Finite Quantum Gravity Amplitudes -- no strings attached

TL;DR

This paper presents a novel approach to quantum gravity scattering amplitudes that are consistent with fundamental physical principles without relying on string theory, by analyzing effective actions with infinite spin towers.

Contribution

It introduces a new framework for quantum gravity amplitudes using Lorentzian effective actions with infinite spin towers, avoiding non-localities and higher-spin particles.

Findings

Amplitudes are compatible with unitarity bounds.

Scattering amplitudes are causal and scale-free at trans-Planckian energies.

The approach avoids non-localities and massive higher-spin particles.

Abstract

We study the gravity-mediated scattering of scalar fields based on a parameterisation 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 non-localities or the massive higher-spin particles that are characteristic in string theory.