Closed string amplitudes around tachyon vacuum solution in Kaku theory

We incorporate closed string field into Kaku’s open string field theory which is defined by using Kaku vertex, and we construct open-closed string field theory. To do this, we define new consistent open-closed vertex and open-open-closed vertex with the Kaku vertex. Because these vertices depend on Chan-Paton parameter such as the Kaku vertex, the open-closed string field theory action that we construct depends on the Chan-Paton parameter such as the Kaku’s theory action. However, we can show that an infinitesimal change of $l$ corresponds to a field redefinition. Furthermore, we compute closed string amplitudes around tachyon vacuum solution in this theory. As a result, we confirm that these are conventional pure closed string amplitudes on surfaces without boundaries.