Fermion helicity flip by parity violating torsion

The helicity flip of a spin-1/2 Dirac fermion interacting with a torsion-fi eld endowed with a pseudo-tensorial extension is analysed. Taking the torsi on to be represented by a Kalb-Ramond field, we show that there is a finite amplitude for helicity flip for massive fermions. The lowest order contrib ution which turns out to be proportional to the pseudo-tensor term. implies a new physical understanding of the phenomenon of helicity flip. (C) 2001 Published by Elsevier Science B.V.