353 research outputs found
Consistent treatment for valence and nonvalence configurations in semileptonic weak deacys
We discuss the semileptonic weak decays of ( denotes a
pseudoscalar meson). In these timelike processes, the problem of the nonvalence
contribution is solved systematically as well as the valence one. These
contributions are related to the light-front quark model (LFQM), and the
numerical results show the nonvalence contribution of the light-to-light
transition is larger than of the heavy-to-light one. In addition, the relevant
CKM matrix elements are calculated. They are consistent with the data of
Particle Data Group.Comment: 14 pages, 5 figures, revised versio
Electromagnetic form factor of the pion in the space- and time-like regions within the front-form dynamics
The pion electromagnetic form factor is calculated in the space- and
time-like regions from -10 up to 10 , within a
front-form model. The dressed photon vertex where a photon decays in a
quark-antiquark pair is depicted generalizing the vector meson dominance
ansatz, by means of the vector meson vertex functions. An important feature of
our model is the description of the on-mass-shell vertex functions in the
valence sector, for the pion and the vector mesons, through the front-form wave
functions obtained within a realistic quark model. The theoretical results show
an excellent agreement with the data in the space-like region, while in the
time-like region the description is quite encouraging.Comment: 9 pages + 4 figures. To appear in Phys. Lett.
Lifetimes of the b-flavored baryons in the light-front quark model
The calculation of lifetimes of heavy-flavored baryons in the light-front
quark model approach is briefly reviewed.Comment: 4 pages, proceedings of the IV International Conference on Hyperons,
Charm and Beauty Hadrons, Valencia, June 27--30, 200
Hard Constituent Quarks and Electroweak Properties of Pseudoscalar Mesons
The high momentum components generated in the wave function of pseudoscalar
mes* by the one-gluon-exchange interaction are investigated within a
relativistic constituent quark model. Adopting the light-cone formalism, the
sensitivity of the weak decay constant and the charge form factor to hard
constituent quarks is illustrated.Comment: 11 pages and 5 figs. (to be requested), LaTeX, INFN-ISS 94/3. To
appear in Physics Lett.
New effective treatment of the light-front nonvalence contribution in timelike exclusive processes
We discuss a necessary nonvalence contribution in timelike exclusive
processes. Following a Schwinger-Dyson type of approach, we relate the
nonvalence contribution to an ordinary light-front wave function that has been
extensively tested in the spacelike exclusive processes. A complicate four-body
energy denominator is exactly cancelled in summing the light-front time-ordered
amplitudes. Applying our method to and
where a rather substantial nonvalence contribution is expected, we find not
only an improvement in comparing with the experimental data but also a
covariance(i.e. frame-independence) of existing light-front constituent quark
model.Comment: 10 pages including 5 figures; Changes: 1-added some sentences;
2-enlarged the figures; 3-added some reference
Panoramic Panoptic Segmentation: Insights Into Surrounding Parsing for Mobile Agents via Unsupervised Contrastive Learning
In this work, we introduce panoramic panoptic segmentation, as the most
holistic scene understanding, both in terms of Field of View (FoV) and
image-level understanding for standard camera-based input. A complete
surrounding understanding provides a maximum of information to a mobile agent.
This is essential information for any intelligent vehicle to make informed
decisions in a safety-critical dynamic environment such as real-world traffic.
In order to overcome the lack of annotated panoramic images, we propose a
framework which allows model training on standard pinhole images and transfers
the learned features to the panoramic domain in a cost-minimizing way. The
domain shift from pinhole to panoramic images is non-trivial as large objects
and surfaces are heavily distorted close to the image border regions and look
different across the two domains. Using our proposed method with dense
contrastive learning, we manage to achieve significant improvements over a
non-adapted approach. Depending on the efficient panoptic segmentation
architecture, we can improve 3.5-6.5% measured in Panoptic Quality (PQ) over
non-adapted models on our established Wild Panoramic Panoptic Segmentation
(WildPPS) dataset. Furthermore, our efficient framework does not need access to
the images of the target domain, making it a feasible domain generalization
approach suitable for a limited hardware setting. As additional contributions,
we publish WildPPS: The first panoramic panoptic image dataset to foster
progress in surrounding perception and explore a novel training procedure
combining supervised and contrastive training.Comment: Accepted to IEEE Transactions on Intelligent Transportation Systems
(T-ITS). Extended version of arXiv:2103.00868. The project is at
https://github.com/alexanderjaus/PP
Exploring the timelike region for the elastic form factor in the light-front quantization
Even though the Drell-Yan-West formulation is the most rigorous and
well-established framework to compute the exclusive processes, its utility has
been limited only to the spacelike region because of the intrinsic kinematic
constraint . We present an explicit example demonstrating how one may
obtain the necessary information (i.e. nonvalence or so called Z-graph
contribution) in the timelike region of exclusive process without encountering
a formidable task of direct calculation that has hindered so far the progress
in this area. In the analysis of bound state form factors using an
exactly solvable model of dimensional scalar field theory interacting
with gauge fields, the results analytically continued from the spacelike region
coincide exactly with the direct results in the timelike region. This example
verifies that the method of analytic continuation is capable of yielding the
effect of complicate nonvalence contributions. The meson peaks analogous to the
vector meson dominance(VMD) phenomena are also generated at the usual VMD
positions.Comment: 21 pages, 8 figures, we changed the title, added some references and
included some paragraphs in the introduction and conclusions; version to
appear in Nucl. Phys.
Lepton polarization and CP-violating effects in "B -> K^* tau^+ tau^-" decay in standard and two Higgs doublet models
The most general model independent expressions for the CP-violating
asymmetry, longitudinal, transversal and normal polarizations of leptons are
derived. Application of these general results to the concrete models such as
Standard model and three different types of two Higgs doublet model is
discussed.Comment: 18 pages, 8 postscripted figure
Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit: Covariant Quark Model Approach
We prove the full covariance of the heavy-to-light weak current matrix
elements based on the Bakamjian-Thomas construction of relativistic quark
models, in the heavy mass limit for the parent hadron and the large energy
limit for the daughter one. Moreover, this quark model representation of the
heavy-to-light form factors fulfills the general relations that were recently
argued to hold in the corresponding limit of QCD, namely that there are only
three independent form factors describing the B -> pi (rho) matrix elements, as
well as the factorized scaling law sqrt(M)z(E) of the form factors with respect
to the heavy mass M and large energy E. These results constitute another good
property of the quark models \`a la Bakamjian-Thomas, which were previously
shown to exhibit covariance and Isgur-Wise scaling in the heavy-to-heavy case.Comment: 11 pages, LaTex2e, no figur
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