The Infrared Behavior of QCD Green's Functions - Confinement, Dynamical Symmetry Breaking, and Hadrons as Relativistic Bound States

Recent studies of QCD Green's functions and their applications in hadronic physics are reviewed. We briefly discuss the issues of gauge fixing, BRS invariance and positivity. Evidence for the violation of positivity by quarks and transverse gluons in the covariant gauge is collected, and it is argued that this is one manifestation of confinement. We summarise the derivation of the Dyson-Schwinger equations (DSEs) of QED and QCD. The influence of instantons on DSEs in a 2-dimensional model is mentioned. Solutions for the Green's functions in QED in 2+1 and 3+1 dimensions provide tests of various schemes to truncate DSEs. We discuss possible extensions to QCD and their limitations. Truncation schemes for DSEs of QCD are discussed in the axial gauge and in the Landau gauge. We review the available results from a systematic non-perturbative expansion scheme established for Landau gauge QCD. Comparisons to related lattice results, where available, are presented. The applications of QCD Green's functions to hadron physics are summarized. Properties of ground state mesons are discussed on the basis of the Bethe-Salpeter equation for quarks and antiquarks. The Goldstone nature of pseudoscalar mesons and mechanisms of diquark confinement are reviewed. We discuss some properties of ground state baryons based on their description as Bethe-Salpeter/Faddeev bound states of quark-diquark correlations in the quantum field theory of confined quarks and gluons.Comment: 212 Pages, LaTeX2e, submitted to Physics Reports; typos corrected, improvements on grammar and style, references adde

What the Infrared Behavior of QCD Green Functions can tell us about Confinement in the Covariant Gauge

We review aspects of confinement in the covariant and local description of QCD and discuss to what extend our present knowledge of the infrared behavior of QCD Green functions can support this description. In particular, we emphasize: the positivity violations of transverse gluon and quark states, the Kugo-Ojima confinement criterion, and the conditions necessary to avoid the decomposition property for colored clusters. We summarize how these issues relate to the infrared behavior of the propagators in Landau gauge QCD as extracted from solutions to truncated Dyson-Schwinger equations and lattice simulations.Comment: 10 Pages, 7 Figures, LaTeX2.09, invited talk presented by L. v. Smekal at ``Quark Confinement and the Hadron Spectrum IV'', Vienna, July 4-8, 200

The Infrared Behavior of QCD Propagators in Landau Gauge

Some features of the solutions to the truncated Dyson-Schwinger equations(DSEs) for the propagators of QCD in Landau gauge are summarized. In particular, the Kugo-Ojima confinement criterion is realized, and positivity of transverse gluons is manifestly violated in these solutions. In Landau gauge, the gluon-ghost vertex function offers a convenient possibility to define a nonperturbative running coupling. The infrared fixed point obtained from this coupling which determines the 2-point interactions of color-octet quark currents implies the existence of unphysical massless states which are necessary to escape the cluster decomposition of colored clusters. The gluon and ghost propagators, and the nonperturbative running coupling, are compared to recent lattice simulations. A significant deviation of the running coupling from the infrared behavior extracted in simulations of 3-point functions is attributed to an inconsistency of asymmetric subtraction schemes due to a consequence of the Kugo-Ojima criterion: infrared enhanced ghosts.Comment: 4 pages, no figures, talk given by R.A. at ``Quark Nuclear Physics 2000'', Adelaide, Feb. 21 - 25, 200

The Kugo-Ojima Confinement Criterion from Dyson-Schwinger Equations

Prerequisites of confinement in the covariant and local description of QCD are reviewed. In particular, the Kugo-Ojima confinement criterion, the positivity violations of transverse gluon and quark states, and the conditions necessary to avoid the decomposition property for colored clusters are discussed. In Landau gauge QCD, the Kugo-Ojima confinement criterion follows from the ghost Dyson-Schwinger equation if the corresponding Green's functions can be expanded in an asymptotic series. Furthermore, the infrared behaviour of the propagators in Landau gauge QCD as extracted from solutions to truncated Dyson-Schwinger equations and lattice simulations is discussed in the light of these issues.Comment: 8 pages, 5 figures; To be published in the proceedings of the Workshop on Dynamical aspects of the QCD phase transition, ECT* Trento, March 12 - 15, 2001. Typos correcte

Internet Resources for Gene Expression Analysis in Arabidopsis thaliana

The number of online databases and web-tools for gene expression analysis in Arabidopsis thaliana has increased tremendously during the last years. These resources permit the database-assisted identification of putative cis-regulatory DNA sequences, their binding proteins, and the determination of common cis-regulatory motifs in coregulated genes. DNA binding proteins may be predicted by the type of cis-regulatory motif. Further questions of combinatorial control based on the interaction of DNA binding proteins and the colocalization of cis-regulatory motifs can be addressed. The database-assisted spatial and temporal expression analysis of DNA binding proteins and their target genes may help to further refine experimental approaches. Signal transduction pathways upstream of regulated genes are not yet fully accessible in databases mainly because they need to be manually annotated. This review focuses on the use of the AthaMap and PathoPlant® databases for gene expression regulation analysis and discusses similar and complementary online databases and web-tools. Online databases are helpful for the development of working hypothesis and for designing subsequent experiments

PathoPlant(®): a platform for microarray expression data to analyze co-regulated genes involved in plant defense responses

Plants react to pathogen attack by expressing specific proteins directed toward the infecting pathogens. This involves the transcriptional activation of specific gene sets. PathoPlant(®), a database on plant–pathogen interactions and signal transduction reactions, has now been complemented by microarray gene expression data from Arabidopsis thaliana subjected to pathogen infection and elicitor treatment. New web tools enable identification of plant genes regulated by specific stimuli. Sets of genes co-regulated by multiple stimuli can be displayed as well. A user-friendly web interface was created for the submission of gene sets to be analyzed. This results in a table, listing the stimuli that act either inducing or repressing on the respective genes. The search can be restricted to certain induction factors to identify, e.g. strongly up- or down-regulated genes. Up to three stimuli can be combined with the option of induction factor restriction to determine similarly regulated genes. To identify common cis-regulatory elements in co-regulated genes, a resulting gene list can directly be exported to the AthaMap database for analysis. PathoPlant is freely accessible at