GW170817 Constraints and Causal Structure

We demonstrate that RCD satisfies the gravitational wave speed constraint |c_T - c|/c < 1e-15 from GW170817. The tensor mode propagates on the conformally related Einstein metric with c_T = c exactly, while scalar disformal propagation applies only to C excitations. This result holds for the minimal disformal action and remains exact under kinetic completion B' (Paper VII).