232 research outputs found
a_0(980) -> gamma gamma and f_0(980) -> gamma gamma: a consistent description
We work out the Linear Sigma Model (LSM) predictions for the 2 gamma decay
rates of the a_0(980),f_0(980) mesons under the assumption that they are
respectively the I=1 and I=0 members of the bar q q scalar nonet. Agreement
with experimental data is achieved provided we include the contribution of a
\kappa meson with mass approx. 900 MeV, and a scalar mixing angle (sigma -f_0
mixing in the {|NS>,|S>} basis) varphi_s approx. -14^\circ, as predicted by the
model.Comment: 9 pages, 1 figur
Scalar sigma meson effects in rho and omega decays into pi0 pi0 gamma
The complementarity between Chiral Perturbation Theory and the Linear Sigma
Model in the scalar channel is exploited to study production in
and radiative decays, where the effects of a low mass scalar
resonance should manifest. The recently reported data on
seem to require the contribution of a low mass and
moderately narrow . The properties of this controversial state
could be fixed by improving the accuracy of these measurements. Data on
can also be accommodated in our framework, but are
much less sensitive to the properties.Comment: 17 pages, 4 figure
The decay Z -> neutrino antineutrino photon in the Standard Model
A complete study of the one-loop induced decay Z -> neutrino antineutrino
photon is presented within the framework of the Standard Model. The advantages
of using a nonlinear gauge are stressed. We have found that the main
contributions come from the electric dipole and the magnetic dipole transitions
of the Z gauge boson and the neutrino, respectively. We obtain a branching
ratio B=7.16E-10, which is about four orders of magnitude smaller than the
bound recentely obtained by the L3 collaboration and thus it leaves open a
window to search for new physics effects in single-photon decays of the Z
boson.Comment: REVTEX,15 pp, 5 eps figures, Approved for publication in Physical
Review
Scalar meson dynamics in Chiral Perturbation Theory
A comparison of the linear sigma model (LM) and Chiral Perturbation
Theory (ChPT) predictions for pion and kaon dynamics is presented. Lowest and
next-to-leading order terms in the ChPT amplitudes are reproduced if one
restricts to scalar resonance exchange. Some low energy constants of the order
ChPT Lagrangian are fixed in terms of scalar meson masses. Present values
of these low energy constants are compatible with the LM dynamics. We
conclude that more accurate values would be most useful either to falsify the
LM or to show its capability to shed some light on the controversial
scalar physics.Comment: 9 pages, REVTeX 4.0. Final version accepted for publicatio
Spin Interacting Fields and Heavy Baryon Chiral Perturbation Theory
We analyze the consistency of the Chiral Lagrangian approach to the
description of the spin 3/2 interacting theory. We argue that to lowest order
in the 1/m expansion, the formalism leads to the appropriated constraints and
the theory is free of the so called ``off shell" ambiguities.Comment: 12 pages, Late
Charge asymmetries in e+e- -> pi+ pi- gamma at the phi resonance
We consider the forward-backward pion charge asymmetry for the
e^{+}e^{-}\to\pi^{+}\pi^{-}\gamma process. At tree level we consider
bremsstrahlung and double resonance contributions. Although the latter
contribution is formally sub-leading, it is enhanced at low dipion invariant
mass due to resonant effects. We consider also four alternative models
to describe the final state radiation at the loop level: Resonance Chiral
Perturbation Theory, Unitarized Chiral Perturbation Theory, Kaon Loop Model and
Linear Sigma Model. The last three models yield results compatible with
experimental data. The Kaon Loop Model requires an energy dependent phase to
achieve the agreement.Comment: Revised version, conclusions changed, 11 pages, 8 figs, version to
appear in PL
Radiative decays of light vector mesons in a quark level linear sigma model
We calculate the P0 to gamma gamma, V0 to P0 gamma and V0to V'0 gamma gamma
decays in the framework of a U(3)xU(3) linear sigma model which includes
constituent quarks. For the first two decays this approach improves results
based on the anomalous Wess-Zumino term, with contributions due to SU(3)
symmetry breaking and vector mixing. The phi to (omega,rho) gamma gamma decays
are dominated by resonant eta' exchange . Our calculation for the later decays
improves and update similar calculations in the -closely related- framework of
vector meson dominance. We obtain BR(phi to rho gamma gamma)=2.5x10^{-5} and
BR(phi to omega gamma gamma)=2.8x10^{-6} within the scope of the
high-luminosity phi factories.Comment: 8 pages, submitted to Phys. Rev.
Mixing and the Decay
We reexamine the decay, adding the
effect of mixing to the amplitude calculated with the aid of
chiral perturbation theory and vector meson dominance. We predict the neutral
decay to occur with a width of \omega \to \pi^{0} \pi^{0} \gamma and also analyze the effect of the mixing
on the \omega \to \pi^{0} \pi^{0} \gamma \omega \to
\pi^{+} \pi^{-} \gamma ratio. Several remarks on the effect of
mixing on certain radiative decays of vector mesons are
presented.Comment: 10 pages, LaTeX, 1 ps-figure. Submitted to Phys. Rev.
A reference case for economic evaluations in osteoarthritis: An expert consensus article from the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO)
Background: General recommendations for a reference case for economic studies in rheumatic diseases were published in 2002 in an initiative to improve the comparability of cost-effectiveness studies in the field. Since then, economic evaluations in osteoarthritis (OA) continue to show considerable heterogeneity in methodological approach. Objectives: To develop a reference case specific for economic studies in OA, including the standard optimal care, with which to judge new pharmacologic and non-pharmacologic interventions. Methods: Four subgroups of an ESCEO expert working group on economic assessments (13 experts representing diverse aspects of clinical research and/or economic evaluations) were charged with producing lists of recommendations that would potentially improve the comparability of economic analyses in OA: outcome measures, comparators, costs and methodology. These proposals were discussed and refined during a face-to-face meeting in 2013. They are presented here in the format of the recommendations of the recently published Consolidated Health Economic Evaluation Reporting Standards (CHEERS) statement, so that an initiative on economic analysis methodology might be consolidated with an initiative on reporting standards. Results: Overall, three distinct reference cases are proposed, one for each hand, knee and hip OA; with diagnostic variations in the first two, giving rise to different treatment options: interphalangeal or thumb-based disease for hand OA and the presence or absence of joint malalignment for knee OA. A set of management strategies is proposed, which should be further evaluated to help establish a consensus on the "standard optimal care" in each proposed reference case. The recommendations on outcome measures, cost itemisation and methodological approaches are also provided. Conclusions: The ESCEO group proposes a set of disease-specific recommendations on the conduct and reporting of economic evaluations in OA that could help the standardisation and comparability of studies that evaluate therapeutic strategies of OA in terms of costs and effectiveness
Exotic state photoproduction
It is shown that the list of unusual mesons planned for a careful study in
photoproduction can be extended by the exotic states with which should be looked for in the decay
channels in the reactions and . The full classification of the states by their
quantum numbers is presented. A simple model for the spin structure of the , , and reaction amplitudes is formulated and the tentative estimates of the
corresponding cross sections at the incident photon energy
GeV are obtained: b, b, b, and b. The problem of the
signal extraction from the natural background due to the other production channels is discussed. In particular the estimates are
presented for the , , and reaction cross sections.
Our main conclusion is that the search for the exotic
states is quite feasible at JEFLAB facility. The expected yield of the events in a 30-day run at the 100% detection
efficiency approximates events.Comment: 19 pages, revtex, 1 figure in postscipt, some comments and references
added, a few minor typos corrected, to be published in Phys. Rev.
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