Power-law Solutions from Heterotic Strings
  In this paper, we search for accelerating power-law and ekpyrotic solutions in heterotic string theory with NS-NS fluxes compactified on half-flat and generalized half-flat manifolds. We restrict our searches to the STZ sector of the theory. We also considered linear order $\alpha'$ corrections for the half-flat case. The power-law solutions that we find are neither accelerating nor ekpyrotic in any of the models. 
Tibra Ali and S. Shajidul Haque
hep-th