132 research outputs found
Spin content of constituent quarks and one-spin asymmetries in inclusive processes
We consider mechanism for one-spin asymmetries observed in inclusive hadron
production. The main role belongs to the orbital angular momentum of the
quark-antiquark cloud in the internal structure of constituent quarks. We argue
that the origin of the asymmetries in pion production is a result of retaining
of this internal angular orbital momentum by the perturbative phase of QCD
under transition from the non-perturbative phase. The non-perturbative hadron
structure is based on the results of chiral quark models. PACS number(s):
11.30.Qc, 12.40.Pp, 13.75.Ni, 13.88.+eComment: 21 pages LaTeX + 8 figures (not included
Consistency in Regularizations of the Gauged NJL Model at One Loop Level
In this work we revisit questions recently raised in the literature
associated to relevant but divergent amplitudes in the gauged NJL model. The
questions raised involve ambiguities and symmetry violations which concern the
model's predictive power at one loop level. Our study shows by means of an
alternative prescription to handle divergent amplitudes, that it is possible to
obtain unambiguous and symmetry preserving amplitudes. The procedure adopted
makes use solely of {\it general} properties of an eventual regulator, thus
avoiding an explicit form. We find, after a thorough analysis of the problem
that there are well established conditions to be fulfiled by any consistent
regularization prescription in order to avoid the problems of concern at one
loop level.Comment: 22 pages, no figures, LaTeX, to appear in Phys.Rev.
Implications of a New Effective Chiral Meson Lagrangian
Based on a recently derived effective chiral meson Lagrangian from the
extended SU(2)\otimes SU(2) Nambu -- Jona-Lasinio (ENJL) model, in the linear
realization of chiral symmetry, we extract to leading order in the 1/N_c
expansion all associated relevant three-point functions \rho \to \pi\pi, \sigma
\to \pi\pi, a_1 \to \rho\pi, a_1 \to \sigma\pi, as well as the amplitude for
\pi\pi scattering. We discuss the formal differences of these amplitudes as
compared with those derived in the literature and calculate the associated
decay widths and scattering parameters. The differences have two origins: i)
new terms, which are proportional to the current quark mass and arise from
taking the correct NJL vacuum from the first steps in a proper-time expansion,
are present in the Lagrangian; ii) an implemented chiral covariant treatment of
the diagonalization in the pseudoscalar - axialvector sector induces new
couplings between three or more mesonic fields. Both effects have been derived
from the chiral Ward Takahashi identities, which are fully taken into account
at each order of the proper-time expansion.Comment: Plain LaTex, 15 page
Spectral Function of Quarks in Quark Matter
We investigate the spectral function of light quarks in infinite quark matter
using a simple, albeit self-consistent model. The interactions between the
quarks are described by the SU(2) Nambu--Jona-Lasinio model. Currently mean
field effects are neglected and all calculations are performed in the chirally
restored phase at zero temperature. Relations between correlation functions and
collision rates are used to calculate the spectral function in an iterative
process.Comment: final version, published in PRC; 15 pages, RevTeX
Diquark Bose Condensates in High Density Matter and Instantons
Instantons lead to strong correlations between up and down quarks with spin
zero and anti-symmetric color wave functions. In cold and dense matter,
and 50 MeV, these pairs Bose-condense,
replacing the usual and
condensates.Comment: 4 pages ReVTeX, 2 eps-figures included using epsf.st
Meson loop effects in the NJL model at zero and non-zero temperature
We compare two different possibilities to include meson-loop corrections in
the Nambu-Jona-Lasinio model: a strict 1/N_c-expansion in next-to-leading order
and a non-perturbative scheme corresponding to a one-meson-loop approximation
to the effective action. Both schemes are consistent with chiral symmetry, in
particular with the Goldstone theorem and the Gell-Mann-Oakes-Renner relation.
The numerical part at zero temperature focuses on the pion and the rho-meson
sector. For the latter the meson-loop-corrections are crucial in order to
include the dominant rho -> pipi-decay channel, while the standard Hartree +
RPA approximation only contains unphysical qqbar-decay channels. We find that
m_\pi, f_\pi, and quantities related to the rho-meson self-energy can
be described reasonably with one parameter set in the 1/N_c-expansion scheme,
whereas we did not succeed to obtain such a fit in the non-perturbative scheme.
We also investigate the temperature dependence of the quark condensate. Here we
find consistency with chiral perturbation theory to lowest order. Similarities
and differences of both schemes are discussed.Comment: 51 pages, 18 figures, to be published in Physics of Atomic Nuclei,
the volume dedicated to the 90th birthday of A.B. Migdal, error in Eq. 4.22
correcte
Effective Chiral Meson Lagrangian For The Extended Nambu-Jona-Lasinio Model
We present a derivation of the low-energy effective meson Lagrangian of the
extended Nambu -- Jona-Lasinio (ENJL) model. The case with linear realization
of broken chiral symmetry is considered. There are two
crucial points why this revision is needed. Firstly it is the explicit chiral
symmetry breaking effect. On the basis of symmetry arguments we show that
relevant contributions related with the current quark mass terms are absent
from the effective Lagrangians derived so far in the literature. Secondly we
suggest a chiral covariant way to avoid non-diagonal terms responsible for the
pseudoscalar -- axial-vector mixing from the effective meson Lagrangian. In the
framework of the linear approach this diagonalization has not been done
correctly. We discuss as well the coset space
parametrization for the revised Lagrangian (nonlinear ansatz). Our Lagrangian
differs in an essential way from those that have been derived till now on the
basis of both linear and nonlinear realizations of chiral symmetry.Comment: 23 pages, plain LaTex, no figure
On asymmetry in inclusive pion production
On the basis of the mechanism proposed for one-spin asymmetries in inclusive
hadron production we specify an --dependence of asymmetries in inclusive
processes of pion production. The main role in generation of this asymmetry
belongs to the orbital angular momentum ofquark-antiquark cloud in internal
structure of constituent quarks. The --dependence of asymmetries in the
charged pion production at large reflects the corresponding dependence of
constituent quark polarization in the polarized proton.Comment: LaTeX, 8 pages, 3 figures. One figure added, as it appears in Phys.
Rev.
Unusual bound states of quark matter within the NJL model
Properties of dense quark matter in and out of chemical equilibrium are
studied within the SU(3) Nambu-Jona-Lasinio model. In addition to the 4-fermion
scalar and vector terms the model includes also the 6-fermion flavour mixing
interaction. First we study a novel form of deconfined matter, meso-matter,
which is composed of equal number of quarks and antiquarks. It can be thought
of as a strongly compressed meson gas where mesons are melted into their
elementary constituents, quarks and antiquarks. Strongly bound states in this
quark-antiquark matter are predicted for all flavour combinations of
quark-antiquark pairs. The maximum binding energy reaches up to 180 MeV per
pair for mixtures with about 70% of strange quark-antiquark pairs. Equilibrated
baryon-rich quark matter with various flavour compositions is also studied. In
this case only shallow bound states appear in systems with a significant
admixture (about 40%) of strange quarks (strangelets). Their binding energies
are quite sensitive to the relative strengths of scalar and vector
interactions. The common property of all these bound states is that they appear
at high particle densities when the chiral symmetry is nearly restored. Thermal
properties of meso-matter as well as chemically equilibrated strange quark
matter are also investigated. Possible decay modes of these bound states are
discussed.Comment: 26 pages, 16 PostScript figures, RevTe
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