String creation and heterotic-type I′ duality Original Research Article

The BPS spectrum of type I′ string theory in a generic background is derived using the duality with the nine-dimensional heterotic string theory with Wilson lines. It is shown that the corresponding mass formula has a natural interpretation in terms of type I′, and it is demonstrated that the relevant states in type I′ preserve supersymmetry. By considering certain BPS states for different Wilson lines an independent confirmation of the string creation phenomenon in the DOD8 system is found. We also comment on the non-perturbative realization of gauge enhancement in type I′, and on the predictions for the quantum mechanics of type I′ DO-branes.