Va. Kostelecky et R. Potting, Analytical construction of a nonperturbative vacuum for the open bosonic string - art. no. 046007, PHYS REV D, 6304(4), 2001, pp. 6007
Using analytical methods, a nonperturbative vacuum is constructed recursive
ly in the field theory for the open bosonic string. Evidence suggests it co
rresponds to the Lorentz-invariant end point of tachyon condensation on a D
25-brane. The corresponding string field is a twisted squeezed state.