EXACT RELATION BETWEEN EINSTEIN AND QUADRATIC QUANTUM-GRAVITY

We show the exact equality of the path integral of the general renorma lizable fourth order gravitational action to the path integral of the Einstein action coupled to a massive spin-0 field and a massive spin-2 ghost-like field with non-polynomial interactions. The metric in the Einstein version is a highly nonlinear function of the metric in the q uadratic version. Both massive excitations are unstable. The respectiv e cosmological constant terms in the two versions can be very differen t. Some implications are briefly discussed.