  We pursue the idea of constructing higher spin fields as solutions to twisted
Dirac operators. As general results we find that twisted prenormally hyperbolic
first order operators (such as the Dirac operator) on globally hyperbolic
Lorentzian spacetime manifolds have unique advanced and retarded Green's
functions and their Cauchy problem is well-posed. The space of compactly
supported Cauchy data can be equipped with a naturally induced Hermitian but
generally indefinite product, which is shown to be independent of the
underlying choice of Cauchy hypersurface.
  As a special result, we study one particular example of twisted Dirac
operator for Fermionic fields of higher spin. It allows a canonical Hermitian
product on the spinor bundle, but the resulting product on the space of
compactly supported Cauchy data fails positivity. Thus, it is shown that this
construction does not allow quantization by forming a C*-algebra representation
of the canonical anti-commutation relations in the well known fashion
generalizing the spin 1/2 construction by Dimock (1982).
  This document is equipped with an introduction to the formalism of 2-spinors
on curved spacetimes in an invariant fashion using abstract index notation.
