13,018 research outputs found
Mass and Flavor Mixing Schemes of Quarks and Leptons
We give an overview of recent progress in the study of fermion mass and
flavor mixing phenomena. The hints exhibited by the quark and lepton mass
spectra towards possible underlying flavor symmetries, from which realistic
models of mass generation could be built, are emphasized. A variety of schemes
of quark mass matrices at low and superhigh energy scales are described, and
their consequences on flavor mixing and CP violation are discussed. Instructive
patterns of lepton mass matrices, which can naturally lead to large flavor
mixing angles, are explored to interpret current data on atmospheric and solar
neutrino oscillations. We expect that B-meson factories and long-baseline
neutrino experiments will soon shed more light on the dynamics of fermion
masses, flavor mixing and CP violation.Comment: LaTex 81 pages. Minor changes made, typing errors corrected, and
references added. Prog. Part. Nucl. Phys. (in printing
Neutrino masses and mixing
Status of determination of the neutrino masses and mixing is formulated and
possible uncertainties, especially due to presence of the sterile neutrinos,
are discussed. The data hint an existence of special ``neutrino'' symmetries.
If not accidental these symmetries have profound implications and can
substantially change the unification program. The key issue on the way to
underlying physics is relations between quarks and leptons. The approximate
quark-lepton symmetry or universality can be reconciled with strongly different
patterns of masses and mixings due to nearly singular character of the mass
matrices or screening of the Dirac structures in the double see-saw mechanism.Comment: 11 pages, latex, iopams.sty, 3 figures. Invited talk given at
TAUP2005, September 10 - 14, 2005, Zaragoza, Spai
Neutrino masses in the Lepton Number Violating MSSM
We consider the most general supersymmetric model with minimal particle
content and an additional discrete Z_3 symmetry (instead of R-parity), which
allows lepton number violating terms and results in non-zero Majorana neutrino
masses. We investigate whether the currently measured values for lepton masses
and mixing can be reproduced. We set up a framework in which Lagrangian
parameters can be initialised without recourse to assumptions concerning
trilinear or bilinear superpotential terms, CP-conservation or
intergenerational mixing and analyse in detail the one loop corrections to the
neutrino masses. We present scenarios in which the experimental data are
reproduced and show the effect varying lepton number violating couplings has on
the predicted atmospheric and solar mass^2 differences. We find that with
bilinear lepton number violating couplings in the superpotential of the order 1
MeV the atmospheric mass scale can be reproduced. Certain trilinear
superpotential couplings, usually, of the order of the electron Yukawa coupling
can give rise to either atmospheric or solar mass scales and bilinear
supersymmetry breaking terms of the order 0.1 GeV^2 can set the solar mass
scale. Further details of our calculation, Lagrangian, Feynman rules and
relevant generic loop diagrams, are presented in three Appendices.Comment: 48 pages, 7 figures, v2 references added, typos corrected, published
versio
SU(3) Family Gauge Symmetry and the Axion
We analyze the structure of a recently proposed effective field theory (EFT)
for the generation of quark and lepton mass ratios and mixing angles, based on
the spontaneous breaking of an SU(3) family gauge symmetry at a high scale F.
We classify the Yukawa operators necessary to seed the masses, making use of
the continuous global symmetries that they preserve. One global U(1), in
addition to baryon number and electroweak hypercharge, remains unbroken after
the inclusion of all operators required by standard-model-fermion
phenomenology. An associated vacuum symmetry insures the vanishing of the
first-family quark and charged-lepton masses in the absence of the family gauge
interaction. If this U(1) symmetry is taken to be exact in the EFT, broken
explicitly by only the QCD-induced anomaly, and if the breaking scale F is
taken to lie in the range 10 to 9 - 10 to 12 GeV, then the associated
Nambu-Goldstone boson is a potential QCD axion.Comment: References added and clarifications in Vacuum Structure sectio
Fermion masses and mixing in models with SO(10) x A_4 symmetry
We study the flavour sector in models where the three families of matter are
unified in a representation of the group. The
necessary ingredients to realize tri-bi-maximal mixing in the lepton sector are
identified systematically. The non-renormalizable operators contributing to the
fermion mass matrices play an important role. We also present a mechanism to
explain the inter-family mass hierarchy of quarks and charged leptons, which
relies on a `universal seesaw' mechanism and is compatible with tri-bi-maximal
mixing.Comment: 24 pages, revte
Bi-large Neutrino Mixing and CP violation in an SO(10) SUSY GUT for Fermion Masses
We construct a simple SO(10) SUSY GUT with family symmetry and low
energy R parity. The model describes fermion mass matrices with 14 parameters
and gives excellent fits to 20 observable masses and mixing angles in both
quark and lepton sectors, giving 6 predictions. Bi-large neutrino mixing is
obtained with hierarchical quark and lepton Yukawa matrices; thus avoiding the
possibility of large lepton flavor violation. The model naturally predicts
small 1-3 neutrino mixing, , and a CP violating
phase close to . Among other interesting predictions is a tiny
effective Majorana mass for neutrinoless double-beta decay. Leptogenesis is
also possible with the decay of the lightest right-handed neutrino giving an
acceptable CP violating asymmetry of order , {\em and
with the correct sign for the resultant baryon asymmetry}. We also show how
similar models with the non-abelian symmetry groups SU(2) or , instead of
, can be constructed.Comment: 16 pages, resubmitted as a PLB letter, appendices were remove
Strong coupling, discrete symmetry and flavour
We show how two principles - strong coupling and discrete symmetry - can work
together to generate the flavour structure of the Standard Model. We propose
that in the UV the full theory has a discrete flavour symmetry, typically only
associated with tribimaximal mixing in the neutrino sector. Hierarchies in the
particle masses and mixing matrices then emerge from multiple strongly coupled
sectors that break this symmetry. This allows for a realistic flavour
structure, even in models built around an underlying grand unified theory. We
use two different techniques to understand the strongly coupled physics:
confinement in N=1 supersymmetry and the AdS/CFT correspondence. Both
approaches yield equivalent results and can be represented in a clear,
graphical way where the flavour symmetry is realised geometrically.Comment: 31 pages, 5 figures, updated references and figure
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