Universally Coupled Massive Gravity, I

Einstein’s equations are derived from a linear theory in flat spacetime using free field gauge invariance and universal coupling. The gravitational potential can be either covariant or contravariant and of almost any density weight. These results are adapted to yield universally coupled massive variants of Einstein’s equations, yielding two one-parameter families of distinct theories with spin 2 and spin 0. The Freund-Maheshwari-Schonberg theory is thus not the unique universally coupled massive generalization of Einstein’s theory, though it is privileged in some respects. The theories derived are a subset of those found by V. I. Ogievetsky and I. V. Polubarinov by other means. The question of positive energy remains open, but might be addressed by numerical relativists in the context of spherical symmetry. A few remarks are made on the issue of causality with two observable metrics. keywords: massive gravity, bimetric, ghost, positive mass