Higher-order curvature operators in causal set quantum gravity

Abstract

We construct higher-order curvature invariants in causal set quantum gravity. The motivation for this work is twofold: first, to characterize causal sets, discrete operators that encode geometric information on the emergent spacetime manifold, e.g., its curvature invariants, are indispensable. Second, to make contact with the asymptotic-safety approach to quantum gravity in Lorentzian signature and find a second-order phase transition in the phase diagram for causal sets, going beyond the discrete analogue of the Einstein-Hilbert action may be critical.\\ Therefore, we generalize the discrete d'Alembertian, which encodes the Ricci scalar, to higher orders. We prove that curvature invariants of the form $R^2 -2 \Box R$ (and similar invariants at higher powers of derivatives) arise in the continuum limit.