A monopole solution in open string theory

Abstract We investigate a solution of the Weyl invariance conditions in open string theory in four dimensions. In the closed string sector this solution is a combination of the SU(2) Wess-Zumino-Witten model and a Liouville theory. The investigation is carried out in the σ model approach where we have coupled all massless modes (especiallyan abelian gauge field via the boundary) and tachyon fields. Neglecting all higher derivatives in the field strength we get an exact result which can be interpreted as a monopole configuration living in non-trivia space-time. The masses of both tachyon fields are quantized by c WZW . But only for massless tachyons ( c WZW = 1) the corresponding vertex operators are well defined.