String Theory on AdS_3 x S^3 x S^3 x S^1
  Spacetime properties of superstrings on AdS_3 x S^3 x S^3 x S^1 are studied. The boundary theory is a two dimensional superconformal field theory with a large N=(4,4) supersymmetry. 
Shmuel Elitzur, Ofer Feinerman, Amit Giveon, David Tsabar