74 research outputs found
The Skyrme model predictions for the mass spectrum and the - mass splittings
The -plet mass spectrum and the - mass splittings are computed in the framework of the minimal SU(3)
extended Skyrme model. As functions of the Skyrme charge and the SU(3)
symmetry breaking parameters the predictions are presented in tabular form. The
predicted mass splitting - is the smallest among
all SU(3) baryonic multiplets.Comment: 4 pages, 2 tables, version to appear in Phys. Rev.
Gluon Bremsstrahlung in Relativistic Heavy Ion Collisions
We study the process at lowest order in QCD perturbation
theory to understand gluon radiation in the fragmentation region of
relativistic heavy-ion collisions. We arrive at a formula for gluon
multiplicity that interpolates between behavior at low
, to at large .Comment: 5 pages, 2 figures Clarifying paragraphs added to Introduction and
Section I
Trace anomaly as signature of conformality in neutron stars
We discuss an interpretation that a peak in the sound velocity in neutron
star matter, as suggested by the observational data, signifies strongly-coupled
conformal matter. The normalized trace anomaly is a dimensionless measure of
conformality leading to the derivative and the non-derivative contributions to
the sound velocity. We find that the peak in the sound velocity is attributed
to the derivative contribution from the trace anomaly that steeply approaches
the conformal limit. Smooth continuity to the behavior of high-density QCD
implies that the matter part of the trace anomaly may be positive definite. We
discuss a possible implication of the positivity condition of the trace anomaly
on the - relation of the neutron stars.Comment: 6 pages, 3 figure
Generalized Quark Transversity Distribution of the Pion in Chiral Quark Models
The transversity generalized parton distributions (tGPDs) of the the pion,
involving matrix elements of the tensor bilocal quark current, are analyzed in
chiral quark models. We apply the nonlocal chiral models involving a
momentum-dependent quark mass, as well as the local Nambu--Jona-Lasinio with
the Pauli-Villars regularization to calculate the pion tGPDs, as well as
related quantities following from restrained kinematics, evaluation of moments,
or taking the Fourier-Bessel transforms to the impact-parameter space. The
obtained distributions satisfy the formal requirements, such as proper support
and polynomiality, following from Lorentz covariance. We carry out the
leading-order QCD evolution from the low quark-model scale to higher lattice
scales, applying the method of Kivel and Mankiewicz. We evaluate several
lowest-order generalized transversity form factors, accessible from the recent
lattice QCD calculations. These form factors, after evolution, agree properly
with the lattice data, in support of the fact that the spontaneously broken
chiral symmetry is the key element also in the evaluation of the transversity
observables.Comment: 17 pages, 17 figures, regular pape
Pion radiative weak decays in nonlocal chiral quark models
We analyze the radiative pion decay pi+ -> e+ nu_e gamma within nonlocal
chiral quark models that include wave function renormalization. In this
framework we calculate the vector and axial-vector form factors FV and FA at
q^2=0 --where q^2 is the (e+ \nu_e) squared invariant mass-- and the slope a of
FV(q^2) at q^2 -> 0. The calculations are carried out considering different
nonlocal form factors, in particular those taken from lattice QCD evaluations,
showing a reasonable agreement with the corresponding experimental data. The
comparison of our results with those obtained in the (local) NJL model and the
relation of FV and a with the form factor in pi^0 -> gamma* gamma decays are
discussed.Comment: 14 pages, 1 figure, minor changes in text introduce
Extended nonlocal chiral-quark model for the heavy-light quark systems
In this talk, we report the recent progress on constructing a
phenomenological effective model for the heavy-light quark systems, which
consist of (u,d,s,c,b) quarks, i.e. extended nonlocal chiral-quark model
(ExNLChQM). We compute the heavy-meson weak-decay constants to verify the
validity of the model. From the numerical results, it turns out that (f_D, f_B,
f_{D_s}, f_{B_s})=(207.54,208.13,262.56,262.39) MeV. These values are in
relatively good agreement with experimental data and various theoretical
estimations.Comment: 3 pages, 4 figures, Talk given at the 20th International IUPAP
Conference on Few-Body Problems in Physics (FB20), 20~25 August 2012,
Fukuoka, Japa
Gravitational and higher-order form factors of the pion in chiral quark models
The gravitational form factor of the pion is evaluated in two chiral quark
models and confronted to the recent full-QCD lattice data. We find good
agreement for the case of the Spectral Quark Model, which builds in the
vector-meson dominance for the charge form factor. We derive a simple relation
between the gravitational and electromagnetic form factors, holding in the
considered quark models in the chiral limit. The relation implies that the
gravitational mean squared radius is half the electromagnetic one. We also
analyze higher-order quark generalized form factors of the pion, related to
higher moments in the symmetric Bjorken X-variable of the generalized parton
distribution functions, and discuss their perturbative QCD evolution, needed to
relate the quark-model predictions to the lattice data. The values of the
higher-order quark form factors at t=0, computed on the lattice, also agree
with our quark model results within the statistical and method uncertainties.Comment: 12 pages, 4 figures, discussion and references adde
Unpolarized fragmentation function for the pion and kaon via the nonlocal chiral-quark model
In this talk we present our recent studies for the unpolarized fragmentation
functions for the pion and kaon, employing the nonlocal chiral quark model,
which manifests the nonlocal interaction between the quarks and pseudoscalar
mesons, in the light-cone frame. It turns out that the nonlocal interaction
produces considerable differences in comparison to typical local-interaction
models.Comment: 4 pages, 2 figures, Talk given at the international conference The
Fifth Asia-Pacific Conference on Few-Body Systems in Physics 2011 (APFB2011),
Seoul, Republic of Korea, 22-26 August 201
Flavored exotic multibaryons and hypernuclei in topological soliton models
The energies of baryon states with positive strangeness, or anti-charm
(-beauty) are estimated in chiral soliton approach, in the "rigid oscillator"
version of the bound state soliton model proposed by Klebanov and Westerberg.
Positive strangeness states can appear as relatively narrow nuclear levels
(Theta-hypernuclei), the states with heavy anti-flavors can be bound with
respect to strong interactions in the original Skyrme variant of the model (SK4
variant). The binding energies of anti-flavored states are estimated also in
the variant of the model with 6-th order term in chiral derivatives in the
lagrangian as solitons stabilizer (SK6 variant). The latter variant is less
attractive, and nuclear states with anti-charm or anti-beauty can be unstable
relative to strong interactions. The chances to get bound hypernuclei with
heavy antiflavors are greater within "nuclear variant" of the model with
rescaled model parameter (Skyrme constant e or e' decreased by ~30%) which is
expected to be valid for baryon numbers greater than B ~10. The rational map
approximation is used to describe multiskyrmions with baryon number up to ~30
and to calculate the quantities necessary for their quantization (moments of
inertia, sigma-term, etc.).Comment: 24 pages, 7 table
Generalized vector form factors of the pion in a chiral quark model
Generalized vector form factors of the pion, related to the moments of the
generalized parton distribution functions, are evaluated in the
Nambu--Jona-Lasinio model with the Pauli-Villars regularization. The lowest
moments (the electromagnetic and the gravitational form factors) are compared
to recent lattice data, with fair agreement. Predictions for higher-order
moments are also made. Relevant features of the generalized form factors in the
chiral quark models are highlighted and the role of the QCD evolution for the
higher-order GFFs is stressed.Comment: Dedicated to the memory of Manoj K. Banerjee, to appear in a special
issue of the Indian Journal of Physics, 6 pages, 4 figure
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