1,286 research outputs found
Supersymmetric SO(10) for fermion masses and mixings: rank-1 structures of flavour
We consider a supersymmetric SO(10) model with a SU(3) symmetry of flavour in
which fermion masses emerge via the see-saw mixing with superheavy fermions in
16+16bar representations. In this model the dangerous D=5 operators of proton
decay are naturally suppressed and flavour-changing supersymmetric effects are
under control. The mass matrices for all fermion types (up and down quarks,
charged leptons as well as neutrinos) appear in the form of combinations of
three rank-1 matrices, common to all types of fermions, with different
coefficients that are successive powers of small parameters, related to each
other by SO(10) symmetry properties. Two versions of the model are considered,
in which approximate grand unification of masses takes place between quarks and
leptons of the first family (with very small \tan\beta) or for the ones of the
second family (predicting moderate \tan\beta ~ 7-8). The second version
exhibits an interesting mechanism of unification of the determinants of the
Yukawa matrices of all types of fermions at the GUT scale and it provides a
perfect fit of the known data for fermion masses, mixing and CP-violation. It
predicts a hierarchical pattern of neutrino masses with non-zero theta_e3,
within 2-7 degrees. In addition, it predicts the correct sign of the baryon
asymmetry of the Universe via the leptogenesys scenario.Comment: 30 Pages, 3 figures. Clarified comments on neutrino scales and on
universal seesaw, updated references. Version appeared on JHE
Towards a grand unified picture for neutrino and quark mixings
The comparison of the CKM mixing angles with the leptonic mixings implied by
the recent atmospheric and solar neutrino data exhibits an interesting
complementarity. This pattern can be understood in the context of the SU(5)
grand unification, assuming that the fermion mass matrices have Fritzsch-like
structures but are not necessarily symmetric. (The present contribution is
based on the paper in ref. \cite{az}.)Comment: Latex file + espcrc2.sty, 5 pages, 3 postscript figures included.
Talk given at the Int. Workshop ``Particles in Astrophysics and Cosmology:
from Theory to Observation'', May 3-8, 1999, Valencia, Spain. To appear in
Nucl. Phys. Proc. Supp
Strong CP problem and mirror world: the Weinberg Wilczek axion revisited
A new possibility for solving the strong CP-problem is suggested,which
assumes that apart of the ordinary world of observable particles described by
standard model, there exits a mirror sector of particles and two sectors share
the same Peccei-Quinn symmetry realized {\it a l\`a} Weinberg-Wilczek model.
The mirror gauge group is completely analogous to that of the standard model
for ordinary particles but having somewhat larger electroweak scale,which in
turn implies the infrared scale of the mirror strong interactions
has to be larger than the ordinary QCD scale . In this way, the axion
mass and interaction constants are actually determined by mirror sector scales
and , while the terms are simultaneously cancelled in
both sectors due to mirror symmetry. The experimental and astrophysical limits
on such an axion is discussed. An interesting parameter window is found where
GeV whereas the axion mass is MeV.Comment: 13 LaTex pages, 3 Postscript figure
Fast Neutron - Mirror Neutron Oscillation and Ultra High Energy Cosmic Rays
If there exists the mirror world, a parallel hidden sector of particles with
exactly the same microphysics as that of the observable particles, then the
primordial nucleosynthesis constraints require that the temperature of the
cosmic background of mirror relic photons should be smaller than that of the
ordinary relic photons, T'/T < 0.5 or so. On the other hand, the present
experimental and astrophysical limits allow a rather fast neutron - mirror
neutron oscillation in vacuum, with an oscillation time s, much
smaller than the neutron lifetime. We show that this could provide a very
efficient mechanism for transporting ultra high energy protons at large
cosmological distances. The mechanism operates as follows: a super-GZK energy
proton scatters a relic photon producing a neutron that oscillates into a
mirror neutron which then decays into a mirror proton. The latter undergoes a
symmetric process, scattering a mirror relic photon and producing back an
ordinary nucleon, but only after traveling a distance times larger
than ordinary protons. This may relax or completely remove the GZK-cutoff in
the cosmic ray spectrum and also explain the correlation between the observed
ultra high energy protons and far distant sources as are the BL Lacs.Comment: 14 pages; to appear in PLB (submitted 28 November 2005
Soft SUSY breaking contributions to proton decay
We show that in supersymmetric grand unified theories new effective D=4 and
D=5 operators for proton decay are induced by soft SUSY-breaking terms, when
heavy GUT gauge bosons are integrated out, in addition to the standard D=6
ones. As a result, the proton lifetime in gauge mediated channels can be
enhanced or even suppressed depending on the size of the heavy Higgses soft
terms.Comment: 16 pages, 2 figures, LaTeX, JHEP3 class, axodra
Baryogenesis in Cosmological Model with Superstring-Inspired E_6 Unification
We have developed a concept of parallel existence of the ordinary (O) and
hidden (H) worlds with a superstring-inspired E_6 unification, broken at the
early stage of the Universe into SO(10) X U(1) - in the O-world, and SU(6)' X
SU(2)' - in the H-world. As a result, we have obtained in the hidden world the
low energy symmetry group G'_SM X SU(2)'_\theta, instead of the Standard Model
group G_SM. The additional non-Abelian SU(2)'_\theta group with massless gauge
fields, "thetons", is responsible for the dark energy. We present a
baryogenesis mechanism with the B-L asymmetry produced by the conversion of
ordinary leptons into particles of the hidden sector.Comment: 15 pages, 2 figure
Inverse Hierarchy Approach to Fermion Masses
The first fermion family might play a special role in understanding the
physics of flavour. This possibility is suggested by the observation that the
up-down splitting within quark families increases with the family number: , , . We construct a model that realizes this
feature of the spectrum in a natural way. The inter-family hierarchy is first
generated by radiative phenomena in a sector of heavy isosinglet fermions and
then transferred to quarks by means of a universal seesaw. A crucial role is
played by left-right parity and up-down isotopic symmetry. No family symmetry
is introduced. The model implies 0.5 and the Cabibbo angle is forced
to be . The top quark is naturally in the 100 GeV range,
but not too heavy: 150 GeV. Inspired by the mass matrices obtained in
the model for quarks, we suggest an ansatz also including charged leptons. The
differences between -, - and -type fermions are simply parametrized by
three complex coefficients \eps{u}, \eps{d} and \eps{e}. Additional
consistent predictions are obtained: =100-150 MeV and 0.75.Comment: 19 pages (standard TeX) + 1 table (cut out and LaTeX separately) + 1
figure (cut out and postscript separately); 2 additional figures available by
fax upon request, LBL-32889, LMU-13/9
A New Approach to Flavor Symmetry and an Extended Naturalness Principle
A class of non-supersymmetric extensions of the Standard Model is proposed in
which there is a multiplicity of light scalar doublets in a multiplet of a
non-abelian family group with the Standard Model Higgs doublet. Anthropic
tuning makes the latter light, and consequently the other scalar doublets
remain light because of the family symmetry. The family symmetry greatly
constrains the pattern of FCNC and proton decay operators coming from
scalar-exchange. Such models show that useful constraints on model-building can
come from an extended naturalness principle when the electroweak scale is
anthropically tuned.Comment: 31 pages, 3 figure
Anomalous U(1) symmetry and missing doublet SU(5) model
We present the supersymmetric models which provide a simple ``all
order'' solution to the doublet-triplet splitting problem through the missing
doublet mechanism. The crucial role is played by the anomalous gauge
symmetry and no additional discrete or global symmetries are needed.
Remarkably, such models can be realized even if the 75-plet Higgs is replaced
by the standard 24-plet. The same symmetry can also guarantee an exact
or approximate conservation of R parity, by suppressing the B and L violating
operators to the needed level. The neutrino masses and the proton decay via
operators are also examined. We also extend the model by incorporating
as a horizontal symmetry for explaining the fermion mass and mixing
hierarchy. Interestingly, in this scheme the necessary mild violation of the
troublesome degeneracy between the down quark and the charged lepton
masses can be induced by certain R-parity violating operators.Comment: 16 pages, LATEX, no figure
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