2,785 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
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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