1,751 research outputs found
An Adult with Episodic Abnormal Limb Posturing
info:eu-repo/semantics/publishedVersio
Covariant spectator theory of quark-antiquark bound states: Mass spectra and vertex functions of heavy and heavy-light mesons
We use the covariant spectator theory with an effective quark-antiquark
interaction, containing Lorentz scalar, pseudoscalar, and vector contributions,
to calculate the masses and vertex functions of, simultaneously, heavy and
heavy-light mesons. We perform least-square fits of the model parameters,
including the quark masses, to the meson spectrum and systematically study the
sensitivity of the parameters with respect to different sets of fitted data. We
investigate the influence of the vector confining interaction by using a
continuous parameter controlling its weight. We find that vector contributions
to the confining interaction between 0% and about 30% lead to essentially the
same agreement with the data. Similarly, the light quark masses are not very
tightly constrained. In all cases, the meson mass spectra calculated with our
fitted models agree very well with the experimental data. We also calculate the
mesons wave functions in a partial wave representation and show how they are
related to the meson vertex functions in covariant form.Comment: 23 pages, 10 figures. Minor corrections of previous version. To be
published in Phys. Rev.
Singularity-free two-body equation with confining interactions in momentum space
We are developing a covariant model for all mesons that can be described as
quark-antiquark bound states in the framework of the Covariant Spectator Theory
(CST) in Minkowski space. The kernel of the bound-state equation contains a
relativistic generalization of a linear confining potential which is singular
in momentum space and makes its numerical solution more difficult. The same
type of singularity is present in the momentum-space Schr\"odinger equation,
which is obtained in the nonrelativistic limit. We present an alternative,
singularity-free form of the momentum-space Schr\"odinger equation which is
much easier to solve numerically and which yields accurate and stable results.
The same method will be applied to the numerical solution of the CST
bound-state equations.Comment: 4 pages, 2 figures, talk presented at the 22nd European Conference on
Few-Body Problems in Physics (EFB22), Krakow, Poland, 9 - 13 September 201
Application of the Covariant Spectator Theory to the study of heavy and heavy-light mesons
As an application of the Covariant Spectator Theory (CST) we calculate the
spectrum of heavy-light and heavy-heavy mesons using covariant versions of a
linear confining potential, a one- gluon exchange, and a constant interaction.
The CST equations possess the correct one-body limit and are therefore
well-suited to describe mesons in which one quark is much heavier than the
other. We find a good fit to the mass spectrum of heavy-light and heavy-heavy
mesons with just three parameters (apart from the quark masses). Remarkably,
the fit parameters are nearly unchanged when we fit to experimental
pseudoscalar states only or to the whole spectrum. Because pseudoscalar states
are insensitive to spin-orbit interactions and do not determine spin-spin
interactions separately from central interactions, this result suggests that it
is the covariance of the kernel that correctly predicts the spin-dependent
quark-antiquark interaction
A covariant constituent-quark formalism for mesons
Using the framework of the Covariant Spectator Theory (CST) [1] we are
developing a covariant model formulated in Minkowski space to study mesonic
structure and spectra. Treating mesons as effective states, we
focused in [2] on the nonrelativistic bound-state problem in momentum space
with a linear confining potential. Although integrable, this kernel has
singularities which are difficult to handle numerically. In [2] we reformulate
it into a form in which all singularities are explicitely removed. The
resulting equations are then easier to solve and yield accurate and stable
solutions. In the present work, the same method is applied to the relativistic
case, improving upon the results of the one-channel spectator equation (1CSE)
given in [3].Comment: 6 pages, 5 figures, Presented at EEF70, Workshop on Unquenched Hadron
Spectroscopy: Non-Perturbative Models and Methods of QCD vs. Experimen
Adaptive multi-agent system for a washing machine production line
This paper describes the implementation of a multi-agent system in a real industrial washing machine production line aiming to integrate process and quality control, allowing the establishment of feedback control loops to support adaptation facing condition changes. For this purpose, the agent-based solution was implemented using the JADE framework, being the shared knowledge structured using a proper ontology, edited and validated in Protégé and posteriorly integrated in the multi-agent system. The solution was intensively tested using historical real production data and it is now being installed in the real production line. The preliminary results confirm the initial expectations in terms of improvement of process performance and product quality
Effects of Merging Digital Elevation Models on Flood Modelling Results
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive
Relativistic phenomenology of meson spectra with a covariant quark model in Minkowski space
In this work, we perform a covariant treatment of quark-antiquark systems. We
calculate the spectra and wave functions using a formalism based on the
Covariant Spectator Theory (CST). Our results not only reproduce very well the
experimental data with a very small set of global parameters, but they also
allow a direct test of the predictive power of covariant kernels
Quarkonia and heavy-light mesons in a covariant quark model
Preliminary calculations using the Covariant Spectator Theory (CST) employed
a scalar linear confining interaction and an additional constant vector
potential to compute the mesonic mass spectra. In this work we generalize the
confining interaction to include more general structures, in particular a
vector and also a pseudoscalar part, as suggested by a recent study. A
one-gluon-exchange kernel is also implemented to describe the short-range part
of the interaction. We solve the simplest CST approximation to the complete
Bethe-Salpeter equation, the one-channel spectator equation, using a numerical
technique that eliminates all singularities from the kernel. The parameters of
the model are determined through a fit to the experimental pseudoscalar meson
spectra, with a good agreement for both quarkonia and heavy-light states.Comment: 4 pages, 2 figures; 21st International Conference on Few-Body
Problems in Physics, May 18 - 22, 2015, Chicago, US
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