Decoupling limits in Renormalizable Quantum Gravity

A natural way to extend Einstein’s General Relativity in the high-energy regime is to introduce higher-order curvature terms in the gravitational Lagrangian. Indeed, by working in the framework of perturbative QFT one can show that quadratic-curvature gravity in four dimensions is strictly renormalizable. The quadratic-curvature terms are multiplied by dimensionless parameters that are related to the masses of the additional gravitational degrees of freedom and to the interaction couplings. In this talk, after having motivated Renormalizable Quantum Gravity, we will study the limits in which those dimensionless parameters tend to zero or to infinity, and show that different types of decoupling can occur. In particular, it will be shown that the presence of a non-zero cosmological constant affects the decoupling in a non-trivial way in the limit where the coefficient of the Weyl-squared term tends to infinity. We will discuss possible physical implications of this mathematical analysis for the high-energy behavior of the spin-2 massive ghost and for the classical limit of the theory. Several concepts that have been developed in the context of massive gravity will naturally emerge in this talk, sometimes with different relevance.