Speaker
Description
Quadratic gravity is an attractively simple approach to quantum gravity where terms quadratic in the curvature are included in the action. Almost 50 years ago, Stelle showed the theory to be renormalizable. Avramidi and Barvinsky then showed it to be asymptotically free. However, like other higher derivative theories, quadratic gravity is plagued by classical instabilities and quantum ghosts. In this talk I will explain how these problems are resolved in a certain limit of quadratic gravity, where the only nontrivial degree of freedom is the local scale factor of spacetime. Through a careful covariant quantization, we show that the quantum theory is causal and measurable due to a hidden ghost parity symmetry. This symmetry is revealed by embedding the four-derivative theory in a larger, two-derivative O(1,1) symmetric theory. The result is a UV-complete, non-perturbative formulation of quantum gravity in four dimensions, albeit without gravitons.