$Q^2$ Independence of $QF_2/F_1$, Poincare Invariance and the   Non-Conservation of Helicity
  A relativistic constituent quark model is found to reproduce the recent data regarding the ratio of proton form factors, $F_2(Q^2)/F_1(Q^2)$. We show that imposing Poincare invariance leads to substantial violation of the helicity conservation rule, as well as an analytic result that the ratio $F_2(Q^2)/F_1(Q^2)\sim 1/Q$ for intermediate values of $Q^2$. 
Gerald A. Miller and Michael R. Frank