Non-Umbilical Quaternionic Contact Hypersurfaces in Hyper-Kahler Manifolds

It is shown that any compact quaternionic contact (qc) hypersurfaces in a hyper-Kahler manifold which is not totally umbilical has an induced qc structure, locally qc homothetic to the standard 3-Sasakian sphere. In the non-compact case, it is proved that a seven-dimensional everywhere non-umbilical qc-hypersurface embedded in a hyper-Kahler manifold is qc-conformal to a qc-Einstein structure which is locally qc-equivalent to the 3-Sasakian sphere, the quaternionic Heisenberg group or the hyperboloid.