  We show that bosonic D-brane states may be represented as coherent states in
an open string representation. By using the Thermo-Field Dynamics (TFD)
formalism, we may construct a condensed state of open string modes which
encodes the information on the D-brane configuration.
  We also introduce a construction alternative to TFD, which does not requires
to assume thermal equilibrium. It is shown that the dynamics of the system
combined with geometric properties of the duplication rules of TFD is
sufficient to obtain the thermal states and their analytic continuations in a
geometric fashion. We use this approach to show that bosonic D-brane state in
the open string sector may also be built as boundary states in a special sense.
  Some implications of this study on the interpretation of the open/closed
duality and on the kinemathic/algebraic structure of an open string field
theory are also commented.

High Energy Physics - Theory