processes. We review the current experimental limits and the main
theoretical models for the flavour structure of fundamental particles. We
analyze the phenomenological consequences of the available data, setting
constraints on explicit models beyond the Standard Model, presenting benchmarks
for the discovery potential of forthcoming measurements both at the LHC and at
low energy, and exploring options for possible future experiments.Comment: Report of Working Group 3 of the CERN Workshop ``Flavour in the era
of the LHC'', Geneva, Switzerland, November 2005 -- March 200