544 research outputs found
Towards an improved understanding of eta --> gamma^* gamma^*
We argue that high-quality data on the reaction
will allow one to determine the double off-shell form factor in a model-independent way with controlled accuracy. This is
an important step towards a reliable evaluation of the hadronic light-by-light
scattering contribution to the anomalous magnetic moment of the muon. When
analyzing the existing data for in the range of
total energies , we demonstrate that the
double off-shell form factor is
consistent with the commonly employed factorization ansatz at least for
, if the effect of the meson is taken into account.
However, better data are needed to draw firm conclusions.Comment: 7 pages, 3 figure
Investigation of a0-f0 mixing
We investigate the isospin-violating mixing of the light scalar mesons
a0(980) and f0(980) within the unitarized chiral approach. Isospin-violating
effects are considered to leading order in the quark mass differences and
electromagnetism. In this approach both mesons are generated through
meson-meson dynamics. Our results provide a description of the mixing
phenomenon within a framework consistent with chiral symmetry and unitarity,
where these resonances are not predominantly q q-bar states. Amongst the
possible experimental signals, we discuss observable consequences for the
reaction J/Psi -> phi pi0 eta in detail. In particular we demonstrate that the
effect of a0-f0 mixing is by far the most important isospin-breaking effect in
the resonance region and can indeed be extracted from experiment.Comment: 15 pages, 9 figures; discussion extended, title changed, version
published in Phys. Rev.
Efficient and realistic device modeling from atomic detail to the nanoscale
As semiconductor devices scale to new dimensions, the materials and designs
become more dependent on atomic details. NEMO5 is a nanoelectronics modeling
package designed for comprehending the critical multi-scale, multi-physics
phenomena through efficient computational approaches and quantitatively
modeling new generations of nanoelectronic devices as well as predicting novel
device architectures and phenomena. This article seeks to provide updates on
the current status of the tool and new functionality, including advances in
quantum transport simulations and with materials such as metals, topological
insulators, and piezoelectrics.Comment: 10 pages, 12 figure
Instant Two-Body Equation in Breit Frame
A quasipotential formalism for elastic scattering from relativistic bound
states is based on applying an instant constraint to both initial and final
states in the Breit frame. This formalism is advantageous for the analysis of
electromagnetic interactions because current conservation and four momentum
conservation are realized within a three-dimensional formalism. Wave functions
are required in a frame where the total momentum is nonzero, which means that
the usual partial wave analysis is inapplicable. In this work, the
three-dimensional equation is solved numerically, taking into account the
relevant symmetries. A dynamical boost of the interaction also is needed for
the instant formalism, which in general requires that the boosted interaction
be defined as the solution of a four-dimensional equation. For the case of a
scalar separable interaction, this equation is solved and the Lorentz
invariance of the three-dimensional formulation using the boosted interaction
is verified. For more realistic interactions, a simple approximation is used to
characterize the boost of the interaction.Comment: 20 pages in revtex 3, 3 figures. Fixed reform/tex errors
Parametrization of Realistic Bethe-Salpeter Amplitude for the Deuteron
The parametrization of the realistic Bethe-Salpeter amplitude for the
deuteron is given. Eight components of the amplitude in the Euclidean space are
presented as an analytical fit to the numerical solution of the Bethe-Salpeter
equation in the ladder approximation. An applicability of the parametrization
to the observables of the deuteron is briefly discussed.Comment: LaTeX, 11 pages, 2 Postscript figures; Text of the Fortran program is
available from the author by reques
Baryon magnetic moments and sigma terms in lattice-regularized chiral perturbation theory
An SU(3) chiral Lagrangian for the lightest decuplet of baryons is
constructed on a discrete lattice of spacetime points, and is added to an
existing lattice Lagrangian for the lightest octets of mesons and baryons. A
nonzero lattice spacing renders all loop integrations finite, and the continuum
limit of any physical observable is identical to the result obtained from
dimensional regularization. Chiral symmetry and gauge invariance are preserved
even at nonzero lattice spacing. Specific calculations discussed here include
the non-renormalization of a conserved vector current, the magnetic moments of
octet baryons, and the pi N and KN sigma terms that relate to the nucleon's
strangeness content. The quantitative difference between physics at a nonzero
lattice spacing and physics in the continuum limit is easily computed, and it
represents an expectation for the size of discretization errors in
corresponding lattice QCD simulations.Comment: 19 pages, 5 figures, one paragraph added to introduction, to appear
in Phys Rev
The pion mass dependence of the nucleon form-factors of the energy momentum tensor in the chiral quark-soliton model
The nucleon form factors of the energy-momentum tensor are studied in the
large-Nc limit in the framework of the chiral quark-soliton model for model
parameters that simulate physical situations in which pions are heavy. This
allows for a direct comparison to lattice QCD results.Comment: 17 pages, 12 figure
Light Meson Dynamics Workshop. Mini proceedings
The mini-proceedings of the Light Meson Dynamics Workshop held in Mainz from
February 10th to 12th, 2014, are presented. The web page of the conference,
which contains all talks, can be found at
https://indico.cern.ch/event/287442/overview .Comment: 46 pages, 17 contributions. Editors: W. Gradl, P. Masjuan, M.
Ostrick, and S. Schere
Electromagnetic corrections in hadronic processes
In quantum field theory, the splitting of the Hamiltonian into a strong and
an electromagnetic part cannot be performed in a unique manner. We propose a
convention for disentangling these two effects: one matches the parameters of
two theories -- with and without electromagnetic interactions -- at a given
scale mu_1, referred to as the matching scale. This procedure enables one to
analyze the separation of strong and electromagnetic contributions in a
transparent manner. We illustrate the method -- in the framework of the loop
expansion -- in a Yukawa model, as well as in the linear sigma model, where we
also investigate the corresponding low-energy effective theory.Comment: 19 pages (LaTex), 5 figures, published version. References in the
introduction added, discussion shortened, 1 figure removed, conclusions
unchange
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