Aspects of model dependence of $$\eta '$$–$$\eta $$ complex treated by going beyond the isospin limit

Abstract

Exploring the extent of model dependence, we study effects of certain Ansaetze for the T-dependence of the correction term in the QCD topological susceptibility. The one producing unwanted effects on results at T > 0 in the eta'-eta complex in the usual limit of isospin symmetry, is largely cured from its peculiar behavior and brought into agreement with the other, when breaking of isospin symmetry is allowed and the realistic quark mass ratio m_u/m_d = 0.50 is adopted.