1 v 1 7 A pr 2 00 0 Electroweak Bloch - Nordsieck violation at the TeV scale : “ strong ” weak interactions ?

Hard processes at the TeV scale exhibit enhanced (double log) EW corrections even for inclusive observables, leading to violation of the Bloch-Nordsieck theorem. This effect, previously related to the non abelian nature of free EW charges in the initial state (ee, ep, pp ...), is here investigated for fermion initiated hard processes and to all orders in EW couplings. We find that the effect is important, especially for lepton initiated processes, producing weak effects that in some cases compete in magnitude with the strong ones. We show that this (double log) BN violating effect has a universal energy dependence, related to the Sudakov form factor in the adjoint representation. The role of this form factor is to suppress cross section differences within a weak isospin doublet, so that at very large energy the cross sections for left-handed electron-positron and neutrino-positron scattering become equal. Finally, we briefly discuss the phenomenological relevance of our results for future colliders.