Constant scalar curvature hypersurfaces in (3+1)-dimensional GHMC Minkowski spacetimes

We prove that every (3+1)-dimensional flat GHMC Minkowski spacetime which is not a translation spacetime or a Misner spacetime carries a unique foliation by spacelike hypersurfaces of constant scalar curvature. In other words, we prove that every such spacetime carries a unique time function with isochrones of constant scalar curvature. Furthermore, this time function is a smooth submersion.