257 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
Identifying the quark content of the isoscalar scalar mesons f_0(980), f_0(1370), and f_0(1500) from weak and electromagnetic processes
The assignments of the isoscalar scalar mesons f0(980), f0(1370), and
f0(1500) in terms of their qqbar substructure is still a matter of heated
dispute. Here we employ the weak and electromagnetic decays D(s)(+) to f0+pi(+)
and f0 two-photon decays, respectively, to identify the f0(980) and f0(1500) as
mostly ssbar, and the f0(1370) as dominantly nonstrange, in agreement with
previous work. The two-photon decays can be satisfactorily described with quark
as well as with meson loops, though the latter ones provide a less
model-dependent and more quantitative description.Comment: v1, 15 pages, plain LaTeX, 1 eps figure. v2, 18 pages, plain LaTeX
(figure included). More discussion, especially on the f0(1370) and its
empirical two-photon widt
On a Neutrino Electroweak Radius
We study a combination of amplitudes for neutrino scattering that can isolate
a (gauge-invariant) difference of chirality-preserving neutrino electroweak
radii for and . This involves both photon and
exchange contributions. It is shown that the construction singles out the
contributions of the hypercharge gauge field in the standard model.
We comment on how gauge-dependent terms from the charge radii cancel with other
terms in the relative electroweak radii defined.Comment: 16 pages, revtex with embedded 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
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
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
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.
The new analysis of the KLOE data on the phi->eta pi0 gamma decay
In this paper we present the fit to the recent high-statistical KLOE data on
the phi -> eta pi^0 gamma decay. This decay mainly goes through the a_0 gamma
intermediate state. The obtained results differ from those of the previous
fits: data prefer a high a_0 mass and a considerably large a_0 coupling to the
K\bar K}.Comment: 11 pages, 2 figure
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