Scalar-tensor gravity theory for dynamical light velocity

A gravity theory is developed with the metric ĝμν=gμν+B∂μφ∂νφ. In the present universe the additional contribution from the scalar field in the metric ĝμν can generate an acceleration in the expansion of the universe, without negative pressure and with a zero cosmological constant. In this theory, gravitational waves will propagate at a different speed from non-gravitational waves. It is suggested that gravitational wave experiments could test this observational signature.