Exact Solutions in Open Bosonic String Field Theory and Marginal Deformation in CFT

In this paper we continue our study of the exact solution in open bosonic string field theory. We present solution in the string field theory defined on the background corresponding to the boundary conformal field theory (BCFT ) describing D25-brane. We then show that the string field theory that arises from the original one by an expansion about this classical solution can be interpreted as the string field theory defined on the new BCFT ′′ that is related to the original BCFT by marginal boundary interaction. In particular we will show that this approach can be useful for the study of the exact time dependent solution in the open bosonic string field theory.