Thanks for the link...
“In theories of quantum gravity, the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravity.
There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity.
In string theory, believed to be a consistent theory of quantum gravity, the graviton is a massless state of a fundamental string.
If it exists, the graviton is expected to be massless because the gravitational force is very long range and appears to propagate at the speed of light.”
https://en.wikipedia.org/wiki/Graviton