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Oct 23 – 27, 2023
Perimeter Institute for Theoretical Physics
America/Toronto timezone

The Case for Renormalizable Quantum Gravity: from local to nonlocal approaches (and back!)

Oct 24, 2023, 11:15 AM
PI/1-100 - Theatre (Perimeter Institute for Theoretical Physics)

PI/1-100 - Theatre

Perimeter Institute for Theoretical Physics



Luca Buoninfante


In the context of perturbative quantum field theory (QFT), the addition of quadratic-curvature invariants to the Einstein-Hilbert action makes it possible to achieve strict renormalizability in four dimensions. This theory exhibits unusual features due to an additional massive spin-2 ghost which, in general, may cause instabilities. In the first part of this talk, we focus on the possibility of giving up locality as a way to avoid ghost-like degrees of freedom and provide a critical assessment on open questions in nonlocal theories of gravity, such as the uniqueness problem. In the second part of the talk, we take a step back and argue that, despite the presence of the ghost and actually thanks to it, Quadratic Gravity can still provide a consistent local perturbative QFT description of the gravitational interaction and explain new physics beyond Einstein's general relativity, e.g., it offers a natural explanation for the inflationary phase. Finally, we argue that a type of nonlocality in gravity can still occur non-perturbatively and show that a new lower bound on scattering amplitudes indicates that the gravitational interaction is intrinsically nonlocal if black holes form.

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