Vertex functions and form factors for conformal spin 1/2 systems

Conformal on-shell wave functions are derived for spin 1/2 particle decaying virtually in spin 0 and spin 1/2. The relation to the off-shell vertex function is worked out and it is shown that shadow singularities are shifted to d'=5/2, d' being the dimension of the particle field. The obtained wave functions are used to compute the conformal contribution to the form factors. For d' < 5/2 the renormalization group result is reproduced. For d' > 5/2 the appearance of infra-red divergences enhances this contribution above the dimensional bound and the enhancement is computed in terms of the dimensions of the various fields