The cosmological constant in Witten's superstring field theory

Using Witten's field theory of superstrings we demonstrate the absence of the recently discovered ambiguity in superstring vacuum loop graphs, provided Wendt's contact term is added to the action. This ambiguity breaks gauge invariance. It gets contributions from the boundaries of the cells into which string field theory decomposes moduli space. Our analysis supplements previous discussions in the Polyakov formalism, where only the boundary of moduli space need be considered. We also show that the cosmological constant vanishes to all orders in perturbation theory. (orig.)