1,320 research outputs found
New Constraints from Electric Dipole Moments on Parameters of the Supersymmetric SO(10) Model
We calculate the chromoelectric dipole moment (CEDM) of d- and s-quark in the
supersymmetric SO(10) model. CEDM is more efficient than quark electric dipole
moment (EDM), in inducing the neutron EDM. New, strict constraints on
parameters of the supersymmetric SO(10) model follow in this way from the
neutron dipole moment experiments. As strict bounds are derived from the upper
limits on the dipole moment of odd isotope of mercury.Comment: 9 pages, latex, 3 figures available at reques
A Maximal Atmospheric Mixing from a Maximal CP Violating Phase
We point out an elegant mechanism to predict a maximal atmospheric angle,
which is based on a maximal CP violating phase difference between second and
third lepton families in the flavour symmetry basis. In this framework, a
discussion of the predictions for theta_{12}, |U_{e3}|, delta and their
possible correlations is provided. We also present an explicit realisation in
terms of an SO(3) flavour symmetry model.Comment: v2=published version: 11 pages, 4 figures, text improved, reference
adde
Dark Scalar Doublets and Neutrino Tribimaximal Mixing from A_4 Symmetry
In the context of A_4 symmetry, neutrino tribimaximal mixing is achieved
through the breaking of A_4 to Z_3 (Z_2) in the charged-lepton (neutrino)
sector respectively. The implied vacuum misalignment of the (1,1,1) and (1,0,0)
directions in A_4 space is a difficult technical problem, and cannot be treated
without many auxiliary fields and symmetries (and perhaps extra dimensions). It
is pointed out here that an alternative scenario exists with A_4 alone and no
redundant fields, if neutrino masses are "scotogenic", i.e. radiatively induced
by dark scalar doublets as recently proposed.Comment: 8 pages, 2 figures, 1 reference and 1 paragraph adde
Electroweak Corrections and Unitarity in Linear Moose Models
We calculate the form of the corrections to the electroweak interactions in
the class of Higgsless models which can be "deconstructed'' to a chain of SU(2)
gauge groups adjacent to a chain of U(1) gauge groups, and with the fermions
coupled to any single SU(2) group and to any single U(1) group along the chain.
The primary advantage of our technique is that the size of corrections to
electroweak processes can be directly related to the spectrum of vector bosons
("KK modes"). In Higgsless models, this spectrum is constrained by unitarity.
Our methods also allow for arbitrary background 5-D geometry, spatially
dependent gauge-couplings, and brane kinetic energy terms. We find that, due to
the size of corrections to electroweak processes in any unitary theory,
Higgsless models with localized fermions are disfavored by precision
electroweak data. Although we stress our results as they apply to continuum
Higgsless 5-D models, they apply to any linear moose model including those with
only a few extra vector bosons. Our calculations of electroweak corrections
also apply directly to the electroweak gauge sector of 5-D theories with a bulk
scalar Higgs boson; the constraints arising from unitarity do not apply in this
case.Comment: 50 pages, 11 eps figures, typos correcte
Constraints on flavour-dependent long-range forces from atmospheric neutrino observations at Super-Kamiokande
In the minimal standard model it is possible to gauge any one of the
following global symmetries in an anomaly free way: (i), (ii)
or (iii) . If the gauge boson corresponding
to (i) or (ii) is (nearly) massless then it will show up as a long range
composition dependent fifth force between macroscopic objects. Such a force
will also influence neutrino oscillations due to its flavour-dependence. We
show that the latter effect is quite significant in spite of very strong
constraints on the relevant gauge couplings from the fifth force experiments.
In particular, the potential of the electrons in the Sun
and the earth is shown to suppress the atmospheric neutrino oscillations which have been observed at Super-Kamiokande. The
Super-K data of oscillation of multi-GeV atmospheric neutrinos can be used to
put an upper bound on coupling and
at 90% CL when the range of the force is
the earth-sun distance. This is an improvement by two orders on the earlier
fifth force bounds in this range.Comment: 5 pages Latex, 3 figure
Top quark effects in composite vector pair production at the LHC
In the context of a strongly coupled Electroweak Symmetry Breaking, composite
light scalar singlet and composite triplet of heavy vectors may arise from an
unspecified strong dynamics and the interactions among themselves and with the
Standard Model gauge bosons and fermions can be described by a Effective Chiral Lagrangian. In this framework, the
production of the and final states at the LHC by
gluon fusion mechanism is studied in the region of parameter space consistent
with the unitarity constraints in the elastic channel of longitudinal gauge
boson scattering and in the inelastic scattering of two longitudinal Standard
Model gauge bosons into Standard Model fermions pairs. The expected rates of
same-sign di-lepton and tri-lepton events from the decay of the
final state are computed and their corresponding backgrounds are estimated. It
is of remarkable relevance that the final state can only be
produced at the LHC via gluon fusion mechanism since this state is absent in
the Drell-Yan process. It is also found that the final state
production cross section via gluon fusion mechanism is comparable with the
Drell-Yan production cross section. The comparison of the
and total cross sections will be crucial for
distinguishing the different models since the vector pair production is
sensitive to many couplings. This will also be useful to determine if the heavy
vectors are only composite vectors or are gauge vectors of a spontaneously
broken gauge symmetry.Comment: 18 pages, 5 tables, 6 figures. Missing figures added. Matches
published versio
Universal Non-Oblique Corrections in Higgsless Models and Beyond
Recently Barbieri, et al. have introduced a formalism to express the
deviations of electroweak interactions from their standard model forms in
"universal" theories, i.e. theories in which the corrections due to new physics
can be expressed solely by modifications to the two-point correlation function
of electroweak gauge currents of fermions. The parameters introduced by these
authors are defined by the properties of the correlation functions at zero
momentum, and differ from the quantities calculated by examining the on-shell
properties of the electroweak gauge bosons. In this letter we discuss the
relationship between the zero-momentum and on-shell parameters. In addition, we
present the results of a calculation of these zero-momentum parameters in an
arbitrary Higgsless model in which the low-energy rho parameter is one and
which can be deconstructed to a linear chain of SU(2) groups adjacent to a
chain of U(1) groups. Our results demonstrate the importance of the universal
"non-oblique" corrections which are present and elucidate the relationships
among various calculations of electroweak quantities in these models. Our
expressions for these zero-momentum parameters depend only on the spectrum of
heavy vector-boson masses; therefore, the minimum size of the deviations
present in these models is related to the upper bound on the heavy vector-boson
masses derived from unitarity. We find that these models are disfavored by
precision electroweak data, independent of any assumptions about the background
metric or the behavior of the bulk coupling.Comment: 13 pages, 2 eps figure
Z_3 Dark Matter and Two-Loop Neutrino Mass
Dark matter is usually distinguished from ordinary matter by an odd-even
parity, i.e. the discrete symmetry Z_2. The new idea of Z_3 dark matter is
proposed with a special application to generating radiative Majorana neutrino
masses in two-loop order.Comment: expanded (9 pages, 2 figures), 2 references adde
Fermion Masses and Mixings in a S4 Based Model
It has been recently claimed that the symmetry group S4 yields to the
Tri-bimaximal neutrino mixing in a "natural" way from the group theory point of
view. Approving of this feature as an indication, we build a supersymmetric
model of lepton and quark masses based on this family symmetry group. In the
lepton sector, a correct mass hierarchy among the charged leptons is achieved
together to a neutrino mass matrix which can be diagonalized by the
Tri-bimaximal pattern. Our model results to be phenomenologically unequivalent
with respect to other proposals based on different flavour groups but still
predicting the Tri-bimaximal mixing. In the quark sector a realistic pattern
for masses and mixing angles is obtained. The flavour structures of the mass
matrices in both the sectors come from the spontaneously symmetry breaking of
S4, due to several scalar fields, which get non-zero vacuum expectation values.
A specific vacuum alignment is required and it is shown to be a natural results
of the minimization of the scalar potential and, moreover, to be stable under
the corrections from the higher order terms.Comment: 25 pages, LaTeX; added references and minor correctio
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