A toy model for generalised parton distributions
  We give the results of a simple model for the diagonal and off-diagonal valence quark distributions of a pion. We show that structure can be implemented in a gauge-invariant manner. This explicit model questions the validityof the momentum sum rule, and gives an explicit counter-example to the Wandzura-Wilczek ansatz for twist-3 GPD's. 
J.R. Cudell, F. Bissey, J. Cugnon, M. Jaminon, J.P. Lansberg, and P.   Stassart