Pseudoscalar vertex, Goldstone boson and quark masses on the lattice

We analyse the Structure Function collaboration data on the quark pseudoscalar vertex and extract the Goldstone boson pole contribution, in 1/p(2). The strength of the pole is found to be quite large at presently accessible scales. We draw the important consequences of this finding for the various definitions of quark masses (short distance and Georgi-Politzer), and point out problems with the operator product expansion and with the non-perturbative renormalisation method. (C) 1999 Published by Elsevier Science B.V. All rights reserved.