Speaker
Description
Quadratic gravity (QG) is an attractively minimal framework for quantum gravity, being renormalizable and asymptotically free. In a certain limit, the only nontrivial degree of freedom is the conformal factor of the metric. The Lorentzian theory is nevertheless rich enough to describe both a cosmological background and particle-like excitations within it. Both are governed by a four-derivative scalar field theory, the perfect square (PS) theory, which we have recently shown to be quantum consistent with unitarity and causality despite the presence of ghosts. We have studied the renormalisation of PS theory in detail, showing it to be free of IR loop divergences and establishing a remarkable correspondence with phi^4 scalar theories. While more work is needed to incorporate gravitons, this work perhaps opens the door to a consistent treatment of quantum gravity in four dimensions. I will briefly discuss some of the cosmological implications.