9,325 research outputs found
Higgs boson of mass 125 GeV in GMSB models with messenger-matter mixing
We investigate the effects of messenger-matter mixing on the lightest CP-even
Higgs boson mass m_h in gauge-mediated supersymmetry breaking models. It is
shown that with such mixings m_h can be raised to about 125 GeV, even when the
superparticles have sub-TeV masses, and when the gravitino has a cosmologically
preferred sub-keV mass. In minimal gauge mediation without messenger-matter
mixing, realizing m_h = 125 GeV would require multi-TeV SUSY spectrum. The
increase in due to messenger-matter mixing is maximal in the case of
messengers belonging to 10+\bar{10} of SU(5) unification, while it is still
significant when they belong to of SU(5). Our results are
compatible with gauge coupling unification, perturbativity, and the unification
of messenger Yukawa couplings. We embed these models into a grand unification
framework with a U(1) flavor symmetry that addresses the fermion mass hierarchy
and generates naturally large neutrino mixing angles. While SUSY mediated
flavor changing processes are sufficiently suppressed in such an embedding,
small new contributions to K^0-\bar{K^0} mixing can resolve the apparent
discrepancy in the CP asymmetry parameters \sin2\beta and \epsilon_K.Comment: 31 pages, LaTe
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
Model for Small neutrino masses at the TeV Scale
We propose a model for neutrino mass generation in wich no physics beyond a
TeV is required. We extend the standard model by adding two charged singlet
fields with lepton number two. Dirac neutrino masses are
generated at the one loop level. Small left handed majorana neutrino masses can
be generated via the seesaw mechanism with right handed neutrino masses
are of order TeV scale.Comment: 13 pages, 2 figure
Flavor Gauge Models Below the Fermi Scale
The mass and weak interaction eigenstates for the quarks of the third
generation are very well aligned, an empirical fact for which the Standard
Model offers no explanation. We explore the possibility that this alignment is
due to an additional gauge symmetry in the third generation. Specifically, we
construct and analyze an explicit, renormalizable model with a gauge boson,
, corresponding to the symmetry of the third family. Having a
relatively light (in the MeV to multi-GeV range), flavor-nonuniversal gauge
boson results in a variety of constraints from different sources. By
systematically analyzing 20 different constraints, we identify the most
sensitive probes: kaon, , and Upsilon decays, mixing,
atomic parity violation, and neutrino scattering and oscillations. For the new
gauge coupling in the range the model is shown to
be consistent with the data. Possible ways of testing the model in physics,
top and decays, direct collider production and neutrino oscillation
experiments, where one can observe nonstandard matter effects, are outlined.
The choice of leptons to carry the new force is ambiguous, resulting in
additional phenomenological implications, such as non-universality in
semileptonic bottom decays. The proposed framework provides interesting
connections between neutrino oscillations, flavor and collider physics.Comment: 44 pages, 7 figures, 3 tables; B physics constraints and references
added, conclusions unchange
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
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
Evaluation of the effectiveness of seminar as an educational tool among the medical post graduate students
Background: The departments of medical colleges have a greater responsibility in making the study methods of their subject innovative, interesting and participatory for the post graduate students. One such method adopted is organizing seminars for the post graduate students. The post graduate education depends on self-learning. Knowledge acquisition through seminars forms an essential part of their training programme.Methods: This study assesses the role of seminar as teaching-learning tool by recording the perception of post graduates on seminars through a questionnaire based survey.Results: The scores for most of the items of a twenty point questionnaire were above three indicating the learning from seminar is satisfactory. Seminar methods of teaching-learning, in contrast to the traditional didactic class room lecture method, is more effective way of learning, which is relevant to self-development and is also interactive. This method provokes discussions and debates which help post graduate students to voice their opinion and clear their doubts. Conclusions: Many of the post graduate students feel that this technique of seminar programme is useful amidst some suggestions to improve quality. Thus the post graduate seminar method is a teaching-learning method that covers the three major domains of teaching i.e., cognitive, affective and psychomotor skills and is thus effective and well -accepted among the post graduate students.
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