Complex Classical Fields: A Framework for Reflection Positivity
  We explore a framework for complex classical fields, appropriate for describing quantum field theories. Our fields are linear transformations on a Hilbert space, so they are more general than random variables for a probability measure. Our method generalizes Osterwalder and Schrader's construction of Euclidean fields. We allow complex-valued classical fields in the case of quantum field theories that describe neutral particles. From an analytic point-of-view, the key to using our method is reflection positivity. We investigate conditions on the Fourier representation of the fields to ensure that reflection positivity holds. We also show how reflection positivity is preserved by various space-time compactifications of Euclidean space. 
Arthur Jaffe, Christian D. J\"akel, and Roberto E. Martinez II
math-ph hep-th math.MP