Complex velocity transformations and the Bisognano--Wichmann theorem for   quantum fields acting on Krein spaces
  It is proven that in indefinite metric quantum field theory there exists a dense set of analytic vectors for the generator of the one parameter group of x^0-x^1 velocity transformations. This makes it possible to define complex velocity transformations also for the indefinite metric case. In combination with the results of Bros -- Epstein -- Moschella, proving Bisognano--Wichmann (BW) analyticity within the linear program, one then obtains a suitable generalization of the BW theorem for local, relativistic quantum fields acting on Krein spaces ("quantum fields with indefinite metric"). 
H. Gottschalk