2,877 research outputs found
Solid weak BCC-algebras
We characterize weak BCC-algebras in which the identity is
satisfied only in the case when elements belong to the same branch
Scattering processes and resonances from lattice QCD
The vast majority of hadrons observed in nature are not stable under the
strong interaction, rather they are resonances whose existence is deduced from
enhancements in the energy dependence of scattering amplitudes. The study of
hadron resonances offers a window into the workings of quantum chromodynamics
(QCD) in the low-energy non-perturbative region, and in addition, many probes
of the limits of the electroweak sector of the Standard Model consider
processes which feature hadron resonances. From a theoretical standpoint, this
is a challenging field: the same dynamics that binds quarks and gluons into
hadron resonances also controls their decay into lighter hadrons, so a complete
approach to QCD is required. Presently, lattice QCD is the only available tool
that provides the required non-perturbative evaluation of hadron observables.
In this article, we review progress in the study of few-hadron reactions in
which resonances and bound-states appear using lattice QCD techniques. We
describe the leading approach which takes advantage of the periodic finite
spatial volume used in lattice QCD calculations to extract scattering
amplitudes from the discrete spectrum of QCD eigenstates in a box. We explain
how from explicit lattice QCD calculations, one can rigorously garner
information about a variety of resonance properties, including their masses,
widths, decay couplings, and form factors. The challenges which currently limit
the field are discussed along with the steps being taken to resolve them
Squeezed correlations of strange particle-antiparticles
Squeezed correlations of hadron-antihadron pairs are predicted to appear if
their masses are modified in the hot and dense medium formed in high energy
heavy ion collisions. If discovered experimentally, they would be an
unequivocal evidence of in-medium mass shift found by means of hadronic probes.
We discuss a method proposed to search for this novel type of correlation,
illustrating it by means of D_s-mesons with in-medium shifted masses. These
particles are expected to be more easily detected and identified in future
upgrades at RHIC.Comment: 6 pages, 3 figures with parts a) and b), SQM 2009 contribution; added
acknowledgmen
Representations of -semigroups by multiplace functions
We describe the representations of -semigroups, i.e. groupoids with
binary associative operations, by partial -place functions and prove
that any such representation is a union of some family of representations
induced by Schein's determining pairs.Comment: 17 page
Representations of Menger -semigroups by multiplace functions
Investigation of partial multiplace functions by algebraic methods plays an
important role in modern mathematics were we consider various operations on
sets of functions, which are naturally defined. The basic operation for
-place functions is an -ary superposition , but there are some
other naturally defined operations, which are also worth of consideration. In
this paper we consider binary Mann's compositions \op{1},...,\op{n} for
partial -place functions, which have many important applications for the
study of binary and -ary operations. We present methods of representations
of such algebras by -place functions and find an abstract characterization
of the set of -place functions closed with respect to the set-theoretic
inclusion
Radiative Transitions in Charmonium from Lattice QCD
Radiative transitions between charmonium states offer an insight into the
internal structure of heavy-quark bound states within QCD. We compute, for the
first time within lattice QCD, the transition form-factors of various
multipolarities between the lightest few charmonium states. In addition, we
compute the experimentally unobservable, but physically interesting vector
form-factors of the and .
To this end we apply an ambitious combination of lattice techniques,
computing three-point functions with heavy domain wall fermions on an
anisotropic lattice within the quenched approximation. With an anisotropy
at we find a reasonable gross spectrum and a
hyperfine splitting , which compares favourably with
other improved actions.
In general, after extrapolation of lattice data at non-zero to the
photopoint, our results agree within errors with all well measured experimental
values. Furthermore, results are compared with the expectations of simple quark
models where we find that many features are in agreement; beyond this we
propose the possibility of constraining such models using our extracted values
of physically unobservable quantities such as the quadrupole moment.
We conclude that our methods are successful and propose to apply them to the
problem of radiative transitions involving hybrid mesons, with the eventual
goal of predicting hybrid meson photoproduction rates at the GlueX experiment.Comment: modified version as publishe
Asymptotic directional structure of radiation for fields of algebraic type D
The directional behavior of dominant components of algebraically special
spin-s fields near a spacelike, timelike or null conformal infinity is studied.
By extending our previous general investigations we concentrate on fields which
admit a pair of equivalent algebraically special null directions, such as the
Petrov type D gravitational fields or algebraically general electromagnetic
fields. We introduce and discuss a canonical choice of the reference tetrad
near infinity in all possible situations, and we present the corresponding
asymptotic directional structures using the most natural parametrizations.Comment: 20 pages, 6 figure
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