Unitary Representations of the Translational Group Acting as Local   Diffeomorphisms of Space-Time
  We develop a new mathematical approach to diffeomorphism invariant quantum states for the quantisation of general field theories such as general relativity and modified gravity. Treating quantum fields as fibre bundles, we discuss operators acting on the fibre algebra that defines a Hilbert space. The algebras of two types of operators are considered in detail, namely the observables as generic physical variables and the quantum operators suitable for describing symmetries and transformations. We then introduce generalised quantum states of these operators and examine their properties. By establishing a link between the commutativity and group cohomology of the translational group as a subgroup of the Poincare group, we show that this leads to the construction of quantum states invariant under the action of the translational group, as the local gauge group of diffeomorphisms, with unitary representations. 
James Moffat, Teodora Oniga, Charles H.-T. Wang
math-ph gr-qc math.MP