7,518 research outputs found
Eliminating the d=5 proton decay operators from SUSY GUTs
A general analysis is made of the question whether the d=5 proton decay
operators coming from exchange of colored Higgsinos can be completely
eliminated in a natural way in supersymmetric grand unified models. It is shown
that they can indeed be in SO(10) while at the same time naturally solving the
doublet-triplet splitting problem, having only two light Higgs doublets, and
using no more than a single adjoint Higgs field. Accomplishing all of this
requires that the vacuum expectation value of the adjoint Higgs field be
proportional to the generator I_{3R} rather than to B-L, as is usually assumed.
It is shown that such models can give realistic quark and lepton masses. We
also point out a new mechanism for solving the \mu problem in the context of
SO(10) SUSY GUTs.Comment: 24 pages in LaTeX, with 3 figure
Neutrino Masses and Mixings in a Minimal SO(10) Model
We consider a minimal formulation of SO(10) Grand Unified Theory wherein all
the fermion masses arise from Yukawa couplings involving one 126 and one 10 of
Higgs multiplets. It has recently been recognized that such theories can
explain, via the type-II seesaw mechanism, the large \nu_\mu - \nu_\tau mixing
as a consequence of b-tau unification at the GUT scale. In this picture,
however, the CKM phase \delta lies preferentially in the second quadrant, in
contradiction with experimental measurements. We revisit this minimal model and
show that the conventional type-I seesaw mechanism generates phenomenologically
viable neutrino masses and mixings, while being consistent with CKM CP
violation. We also present improved fits in the type-II seesaw scenario and
suggest fully consistent fits in a mixed scenario.Comment: 27 pages, 13 eps figures, revtex4; references added, some minor
correction
Brownian cluster dynamics with short range patchy interactions. Its application to polymers and step-growth polymerization
We present a novel simulation technique derived from Brownian cluster
dynamics used so far to study the isotropic colloidal aggregation. It now
implements the classical Kern-Frenkel potential to describe patchy interactions
between particles. This technique gives access to static properties, dynamics
and kinetics of the system, even far from the equilibrium. Particle thermal
motions are modeled using billions of independent small random translations and
rotations, constrained by the excluded volume and the connectivity. This
algorithm, applied to a single polymer chain leads to correct static and
dynamic properties, in the framework where hydrodynamic interactions are
ignored. By varying patch angles, various chain flexibilities can be obtained.
We have used this new algorithm to model step-growth polymerization under
various solvent qualities. The polymerization reaction is modeled by an
irreversible aggregation between patches while an isotropic finite square-well
potential is superimposed to mimic the solvent quality. In bad solvent
conditions, a competition between a phase separation (due to the isotropic
interaction) and polymerization (due to patches) occurs. Surprisingly, an
arrested network with a very peculiar structure appears. It is made of strands
and nodes. Strands gather few stretched chains that dip into entangled globular
nodes. These nodes act as reticulation points between the strands. The system
is kinetically driven and we observe a trapped arrested structure. That
demonstrates one of the strengths of this new simulation technique. It can give
valuable insights about mechanisms that could be involved in the formation of
stranded gels.Comment: 55 pages, 32 figure
Quark-Lepton Quartification
We propose that quarks and leptons are interchangeable entities in the
high-energy limit. This naturally results in the extension of [SU(3)]^3
trinification to [SU(3)]^4 quartification. In addition to the unbroken color
SU(3)_q of quarks, there is now also a color SU(3)_l of leptons which reduces
to an unbroken SU(2)_l. We discuss the natural occurrence of SU(2)_l doublets
at the TeV energy scale, which leads remarkably to the unification of all gauge
couplings without supersymmetry. Proton decay occurs through the exchange of
scalar bosons, with a lifetime in the range 10^{34} - 10^{36} years.Comment: 12 pages, 4 figures. Reference adde
Bimaximal Mixings from the Texture of the Right-handed Majorana Neutrino Mass Matrix
We study the origin of neutrino masses and mixing angles which can accomodate
the LMA MSW solutions of the solar neutrino anomaly as well as the solution of
the atmospheric neutrino problem, within the framework of the see-saw
mechanism. We employ the diagonal form of the Dirac neutrino mass matrices with
the physical masses as diagonal elements in the hierarchical order. Such choice
has been motivated from the fact that the known CKM angles for the quark
sector, are relatively small. We consider both possibilities where the Dirac
neutrino mass matrix is either the charged lepton or the up-quark mass matrix
within the framework of SO(10) GUT with or without supersymmetry. The non-zero
texture of the right-handed Majorana neutrino mass matrix is used for
the generation of the desired bimaximal mixings in a model independent way.
Both hierarchical and inverted hierarchical models of the left-handed Majorana
neutrino mass matrices are generated and then discussed with examples
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