The CSI_K conjecture for higher-dimensional Kundt spacetimes

Let a spacetime be a constant scalar invariant (CSI) spacetime, meaning that all scalar polynomial curvature invariants are constant. The higher-dimensional Kundt CSI class consists of the Kundt spacetimes with constant scalar invariants considered in the source. CSI_K conjecture. If a spacetime is CSI, then it is either locally homogeneous or belongs to the higher-dimensional Kundt CSI class. This is presented as a consequence of the CSI_F conjecture, assuming that its preferred null frame exists, and remains conjectural.