UV/IR Mixing via Closed Strings and Tachyonic Instabilities

We discuss UV/IR mixing effects in non-supersymmetric noncommutative U(N) gauge theories. We show that the singular (nonplanar) terms in the 2and 3-point functions, namely the poles and the logarithms, can be obtained from a manifestly gauge invariant effective action. The action, which involves open Wilson line operators, can be derived from closed strings exchange between two stacks of Dbranes. Our concrete example is type 0B string theory and the field theory that lives on a collection of N electric D3-branes. We show that one of the closed string modes that couple to the field theory operator which is responsible for the infrared poles, is the type 0 tachyon.