eta and eta' in a coupled Schwinger-Dyson and Bethe-Salpeter approach

Extending our earlier treatments of pi0, eta_c and eta_b, we study the eta-eta' system and its gamma-gamma decays using a model which is a leading version of the consistently coupled Schwinger-Dyson (SD) and Bethe-Salpeter (BS) approach. The electromagnetic interactions are incorporated through a (generalized) impulse approximation consistent with this bound-state approach, so that the Ward-Takahashi identities of QED are preserved when quarks are dynamically dressed. To overcome some of the limitations due to the ladder approximation, we introduce a minimal extension to the bound--state approach employed, so that the U_A(1) problem is avoided. Pointing out which of our predictions hold in the coupled SD-BS approach in general, and which are the consequences of the specific, chosen model, we present the results for the axial-current decay constants of eta_8, eta_0, and of their physical combinations eta and eta', the results for the gamma-gamma decay constants of eta_0 and eta_8, for the two-photon decay widths of eta and eta', and for the mixing-independent R-ratio constructed from them.Comment: 30 pages, RevTeX, 2 eps figures, title changed, material reorganized, refereces updated; to appear in Phys. Rev.

Pseudoscalar qqbar mesons and effective QCD coupling enhanced by <A^2> condensate

Recent developments provided evidence that the dimension 2 gluon condensate is important for the nonperturbative regime of Yang-Mills theories (quantized in the Landau gauge). We show that it may be relevant for the Dyson-Schwinger approach to QCD. In order that this approach leads to a successful hadronic phenomenology, an enhancement of the effective quark-gluon interaction seems to be needed at intermediate (p^2 \sim 0.5 GeV^2) momenta. It is shown that the gluon condensate provides such an enhancement. It is also shown that the resulting effective strong running coupling leads to the sufficiently strong dynamical chiral symmetry breaking and successful phenomenology at least in the light sector of pseudoscalar mesons.Comment: revtex4, 4 eps figures, 8 pages, improved presentation, to appear in Phys. Rev.

Schwinger-Dyson approach and generalized impulse approximation for the π0γ*γ transition

We review the pion-photon transition form factor calculated in the Schwinger-Dyson approach and an impulse approximation. We present results for it far above the scales presently accessible for measurement, up to 36 GeV^2, and demonstrate agreement with the analytically inferred asymptotic behavior, for which we also provide a new derivation. We discuss how measurements at Jefferson Lab can provide information on how quarks are dynamically dressed

The dependence of the asymptotic behaviour of the γ* γ → π^0 transition on the dressed quark-photon vertices

It is discussed how various Ansätze for the dressed quark-photon (qqγ) vertices Γ^µ(q,q´) influence the asymptotics of the γ* γ→ π^0 transition form factor. In this regard, we rectify certain misconceptions present in the literature

Schwinger-Dysonov pristup i poopćena impulsna aproksimacija za π 0γ ⋆γ prijelaz

We review the pion-photon transition form factor calculated in the Schwinger-Dyson approach and an impulse approximation. We present results for it far above the scales presently accessible for measurement, up to 36 GeV2, and demonstrate agreement with the analytically inferred asymptotic behavior, for which we also provide a new derivation. We discuss how measurements at Jefferson Lab can provide information on how quarks are dynamically dressed.Razmatramo faktor oblika prijelaza pion-foton u Schwinger-Dysonovom pristupu i impulsnoj aproksimaciji. Izlažemo rezultate za mnogo veće energije od sada dostupnih, do 36 GeV2 , i pokazujemo slaganje s asimptotički izvedenim ponašanjem, za koje također dajemo nov izvod. Raspravljamo kako mjerenja u Jefferson Labu mogu dati podatke o dinamičkom oblaganju kvarkova