84 research outputs found
Kugo-Ojima confinement and QCD Green's functions in covariant gauges
In Landau gauge QCD the Kugo-Ojima confinement criterion and its relation to
the infrared behaviour of the gluon and ghost propagators are reviewed. It is
demonstrated that the realization of this confinement criterion (which is
closely related to the Gribov-Zwanziger horizon condition) results from quite
general properties of the ghost Dyson-Schwinger equation. The numerical
solutions for the gluon and ghost propagators obtained from a truncated set of
Dyson--Schwinger equations provide an explicit example for the anticipated
infrared behaviour. The results are in good agreement, also quantitatively,
with corresponding lattice data obtained recently. The resulting running
coupling approaches a fixed point in the infrared, .
Solutions for the coupled system of Dyson--Schwinger equations for the quark,
gluon and ghost propagators are presented. Dynamical generation of quark masses
and thus spontaneous breaking of chiral symmetry takes place. In the quenched
approximation the quark propagator functions agree well with those of
corresponding lattice calculations. For a small number of light flavours the
quark, gluon and ghost propagators deviate only slightly from the ones in
quenched approximation. While the positivity violation of the gluon spectral
function is manifest in the gluon propagator, there are no clear indications of
analogous positivity violations for quarks so far.Comment: 10 pages, 5 figures; Talk given by R.A. at the International School
on Nuclear Physics ``Quarks in Hadrons and Nuclei'' in Erice (Italy),
September 16 - 24, 200
Infrared Exponents and Running Coupling of SU(N) Yang-Mills Theories
We present approximate solutions for the gluon and ghost propagators as well
as the running coupling in Landau gauge Yang-Mills theories. We solve the
corresponding Dyson-Schwinger equations in flat Euclidean space-time without
any angular approximation. This supplements recently obtained results employing
a four-torus, i.e. a compact space-time manifold, as infrared regulator. We
confirm previous findings deduced from an extrapolation with tori of different
volumes: the gluon propagator is weakly vanishing in the infrared and the ghost
propagator is highly singular. For non-vanishing momenta our propagators are in
remarkable agreement with recent lattice calculations.Comment: 11 pages, 4 figure
Angiogenesis in the synovium and at the osteochondral junction in osteoarthritis
SummaryObjectivesWe hypothesised that osteochondral and synovial angiogenesis in osteoarthritis (OA) are independent processes. We investigated whether indices of osteochondral and synovial angiogenesis display different relationships with synovitis, disease severity and chondrocalcinosis in patients with OA.DesignSynovium and medial tibial plateaux were obtained from 62 patients undergoing total knee joint replacement for OA (18 [29%] had chondrocalcinosis) and from 31 recently deceased people with no evidence of joint pathology post-mortem (PM). Vascular endothelium, proliferating endothelial cells (ECs) and macrophages were quantified by immunohistochemistry for CD34, CD31/Ki67 and CD14, respectively. Grades were assigned for radiographic and histological OA disease severity, clinical disease activity and histological synovitis (based on cellular content of the synovium).ResultsBlood vessels breached the tidemark in 60% of patients with OA and 20% of PM controls. Osteochondral vascular density increased with increasing cartilage severity and clinical disease activity scores, but not with synovitis. Synovial EC proliferation, inflammation and macrophage infiltration were higher in OA than in PM controls. Synovial angiogenesis indices increased with increasing histological synovitis, but were not related to osteochondral vascular density or other indices of OA disease severity. OA changes were more severe in patients with concurrent chondrocalcinosis. Chondrocalcinosis was not associated with increased angiogenesis or histological synovitis beyond that seen in OA alone.ConclusionOsteochondral and synovial angiogenesis appear to be independent processes. Osteochondral vascularity is associated with the severity of OA cartilage changes and clinical disease activity, whereas synovial angiogenesis is associated with histological synovitis. Modulation of osteochondral and synovial angiogenesis may differentially affect OA disease
Quark-gluon vertex in general kinematics
The original publication can be found at www.springerlink.com Submitted to Cornell University’s online archive www.arXiv.org in 2007 by Jon-Ivar Skullerud. Post-print sourced from www.arxiv.org.We compute the quark–gluon vertex in quenched lattice QCD in the Landau gauge, using an off-shell mean-field O(a)-improved fermion action. The Dirac-vector part of the vertex is computed for arbitrary kinematics. We find a substantial infrared enhancement of the interaction strength regardless of the kinematics.Ayse Kizilersu, Derek B. Leinweber, Jon-Ivar Skullerud and Anthony G. William
Non-perturbative Propagators, Running Coupling and Dynamical Quark Mass of Landau gauge QCD
The coupled system of renormalized Dyson-Schwinger equations for the quark,
gluon and ghost propagators of Landau gauge QCD is solved within truncation
schemes. These employ bare as well as non-perturbative ansaetze for the
vertices such that the running coupling as well as the quark mass function are
independent of the renormalization point. The one-loop anomalous dimensions of
all propagators are reproduced. Dynamical chiral symmetry breaking is found,
the dynamically generated quark mass agrees well with phenomenological values
and corresponding results from lattice calculations. The effects of unquenching
the system are small. In particular the infrared behavior of the ghost and
gluon dressing functions found in previous studies is almost unchanged as long
as the number of light flavors is smaller than four.Comment: 34 pages, 10 figures, version to be published by Phys. Rev.
Analytic structure of the gluon and quark propagators in Landau gauge QCD
In Landau gauge QCD the infrared behavior of the propagator of transverse
gluons can be analytically determined to be a power law from Dyson-Schwinger
equations. This propagator clearly shows positivity violation, indicating the
absence of the transverse gluons from the physical spectrum, i.e. gluon
confinement. A simple analytic structure for the gluon propagator is proposed
capturing all important features. We provide arguments that the Landau gauge
quark propagator possesses a singularity on the real timelike axis. For this
propagator we find a positive definite Schwinger function.Comment: 6 pages, 3 figures; summary of a talk given at several occasions; to
be published in the proceedings of the international conference QCD DOWN
UNDER, March 10 - 19, Adelaide, Australi
Nonperturbative structure of the quark-gluon vertex
The complete tensor structure of the quark--gluon vertex in Landau gauge is
determined at two kinematical points (`asymmetric' and `symmetric') from
lattice QCD in the quenched approximation. The simulations are carried out at
beta=6.0, using a mean-field improved Sheikholeslami-Wohlert fermion action,
with two quark masses ~ 60 and 115 MeV. We find substantial deviations from the
abelian form at the asymmetric point. The mass dependence is found to be
negligible. At the symmetric point, the form factor related to the
chromomagnetic moment is determined and found to contribute significantly to
the infrared interaction strength.Comment: 16 pages, 11 figures, JHEP3.cl
Low energy effects of neutrino masses
While all models of Majorana neutrino masses lead to the same dimension five
effective operator, which does not conserve lepton number, the dimension six
operators induced at low energies conserve lepton number and differ depending
on the high energy model of new physics. We derive the low-energy dimension six
operators which are characteristic of generic Seesaw models, in which neutrino
masses result from the exchange of heavy fields which may be either fermionic
singlets, fermionic triplets or scalar triplets. The resulting operators may
lead to effects observable in the near future, if the coefficients of the
dimension five and six operators are decoupled along a certain pattern, which
turns out to be common to all models. The phenomenological consequences are
explored as well, including their contributions to and new
bounds on the Yukawa couplings for each model.Comment: modifications: couplings in appendix B, formulas (121)-(122) on rare
leptons decays (to match with published version) and consequently bounds in
table
Vertex functions and infrared fixed point in Landau gauge SU(N) Yang-Mills theory
The infrared behaviour of vertex functions in an SU(N) Yang-Mills theory in
Landau gauge is investigated employing a skeleton expansion of the
Dyson-Schwinger equations. The three- and four-gluon vertices become singular
if and only if all external momenta vanish while the dressing of the
ghost-gluon vertex remains finite in this limit. The running coupling as
extracted from either of these vertex functions possesses an infrared fixed
point. In general, diagrams including ghost-loops dominate in the infrared over
purely gluonic ones.Comment: 14 pages, 8 figures, v2: typos corrected, version to be published in
PL
On the Nature of the Phase Transition in SU(N), Sp(2) and E(7) Yang-Mills theory
We study the nature of the confinement phase transition in d=3+1 dimensions
in various non-abelian gauge theories with the approach put forward in [1]. We
compute an order-parameter potential associated with the Polyakov loop from the
knowledge of full 2-point correlation functions. For SU(N) with N=3,...,12 and
Sp(2) we find a first-order phase transition in agreement with general
expectations. Moreover our study suggests that the phase transition in E(7)
Yang-Mills theory also is of first order. We find that it is weaker than for
SU(N). We show that this can be understood in terms of the eigenvalue
distribution of the order parameter potential close to the phase transition.Comment: 15 page
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