The calculation of the eta-prime hairpin diagram is carried out in the modified quenched approximation (MQA) in which the lattice artifact which causes exceptional configurations is removed by shifting observed poles at kappa<kappa_c in the quark propagators to the critical value of hop ping parameter. By this method, the eta-prime propagator can be accurately calculated even for very light quark mass. A determination of the topological susceptibility for quenched QCD is also obtained, using the fermionic method of Smit and Vink to calculate winding numbers.
@article{arxiv.hep-lat/9711020,
title = {The eta-prime propagator in quenched QCD},
author = {W. Bardeen and A. Duncan and E. Eichten and S. Perrucci and H. Thacker},
journal= {arXiv preprint arXiv:hep-lat/9711020},
year = {2009}
}