6,990 research outputs found
Collective treatment of High Energy Thresholds in SUSY - GUTs
Supersymmetric GUTs are the most natural extension of the Standard model
unifying electroweak and strong forces. Despite their indubitable virtues,
among these the gauge coupling unification and the quantization of the electric
charge, one of their shortcomings is the large number of parameters used to
describe the high energy thresholds (HET), which are hard to handle. We present
a new method according to which the effects of the HET, in any GUT model, can
be described by fewer parameters that are randomly produced from the original
set of the parameters of the model. In this way, regions favoured by the
experimental data are easier to locate, avoiding a detailed and time consuming
exploration of the parameter space, which is multidimensional even in the most
economic unifying schemes. To check the efficiency of this method, we directly
apply it to a SUSY SO(10) GUT model in which the doublet-triplet splitting is
realized through the Dimopoulos-Wilczek mechanism. We show that the demand of
gauge coupling unification, in conjunction with precision data, locates regions
of the parameter space in which values of the strong coupling \astrong are
within the experimental limits, along with a suppressed nucleon decay, mediated
by a higgsino driven dimension five operators, yielding lifetimes that are
comfortably above the current experimental bounds. These regions open up for
values of the SUSY breaking parameters m_0, M_1/2 < 1 TeV being therefore
accessible to LHC.Comment: 21 pages, 8 figures, UA-NPPS/BSM-10/02 (added
Pure Gravity Mediation and Spontaneous B-L Breaking from Strong Dynamics
In pure gravity mediation (PGM), the most minimal scheme for the mediation of
supersymmetry (SUSY) breaking to the visible sector, soft masses for the
standard model gauginos are generated at one loop rather than via direct
couplings to the SUSY-breaking field. In any concrete implementation of PGM,
the SUSY-breaking field is therefore required to carry nonzero charge under
some global or local symmetry. As we point out in this note, a prime candidate
for such a symmetry might be B-L, the Abelian gauge symmetry associated with
the difference between baryon number B and lepton number L. The F-term of the
SUSY-breaking field then not only breaks SUSY, but also B-L, which relates the
respective spontaneous breaking of SUSY and B-L at a fundamental level. As a
particularly interesting consequence, we find that the heavy Majorana neutrino
mass scale ends up being tied to the gravitino mass, Lambda_N ~ m_3/2. Assuming
nonthermal leptogenesis to be responsible for the generation of the baryon
asymmetry of the universe, this connection may then explain why SUSY
necessarily needs to be broken at a rather high energy scale, so that m_3/2 >~
1000 TeV in accord with the concept of PGM. We illustrate our idea by means of
a minimal model of dynamical SUSY breaking, in which B-L is identified as a
weakly gauged flavor symmetry. We also discuss the effect of the B-L gauge
dynamics on the superparticle mass spectrum as well as the resulting
constraints on the parameter space of our model. In particular, we comment on
the role of the B-L D-term.Comment: 25 pages, 1 figur
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
Thermal buckling analysis of skew fibre-reinforced composite and sandwich plates using shear deformable finite element models
The paper considers the elastic buckling of skew fibre-reinforced composite and sandwich plates subjected to thermal loads. To the best of the authors' knowledge, there is no paper in the open literature on this subject and the present paper attempts to fill this gap. Two shear deformable finite element models, one based on first-order shear deformation theory and the other based on higher-order shear deformation theory, are employed to obtain thermal buckling solutions. Extensive numerical results are presented for both thin and thick laminated composite plates with various skew angles, lamination parameters and boundary conditions. A few results for skew sandwiches are obtained for various geometric parameters and skew angles. Results presented, not available so far, could be useful to designers and researchers who may use them as benchmark values to validate their numerical techniques and software for similar problems
Influence of a fish bacterium Lactobacillus sp. on the production of swordtail xiphophorus helleri (Heckel 1848)
The influence of a fish gut bacterium Lactobacillus sp on the production of swordtail Xiphophorus helleri was studied for a period of one year. The Lactobacillus sp P21 produced bacteriocin-like inhibitory substance and exhibited wide spectrum of action against Aeromonas hydrophila, Bacillus spp, Pseudomonas spp and Citrobacter freundi in vitro. The growth performance of X. helleri reared in the presence of Lactobacillus P21 at 106/ml rearing water was better than the control. The total plate counts, total MRS agar counts and the counts of motile aeromonads, presumptive pseudomonads, lactose fermenters and lactose non-fermenters in the gut of probiotic group were comparatively low than the control. On day 60 the count of Lactobacillus sp P21 was observed to be log 5.28/g in the gut of X. helleri indicating colonization of this bacterium in the gastrointestinal tract. The fecundity of X. helleri was in the range of 9-134. On average, it produced from 39.42±18.72 fry/female in control group to 53.00±23.57 fry/female in probiotic group. The increase in average fecundity in probiotic group over the control group was about 25%. There existed significant difference between probiotic group and control in respect of average fecundity/female (p<0.02), average number of fry survived /female (p<0.006) and average number of fry dead/female (p<0.029). The results of the present study demonstrated that the rearing of X. helleri in probiotic-enriched water have growth inducing ability and favourably influenced the reproductive performance in terms of high fecundity, high fry survival, reduced fry mortality and reduced fry deformity
Recent direct measurement of the Top quark mass and quasi-infrared fixed point
We note that the recent direct measurement of the top quark mass at by D0 collaboration severely constrains the
theoretically attractive infra-red fixed point scenario of the top quark Yukawa
coupling in supersymmetric GUTs. For one-step unified models the above
mentioned measurement bounds the arbitrary but experimentally determinable
parameter to the range . Further
crunch on the top quark mass may determine even more accurately
within the fixed point scenario. On the other hand an experimental value of
will rule out the fixed point scenario bounding
to 0.022 from above.Comment: 7 pages, Latex with epsf style, 1 figure, captions.st
New Lepton Family Symmetry and Neutrino Tribimaximal Mixing
The newly proposed finite symmetry Sigma(81) is applied to the problem of
neutrino tribimaximal mixing. The result is more satisfactory than those of
previous models based on A_4 in that the use of auxiliary symmetries (or
mechanisms) may be avoided. Deviations from the tribimaximal pattern are
expected, but because of its basic structure, only tan^2 (theta_12) may differ
significantly from 0.5 (say 0.45) with sin^2 (2 theta_23) remaining very close
to one, and theta_13 very nearly zero.Comment: 8 pages, no figur
Natural Gauge Hierarchy in SO(10)
It is shown that a natural gauge hierarchy and doublet-triplet splitting can
be achieved in SO(10) using the Dimopoulos-Wilczek mechanism. Artificial
cancellations (fine-tuning) and arbitrary forms of the superpotential are
avoided, the superpotential being the most general compatible with a symmetry.
It is shown by example that the Dimopoulos-Wilczek mechanism can be protected
against the effects of higher-dimension operators possibly induced by
Planck-scale physics. Natural implementation of the mechanism leads to an
automatic Peccei-Quinn symmetry. The same local symmetries that would protect
the gauge hierarchy against Planck-scale effects tend to protect the axion
also. It is shown how realistic quark and lepton masses might arise in this
framework. It is also argued that ``weak suppression'' of proton decay can be
implemented more economically than can ``strong suppression'', offering some
grounds to hope (in the context of SO(10)) that proton decay could be seen at
Superkamiokande.Comment: 26 pages in plain LaTeX, 5 figures available on request, BA-94-0
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