Super-Yang-Mills quantum mechanics and supermembrane spectrum
  It is shown that the mass spectrum of supermembrane theory is continuous. This fact is due to the trivial circumstance that a membrane can emit "needles" of zero area with no cost in energy. In supersymmetric case, this classical degeneracy is not lifted by quantum corrections. This unpleasant property may be cured, perhaps, for the supermembrane with a modified action involving higher derivative terms. 
A.V. Smilga
hep-th