On Isometric Embeddings into Anti-de Sitter Space-times
  We show that any metric on $S^2$ with Gauss curvature $K \geq -\kappa$ admits a $C^{1,1}$-isometric embedding into the hyperbolic space with sectional curvature $-\kappa$. We also give a sufficient condition for a metric on $S^2$ to be isometrically embedded into anti-de Sitter spacetime with the prescribed cosmological time function. 
Ye-Kai Wang and Chen-Yun Lin
math.DG