# On amplitudes, resonances and the ultraviolet completion of gravity

## TL;DR

This paper proposes a possible ultraviolet completion of gravity using on-shell methods, predicting an infinite tower of resonances and deviations from General Relativity, with implications for string theory and spacetime structure.

## Contribution

It introduces a novel bottom-up approach to gravity's ultraviolet completion using on-shell techniques, incorporating an infinite resonance spectrum and duality relations.

## Key findings

- Predicts an infinite tower of resonances with increasing spin and mass.
- Suggests deviations from General Relativity in gravity-fermion couplings.
- Links the amplitude structure to string theory-like form factors.

## Abstract

This letter constructs, making use of the on-shell spinor-helicity formalism, a possible ultraviolet completion of gravity following a "bottom-up" approach. The assumptions of locality, unitarity and causality i) require an infinite tower of resonances with increasing spin and quantized mass, ii) introduce a duality relation among crossed scattering channels, and iii) dress all gravitational amplitudes in the Standard Model with a form factor that closely resembles either the Veneziano or the Virasoro-Shapiro amplitude in string theory. As a consequence of unitarity, the theory predicts leading order deviations from General Relativity in the coupling of gravity to fermions that could be explained if space-time has torsion in addition to curvature.