Coset Construction of Noncompact Spin(7) and G_2 CFTs
  We provide a new class of exactly solvable superconformal field theories that corresponds to type II compactification on manifolds with exceptional holonomies. We combine N=1 Liouville field and N=1 coset models and construct modular invariant partition functions of strings moving on these manifolds. The resulting theories preserve spacetime supersymmetry. Also we explicitly construct chiral currents in these models to realize consistent string theories. 
Katsuyuki Sugiyama and Satoshi Yamaguchi