136 research outputs found
Circumventing the axial anomalies and the strong CP problem
Many meson processes are related to the U_A(1) axial anomaly, present in the
Feynman graphs where fermion loops connect axial vertices with vector vertices.
However, the coupling of pseudoscalar mesons to quarks does not have to be
formulated via axial vertices. The pseudoscalar coupling is also possible, and
this approach is especially natural on the level of the quark substructure of
hadrons. In this paper we point out the advantages of calculating these
processes using (instead of the anomalous graphs) the graphs where axial
vertices are replaced by pseudoscalar vertices. We elaborate especially the
case of the processes related to the Abelian axial anomaly of QED, but we
speculate that it seems possible that effects of the non-Abelian axial anomaly
of QCD can be accounted for in an analogous way.Comment: 13 pages, some typos corrected, published in Prof. D. Tadic's
memorial issue of Fizika B, expanded version of hep-ph/051212
A symmetry restoration scenario supported by the generalized Witten-Veneziano relation and its analytic solution
The Witten-Veneziano relation, or, alternatively, its generalization proposed
by Shore, facilitates understanding and describing the complex of eta and eta'
mesons. We present an analytic, closed-form solution to Shore's equations which
gives results on the eta-eta' complex in full agreement with results previously
obtained numerically. Although the Witten-Veneziano relation and Shore's
equations are related, the ways they were previously used in the context of
dynamical models to calculate eta and eta' properties, were rather different.
However, with the analytic solution, the calculation can be formulated
similarly to the approach through the Witten-Veneziano relation, and with some
conceptual improvements. In the process, one strengthens the arguments in favor
of a possible relation between the U_A(1) and SU_A(3) chiral symmetry breaking
and restoration. To test this scenario, the experiments such as those at RHIC,
NICA and FAIR, which extend the RHIC (and LHC) high-temperature scans also to
the finite-density parts of the QCD phase diagram, should pay particular
attention to the signatures from the eta'-eta complex indicating the symmetry
restoration.Comment: elsarticle style, 6 page
eta and eta' mesons and dimension 2 gluon condensate <A^2>
The study of light pseudoscalar quark-antiquark bound states in the
Dyson-Schwinger approach with the effective QCD coupling enhanced by the
interplay of the dimension 2 gluon condensate and dimension 4 gluon
condensate , is extended to the eta-eta' complex. We include the effects
of the gluon axial anomaly into the Dyson-Schwinger approach to mesons. The
calculated masses, mixing and two-photon decay widths of eta and eta' mesons
are in agreement with experiment. Also, in a model-independent way, we give the
modification of the Gell-Mann--Okubo and Schwinger nonet relations due to the
interplay of the gluon anomaly and SU(3) flavor symmetry breaking.Comment: 15 pages, 2 tables, 1 eps figure, revtex
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