Closed Superstrings in a Constant Magnetic Field and Regularization Criterion

We propose a new type of interaction of closed superstrings with the electromagnetic field, other than the usual Kaluza-Klein type or a gauge field with internal gauge group origin. This model with a constant magnetic field is also shown to have an exact solution. We consider a regularization criterion. Some models will be excluded according to this criterion. The spectrum-generating algebra is also constructed in our interacting model.