Causal transformations of Wightman localizations

Causal transformations of Wightman localizations are studied without assuming further symmetries (e.g., Galilean or Lorentz invariance). They are characterized completely by a condition which imposes analyticity and restricted growth on the matrix elements and implies a close connection between the helicity components. This condition is applied to obtain causal time evolutions. Spin-0 and spin-1/2 systems and, generally, all simple systems of definite spin are considered in detail. The factorizing causal time evolutions are determined completely.