2,139 research outputs found
Proton mass effects in wide-angle Compton scattering
We investigate proton mass effects in the handbag approach to wide-angle
Compton scattering. We find that theoretical uncertainties due to the proton
mass are significant for photon energies presently studied at Jefferson Lab.
With the proposed energy upgrade such uncertainties will be clearly reduced.Comment: 4 pages, uses revtex, 3 figure
Decays of and into vector and pseudoscalar meson and the pseudoscalar glueball- mixing
We introduce a parametrization scheme for where
the effects of SU(3) flavor symmetry breaking and doubly OZI-rule violation
(DOZI) can be parametrized by certain parameters with explicit physical
interpretations. This scheme can be used to clarify the glueball-
mixing within the pseudoscalar mesons. We also include the contributions from
the electromagnetic (EM) decays of and via
. Via study of the isospin violated
channels, such as , ,
and , reasonable constraints on the EM decay
contributions are obtained. With the up-to-date experimental data for
, and , etc, we arrive at a consistent description of the mentioned
processes with a minimal set of parameters. As a consequence, we find that
there exists an overall suppression of the form factors,
which sheds some light on the long-standing " puzzle". By determining
the glueball components inside the pseudoscalar and in
three different glueball- mixing schemes, we deduce that the lowest
pseudoscalar glueball, if exists, has rather small component, and it
makes the a preferable candidate for glueball.Comment: Revised version to appear on J. Phys. G; An error in the code was
corrected. There's slight change to the numerical results, while the
conclusion is intac
Partition Function Zeros of a Restricted Potts Model on Lattice Strips and Effects of Boundary Conditions
We calculate the partition function of the -state Potts model
exactly for strips of the square and triangular lattices of various widths
and arbitrarily great lengths , with a variety of boundary
conditions, and with and restricted to satisfy conditions corresponding
to the ferromagnetic phase transition on the associated two-dimensional
lattices. From these calculations, in the limit , we determine
the continuous accumulation loci of the partition function zeros in
the and planes. Strips of the honeycomb lattice are also considered. We
discuss some general features of these loci.Comment: 12 pages, 12 figure
Mirror matter admixtures in K_L \to \gamma\gamma
Based on possible albeit tiny, admixtures of mirror matter in ordinary mesons
we study the K_L \to \gamma\gamma transition. We find that this process can be
described with a small SU(3) symmetry breaking of only 3%. We also determine
the eta-eta' mixing angle and the pseudoscalar decay constants. The results for
these parameters are consistent with some obtained in the literature. They
favor two recent determinations; one based on two analytical constraints, and
another one based on next-to-leading order power corrections
Choice of steel material for bridge bearings to avoid brittle fracture
Bridge bearings need verification against brittle failure at low temperatures. The design of bearings according to EN 1337 may lead to structural components with thicknesses no longer covered in the relevant technical construction regulations. Due to its specific geometry, the loading and stressing and the fabrication process the prerequisites for using the rules in EN 1993 1 10 lead to conservative restrictions or uneconomical choice of steel material. For an economical bearing design further modifications of the existing rules are necessary. This report adapts the fracture mechanical approach used in EN 1993 1 10 and gives information for a âsafe-sidedâ choice of steel material for bearings. The main modifications refer to the hypothetical design crack scenario and the definition of the ânominal design stressâ at the geometric âhot-spotâ. An advanced methodology using Finite Elements and a simplified method using linear bending theory are evaluated.JRC.G.5-European laboratory for structural assessmen
Characterising New Physics Models by Effective Dimensionality of Parameter Space
We show that the dimension of the geometric shape formed by the
phenomenologically valid points inside a multi-dimensional parameter space can
be used to characterise different new physics models and to define a
quantitative measure for the distribution of the points. We explain a simple
algorithm to determine the box-counting dimension from a given set of parameter
points, and illustrate our method with examples from different models that have
recently been studied with respect to precision flavour observables.Comment: 14 pages, 8 figure
Intersubband gain in a Bloch oscillator and Quantum cascade laser
The link between the inversion gain of quantum cascade structures and the
Bloch gain in periodic superlattices is presented. The proposed theoretical
model based on the density matrix formalism is able to treat the gain mechanism
of the Bloch oscillator and Quantum cascade laser on the same footing by taking
into account in-plane momentum relaxation. The model predicts a dispersive
contribution in addition to the (usual) population-inversion-dependent
intersubband gain in quantum cascade structures and - in the absence of
inversion - provides the quantum mechanical description for the dispersive gain
in superlattices. It corroborates the predictions of the semi-classical
miniband picture, according to which gain is predicted for photon energies
lower than the Bloch oscillation frequency, whereas net absorption is expected
at higher photon energies, as a description which is valid in the
high-temperature limit. A red-shift of the amplified emission with respect to
the resonant transition energy results from the dispersive gain contribution in
any intersubband transition, for which the population inversion is small.Comment: 10 pages, 6 figure
Spectral Function of 2D Fermi Liquids
We show that the spectral function for single-particle excitations in a
two-dimensional Fermi liquid has Lorentzian shape in the low energy limit.
Landau quasi-particles have a uniquely defined spectral weight and a decay rate
which is much smaller than the quasi-particle energy. By contrast, perturbation
theory and the T-matrix approximation yield spurious deviations from Fermi
liquid behavior, which are particularly pronounced for a linearized dispersion
relation.Comment: 6 pages, LaTeX2e, 5 EPS figure
Flavor SU(3) symmetry and QCD factorization in and decays
Using flavor SU(3) symmetry, we perform a model-independent analysis of
charmless decays. All the relevant
topological diagrams, including the presumably subleading diagrams, such as the
QCD- and EW-penguin exchange diagrams and flavor-singlet weak annihilation
ones, are introduced. Indeed, the QCD-penguin exchange diagram turns out to be
important in understanding the data for penguin-dominated decay modes. In this
work we make efforts to bridge the (model-independent but less quantitative)
topological diagram or flavor SU(3) approach and the (quantitative but somewhat
model-dependent) QCD factorization (QCDF) approach in these decays, by
explicitly showing how to translate each flavor SU(3) amplitude into the
corresponding terms in the QCDF framework. After estimating each flavor SU(3)
amplitude numerically using QCDF, we discuss various physical consequences,
including SU(3) breaking effects and some useful SU(3) relations among decay
amplitudes of and .Comment: 47 pages, 3 figures, 28 table
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