## Interaction vertices in reduced string field theories

In contrast with previous expectations, covariant overlap vertices are not always suitable for gauge-covariant formulations of bosonic string field theory with a reduced supplementary field content. This is demonstrated for the version of the theory suggested by Neveu, Schwarz, and West. The method to construct the interaction, as formulated by Neveu and West, fails at one level higher than these authors have considered as long as the reduced field content is retained. The condition for a general vertex to describe formally a local gauge-invariant interaction is derived. The solution for the action functional and the gauge transformation law is exhibitedmore »