366 research outputs found
Maximal Neutrino Mixing from a Minimal Flavor Symmetry
We study a number of models, based on a non-Abelian discrete group, that
successfully reproduce the simple and predictive Yukawa textures usually
associated with U(2) theories of flavor. These models allow for solutions to
the solar and atmospheric neutrino problems that do not require altering
successful predictions for the charged fermions or introducing sterile
neutrinos. Although Yukawa matrices are hierarchical in the models we consider,
the mixing between second- and third-generation neutrinos is naturally large.
We first present a quantitative analysis of a minimal model proposed in earlier
work, consisting of a global fit to fermion masses and mixing angles, including
the most important renormalization group effects. We then propose two new
variant models: The first reproduces all important features of the SU(5)xU(2)
unified theory with neither SU(5) nor U(2). The second demonstrates that
discrete subgroups of SU(2) can be used in constructing viable supersymmetric
theories of flavor without scalar universality even though SU(2) by itself
cannot.Comment: 34 pages LaTeX, 1 eps figure, minor revisions and references adde
A Supersymmetric Theory of Flavor and R Parity
We construct a renormalizable, supersymmetric theory of flavor and parity
based on the discrete flavor group . The model can account for all the
masses and mixing angles of the Standard Model, while maintaining sufficient
squark degeneracy to circumvent the supersymmetric flavor problem. By starting
with a simpler set of flavor symmetry breaking fields than we have suggested
previously, we construct an economical Froggatt-Nielsen sector that generates
the desired elements of the fermion Yukawa matrices. With the particle content
above the flavor scale completely specified, we show that all renormalizable
-parity-violating interactions involving the ordinary matter fields are
forbidden by the flavor symmetry. Thus, parity arises as an accidental
symmetry in our model. Planck-suppressed operators that violate parity, if
present, can be rendered harmless by taking the flavor scale to be GeV.Comment: 28 pp. LaTeX, 1 Postscript Figur
Discerning Noncommutative Extra Dimensions
Experimental limits on the violation of four-dimensional Lorentz invariance
imply that noncommutativity among ordinary spacetime dimensions must be small.
Noncommutativity among extra, compactified spatial dimensions, however, is far
less constrained and may have discernable collider signatures. Here we study
the experimental consequences of noncommutative QED in six dimensions, with
noncommutativity restricted to a TeV-scale bulk. Assuming the orbifold T^2/Z_2,
we construct the effective four-dimensional theory and study interactions
unique to the noncommutative case. New vertices involving the Kaluza-Klein (KK)
excitations of the photon yield order 100% corrections to the pair production
and to the decays of some of the lighter modes. We show that these effects are
difficult to resolve at the LHC, but are likely within the reach of a future
Very Large Hadron Collider (VLHC).Comment: 20 pages LaTeX, 8 eps figures (minor revisions, version to appear in
Phys. Rev. D
Gauge Unification and Dynamical Supersymmetry Breaking
Under the assumption that all the gauge groups in supersymmetric theories
unify at the fundamental scale, the numbers and the mass scales of messenger
quarks and leptons, as well as the beta-function coefficient of the sector for
dynamical supersymmetry breaking are constrained depending on various gauge
mediation mechanisms. For this, we use one-loop renormalization group equations
and draw constraints on the scales in each gauge mediation model.Comment: 13 pages, Latex. Improved significantly, reference expended,
disagreement with Dubovsky, et.al. [hep-ph/9707357] clarifie
The event generator DECAY4 for simulation of double beta processes and decay of radioactive nuclei
The computer code DECAY4 is developed to generate initial energy, time and
angular distributions of particles emitted in radioactive decays of nuclides
and nuclear (atomic) deexcitations. Data for description of nuclear and atomic
decay schemes are taken from the ENSDF and EADL database libraries. The
examples of use of the DECAY4 code in several underground experiments are
described.Comment: 8 pages, 1 fi
Neutrino mass matrix with U(2) flavor symmetry and neutrino oscillations
The three neutrino mass matrices in the model are studied
focusing on the neutrino oscillation experiments. The atmospheric neutrino
anomaly could be explained by the large oscillation.
The long baseline experiments are expected to detect signatures of the neutrino
oscillation even if the atmospheric neutrino anomaly is not due to the neutrino
oscillation. However, the model cannot solve the solar neutrino deficit while
it could be reconciled with the LSND data.Comment: 12 pages, LaTex file, to be published in PR
Next-to-Minimal Supersymmetric Standard Model with the Gauge Mediation of Supersymmetry Breaking
We study the Next-to-Minimal Supersymmetric Standard Model (NMSSM) as the
simplest candidate solution to the -problem in the context of the gauge
mediation of supersymmetry breaking (GMSB). We first review various proposals
to solve the -problem in models with the GMSB. We find none of them
entirely satisfactory and point out that many of the scenarios still lack
quantitative studies, and motivate the NMSSM as the simplest possible solution.
We then study the situation in the Minimal Supersymmetric Standard Model (MSSM)
with the GMSB and find that an order 10% cancellation is necessary between the
-parameter and the soft SUSY-breaking parameters to correctly reproduce
. Unfortunately, the NMSSM does not to give a phenomenologically viable
solution to the -problem. We present quantitative arguments which apply
both for the low-energy and high-energy GMSB and prove that the NMSSM does not
work for either case. Possible modifications to the NMSSM are then discussed.
The NMSSM with additional vector-like quarks works phenomenologically, but
requires an order a few percent cancellation among parameters. We point out
that this cancellation has the same origin as the cancellation required in the
MSSM.Comment: 36 pages, LaTeX, epsf.sty, 5 figures, references added, comments on
some other papers based on our misundestanding corrected, none of our results
change
Gauge coupling unification with large extra dimensions
We make a detailed study of the unification of gauge couplings in the MSSM
with large extra dimensions. We find some scenarios where unification can be
achieved (with the strong coupling constant at the Z mass within one standard
deviation of the experimental value) with both the compactification scale and
the SUSY breaking scale in the few TeV range. No enlargement of the gauge group
or particle content is needed. One particularly interesting scenario is when
the SUSY breaking scale is larger than the compactification scale, but both are
small enough to be probed at the CERN LHC. Unification in two scales scenarios
is also investigated and found to give results within the LHC.Comment: 17 pages, 3 figures, some discussions added, few additional
references included. Version to appear in Phys. Rev.
Fermion Mass Hierarchies and Small Mixing Angles from Extra Dimensions
In this paper we study renormalization-group evolutions of Yukawa matrices
enhanced by Kaluza-Klein excited modes and analyze their infrared fixed-point
structure. We derive necessary conditions to obtain hierarchies between
generations on the fixed point. These conditions restrict how the fields in the
models can extend to higher dimension. Several specific mechanisms to realize
the conditions are presented. We also take account of generation mixing effects
and find a scenario where the mixing angles become small at low energy even
with large initial values at high-energy scale. A toy model is shown to lead
realistic quark mass matrices.Comment: 23 pages, 7 figures, LaTeX, a supplementary explanation and
references adde
Negative Parity 70-plet Baryon Masses in the 1/Nc Expansion
The masses of the negative parity SU(6) 70-plet baryons are analyzed in the
1/Nc expansion to order 1/Nc and to first order in SU(3) breaking. At this
level of precision there are twenty predictions. Among them there are the well
known Gell-Mann Okubo and equal spacing relations, and four new relations
involving SU(3) breaking splittings in different SU(3) multiplets. Although the
breaking of SU(6) symmetry occurs at zeroth order in 1/Nc, it turns out to be
small. The dominant source of the breaking is the hyperfine interaction which
is of order 1/Nc. The spin-orbit interaction, of zeroth order in 1/Nc, is
entirely fixed by the splitting between the singlet states Lambda(1405) and
Lambda(1520), and the spin-orbit puzzle is solved by the presence of other
zeroth order operators involving flavor exchange.Comment: 31 pages, 3 figure
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