A generalized mass involving higher order symmetric function of the   curvature tensor
  We define a generalized mass for asymptotically flat manifolds using some higher order symmetric function of the curvature tensor. This mass is non-negative when the manifold is locally conformally flat and the $\sigma_k$ curvature vanishes at infinity. In addition, with the above assumptions, if the mass is zero, then, near infinity, the manifold is isometric to a Euclidean end. 
YanYan Li, Luc Nguyen
gr-qc math.DG