277 research outputs found
The Mesonic Fluctuations and Corrections in the Chiral Symmetry Breaking Vacuum
The mesonic quantum fluctuations and their corrections on the chiral
condensate and pion polarization function are investigated in the
self-consistent scheme of SU(2) Nambu-Jona-Lasinio model by exactly calculating
the next-to-leading order (NLO) Feynman diagrams in expansion. While
the fluctuations and corrections depend strongly on the meson's three-momentum
cut-off , no chiral symmetry restoration is found since the
cancellation between the NLO and the one-quark-loop diagram with quark mass
deviated from the mean-field value.Comment: 15 pages with 3 figures, abstract, introduction, conclusion revise
Meson Properties in the 1/N_c-corrected NJL model
Properties of mesons are investigated within the Nambu--Jona-Lasinio model.
We include meson-loop corrections, which are generated via a systematic
1/N_c-expansion in next-to-leading order. We show that our scheme is consistent
with chiral symmetry, in particular with the Goldstone theorem and the
Gell-Mann Oakes Renner relation. The numerical part focuses on the pion and the
rho-meson sector. For the latter the 1/N_c-corrections are crucial in order to
include the dominant rho -> pi pi-decay channel, while the leading-order
approximation only contains unphysical q\bar q-decay channels. We show that a
satisfactory description of the pion electromagnetic form factor can be
obtained. Similarities and differences to hadronic models are discussed.Comment: 26 pages, 11 figures include
Various types of phase transitions in the AdS soliton background
We study the basic holographic insulator and superconductor phase transition
in the AdS soliton background by generalizing the spontaneous breaking of a
global U(1) symmetry to occur via Stckelberg mechanism. We construct
the soliton solutions with backreaction and examine the effects of the
backreaction on the condensation of the scalar hair in the generalized
Stckelberg Lagrangian. We disclose rich physics in various phase
transitions. In addition to the AdS soliton configuration, we also examine the
property of the phase transition in the AdS black hole background.Comment: 11 pages, accepted for publication in Phys.Lett.
Summation of Power Series by Self-Similar Factor Approximants
A novel method of summation for power series is developed. The method is
based on the self-similar approximation theory. The trick employed is in
transforming, first, a series expansion into a product expansion and in
applying the self-similar renormalization to the latter rather to the former.
This results in self-similar factor approximants extrapolating the sought
functions from the region of asymptotically small variables to their whole
domains. The method of constructing crossover formulas, interpolating between
small and large values of variables is also analysed. The techniques are
illustrated on different series which are typical of problems in statistical
mechanics, condensed-matter physics, and, generally, in many-body theory.Comment: 30 pages + 5 ps figures, some misprints have been correcte
Baryon-Baryon Interactions
After a short survey of some topics of interest in the study of baryon-baryon
scattering, the recent Nijmegen energy dependent partial wave analysis (PWA) of
the nucleon-nucleon data is reviewed. In this PWA the energy range for both pp
and np is now 0 < Tlab < 350 MeV and a chi^2_{d.o.f.}=1.08 was reached. The
implications for the pion-nucleon coupling constants are discussed. Comments
are made with respect to recent discussions around this coupling constant in
the literature. In the second part, we briefly sketch the picture of the baryon
in several, more or less QCD-based, quark-models that have been rather
prominent in the literature. Inspired by these pictures we constructed a new
soft-core model for the nucleon-nucleon interaction and present the first
results of this model in a chi^2 -fit to the new multi-energy Nijmegen PWA.
With this new model we succeeded in narrowing the gap between theory and
experiment at low energies. For the energies Tlab = 25-320 MeV we reached a
record low chi^2_{p.d.p.} = 1.16. We finish the paper with some conclusions and
an outlook describing the extension of the new model to baryon-baryon
scattering.Comment: 12 pages LaTeX and one postscript figure included. Invited talk
presented at the XIVth European Conference of Few-Body Problems in Physics,
Amsterdam, August 23-28, 199
Parquet Graph Resummation Method for Vortex Liquids
We present in detail a nonperturbative method for vortex liquid systems. This
method is based on the resummation of an infinite subset of Feynman diagrams,
the so-called parquet graphs, contributing to the four-point vertex function of
the Ginzburg-Landau model for a superconductor in a magnetic field. We derive a
set of coupled integral equations, the parquet equations, governing the
structure factor of the two-dimensional vortex liquid system with and without
random impurities and the three-dimensional system in the absence of disorder.
For the pure two-dimensional system, we simplify the parquet equations
considerably and obtain one simple equation for the structure factor. In two
dimensions, we solve the parquet equations numerically and find growing
translational order characterized by a length scale as the temperature is
lowered. The temperature dependence of is obtained in both pure and
weakly disordered cases. The effect of disorder appears as a smooth decrease of
as the strength of disorder increases.Comment: 15 pages, 12 PostScript figures, uses multicols.sty and epsf.st
Extrapolation of power series by self-similar factor and root approximants
The problem of extrapolating the series in powers of small variables to the
region of large variables is addressed. Such a problem is typical of quantum
theory and statistical physics. A method of extrapolation is developed based on
self-similar factor and root approximants, suggested earlier by the authors. It
is shown that these approximants and their combinations can effectively
extrapolate power series to the region of large variables, even up to infinity.
Several examples from quantum and statistical mechanics are analysed,
illustrating the approach.Comment: 21 pages, Latex fil
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
Gravitational Geometric Phase in the Presence of Torsion
We investigate the relativistic and non-relativistic quantum dynamics of a
neutral spin-1/2 particle submitted an external electromagnetic field in the
presence of a cosmic dislocation. We analyze the explicit contribution of the
torsion in the geometric phase acquired in the dynamic of this neutral
spinorial particle. We discuss the influence of the torsion in the relativistic
geometric phase. Using the Foldy-Wouthuysen approximation, the non-relativistic
quantum dynamics are studied and the influence of the torsion in the
Aharonov-Casher and He-McKellar-Wilkens effects are discussed.Comment: 14 pages, no figur
Baryons as non-topological chiral solitons
The present review gives a survey of recent developments and applications of
the Nambu--Jona-Lasinio model with and quark flavors for the
structure of baryons. The model is an effective chiral quark theory which
incorporates the SU(N)SU(N)U(1) approximate
symmetry of Quantum chromodynamics. The approach describes the spontaneous
chiral symmetry breaking and dynamical quark mass generation. Mesons appear as
quark-antiquark excitations and baryons arise as non-topological solitons with
three valence quarks and a polarized Dirac sea. For the evaluation of the
baryon properties the present review concentrates on the non-linear
Nambu--Jona-Lasinio model with quark and Goldstone degrees of freedom which is
identical to the Chiral quark soliton model obtained from the instanton liquid
model of the QCD vacuum. In this non-linear model, a wide variety of
observables of baryons of the octet and decuplet is considered. These include,
in particular, electromagnetic, axial, pseudoscalar and pion nucleon form
factors and the related static properties like magnetic moments, radii and
coupling constants of the nucleon as well as the mass splittings and
electromagnetic form factors of hyperons. Predictions are given for the strange
form factors, the scalar form factor and the tensor charge of the nucleon.Comment: 104 pages, 27 figures as uuencoded and compressed postscript files ,
hardcopy available upon request; Prog.Part.Nucl.Phys. 37 (1996) (in print
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