Alessia Platania: Non-perturbative unitarity and fictitious ghosts in quantum gravity

According to the asymptotic-safety conjecture, a (non-perturbatively) renormalizable quantum field theory of gravity could be constructed based on the existence of a non-trivial fixed point of the gravitational renormalization group flow. The existence of this fixed point can be established, e.g., via the non-perturbative methods of the functional renormalization group (FRG). In practice, the use of the FRG methods requires to work within truncations of the gravitational action, and higher-derivative operators naturally lead to the presence of several poles in the propagator. The question is whether these poles represent a real problem for the unitarity of the theory. In this talk I will show with explicit examples that the inclusion of quantum effects at all scales is of crucial importance to assess unitarity of field theories. In particular, poles appearing in truncations of the action could correspond to fake degrees of freedom of the theory. Possible conditions to determine, within truncations, whether a pole represents a fake or a genuine degree of freedom of the theory will be discussed.

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