That's what the article (https://arxiv.org/pdf/1712.07962.pdf https://arxiv.org/pdf/1712.07962.pdf) says: > In theories of quantum gravity, gravitation is medi

That's what the article (https://arxiv.org/pdf/1712.07962.pdf https://arxiv.org/pdf/1712.07962.pdf) says: > In theories of quantum gravity, gravitation is mediated by the graviton – a massless, spin-2, boson. This means that any pair of negative masses would attract, and not repel as suggested in this theory. However, there are also theoretical arguments that gravitons cannot, and will not ever, be detected experimentally (Rothman & Boughn 2006). There appear to be two options: either it is possible that the graviton could be modelled as a bound state of a positive and a negative mass, in a theory of composite gravity or some other mechanism which provides a modification of graviton properties. Alternatively, this could also indicate that the proposed theory cannot be modelled by real, physical, particles, but rather by the presence of effective negative masses within a superseding theory.