A closed string as a source of the Yang-Mills field

A closed string as a source of the Yang-Mills field is discussed in the range of the classical theory. It is shown that under certain conditions, the Yang-Mills field can be expressed in a non-linear combination of two Abelian gauge fields produced by the string and its center of mass and that the field from the string forms a singular flux with quantized magnitude. Discussions for the massive Yang-Mills field are also given and the effective action of the string is derived from the action of the field in the presence of its source. The Regge slope parameter associated with the string is shown to be proportional to the effective coupling constant of the interaction which is obtained by approximating the interaction via the massive Yang-Mills field as a direct one. (auth.)