Chaplygin Gas Cosmology - Unification of Dark Matter and Dark Energy
  The models that unify dark matter and dark energy based upon the Chaplygin gas fail owing to the suppression of structure formation by the adiabatic speed of sound. Including string theory effects, in particular the Kalb-Ramond field, we show how nonadiabatic perturbations allow a successful structure formation. 
Neven Bilic, Gary B. Tupper and Raoul D. Viollier