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Little groups and Maxwell-type tensors for massive and massless particles

Baskal, S
Kim, YS
The massive and massless representations of four-vectors and Maxwell-type tensors are constructed as bilinear combinations of SL(2, C)-spinors and are evaluated on a unified description upon adopting the group contraction procedure of O(3)-like little group to E(2)-like little group. Contraction of massive particle representations leads to gauge-dependent vectors as well as the gauge-independent ''state vectors'' constructed by Weinberg. It, is shown that gauge degrees of freedom associated with the translation-like transformations of the E(2)-like little group can be traced to the spinors that undergo spin hips in the infinite-momentum/zero-mass limit.