  Nontrivial translation matrices occur for spin (A,B)+(C,D) with |A-C| = |B-D|
= 1/2, necessarily associating a (C,D) field with a spin (A,B) field. Including
translation matrices in covariant non-unitary Poincare representations also
introduces new gauge terms in the construction of massless particle fields from
canonical unitary fields. In the usual procedure without spacetime translation
matrices, gauge terms arise from `translations' of the massless little group;
the little group combines spacetime rotations and boosts making a group
isomorphic with the Euclidean group E2, including E2 translations. The usual
remedy is to invoke gauge invariance. But here, the spacetime translation gauge
terms can cancel the little group gauge terms, trading the need for gauge
invariance with the need to specify displacements and to freeze two little
group degrees of freedom that are not wanted anyway. The cancelation process
restricts the helicity to A-B-1 for A-C = -(B-D) = 1/2 and A-B+1 for A-C =
-(B-D) = -1/2. However, the cancelation only works for the little group
standard momentum and specific transformations and, in general, gauge
invariance is still needed to obtain massless particle fields. Expressions for
massless particle fields for each spin type are found.
