Restricting One-Loop radiative effects in quantum gravity: Demonstrating 4D GR as an EFT and its consistent unification with the Standard Model

Abstract: In "On Restricting to One-Loop Order the Radiative Effects in Quantum Gravity" (Brandt, Frenkel, and McKeon, 2020), a Lagrange multiplier (LM) field is introduced into the Einstein-Hilbert action, removing all multi-loop graviton diagrams and confining quantum-gravity corrections to just one loop. The resulting one-loop effective action carries a term proportional to $\ln(\mu/\Lambda)$, which they suggest could be experimentally determined, hinting at direct measurements of quantum-gravity effects. We show, however, that $\mu$ and $\Lambda$ emerge from a chosen \emph{renormalization scheme}, not from physical observables, implying that $\ln(\mu/\Lambda)$ signals a finite UV cutoff in this ``LM renormalization scheme.'' Although Newton's constant remains fixed (no running of $G_N$, the resulting logarithmic dependence encodes a limited domain of validity for General Relativity (GR) in four dimensions, thereby demonstrating explicitly that 4D GR behaves as an effective field theory (EFT) for energies below the cutoff. We then illustrate how this truncated, renormalized gravity sector can be consistently unified with the Standard Model (SM), yielding a finite and renormalized EFT encompassing both gravity and particle physics up to a scale $\Lambda_{\text{grav}}$.