Peculiar spaces of relativistic quantum fields
  We study how quantum field theory models are modified under the reparametrizations of the space-time coordinates and some simultaneous transformations of the field function. The transformations that turn the action of the massive field in the Minkowski space-time into the action of the massless field in some curved space are presented. 
V.V. Belokurov and E.T. Shavgulidze
hep-th