Space-time singularities and the axion in the Poincare coset models   ISO(2,1)/H
  By promoting an invariant subgroup $H$ of $ISO(2,1)$ to a gauge symmetry of a WZWN action, we obtain the description of a bosonic string moving either in a curved 4-dimensional space--time with an axion field and curvature singularities or in 3-dimensional Minkowski space--time. 
Roberto Casadio (INFN, Sezione di Bologna, Italy), Benjamin Harms,   (University of Alabama)