761 research outputs found
Resonant Leptogenesis with nonholomorphic R-Parity violation and LHC Phenomenology
In R-parity violating supersymmetric models both leptogenesis and the correct
neutrino masses are hard to achieve together. The presence of certain soft
nonholomorphic R-parity violating terms helps to resolve this problem. We
consider a scenario where the lightest and the second-lightest neutralino are
nearly degenerate in mass and enough CP-asymmetry can be produced through
resonant leptogenesis. In this model, the lighter chargino and the lightest
neutralino are highly degenerate. We have relatively lighter gauginos which can
be produced at the LHC leading to heavily ionizing charged tracks. At the same
time this model can also generate the correct neutrino mass scale. Thus our
scenario is phenomenologically rich and testable at colliders.Comment: 17 pages, 7 figures, Numerical results are improved and new plots are
added, Journal version. arXiv admin note: text overlap with
arXiv:hep-ph/0006173 by other author
Leptogenesis implications in models with Abelian family symmetry and one extra real Higgs singlet
We show that the neutrino models, as suggested by Low, which have an
additional Abelian family symmetry and a real Higgs singlet to the default
see-saw do not hinder the possibility of successful thermal leptogenesis. For
these models (neglecting radiative effects), we have investigated the situation
of strong washout in both the one-flavor approximation and when flavor effects
are included. The result is that while such models predict that theta_{13}=0
and that one light neutrino to be massless, they do not modify or provide
significant constraints on the typical leptogenesis scenario where the final
asymmetry is dominated by the decays of the lightest right-handed neutrinos.Comment: 18 pages, RevTeX4, accepted by Phys. Rev. D. v2: minor corrections,
note and 1 ref. added, same content as published versio
`Natural Masslessness Conservation' for neutrinos in two Higgs-doublet models
We present a model which supplements the Standard Electroweak Model with
three right-handed neutrinos and one extra scalar doublet which does not
develop a vacuum expectation value. With the aid of a discrete symmetry the
neutrinos are kept strictly massless. This model has several interesting
features. It has unsuppressed lepton flavour violating processes, in particular
, hinting at the possibility that these may soon be
within experimental reach. The and interactions become non-diagonal at
one loop level. In particular, a non-trivial leptonic mixing matrix is seen to
arise from the clash between the charged gauge boson and the charged scalar
interactions.Comment: (Latex file, 12 pages. Two figures available upon request).
CMU-preprin
The Anomalous Magnetic Moment of the Muon and Higgs-Mediated Flavor Changing Neutral Currents
In the two-Higgs doublet extension of the standard model, flavor-changing
neutral couplings arise naturally. In the lepton sector, the largest such
coupling is expected to be $\mu-\tau-\phi#. We consider the effects of this
coupling on the anomalous magnetic moment of the muon. The resulting bound on
the coupling, unlike previous bounds, is independent of the value of other
unknown couplings. It will be significantly improved by the upcoming E821
experiment at Brookhaven National Lab.Comment: 7 pages Latex, 2 figure
A model of CP Violation from Extra Dimension
We construct a realistic model of CP violation in which CP is broken in the
process of dimensional reduction and orbifold compactification from a five
dimensional theories with gauge symmetry. CP
violation is a result of the Hosotani type gauge configuration in the higher
dimension.Comment: 5 page
Thermal leptogenesis in a 5D split fermion scenario with bulk neutrinos
We study the thermal leptogenesis in a hybrid model, which combines the so
called split fermion model and the bulk neutrino model defined in five
dimensional spacetime. This model predicts the existence of a heavy neutrino
pair nearly degenerate in mass, whose decays might generate a CP violation
large enough for creating the baryon asymmetry of the universe through
leptogenesis. We investigate numerically the constraints this sets on the
parameters of the model such as the size of the compactified fifth dimension.Comment: 22 pages, 9 figure
Constraints on the Universal Contact Interaction
Forces beyond those of the standard model may manifest themselves at low
energies as four-fermion contact interactions. If these new forces are
independent of colour and flavour quantum numbers including baryon and lepton
number, then all low energy constraints, arising from quark-lepton
universality, flavour-changing neutral currents and atomic parity violation are
evaded. This is due to the global U(45) symmetry which the standard model
exhibits in the limit of vanishing gauge and Yukawa couplings. The
corresponding contact interaction is a unique current-current interaction.
Constraints from LEP2 imply that this universal contact interaction cannot be
the origin of the recently observed high- events at HERA.Comment: 6 pages Latex, no figure
Relativistic quantum theories and neutrino oscillations
Neutrino oscillations are examined under the broad requirements of
Poincar\'e-invariant scattering theory in an S-matrix formulation.
This approach can be consistently applied to theories with either field or
particle degrees of freedom. The goal of this paper is to use this general
framework to identify all of the unique physical properties of this problem
that lead to a simple oscillation formula. We discuss what is in principle
observable, and how many factors that are important in principle end up being
negligible in practice.Comment: 21 pages, no figure
High-Energy Tests of Lorentz Invariance
We develop a perturbative framework with which to discuss departures from
exact Lorentz invariance and explore their potentially observable
ramifications. Tiny non-invariant terms introduced into the standard model
Lagrangian are assumed to be renormalizable (dimension ), invariant
under gauge transformations, and rotationally
and translationally invariant in a preferred frame. There are a total of 46
independent TCP-even perturbations of this kind, all of which preserve anomaly
cancellation. They define the energy-momentum eigenstates and their maximal
attainable velocities in the high-energy limit. The effects of these
perturbations increase rapidly with energy in the preferred frame, more rapidly
than those of TCP-odd perturbations. Our analysis of Lorentz-violating
kinematics reveals several striking new phenomena that are relevant both to
cosmic-ray physics ({\it e.g.,} by undoing the GZK cutoff) and neutrino physics
({\it e.g.,} by generating novel types of neutrino oscillations). These may
lead to new and sensitive high-energy tests of special relativity.Comment: 33 pages, uses harvmac. This 2nd revision corrects two typos, an
error in the Appendix, and includes further acknowledgement
Minimal Trinification
We study the trinified model, SU(3)_C x SU(3)_L x SU(3)_R x Z_3, with the
minimal Higgs sector required for symmetry breaking. There are five Higgs
doublets, and gauge-coupling unification results if all five are at the weak
scale, without supersymmetry. The radiative see-saw mechanism yields sub-eV
neutrino masses, without the need for intermediate scales, additional Higgs
fields, or higher-dimensional operators. The proton lifetime is above the
experimental limits, with the decay modes p -> \bar\nu K^+ and p -> \mu^+ K^0
potentially observable. We also consider supersymmetric versions of the model,
with one or two Higgs doublets at the weak scale. The radiative see-saw
mechanism fails with weak-scale supersymmetry due to the nonrenormalization of
the superpotential, but operates in the split-SUSY scenario.Comment: 23 pages, uses axodra
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