The BRST treatment of stretched membranes
  The BRST-invariant formulation of the bosonic stretched membrane is considered. In this formulation the stretched membrane is given as a perturbation around zero-tension membranes, where the BRST-charge decomposes as a sum of a string-like BRST-charge and a perturbation. It is proven, by means of cohomology techniques, that there exists to any order in perturbation theory a canonical transformation that reduces the full BRST-charge to the string-like one. It is also shown that one may extend the results to the quantum level yielding a nilpotent charge in 27 dimensions. 
Jonas Bjornsson, Stephen Hwang