3,458 research outputs found
Pure Leptonic Radiative Decays and the Annihilation Graph
Pure leptonic radiative decays of heavy-light mesons are calculated using a
very simple non-relativistic model. Dominant contribution originates from
photon emission from light initial quark. We find
and . The importance of these reactions to
clarify the dynamics of the annihilation graph is emphasized.Comment: 7 pages, LaTeX, 3 figure
CP Nonconservation in
CP violation effects in are examined. CP-odd,
-odd and -even observables can both be used to extract information on
the real and imaginary parts of Feynman amplitudes. Two Higgs doublet model
with CP violating phase from neutral Higgs exchange is used to estimate
possible effects.Comment: 9 pages, 4 Figures, Late
Bounds on charged higgs boson in the 2HDM type III from Tevatron
We consider the Two Higgs Doublet Model (2HDM) of type III which leads to
Flavour Changing Neutral Currents (FCNC) at tree level. In the framework of
this model we can use an appropriate form of the Yukawa Lagrangian that makes
the type II model limit of the general type III couplings apparent. This way is
useful in order to compare with the experimental data which is model dependent.
The analytical expressions of the partial width are
derived and we compare with the data available at this energy range. We examine
the limits on the new parameters from the validness of
perturbation theory.Comment: 14 pages, 4 figures, Universidad Nacional de Colombia. typos
correcte
Increased Productivity of a Cover Crop Mixture Is Not Associated with Enhanced Agroecosystem Services
Cover crops provide a variety of important agroecological services within cropping systems. Typically these crops are grown as monocultures or simple graminoid-legume bicultures; however, ecological theory and empirical evidence suggest that agroecosystem services could be enhanced by growing cover crops in species-rich mixtures. We examined cover crop productivity, weed suppression, stability, and carryover effects to a subsequent cash crop in an experiment involving a five-species annual cover crop mixture and the component species grown as monocultures in SE New Hampshire, USA in 2011 and 2012. The mean land equivalent ratio (LER) for the mixture exceeded 1.0 in both years, indicating that the mixture over-yielded relative to the monocultures. Despite the apparent over-yielding in the mixture, we observed no enhancement in weed suppression, biomass stability, or productivity of a subsequent oat (Avena sativa L.) cash crop when compared to the best monoculture component crop. These data are some of the first to include application of the LER to an analysis of a cover crop mixture and contribute to the growing literature on the agroecological effects of cover crop diversity in cropping systems
Transverse Tau Polarization in Decays of the Top and Bottom Quarks in the Weinberg Model of CP Non-conservation
We show that the transverse polarization asymmetry of the -lepton in
the decay is extremely sensitive to CP violating
phases arising from the charged Higgs exchange in the Weinberg model of CP
non-conservation. Qualitatively, the polarization asymmetries are enhanced over
rate or energy asymmetries by a factor of . Thus for optimal values of the parameters the method requires top pairs to be observable rather than needed for rate or energy
asymmetries. We also examine polarization in b decays via and find that it can also be very effective in constraining the CP
violation parameters of the extended Higgs sector.Comment: 11,1 figure, SLAC-PUB-608
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LENS® and SFF: Enabling Technologies for Optimized Structures
Optimized, lightweight, high-strength structures are needed in many applications from aerospace
to automotive. In pursuit of such structures, there have been proposed analytical solutions and
some specialized FEA solutions for specific structures such as automobile frames. However,
generalized 3D optimization methods have been unavailable for use by most designers.
Moreover, in the cases where optimized structural solutions are available, they are often hollow,
curving, thin wall structures that cannot be fabricated by conventional manufacturing methods.
Researchers at Sandia National Laboratories and the University of Rhode Island teamed to solve
these problems. The team has been pursuing two methods of optimizing models for generalized
loading conditions, and also has been investigating the methods needed to fabricate these
structures using Laser Engineered Net Shaping™ (LENS®) and other rapid prototyping
methods. These solid freeform fabrication (SFF) methods offer the unique ability to make
hollow, high aspect ratio features out of many materials. The manufacturing development
required for LENS to make these complex structures has included the addition of rotational axes
to Sandia’s LENS machine bringing the total to 5 controlled axes. The additional axes have
required new efforts in process planning. Several of the unique structures that are only now
possible through the use of SFF technology are shown as part of the discussion of this exciting
new application for SFF.Mechanical Engineerin
Two body decays of the -quark: Applications to direct CP violation, searches for electro-weak penguins and new physics
A systematic experimental search for two-body hadronic decays of the b-quark
of the type b to quark + meson is proposed. These reactions have a well defined
experimental signature and they should be theoretically cleaner compared to
exclusive decays. Many modes have appreciable branching ratios and partial rate
asymmetries may also be quite large (about 8-50%) in several of them. In a few
cases electroweak penguins appear to be dominant and may be measurable. CP
violating triple correlation asymmetries provide a clean test of the Standard
Model.Comment: 12 pages 1 figure 1 tabl
CP Nonconservation in at the Tevatron
The reaction is found to be rather rich in exhibiting
several different types of CP asymmetries. The spin of the top quark plays an
important role. Asymmetries are related to form factors arising from radiative
corrections of the production vertex due to non-standard physics. As
illustrations, effects are studied in two Higgs Doublet Models and in
Supersymmetric Models; asymmetries up to a few percent may be possible.Comment: 14 pages, 3 figures. Note: replaced due to minor problems that
appeared on some postscript previewers. No change in conten
Lepton Flavor Violation in the Two Higgs Doublet Model type III
We consider the Two Higgs Doublet Model (2HDM) of type III which leads to
Flavour Changing Neutral Currents (FCNC) at tree level in the leptonic sector.
In the framework of this model we can have, in principle, two situations: the
case (a) when both doublets acquire a vacuum expectation value different from
zero and the case (b) when only one of them is not zero. In addition, we show
that we can make two types of rotations for the flavor mixing matrices which
generates four types of lagrangians, with the rotation of type I we recover the
case (b) from the case (a) in the limit , and with the
rotation of type II we obtain the case (b) from (a) in the limit Moreover, two of the four possible lagrangians correspond to the models
of types I and II plus Flavor Changing (FC) interactions. The analitical
expressions of the partial lepton number violating widths and are derived for the cases (a) and (b) and both
types of rotations.In all cases these widths go asymptotically to zero in
the decoupling limit for all Higgses. We present from our analysis upper bounds
for the flavour changing transition and we show that such bounds
are sensitive to the VEV structure and the type of rotation utilized.Comment: 7 pages RevTeX4, 4 figures postscript, new section added and some new
reference
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