The Bogolubov group and quantisation of scalar fields

The authors present an approach to the Bogolubov group for a Klein-Gordon field on a curved background, based on the structure of the space of solutions of the field equation. This suggests a modified formalism for quantising fields on a curved background. Creation and annihilation operators are replaced by a single 'universal' object, from which observables may be constructed by means of certain projectors giving the appropriate creation and annihilation parts. They conclude with some remarks on the implementation of the adiabatic approximation method and on a new geometrical framework for quantisation on a curved background.