Eta-Eta' mixing and the derivative of the topological susceptibility at zero momentum transfer

Abstract

The couplings of the isosinglet axial-vector currents to the Eta and Eta' mesons are evaluated in a stable, model independent way by use of polynomial kernels in dispersion integrals. The corrections to the Gell-Mann-Oakes-Renner relation in the isoscalar channel are deduced. The derivative of the topological susceptibility at the origin is calculated taking into account instantons and instanton screening.

Comments: Mistakes corrected. Text after eq.3.14 changed. An evaluation of the topological susceptibility itself is presented in addition