Toward QCD String: No Folds
  We propose a string theory model which explains several features of two dimensional YM theory. Folds are suppressed. This in turn leads to the empty theory in flat target spaces. The Nambu-Goto action appears in the usual way. The model naturally splits into two (chiral) sectors: orientation preserving maps and orientation reversing maps. Moreover it has a straightforward extension to 3 and 4 dimensional space-times, which could be the rigid string with the self-intersection number at $\theta=\pi$. 
Jacek Pawe{\l}czyk