Finite Quantum Gravity Amplitudes: No Strings Attached

Abstract

We study the gravity-mediated scattering of scalar fields based on a parameterization of the Lorentzian quantum effective action. We demonstrate that the interplay of infinite towers of spin zero and spin two poles at imaginary squared momentum leads to scattering amplitudes that are compatible with unitarity bounds, causal, and scale-free at trans-Planckian energy. Our construction avoids introducing nonlocalities or the massive higher-spin particles that are characteristic in string theory.