31 research outputs found
Hyperon semileptonic decays and quark spin content of the proton
We investigate the hyperon semileptonic decays and the quark spin content of
the proton taking into account flavor SU(3) symmetry breaking.
Symmetry breaking is implemented with the help of the chiral quark-soliton
model in an approach, in which the dynamical parameters are fixed by the
experimental data for six hyperon semileptonic decay constants. As a result we
predict the unmeasured decay constants, particularly for ,
which will be soon measured and examine the effect of the SU(3) symmetry
breaking on the spin content of the proton. Unfortunately
large experimental errors of decays propagate in our analysis making
and practically undetermined. We conclude that
statements concerning the values of these two quantities, which are based on
the exact SU(3) symmetry, are premature. We stress that the meaningful results
can be obtained only if the experimental errors for the decays are
reduced.Comment: The final version accepted for publication in Phys. Rev. D. 18 pages,
RevTex is used with 4 figures include
Strange form factors in the context of SAMPLE, HAPPEX, and A4 experiments
The strange properties of the nucleon are investigated within the framework
of the SU(3) chiral quark-soliton model assuming isospin symmetry and applying
the symmetry conserving SU(3) quantization. We present the form factors
, and the electric and magnetic strange form
factors incorporating pion and kaon asymptotics. The results
show a fairly good agreement with the recent experimental data from the SAMPLE
and HAPPEX collaborations. We also present predictions for future measurements
including the A4 experiment at MAMI (Mainz).Comment: 10 pages with four figures. RevTeX4 is used. Few lines are changed.
Accepted for publication in Phys.Rev.
Electromagnetic Form Factors of the SU(3) Octet Baryons in the semibosonized SU(3) Nambu-Jona-Lasinio Model
The electromagnetic form factors of the SU(3) octet baryons are investigated
in the semibosonized SU(3) Nambu--Jona-Lasinio model (chiral quark-soliton
model). The rotational and strange quark mass corrections in linear
order are taken into account. The electromagnetic charge radii of the nucleon
and magnetic moments are also evaluated. It turns out that the model is in a
remarkable good agreement with the experimental data.Comment: RevTex is used. 37 pages. The final version to appear in Phys. Rev.
D. 13 figures are include
Evidence Against Instanton Dominance of Topological Charge Fluctuations in QCD
The low-lying eigenmodes of the Dirac operator associated with typical gauge
field configurations in QCD encode, among other low-energy properties, the
physics behind the solution to the problem (i.e. the origin of the
mass), the nature of spontaneous chiral symmetry breaking, and the
physics of string-breaking, quark-antiquark pair production, and the OZI rule.
Moreover, the space-time chiral structure of these eigenmodes reflects the
space-time topological structure of the underlying gauge field. We present
evidence from lattice QCD on the local chiral structure of low Dirac eigenmodes
leading to the conclusion that topological charge fluctuations of the QCD
vacuum are not instanton-dominated. The result supports Witten's arguments that
topological charge is produced by confinement-related gauge fluctuations rather
than instantons.Comment: 35 pages, 11 figure
Spectral quark model and low-energy hadron phenomenology
We propose a spectral quark model which can be applied to low energy hadronic
physics. The approach is based on a generalization of the Lehmann
representation of the quark propagator. We work at the one-quark-loop level.
Electromagnetic and chiral invariance are ensured with help of the gauge
technique which provides particular solutions to the Ward-Takahashi identities.
General conditions on the quark spectral function follow from natural physical
requirements. In particular, the function is normalized, its all positive
moments must vanish, while the physical observables depend on negative moments
and the so-called log-moments. As a consequence, the model is made finite,
dispersion relations hold, chiral anomalies are preserved, and the twist
expansion is free from logarithmic scaling violations, as requested of a
low-energy model. We study a variety of processes and show that the framework
is very simple and practical. Finally, incorporating the idea of vector-meson
dominance, we present an explicit construction of the quark spectral function
which satisfies all the requirements. The corresponding momentum representation
of the resulting quark propagator exhibits only cuts on the physical axis, with
no poles present anywhere in the complex momentum space. The momentum-dependent
quark mass compares very well to recent lattice calculations. A large number of
predictions and relations can be deduced from our approach for such quantities
as the pion light-cone wave function, non-local quark condensate, pion
transition form factor, pion valence parton distribution function, etc.Comment: revtex, 24 pages, 3 figure
Effective chiral lagrangian in the chiral limit from the instanton vacuum
We study the effective chiral Lagrangian in the chiral limit from the
instanton vacuum. Starting from the nonlocal effective chiral action, we derive
the effective chiral Lagrangian, using the derivative expansion to order
in the chiral limit. The low energy constants, , , and
are determined and compared with various models and the corresponding empirical
data. The results are in a good agreement with the data. We also discuss about
the upper limit of the sigma meson, based on the present results.Comment: 14 pages, 5 figures, submitted to Phys.Rev.
Baryon Tri-local Interpolating Fields
We systematically investigate tri-local (non-local) three-quark baryon fields
with U_L(2)*U_R(2) chiral symmetry, according to their Lorentz and isospin
(flavor) group representations. We note that they can also be called as
"nucleon wave functions" due to this full non-locality. We study their chiral
transformation properties and find all the possible chiral multiplets
consisting J=1/2 and J=3/2 baryon fields. We find that the axial coupling
constant |g_A| = 5/3 is only for nucleon fields belonging to the chiral
representation (1/2,1)+(1,1/2) which contains both nucleon fields and Delta
fields. Moreover, all the nucleon fields belonging to this representation have
|g_A| = 5/3.Comment: 8 pages, 3 tables, accepted by EPJ
Semileptonic decay constants of octet baryons in the chiral quark-soliton model
Based on the recent study of the magnetic moments and axial constants within
the framework of the chiral quark-soliton model, we investigate the baryon
semileptonic decay constants and . Employing the
relations between the diagonal transition matrix elements and off-diagonal ones
in the vector and axial-vector channels, we obtain the ratios of baryon
semileptonic decay constants and . The ratio is also
discussed and found that the value predicted by the present model naturally
lies between that of the Skyrme model and that of the nonrelativistic quark
model. The singlet axial constant can be expressed in terms of the
ratio and in the present model and turns out to be small. The
results are compared with available experimental data and found to be in good
agreement with them. In addition, the induced pseudotensor coupling constants
are calculated, the SU(3) symmetry breaking being considered. The
results indicate that the effect of SU(3) symmetry breaking might play an
important role for some decay modes in hyperon semileptonic decay.Comment: 16 pages, RevTeX is used. No figure. Accepted for publication in
Phys. Rev.
The chirally-odd twist-3 distribution function e(x) in the chiral quark-soliton model
The chirally-odd twist-3 nucleon distribution e(x) is studied in the large-Nc
limit in the framework of the chiral quark-soliton model at a low normalization
point of about 0.6 GeV. The remarkable result is that in the model e(x)
contains a delta-function-type singularity at x=0. The regular part of e(x) is
found to be sizeable at the low scale of the model and in qualitative agreement
with bag model calculations.Comment: 16 pages, 6 figures, revtex, Ref.[50] and footnote 3 adde
Low Energy Chiral Lagrangian in Curved Space-Time from the Spectral Quark Model
We analyze the recently proposed Spectral Quark Model in the light of Chiral
Perturbation Theory in curved space-time. In particular, we calculate the
chiral coefficients , as well as the coefficients ,
, and , appearing when the model is coupled to gravity. The
analysis is carried for the SU(3) case. We analyze the pattern of chiral
symmetry breaking as well as elaborate on the fulfillment of anomalies.
Matching the model results to resonance meson exchange yields the relation
between the masses of the scalar, tensor and vector mesons,
. Finally, the
large- limit suggests the dual relations in the vector and scalar
channels, and .Comment: 18 pages, no figure