Analysis of information sources in references of the Wikipedia article "Bimetric gravity" in English language version.
One interesting by-product of this was the knocking down of the Rosen bimetric theory of gravity, which hitherto was in agreement with solar system experiments. The theory turned out to make radically different predictions for gravitational wave energy loss than general relativity, and was in severe disagreement with the observations.
An alternate model that how negative mass might behave: in so-called 'bimetric gravity' you can have positive and negative masses, but each is described by its own set of Einstein field equations. That's kinda like having 'parallel spacetimes', one with positive and one with negative masses, which can still interact gravitationally. In these models, like masses attract and opposite masses repel… and you don't get the crazy 'runaway motion' that occurs if you put both positive and negative masses in the same spacetime. So no perpetual motion machines… It can also be used to explain dark energy and dark matter.
