Topological and rigidity results for four-dimensional hypersurfaces in space forms
This paper establishes topological and rigidity results for four-dimensional hypersurfaces in five-dimensional space forms by characterizing isoparametric hypersurfaces via the Weyl tensor, deriving sharp bounds on the Weyl functional, estimating the second fundamental form in terms of the Euler characteristic, and proving rigidity through integral inequalities, with extensions to locally conformally flat ambient spaces.