The Bargmann-Wigner (BW) scalar product is a particular case of a larger class of scalar products parametrized by a family of world-vectors. The choice of null and $p$-dependent world-vectors leads to BW amplitudes which behave as local $SU(2)$ spinors (BW-spinors) if { \it passive\/} transformations are concerned. The choice of null directions leads to a simplified formalism which allows for an application of ordinary, manifestly covariant spinor techniques in the context of infinite dimensional unitary representations of the Poincar\'e group.
Categories: quant-ph gr-qc hep-th