Closed string amplitudes around tachyon vacuum solution in Kaku theory

A bstract We incorporate closed string field into Kaku’s open string field theory which is defined 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 in 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 amplitudes are conventional pure closed string amplitudes on surfaces without boundaries.