UV/IR mixing in noncommutative field theory via open string loops

We explicitly evaluate one-loop (annulus) planar and nonplanar open string amplitudes in the presence of the background NS-NS two-form field. In the d ecoupling limit of Seiberg and Witten, we find that the nonplanar string am plitudes reproduce the UV/IR mixing of noncommutative field theories. In pa rticular, the investigation of the UV regime of the open string amplitudes shows that certain IR closed string degrees of freedom survive the decoupli ng limit as previously predicted from the noncommutative field theory analy sis. These degrees of freedom are responsible for the quadratic, linear and logarithmic IR singularities when the D-branes embedded in space-time have the codimension zero, one and two, respectively. The analysis is given for both bosonic and supersymmetric open strings. (C) 2000 Elsevier Science B. V. All rights reserved.