where g is the metric determinant, R is the Ricci scalar constructed from the metric g μ μ ν ν , μ μ is a coupling constant with the dimensions L − − 1 M − − 1 T 2 , V ( Φ Φ ) is the scalar-field potential, L m is the material Lagrangian and Ψ Ψ represents the non-gravitational fields. Here, the Brans–Dicke parameter ω ω has been generalized to a function. Although μ μ is often written as being 8 π π G / c 4 , one has to keep in mind that the fundamental constant G there, is not the constant of gravitation that can be measured with, for instance, Cavendish type experiments. Indeed, the empirical gravitational constant is generally no longer a constant in scalar–tensor theories, but a function of the scalar field Φ Φ . The metric and scalar-field equations respectively write: