Scalar Quantum Field Theory with Cubic Interaction
  In this paper it is shown that an i phi^3 field theory is a physically acceptable field theory model (the spectrum is positive and the theory is unitary). The demonstration rests on the perturbative construction of a linear operator C, which is needed to define the Hilbert space inner product. The C operator is a new, time-independent observable in PT-symmetric quantum field theory. 
Carl M. Bender, Dorje C. Brody, and Hugh F. Jones