On the unitarity of linearized General Relativity coupled to matter

TL;DR

This paper investigates the unitarity of the S-matrix in linearized General Relativity coupled with matter, showing that particle content influences the unitarity violation scale and constrains model building.

Contribution

It analyzes how renormalization group effects impact unitarity bounds in matter-coupled linearized gravity, providing new constraints on particle content.

Findings

Unitarity violation scale depends on particle content.

Bounds on particle content are derived from unitarity requirements.

Unitarity is maintained up to the strong quantum gravity scale.

Abstract

We consider the unitarity of the S-matrix for linearized General Relativity coupled to particle physics models. Taking renormalization group effects of the Planck mass into account, we find that the scale at which unitarity is violated is strongly dependent on the particle content of the theory. We find that the requirement that the S-matrix be unitary up to the scale at which quantum gravitational effects become strong implies a bound on the particle content of the model.