540 research outputs found
Two photon decay and photoproduction of radial excitation of pion
Within the framework of non-local quark model of Nambu--Jona-Lasinio type the
two-photon decay of radial excited state of -meson -- -- is
found to be 3.6\KeV. The radial excitation of pion is described with the use
of polynomial formfactor of second order over where is the
transverse momentum, which corresponds to relative motion of quark-antiquark
pair within the energy range from 0 up to 1\GeV.
The probabilities of production of and states in
the electron-positron colliders are estimated. The production of -meson
in the interaction of photon with electron or muon is as well considered
(Primakoff effect). The relevant total cross sections are 0.14 or 0.06\nb.Comment: 10 page
Processes in the NJL model
The processes of electron-positron annihilation into and into
are considered within the NJL model. Intermediate vector
mesons , , , and are taken into
account. The latter two mesons are treated as the first radial excited states.
They are incorporated into the NJL model by means of a polynomial form factor.
Numerical predictions for the cross sections of these processes are received
for the center-of-mass energies below 2 GeV. Our results for the
production are in agreement with experimental data received in the energy
region 600 -- 1020 MeV.Comment: 4 pages, 5 figure
Nonlocal quark model beyond mean field and QCD phase transition
A nonlocal chiral quark model is consistently extended beyond mean field
using a strict 1/Nc expansion scheme. The parameters of the nonlocal model are
refitted to the physical values of the pion mass and the weak pion decay
constant. The size of the 1/Nc correction to the quark condensate is carefully
studied in the nonlocal and the usual local Nambu-Jona-Lasinio models. It is
found that even the sign of the corrections can be different. This can be
attributed to the mesonic cut-off of the local model. It is also found that the
1/Nc corrections lead to a lowering of the temperature of the chiral phase
transition in comparison with the mean-field result. On the other hand, near
the phase transition the 1/Nc expansion breaks down and a non-perturbative
scheme for the inclusion of mesonic correlations is needed in order to describe
the phase transition point.Comment: 4 pages, 4 figures, talk at the 3rd Joint International Hadron
Structure'09 Conference, Tatranska Strba (Slovak Republic), Aug. 30-Sept. 3,
200
Radiative decays of pseudoscalar (P) and vector (V) mesons and the process e^+e^- \to \eta' \rho
Radiative decays of pseudoscalar and vector mesons are calculated in the
framework of the chiral Nambu-Jona-Lasinio (NJL) model. We use the amplitude
for triangle quark loops of anomalous type. In evaluating these loop integrals
we use two methods. In the first one, we neglect the dependence of external
momenta by reproducing the Wess-Zumino-Witten terms of effective chiral meson
Lagrangian. In the second method, we take into account the momentum dependence
of loop integrals omitting their imaginary part. This makes it possible to
allow for quark confinement. As applied both the methods is in qualitative
agreement with each other and with experimental data. The second method allows
us to describe the electron-positron annihilation with production of
and mesons in the center of mass energy range from 1.6 to 3.5\GeV. The
comparison with the recent experimental data is presented.Comment: 7 pages, 4 figures, 1 tabl
1/N_c- expansion of the quark condensate at finite temperature
Previously the quark and meson properties in a many quark system at finite
temperature have been studied within effective QCD approaches in the Hartree
approximation. In the present paper we consider the influence of the mesonic
correlations on the quark self-energy and on the quark propagator within a
systematic - expansion. Using a general separable ansatz for the
nonlocal interaction, we derive a selfconsistent equation for the
correction to the quark propagator. For a separable model with cut-off
formfactor, we obtain a decrease of the condensate of the order of 20\% at zero
temperature. A lowering the critical temperature for the onset of the chiral
restoration transition due to the inclusion of mesonic correlations is obtained
what seems to be closer to the results from lattice calculations.Comment: 19 pages, REVTeX, 5 figure
Scalar Mesons in a Chiral Quark Model with Glueball
Ground-state scalar isoscalar mesons and a scalar glueball are described in a
U(3)xU(3) chiral quark model of the Nambu--Jona-Lasinio (NJL) type with 't
Hooft interaction. The latter interaction produces singlet-octet mixing in the
scalar and pseudoscalar sectors. The glueball is introduced into the effective
meson Lagrangian as a dilaton on the base of scale invariance. The mixing of
the glueball with scalar isoscalar quarkonia and amplitudes of their decays
into two pseudoscalar mesons are shown to be proportional to current quark
masses, vanishing in the chiral limit. Mass spectra of the scalar mesons and
the glueball and their main modes of strong decay are described.Comment: 10 pages, LaTeX text, requires svjour.cls and svepj.cl
Light Quark Masses in Multi-Quark Interactions
We suggest and discuss in detail a multi-quark three flavor Lagrangian of the
Nambu -- Jona-Lasinio type, which includes a set of effective interactions
proportional to the current quark masses. It is shown that within the dynamical
chiral symmetry breaking regime, the masses of the pseudo Goldstone bosons and
their chiral partners, members of the low lying scalar nonet, are in perfect
agreement with current phenomenological expectations. The role of the new
interactions is analyzed.Comment: 8 pages, published versio
Density Effect on Hadronization of a Quark Plasma
The hadronization cross section in a quark plasma at finite temperature and
density is calculated in the framework of Nambu--Jona-lasinio model with
explicit chiral symmetry breaking. In apposition to the familiar temperature
effect, the quark plasma at high density begins to hadronize suddenly. It leads
to a sudden and strong increase of final state pions in relativistic heavy ion
collisions which may be considered as a clear signature of chiral symmetry
restoration.Comment: Latex2e, 11 pages, 7 Postscript figures, submitted to Phys. Rev.
Abnormal number of Nambu-Goldstone bosons in the color-asymmetric 2SC phase of an NJL-type model
We consider an extended Nambu--Jona-Lasinio model including both (q \bar q)-
and (qq)-interactions with two light-quark flavors in the presence of a single
(quark density) chemical potential. In the color superconducting phase of the
quark matter the color SU(3) symmetry is spontaneously broken down to SU(2). If
the usual counting of Goldstone bosons would apply, five Nambu-Goldstone (NG)
bosons corresponding to the five broken color generators should appear in the
mass spectrum. Unlike that expectation, we find only three gapless diquark
excitations of quark matter. One of them is an SU(2)-singlet, the remaining two
form an SU(2)-(anti)doublet and have a quadratic dispersion law in the small
momentum limit. These results are in agreement with the Nielsen-Chadha theorem,
according to which NG-bosons in Lorentz-noninvariant systems, having a
quadratic dispersion law, must be counted differently. The origin of the
abnormal number of NG-bosons is shown to be related to a nonvanishing
expectation value of the color charge operator Q_8 reflecting the lack of color
neutrality of the ground state. Finally, by requiring color neutrality, two
massive diquarks are argued to become massless, resulting in a normal number of
five NG-bosons with usual linear dispersion laws.Comment: 13 pages, 4 figures, revtex
Virtual Compton Scattering off the Pseudoscalar Meson Octet
We present a calculation of the virtual Compton scattering amplitude for the
pseudoscalar meson octet in the framework of chiral perturbation theory at
. We calculate the electromagnetic generalized polarizabilities
and compare the results in the real Compton scattering limit to available
experimental values. Finally, we give predictions for the differential cross
section of electron-meson bremsstrahlung.Comment: 9 pages, Latex, uses cjp3.sty (included), 4 eps figures, to be
published in the proceedings of the 13th Indian-Summer School "Understanding
the Structure of Hadrons," August 28 - September 1, 2000, Prague, Czech
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