Codimension two spacelike submanifolds into null hypersurfaces of generalized Robertson-Walker spacetimes

We study codimension two spacelike submanifolds contained into a general class of null hypersurfaces in generalized Robertson-Walker spacetimes, refer to as nullcones. In particular we analyze light cones and lightlike cylinders in Lorentz-Minkowski spacetime, as well as null cones in de Sitter spacetime. We give conditions on a radial coordinate that guarantee that such a spacelike submanifold is conformally diffeomorphic to the hyperbolic space, a round cylinder a sphere; respectively. We also provide some non-existence results for weakly trapped submanifolds.