On the classical solution for the double-brane background in open string   field theory
  Murata and Schnabl recently proposed solutions for the multiple-brane backgrounds in Witten's open bosonic string field theory. The solutions contain some singularities, and in one particular regularization, the double-brane solution reproduces the desired energy and the Ellwood invariant, which is conjectured to represent coupling to a closed string. However, it turned out that the equation of motion is slightly violated. In this paper, we propose another regularization method for the double-brane solution. The regularized solution is realized as a superposition of the wedge states with operator insertions. It respects the equation of motion both contracted with the solution itself and with the states in the Fock space. It reproduces the desired double-brane tension, while the expected Ellwood invariant is not obtained. 
Toru Masuda
hep-th