CONSTRUCTION OF INTERACTING ACTIONS OF BOSONIC OPEN STRINGS AND CLOSED STRINGS BY SYMMETRY PRINCIPLES

Following Kaku's way, various interacting actions of bosonic open strings as well as closed strings are constructed, which are invariant under. local reparametrization transformations, string group and global transformations of a Lie group. Similar to open string, a multiplication rule of closed string fields is given which also satisfies associative law as in open string case.