96 research outputs found
Hyperon Beta-Decay and Axial Charges of the Lambda in view of Strongly Distorted Baryon Wave-Functions
Within the collective coordinate approach to chiral soliton models we suggest
that breaking of SU(3) flavor symmetry mainly resides in the baryon
wave-functions while the charge operators maintain a symmetric structure.
Sizable symmetry breaking in the wave-functions is required to reproduce the
observed spacing in the spectrum of the (1/2)^+ baryons. The matrix elements of
the flavor symmetric charge operators nevertheless yield g_A/g_V ratios for
hyperon beta-decay which agree with the empirical data approximately as well as
the successful F&D parameterization of the Cabibbo scheme. Demanding the
strangeness component in the nucleon to vanish in the two flavor limit of the
model, determines the structure of the singlet axial charge operator and yields
the various quark flavor components of the axial charge of the \Lambda-hyperon.
The suggested picture gains support from calculations in a realistic model
using pion and vector meson degrees of freedom to build up the soliton.Comment: 14 pages, minor revisions, paper accepted for publication in Nucl.
Phys.
General Structure of Relativistic Vector Condensation
We study relativistic massive vector condensation due to a non zero chemical
potential associated to some of the global conserved charges of the theory. We
show that the phase structure is very rich. More specifically there are three
distinct phases depending on the value of one of the zero chemical potential
vector self interaction terms. We also develop a formalism which enables us to
investigate the vacuum structure and dispersion relations in the spontaneously
broken phase of the theory. We show that in a certain limit of the couplings
and for large chemical potential the theory is not stable. This limit,
interestingly, corresponds to a gauge type limit often employed to economically
describe the ordinary vector mesons self interactions in QCD. We finally
indicate for which physical systems our analysis is relevant.Comment: RevTex4 14 pages,4 figure
Soliton Models for the Nucleon and Predictions for the Nucleon Spin Structure
In these lectures the three flavor soliton approach for baryons is reviewed.
Effects of flavor symmetry breaking in the baryon wave--functions on axial
current matrix elements are discussed. A bosonized chiral quark model is
considered to outline the computation of spin dependent nucleon structure
functions in the soliton picture.Comment: 12 pages, Lectures presented at the Advanced Study Institute Symmetry
and Spin, Prague, 2001, to appear in the proceedings. References correcte
Vacuum stability and the Cholesky decomposition
We discuss how the Cholesky decomposition may be used to ascertain whether a
critical point of the field theory scalar potential provides a stable vacuum
configuration. We then use this method to derive the stability conditions in a
specific example.Comment: 7 page
Strangeness in the nucleon and the ratio of proton-to-neutron neutrino-induced quasi-elastic yield
The electroweak form factors of the nucleon as obtained within a three flavor
pseudoscalar vector meson soliton model are employed to predict the ratio of
the proton and neutron yields from , which are induced by quasi-elastic
neutrino reactions. These predictions are found to vary only moderately in the
parameter space allowed by the model. The antineutrino flux of the up-coming
experiment determining this ratio was previously overestimated. The
corresponding correction is shown to have only a small effect on the predicted
ratio. However, it is found that the experimental result for the ratio
crucially depends on an accurate measurement of the energy of the knocked out
nucleon.Comment: 17 pages, LaTeX, 2 tables, 4 figures, Discussion on shape of strange
form factors added, Z. Phys. A, to be publishe
Effective chiral Lagrangians for spin-1 mesons
The commonly used types of effective theory for vector mesons are reviewed
and their relationships clarified. They are shown to correspond to different
choices of field for spin-1 particles and the rules for transforming between
them are described. The importance of respecting chiral symmetry is stressed.
The choice of fields that transform homogeneously under the nonlinear
realisation of chiral symmetry imposes no preconceptions about the types of
coupling for the mesons. This representation thus provides a convenient
framework for relating different theories. It is also used to elucidate the
nature of the assumptions in specific hidden-gauge and massive Yang-Mills
models that have been widely used.Comment: 46 pages (RevTeX
The Pion Decay Constants and the Rho-Meson Mass at Finite Temperature in the Hidden Local Symmetry
We study the temperature dependence of the pion decay constant and rho-meson
mass in the hidden local symmetry model at one loop. Using the standard
imaginary time formalism, we include the thermal effect of rho meson as well as
that of pion. We show that the pion gives a dominant contribution to the pion
decay constant and rho-meson contribution slightly decreases the critical
temperature. The rho-meson pole mass increases as T^4/m_\rho^2 at low
temperature dominated by the pion-loop effect. At high temperature, although
the pion-loop effect decreases the rho-meson mass, the rho-loop contribution
overcomes the pion-loop contribution and rho-meson mass increases with
temperature. We also show that the conventional parameter a is stable as the
temperature increases.Comment: We added a comment on the correction to the rho-meson mass from the
omega-pi loop. This is the final version to be published in Phys. Rev. D. 19
pages (LaTeX-RevTeX), 7 PostScript figure
Role of Light Vector Mesons in the Heavy Particle Chiral Lagrangian
We give the general framework for adding "light" vector particles to the
heavy hadron effective chiral Lagrangian. This has strong motivations both from
the phenomenological and aesthetic standpoints. An application to the already
observed D \rightarrow \overbar{K^*} weak transition amplitude is discussed.Comment: 19 pages, LaTeX documen
AdS/QCD: The Relevance of the Geometry
We investigate the relevance of the metric and of the geometry in
five-dimensional models of hadrons. Generically, the metric does not affect
strongly the results and even flat space agrees reasonably well with the data.
Nevertheless, we observe a preference for a decreasing warp factor, for example
AdS space. The Sakai-Sugimoto model reduces to one of these models and the
level of agreement is similar to the one of flat space. We also consider the
discrete version of the five-dimensional models, obtained by dimensional
deconstruction. We find that essentially all the relevant features of
"holographic" models of QCD can be reproduced with a simple 3-site model
describing only the states below the cut-off of the theory.Comment: 25 pages + appendix. v2 minor changes and Refs. adde
Fate of Vector Dominance in the Effective Field Theory
We reveal the full phase structure of the effective field theory for QCD,
based on the hidden local symmetry (HLS) through the one-loop renormalization
group equation including quadratic divergences. We then show that vector
dominance (VD) is not a sacred discipline of the effective field theory but
rather an accidental phenomenon peculiar to three-flavored QCD. In particular,
the chiral symmetry restoration in HLS model takes place in a wide phase
boundary surface, on which the VD is realized nowhere. This suggests that VD
may not be valid for chiral symmetry restoration in hot and/or dense QCD.Comment: 4 pages, 3 figures. One reference added. Minor modification to
shorten the manuscript. This is the version to appear in Physical Review
Letter
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