Causal Quantum Gravity

Abstract

I discuss some issues of perturbative quantum gravity, namely of a theory of self-interacting massless spin-2 quantum gauge fields, the gravitons, on flat space-time, in the framework of causal perturbation theory. The central aspects of this approach lie in the construction of the scattering matrix by means of causality and Poincare covariance and in the analysis of the gauge structure of the theory. For this purpose, two main tools will be used: the Epstein-Glaser inductive and causal construction of the perturbation series for the scattering matrix and the concept of perturbative operator quantum gauge invariance borrowed from non-Abelian quantum gauge theories. The first method deals with the ultraviolet problem of quantum gravity and the second one ensures gauge invariance at the quantum level, formulated by means of a gauge charge, in each order of perturbation theory. The gauge charge leads to a characterization of the physical subspace of the graviton Fock space. Aspects of quantum gravity coupled to scalar matter fields are also discussed.