Geons and the Instability of Anti-de Sitter Spacetime
  We briefly review the evidence that anti-de Sitter spacetime is nonlinearly unstable, and the perturbative arguments that there should exist geons - nonsingular solutions to Einstein's equation with a helical symmetry. We then explicitly construct these geons numerically and discuss some of their properties. We conclude with some open questions. 
Gary T. Horowitz and Jorge E. Santos
gr-qc hep-th