Can two or more gauge bosons propagate in the light-front?
  Gauge fields in the light-front are usually fixed via the nA=0 condition yielding the non-local singularities of the type (kn)^(-a)=0 and a=1,2,.. in the gauge boson propagator which must be addressed conveniently. In calculating this propagator for n noncovariant gauge bosons those non-local terms demand the use of a prescription to ensure causality. We show that from 2 gauge bosons onward the implementation of such a prescription does not remove certain pathologies such as the non existence of two or more free propagating gauge bosons in the light-front form. 
A. T. Suzuki and J. H. O. Sales