2,364 research outputs found
Isospin Symmetry Breaking within the HLS Model: A Full () Mixing Scheme
We study the way isospin symmetry violation can be generated within the
Hidden Local Symmetry (HLS) Model. We show that isospin symmetry breaking
effects on pseudoscalar mesons naturally induces correspondingly effects within
the physics of vector mesons, through kaon loops. In this way, one recovers all
features traditionally expected from \rho-\omg mixing and one finds support
for the Orsay phase modelling of the e^+e^- \ra \pi^+ \pi^- amplitude. We
then examine an effective procedure which generates mixing in the whole ,
\omg, sector of the HLS Model. The corresponding model allows us to
account for all two body decays of light mesons accessible to the HLS model in
modulus and phase, leaving aside the \rho \ra \pi \pi and K^* \ra K \pi
modes only, which raise a specific problem. Comparison with experimental data
is performed and covers modulus and phase information; this represents 26
physics quantities successfully described with very good fit quality within a
constrained model which accounts for SU(3) breaking, nonet symmetry breaking in
the pseudoscalar sector and, now, isospin symmetry breaking.Comment: 38 pages, version published in Eur. Phys. J.
VMD, the WZW Lagrangian and ChPT: The Third Mixing Angle
We show that the Hidden Local Symmetry Model, supplemented with well-known
procedures for breaking flavor SU(3) and nonet symmetry, provides all the
information contained in the standard Chiral Perturbation Theory (ChPT)
Lagrangian . This allows to rely on radiative
decays of light mesons ( and ) in order to extract
some numerical information of relevance to ChPT: a value for , a quark mass ratio of , and a negligible
departure from the Gell-Mann--Okubo mass formula. The mixing angles are
and . We also give the values of all decay constants. It is shown that
the common mixing pattern with one mixing angle is actually quite
appropriate and algebraically related to the mixing pattern
presently preferred by the ChPT community. For instance the traditional
is functionally related to the ChPT and fulfills
. The vanishing of , supported by all
data on radiative decays, gives a novel relation between mixing angles and the
violation of nonet symmetry in the pseudoscalar sector. Finally, it is shown
that the interplay of nonet symmetry breaking through U(3) \ra SU(3)
U(1) satisfies all requirements of the physics of radiative decays without any
need for additional glueballs.Comment: 31 pages, 1 figur
Pseudoscalar Meson Mixing in Effective Field Theory
We show that for any effective field theory of colorless meson fields, the
mixing schemes of particle states and decay constants are not only related but
also determined exclusively by the kinetic and mass Lagrangian densities. In
the general case, these are bilinear in terms of the intrinsic fields and
involve non-diagonal kinetic and mass matrices. By applying three consecutive
steps this Lagrangian can be reduced into the standard quadratic form in terms
of the physical fields. These steps are : (i) the diagonalization of the
kinetic matrix, (ii) rescaling of the fields, and (iii) the diagonalization of
the mass matrix. In case, where the dimensions of the non-diagonal kinetic and
mass sub-matrices are respectively, and , this procedure
leads to mixing schemes which involve angles and
field rescaling parameters. This observation holds true irrespective with the
type of particle interactions presumed. The commonly used mixing schemes,
correspond to a proper choice of the kinetic and mass matrices, and are derived
as special cases. In particular, - mixing, requires one angle, if
and only if, the kinetic term with the intrinsic fields has a quadratic form.Comment: REVTeX, 6 page
A Global Treatment Of VMD Physics Up To The : I. Annihilations, Anomalies And Vector Meson Partial Widths
The HLS Model, equipped with a mechanism providing the breaking of U(3)/SU(3)
symmetry and an isospin symmetry breaking leading naturally to vector meson
mixing, has been recently shown to successfully account for e^+ e^- \ra
\pi^+\pi^- cross section and for the dipion spectrum in decay. The
present study shows that the full anomalous sector of the HLS model can be
considered and is validated by the experimental data. Indeed, this extended
model provides a successful simultaneous fit to the e^+ e^- \ra \pi^+\pi^-
data together with the available data on e^+ e^- \ra \pi^0\gamma, e^+ e^-
\ra \eta\gamma and e^+ e^- \ra \pi^0 \pi^+\pi^- cross sections. It is shown
that the fit of these data sets also predicts an accurate description of the
\eta/\eta^\prime \ra \pi^+ \pi^- \gamma decays fully consistent with the
reported information on their branching fractions and spectra. Finally, one
also derives from our global fits products of widths of the form \Gamma (V \ra
f_1)\Gamma(V \ra e^+ e^-) and ratios of the form \Gamma (V \ra f_1)/\Gamma
(V \ra f_2) describing decays of vector mesons to several non--leptonic final
states.Comment: 58 pages, 10 figures Corrected a few misprints. Footnote 10 change
A Global Treatment Of VMD Physics Up To The : I. Annihilations, Anomalies And Vector Meson Partial Widths
The HLS Model, equipped with a mechanism providing the breaking of U(3)/SU(3)
symmetry and an isospin symmetry breaking leading naturally to vector meson
mixing, has been recently shown to successfully account for e^+ e^- \ra
\pi^+\pi^- cross section and for the dipion spectrum in decay. The
present study shows that the full anomalous sector of the HLS model can be
considered and is validated by the experimental data. Indeed, this extended
model provides a successful simultaneous fit to the e^+ e^- \ra \pi^+\pi^-
data together with the available data on e^+ e^- \ra \pi^0\gamma, e^+ e^-
\ra \eta\gamma and e^+ e^- \ra \pi^0 \pi^+\pi^- cross sections. It is shown
that the fit of these data sets also predicts an accurate description of the
\eta/\eta^\prime \ra \pi^+ \pi^- \gamma decays fully consistent with the
reported information on their branching fractions and spectra. Finally, one
also derives from our global fits products of widths of the form \Gamma (V \ra
f_1)\Gamma(V \ra e^+ e^-) and ratios of the form \Gamma (V \ra f_1)/\Gamma
(V \ra f_2) describing decays of vector mesons to several non--leptonic final
states.Comment: 58 pages, 10 figures Corrected a few misprints. Footnote 10 change
Can VMD improve the estimate of the muon g-2 ?
We show that a VMD based theoretical input allows for a significantly
improved accuracy for the hadronic vacuum polarization of the photon which
contributes to the theoretical estimate of the muon g-2. We also show that the
only experimental piece of information in the decay which cannot be
accounted for is the accepted value for {\rm Br}(\tau \ra \pi \pi \nu_\tau),
while the spectum lineshape is in agreement with expectations from
annihilations.Comment: 6 pages, 1 figure Proceedings of the PhiPsi09, Oct. 13-16, 2009,
Beijing, Chin
The Dipion Mass Spectrum In e+e- Annihilation and tau Decay: A Dynamical (rho0, omega, phi) Mixing Approach
We readdress the problem of finding a simultaneous description of the pion
form factor data in e+e- annihilations and in tau decays. For this purpose, we
work in the framework of the Hidden Local Symmetry (HLS) Lagrangian and modify
the vector meson mass term by including the pion and kaon loop contributions.
This leads us to define the physical rho, omega and phi fields as linear
combinations of their ideal partners, with coefficients being meromorphic
functions of s, the square of the 4--momentum flowing into the vector meson
lines. This allows us to define a dynamical, i.e. s-dependent, vector meson
mixing scheme. The model is overconstrained by extending the framework in order
to include the description of all meson radiative (V P gamma and P gamma gamma
couplings) and leptonic (Ve+e- couplings) decays and also the isospin breaking
(omega/ phi --> pi+ pi-) decay modes. The model provides a simultaneous,
consistent and good description of the e+e- and tau dipion spectra. The
expression for pion form factor in the latter case is derived from those in the
former case by switching off the isospin breaking effects specific to e+e- and
switching on those for tau decays. Besides, the model also provides a good
account of all decay modes of the form V P gamma, Pgamma gamma as well as the
isospin breaking decay modes. It leads us to propose new reference values for
the rho^0 --> e+ e- and omega --> pi+ pi- partial widths which are part of our
description of the pion form factor. Other topics (phi --> K anti K, the rho
meson mass and width parameters) are briefly discussed. Therefore, we confirm
the 3.3 sigma discrepancy between the theoretical estimate of a_mu based on
e+e- and its direct BNL measurement.Comment: 71 pages, 8 figures. Accepted by EPJ C. Version 3: correct minor
typos, minor changes spread out into the text. Extension of Sections 12.2 and
12.3.5 and introduction of the new Appendix
New results in rho^0 meson physics
We compare the predictions of a range of existing models based on the Vector
Meson Dominance hypothesis with data on e^+ e^- -> pi^+ pi^$ and e^+ e^- ->
mu^+ mu^- cross-sections and the phase and near-threshold behavior of the
timelike pion form factor, with the aim of determining which (if any) of these
models is capable of providing an accurate representation of the full range of
experimental data. We find that, of the models considered, only that proposed
by Bando et al. is able to consistently account for all information, provided
one allows its parameter "a" to vary from the usual value of 2 to 2.4. Our fit
with this model gives a point-like coupling (gamma pi^+ \pi^-) of magnitude ~
-e/6, while the common formulation of VMD excludes such a term. The resulting
values for the rho mass and pi^+ pi^- and e^+e^- partial widths as well as the
branching ratio for the decay omega -> pi^+ pi^- obtained within the context of
this model are consistent with previous results.Comment: 34 pages with 7 figures. Published version also available at
http://link.springer.de/link/service/journals/10052/tocs/t8002002.ht
SU(3) breaking and Hidden Local Symmetry
We study the various existing implementations of SU(3) breaking in the Hidden
Local Symmetry model for the low energy hadronic sector following a mechanism
originally proposed by Bando, Kugo and Yamawaki (BKY). We pay particular
attention to hermiticity and current conservation. Following this, we present a
new method for including symmetry breaking effects which preserves the BKY mas
s relation among vector mesons. Symmetry breaking (SB) necessarily requires a
transformation of the pseudoscalar fields, which, following BKY, we refer to a
s field renormalization. We examine the consequences of propagating this throug
h all Lagrangian terms including the anomalous ones. We thus explore the
consequences of these various SB schemes for both charged and neutral
pseudoscalar decay constants as measured in weak and anomalous decays
respectively.Comment: 18 pages, REVTEX. Publication details added to title page. Published
version available at
http://publish.aps.org/ejnls/prdfetch/abstract/PRD/V58/E074006
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