$Q^2$ independence of ${\mathrm{QF}}_2{/F}_1,$ Poincaré invariance, and the nonconservation of helicity

A relativistic constituent quark model is found to reproduce the recent data regarding the ratio of proton form factors, $F_2{(Q}^2{)/F}_1{(Q}^2).\mathrm{}$ We show that imposing Poincaré invariance leads to substantial violation of the helicity conservation rule, and an analytic result that the ratio $F_2{(Q}^2{)/F}_1{(Q}^2)\sim 1/Q$ for intermediate values of $Q^2.$