Large pion pole in Z_{S}^{MOM}/Z_{P}^{MOM} from Wilson action data

Abstract

We show that, contrarily to recent claims, data from the Wilson (unimproved) fermionic action at three different beta values demonstrate the presence of a large Goldstone boson contribution in the quark pseudoscalar vertex, quantitatively close to our previous estimate based on the SW action with c_{SW}=1.769. We show that discretisation errors on Z_{S}^{MOM}/Z_{P}^{MOM} seem to be much smaller than the Goldstone pole contribution over a very large range of momenta. The subtraction of this non perturbative contribution leads to numbers close to one-loop BPT.

Comments: 12 pages, 5 figures, laTeX, minor corrections of typos, beta dependence made more explicit, added one table giving the contribution of the Goldstone vs. the discretisation errors at ap=1