Newton, entanglement, and the graviton

TL;DR

This paper explores how experiments testing gravitational entanglement can also serve as tests for the existence of gravitons, linking quantum entanglement with fundamental particle physics assumptions.

Contribution

It demonstrates that gravitational entanglement experiments imply the existence of massless bosons, such as gravitons, under unitarity and Lorentz invariance assumptions.

Findings

Gravitational entanglement requires massless bosons.

Experiments can potentially distinguish graviton types.

Unitarity and Lorentz invariance are crucial assumptions.

Abstract

Many experiments have recently been proposed to test whether non-relativistic gravitational interactions can generate entanglement. In this note, I consider the extent to which these experiments can test if the graviton exists. Assuming unitarity and Lorentz invariance of the $S$-matrix, I demonstrate that this "Newtonian entanglement" requires the existence of massless bosons, universally coupled to mass, in the Hilbert space of low-energy scattering states. These bosons could be the usual spin-2 gravitons, but in principle there are other possibilities like spin-0 scalar gravitons. I suggest a concept for a more refined experiment to rule these out. The special role of $d=3+1$ spacetime dimensions and the possibility that unitarity is violated by gravity are highlighted.