Non‑perturbative stability of quadratic and non‑local gravity

Investigate whether non‑perturbative and classical instabilities occur in quadratic‑curvature gravity and in ghost‑free non‑local gravity, despite perturbative indications of stability, and determine conditions under which these theories are stable.

Background

Quadratic gravity and non‑local gravity can avoid perturbative pathologies and appear stable at that level. However, their non‑perturbative and classical behavior may differ.

The panel explicitly recognized uncertainty about potential instabilities beyond perturbation theory, highlighting the need for rigorous non‑perturbative analyses.