We study biharmonic hypersurfaces in a generic Riemannian manifold. We first derive an invariant equation for such hypersurfaces generalizing the biharmonic hypersurface equation in space forms studied by Jiang, Chen, Caddeo, Montaldo, and Oniciuc. We then apply the equation to show that the generalized Chen conjecture is true for totally umbilical biharmonic hypersurfaces in an Einstein space, and construct a 2-parameter family of conformally flat metrics and a 4-parameter family of multiply warped product metrics, each of which turns the foliation of an upper-half space of ޒ m by parallel hyperplanes into a foliation with each leaf a proper biharmonic hypersurface. We also study the biharmonicity of Hopf cylinders of a Riemannian submersion.
Biharmonic maps and submanifoldsAll manifolds, maps, and tensor fields that appear in this paper are assumed to be smooth unless stated otherwise.A biharmonic map is a map ϕ : (M, g) → (N , h) between Riemannian manifolds that is a critical point of the bienergy functionalfor every compact subset of M, where τ (ϕ) = Trace g ∇dϕ is the tension field of ϕ. The Euler-Lagrange equation of this functional gives the biharmonic map equation [Jiang 1986b] (which states that ϕ is biharmonic if and only if its bitension field τ 2 (ϕ) vanishes identically. In this equation we used R N to denote the curvature operator of (N , h) MSC2000: 53C12, 58E20, 53C42.