Unification of gravitation with particle physics via metric-connection theories

This article discusses some progress which has been made towards the construction of perturbatively sensible quantum field theories based on a new proposal for the unification of general relativity with Yang-Mills theories. These new theories are called metric-connection theories because they result from a generalization of Einstein-Yang-Mills theory in which, for both spacetime and the internal geometries, the relevant metric and connection variables are both dynamical and unconstrained. This program has led to the discovery of a new class of gauge theories which are renormalizable and perturbatively unitary and causal, and there is some reason to believe it will lead to the construction of a class of gravitational theories with these properties