Stretched strings in noncommutative field theory - art. no. 066003

Motivated by recent discussions of TR-UV mixing in noncommutative field the ories, we perform a detailed analysis of the nonplanar amplitudes of the bo sonic open string in the presence of an external B field at the one-loop le vel. We carefully isolate, at the string theory level, the contribution whi ch is responsible for the IR-UV behavior in the field theory limit. We show that it is a pure open string effect by deriving it from the factorization of the one-loop amplitude into the disk amplitudes of intermediate open st ring insertions. We suggest that it is natural to understand IR-UV mixing a s the creation of intermediate "stretched strings."