Frame dependence of spin-one angular conditions in light-front dynamics

We elaborate the frame dependence of the angular conditions for spin-1 form factors. An extra angular condition is found in addition to the usual angular condition relating the four helicity amplitudes. Investigating the frame dependence of angular conditions, we find that the extra angular condition is in general as complicated as the usual one, although it becomes very simple in the ${q}^{+}=0$ frame involving only two helicity amplitudes. It is confirmed that the angular conditions are identical in frames that are connected by kinematical transformations. The high-${Q}^{2}$ behavior of the physical form factors and the limiting behavior in special reference frames are also discussed.