mass, denoted and respectively. The interaction potential is the same as in dRGT massive gravity. The are dimensionless coupling constants and (or specifically ) is related to the mass of the massive graviton. This theory propagates seven degrees of freedom, corresponding to a massless graviton and a massive graviton (although the massive and massless states do not align with either of the metrics). The interaction potential is built out of the elementary symmetric polynomials of the eigenvalues of the matrices or , parametrized by dimensionless coupling constants or , respectively. Here is the matrix square root of the matrix . Written in index notation, is defined by the relation The can be written directly in terms of as where brackets indicate a trace, . It is the particular antisymmetric combination of terms in each of the which is responsible for rendering the Boulware–Deser ghost nondynamical. See also Alternatives to general relativity DGP model Scalar–tensor theory References Theories of gravity General relativity