Codimension-two critical behavior in vacuum gravitational collapse
  We consider the critical behavior at the threshold of black hole formation for the five dimensional vacuum Einstein equations satisfying the cohomogeneity-two triaxial Bianchi IX ansatz. Exploiting a discrete symmetry present in this model we predict the existence of a codimension-two attractor. This prediction is confirmed numerically and the codimension-two attractor is identified as a discretely self-similar solution with two unstable modes. 
Piotr Bizo\'n, Tadeusz Chmaj, Bernd G. Schmidt