A Modified Gravity and Its Consequences for the Solar System, Astrophysics and Cosmology∗

A relativistic modified gravity (MOG) called Scalar-Tensor-Vector Gravity (STVG) desribes a self-consistent, stable gravity theory that contains Einstein’s general relativity in a well-defined limit. The theory has an extra degree of freedom, a vector field called a “phion” field whose curl is a skew symmetric field that couples to matter (“fifth force”). The spacetime geometry is described by a symmetric Einstein metric. An alternative relativistic gravity theory called Metric-Skew-Tensor Gravity (MSTG) has also been formulated in which the spacetime is described by a symmetric metric, and the extra degree of freedom is a skew symmetric second rank tensor field. Both of these theories yield the same weak field consequences for physical systems. The classical STVG theory allows the gravitational coupling “constant” G and the coupling of the phion field and its effective mass to vary with space and time as scalar fields. A MOG should explain the following physical phenomena: