Local aspects of free open bosonic string field theory
  We show that strictly local observables with arbitrarily small support in space-time exist in covariant free open bosonic string field theory. The main ingredient of the proof is a modified version of the well known DDF operators, which we rigourously define. This result allows in principle the definition of a net of local observable algebras and should be considered as a first step towards the application of algebraic quantum field theory to this case 
Luca Tomassini