Instantons and Nucleon Magnetism

We construct improved QCD sum rules for the nucleon magnetic moments by implementing direct-instanton contributions to the operator product expansion of the nucleon correlator in a magnetic background field. The instanton contributions are found to affect only those sum rules which had previously been considered unstable. The new sum rules show a high degree of stability and reproduce the experimental values of the nucleon magnetic moments for values of the magnetic quark condensate susceptibility which are consistent with other estimates.Comment: 10 pages, 2 figures. Invited talk given at "Hadron Physics 2000", Caraguatatuba, Sao Paulo, Brazil (April 10-15, 2000

QCD Vacuum Topology and Glueballs

We outline a comprehensive study of spin-0 glueball properties which, in particular, keeps track of the topological gluon structure. Specifically, we implement (semi-hard) topological instanton physics as well as topological charge screening in the QCD vacuum into the operator product expansion (OPE) of the glueball correlators. A realistic instanton size distribution and the (gauge-invariant) renormalization of the instanton contributions are also implemented. Predictions for 0^{++} and 0^{-+} glueball properties are presented.Comment: 3 pages, no figure

Exploring gauge-invariant vacuum wave functionals for Yang-Mills theory

We study gauge-invariant approximations to the Yang-Mills vacuum wave functional in which asymptotic freedom and a detailed description of the infrared dynamics are encoded through squeezed core states. After variationally optimizing these trial functionals, dimensional transmutation, gluon condensation and a dynamical mass gap of the expected magnitude emerge transparently. The dispersion properties of the soft gauge modes are modified by higher-gradient interactions and suggest a negative differential color resistance of the Yang-Mills vacuum. Casting the soft-mode dynamics into the form of an effective action for gauge-invariant collective fields, furthermore, allows to identify novel infrared degrees of freedom. The latter are gauge-invariant saddle-point fields which summarize dominant and universal contributions from various gauge-field orbits to all amplitudes. Their analysis provides new insights into how the vacuum gluon fields generate gauge-invariant excitations. Examples include a dynamical size stabilization mechanism for instantons and merons, a gauge-invariant representation of their effects as well as a new physical interpretation for Faddeev-Niemi knots.Comment: 13 pages, 3 figures, invited talk at the International Workshop on QCD Green's Functions, Confinement and Phenomenology, Trento, Italy, 5-9 Sept. 201

Exotic hadron holography from anomalous dimensions

The anomalous dimensions of hadronic interpolators contain dynamical information on the properties of the associated hadron states. We point out that they provide, in particular, a link by which gauge-invariant information on exotic contributions to hadronic wavefunctionals can be obtained from approximate gravity duals for QCD. This is demonstrated by the holographic description of a dominant tetraquark component in the lightest scalar mesons.Comment: 5 page