13,658 research outputs found
Analysis of Leptogenesis in Supersymmetric Triplet Seesaw Model
We analyze leptogenesis in a supersymmetric triplet seesaw scenario that
explains the observed neutrino masses, adopting a phenomenological approach
where the decay branching ratios of the triplets and the amount of
CP--violation in its different decay channels are assumed as free parameters.
We find that the solutions of the relevant Boltzmann equations lead to a rich
phenomenology, in particular much more complex compared to the
non--supersymmetric case, mainly due to the presence of an additional Higgs
doublet. Several unexpected and counter--intuitive behaviors emerge from our
analysis: the amount of CP violation in one of the decay channels can prove to
be be irrelevant to the final lepton asymmetry, leading to successful
leptogenesis even in scenarios with a vanishing CP violation in the leptonic
sector; gauge annihilations can be the dominant effect in the determination of
the evolution of the triplet density up to very high values of its mass,
leading anyway to a sizeable final lepton asymmetry, which is also a growing
function of the wash--out parameter K=Gamma_d/H, defined as usual as the ratio
between the triplet decay amplitude Gamma_d and the Hubble constant H; on the
other hand, cancellations in the Boltzmann equations may lead to a vanishing
lepton asymmetry if in one of the decay channels both the branching ratio and
the amount of CP violation are suppressed, but not vanishing. The present
analysis suggests that in the supersymmetric triplet see-saw model successful
leptogenesis can be attained in a wide range of scenarios, provided that an
asymmetry in the decaying triplets can act as a lepton--number reservoir.Comment: 14 pages, 6 figure
Leptogenesis origin of Dirac gaugino dark matter
The Dirac nature of the gauginos (and also the Higgsinos) can be realized in
-symmetric supersymmetry models. In this class of models, the Dirac bino (or
wino) with a small mixture of the Dirac Higgsinos is a good dark matter
candidate. When the seesaw mechanism with Higgs triplet superfields is
implemented to account for the neutrino masses and mixing, the leptogenesis
driven by the heavy triplet decay is shown to produce not only the
matter-antimatter asymmetry but also the asymmetric relic density of the Dirac
gaugino dark matter. The dark matter mass turns out to be controlled by the
Yukawa couplings of the heavy Higgs triplets, and it can be naturally at the
weak scale for a mild hierarchy of the Yukawa couplings.Comment: 9 pages. Restructured for clear presentation, corrected some errors
and typos. No change in conclusio
Dilaton Stabilization and Inflation in the D-brane World
We study the dilaton stabilization in the D-brane world in which a D-brane
constitutes our universe. The dilaton can be stabilized due to the interplay
between the D-brane tension and the negative scalar curvature of extra
dimensions. Cosmic evolution of the dilaton is investigated with the obtained
dilaton potential and it is found that inflation can be realized before the
settlement of the dilaton.Comment: 10 pages, abstract correcte
U(2) and Maximal Mixing of nu_{mu}
A U(2) flavor symmetry can successfully describe the charged fermion masses
and mixings, and supress SUSY FCNC processes, making it a viable candidate for
a theory of flavor. We show that a direct application of this U(2) flavor
symmetry automatically predicts a mixing of 45 degrees for nu_mu to nu_s, where
nu_s is a light, right-handed state. The introduction of an additional flavor
symmetry acting on the right-handed neutrinos makes the model
phenomenologically viable, explaining the solar neutrino deficit as well as the
atmospheric neutrino anomaly, while giving a potential hot dark matter
candidate and retaining the theory's predictivity in the quark sector.Comment: 20 pages, 1 figur
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