3,348 research outputs found
Soft Leptogenesis in Higgs Triplet Model
We consider the minimal supersymmetric triplet seesaw model as the origin of
neutrino masses and mixing as well as of the baryon asymmetry of the Universe,
which is generated through soft leptogenesis employing a CP violating phase and
a resonant behavior in the supersymmetry breaking sector. We calculate the full
gauge--annihilation cross section for the Higgs triplets, including all
relevant supersymmetric intermediate and final states, as well as
coannihilations with the fermionic superpartners of the triplets. We find that
these gauge annihilation processes strongly suppress the resulting lepton
asymmetry. As a consequence of this, successful leptogenesis can occur only for
a triplet mass at the TeV scale, where the contribution of soft supersymmetry
breaking terms enhances the CP and lepton asymmetry. This opens up an
interesting opportunity for testing the model in future colliders.Comment: 17 pages, 5 figures; version accepted for publicatio
The Private Higgs
We introduce Higgs democracy in the Yukawa sector by constructing a model
with a private Higgs and a dark scalar for each fermion thus addressing the
large hierarchy among fermion masses. The model has interesting implications
for the LHC, while the Standard Model phenomenology is recovered at low
energies. We discuss some phenomenological implications such as FCNC, new
Higgses at the TeV scale and dark matter candidates.Comment: 8 pages, no figures. Version published in Phys. Lett.
Light active and sterile neutrinos from compositeness
Neutrinos can have naturally small Dirac masses if the Standard Model singlet
right-handed neutrinos are light composite fermions. Theories which produce
light composite fermions typically generate many of them, three of which can
marry the left-handed neutrinos with small Dirac masses. The rest can serve as
sterile states which can mix with the Standard Model neutrinos. We present
explicit models illustrating this idea.Comment: 6 pages, revte
Leptogenesis from Neutralino Decay with Nonholomorphic R-Parity Violation
In supersymmetric models with lepton-number violation, hence also R-parity
violation, it is easy to have realistic neutrino masses, but then leptogenesis
becomes difficult to achieve. After explaining the general problems involved,
we study the details of a model which escapes these constraints and generates a
lepton asymmetry, which gets converted into the present observed baryon
asymmetry of the Universe through the electroweak sphalerons. This model
requires the presence of certain nonholomorphic R-parity violating terms. For
completeness we also present the most general R-parity violating Lagrangian
with soft nonholomorphic terms and study their consequences for the
charged-scalar mass matrix. New contributions to neutrino masses in this
scenario are discussed.Comment: 30 pages, 6 figure
Soft leptogenesis in the inverse seesaw model
We consider leptogenesis induced by soft supersymmetry breaking terms ("soft
leptogenesis"), in the context of the inverse seesaw mechanism. In this model
there are lepton number (L) conserving and L-violating soft
supersymmetry-breaking B-terms involving the singlet sneutrinos which, together
with the -- generically small-- L-violating parameter responsible of the
neutrino mass, give a small mass splitting between the four singlet sneutrino
states of a single generation. In combination with the trilinear soft
supersymmetry breaking terms they also provide new CP violating phases needed
to generate a lepton asymmetry in the singlet sneutrino decays. We obtain that
in this scenario the lepton asymmetry is proportional to the L-conserving soft
supersymmetry-breaking B-term, and it is not suppressed by the L-violating
parameters. Consequently we find that, as in the standard see-saw case, this
mechanism can lead to sucessful leptogenesis only for relatively small value of
the relevant soft bilinear coupling. The right-handed neutrino masses can be
sufficiently low to elude the gravitino problem. Also the corresponding Yukawa
couplings involving the lightest of the right-handed neutrinos are constrained
to be \sum |Y_{1k}|^2\lesssim 10^{-7} which generically implies that the
neutrino mass spectrum has to be strongly hierarchical.Comment: 28 pages, 1 figure; some references added; final version to appear in
JHE
Sneutrino-Antisneutrino Mixing and Neutrino Mass in Anomaly--mediated Supersymmetry Breaking Scenario
In supersymmetric models with nonzero Majorana neutrino mass, the sneutrino
and antisneutrino mix, which may lead to same sign dilepton signals in future
collider experiments. We point out that the anomaly-mediated supersymmetry
breaking scenario has a good potential to provide an observable rate of such
signals for the neutrino masses suggested by the atmospheric and solar neutrino
oscillations. The sneutrino mixing rate is naturally enhanced by
m_{3/2}/m_{\tilde{\nu}}={\cal O}(4\pi/\alpha) while the sneutrino decay rate is
small enough on a sizable portion of the parameter space. We point out also
that the sneutrino-antisneutrino mixing can provide much stronger information
on some combinations of the neutrino masses and mixing angles than neutrino
experiments.Comment: Revtex, 13 pages, 2 figure
Massive Neutrinos and Lepton Mixing in Unified Theories
The recent GUT (x SUSY) models which can predict the neutrino properties are
reviewed.Comment: 8 pages, Talk presented at the XVI International Workshop on Weak
Interactions and Neutrinos, Capri, 199
Efficiency and maximal CP-asymmetry of scalar triplet leptogenesis
We study thermal leptogenesis induced by decays of a scalar SU(2)_L triplet.
Despite the presence of gauge interactions, unexpected features of the
Boltzmann equations make the efficiency close to maximal in most of the
parameter space. We derive the maximal CP asymmetry in triplet decays, assuming
that it is generated by heavier sources of neutrino masses: in this case
successful leptogenesis needs a triplet heavier than 2.8 10^{10} GeV and does
not further restrict its couplings, allowing detectable mu --> e gamma, tau -->
mu gamma rates in the context of supersymmetric models. Triplet masses down to
the TeV scale are viable in presence of extra sources of CP-violation.Comment: 12 pages, 6 figures. Interference term added to eq. (16d), figures
recomputed (the difference is almost invisible
Probing the Majorana nature of TeV-scale radiative seesaw models at collider experiments
A general feature of TeV-scale radiative seesaw models, in which tiny
neutrino masses are generated via loop corrections, is an extended scalar
(Higgs) sector. Another feature is the Majorana nature; e.g., introducing
right-handed neutrinos with TeV-scale Majorana masses under the discrete
symmetry, or otherwise introducing some lepton number violating interactions in
the scalar sector. We study phenomenological aspects of these models at
collider experiments. We find that, while properties of the extended Higgs
sector of these models can be explored to some extent, the Majorana nature of
the models can also be tested directly at the International Linear Collider via
the electron-positron and electron-electron collision experiments.Comment: 19 pages, 7 figures, version published in Physics Letters
Majorana neutrinos with split fermions in extra dimensions
We propose new solutions to the neutrino mass problem in theories with large
extra dimensions in a thick wall scenario. It has recently been argued that our
3-brane could be a thick wall at the boundary of the bulk. The gauge bosons and
the Higgs scalars have an almost flat profile on this wall, while fermions
could have localized profile with left-handed and right-handed components
displaced with respect to each other. We point out that with split fermions it
is possible to generate Majorana neutrino masses contributing to the
neutrinoless double beta decay. The almost degenerate neutrinos can also come
out naturally in this case. Unlike other models of neutrino masses in extra
dimensions there are no bulk fields in this scenario.Comment: 12 pages, 1 figure, revise
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