Paramagnetic dominance, the sign of the beta function and UV/IR mixing in non-commutative U(1)

U(1) gauge theory on non-commutative Minkowski spacetime in the Feynman-'t Hooft background gauge is studied. In particular, UV divergences and non-co mmutative IR divergent contributions to the two, three and four-point funct ions are explicitly computed at one loop. We show that the negative sign of the beta function results from paramagnetism - producing UV charge anti-sc reening - prevailing over diamagnetism - giving rise to UV charge screening . This dominance in the field theory setting corresponds to tachyon magnifi cation dominance in the string theory framework. Our calculations provide a n explicit realization of UV/IR mixing and lead to an LR renormalization of the coupling constant, where now paramagnetic contributions produce screen ing and diamagnetic contributions anti-screening. (C) 2001 Elsevier Science B.V. All rights reserved.