Principal configurations around umbilics of spacelike surfaces in null hypersurfaces of R-1(4)

摘要

We study the principal configurations around an isolated eta-umbilical point on a generic spacelike surface S immersed in a null hypersurface M of Minkowski space R-1(4) relative to a well-defined null vector field eta orthogonal to the surface S. In the particular case of M being a null rotation hypersurface of R-1(4) we also recover the local Darbouxian principal configurations around that kind of eta-umbilical points. (C) 2019 Elsevier B.V. All rights reserved.