Finite size effects of a pion matrix element
  We investigate finite size effects of the pion matrix element of the non-singlet, twist-2 operator corresponding to the average momentum of non-singlet quark densities. Using the quenched approximation, they come out to be surprisingly large when compared to the finite size effects of the pion mass. As a consequence, simulations of corresponding nucleon matrix elements could be affected by finite size effects even stronger which could lead to serious systematic uncertainties in their evaluation. 
M. Guagnelli, K. Jansen, F. Palombi, R. Petronzio, A. Shindler, I.   Wetzorke