We use equivariant geometry methods to show the existence of complete hypersurfaces in euclidean spaces with constant negative 2n-th curvature.
Introduction.A classic theorem by Hilbert states that there are no complete surfaces in R 3 with constant negative gaussian curvature. Attempting to generalize this theorem to higher dimensions, it is natural to analyze first some examples of hypersurfaces in euclidean space with constant negative r-th curvature σ r , σ r being the r-th symmetric function of the principal curvatures of the hypersurface. As this universe is still large, we restrict further to those such hypersurfaces which are invariant under a given group of isometries of the euclidean space. Following the classification of the low cohomogeneity isometry groups given by W. Y. Hsiang and H. B. Lawson in [2], the author studied rotational (i.e., SO(n)-invariant) hypersurfaces in space forms in [5], and concluded, on one hand, that for each r odd and each σ < 0 there exists a 1-parameter family of complete rotational hypersurfaces in R n+1 with σ r = σ ; and, on the other hand, that there are no complete rotational hypersurfaces with constant negative σ r for r even. It should be mentioned that these results generalize those obtained by M. L. Leite in [3] and J. Hounie and Leite in [1].This result would suggest a generalization of Hilbert's theorem for constant negative σ r and r even, but T. Okayasu [4] built the first example of a complete hypersurface in R 4 with constant negative scalar curvature (so that σ 2 < 0), using the cohomogeneity two isometry group O(2)×O(2). Here we extend Okayasu's result to higher dimensions. More precisely, we prove