ON A NONPERTURBATIVE VACUUM FOR THE OPEN BOSONIC STRING

In the context of covariant string field theory, we investigate the existence and properties of nonperturbative vacua for the open bosonic string. The study is performed using successive orders in a level-truncation method. We find a candidate nonperturbative vacuum and obtain numerical values for nonzero expectation values of all fields to level two. Perturbation theory about this vacuum is shown to be well defined. The occurence and location of poles in the propagators of all fields to level two are established. We observe that string theories necessarily have running couplings at tree level and that the open bosonic string is asymptotically free. The nontrivial momentum dependence means that certain poles seen in the canonical vacuum are absent in the nonperturbative vacuum. This result follows from the nature of the string as an extended object and is likely to hold for general string theories. © 1990.