Viability of quadratic gravity as a realistic quantum gravity framework

Determine whether quadratic gravity, defined by a renormalizable curvature-squared action with R^2 and R^{\mu\nu}R_{\mu\nu} terms (agravity), constitutes a viable and realistic framework for quantum gravity, and ascertain its consistency as a quantum theory across relevant energy scales.

Background

The paper reviews quadratic (curvature-squared) gravity, which improves ultraviolet behavior and renders the theory perturbatively renormalizable, but may introduce ghostlike degrees of freedom and potential unitarity issues. While some works argue for acceptable behavior of scattering amplitudes at ultra-Planckian energies, the overall consistency and realism of quadratic gravity remain debated.

In this context, the authors emphasize that the broader question of the viability of quadratic gravity as a practical and consistent quantum gravity framework is not settled and requires further investigation.

References

The viability of quadratic gravity as a realistic framework for quantum gravity therefore remains an open question requiring additional investigation.

— On the physical running of the electric charge in a dimensionless theory of gravity  (2512.11742 - Gomes et al., 12 Dec 2025) in Introduction (Section 1)

This observation has led to our conjecture that the massive ghost might be confined as quarks and gluons in QCD which are controled by the asymptotically free coupling constant as well.

— Massive Ghost Confinement, Dipole Equation and Multipole States in Quadratic Gravity  (2608.26085 - Oda, 26 Aug 2026) in Section 2, paragraph following Eq. (\ref{Couplings})