No abstract

The pinch technique (PT) is applied to neutral current amplitudes, focusing on the mixing problem. Extending recent arguments due to Papavassiliou and Pilaftsis, it is shown that the use of the PT self-energies does not shift the complex-valued position of the pole through order O(g 4 ). This leads (to the same accuracy) to a simple interpretation of M Z , the mass measured at LEP, in terms of the PT self-energies. It is pointed out that the PT approach provides a convenient and rather elegant formalism to discuss important neutral current amplitudes, such as those relevant to four-fermion processes and LEP2.

We present a new, model independent method for extracting bounds for the anomalous ␥WW couplings from hadron collider experiments. At the partonic level we introduce a set of three observables which are constructed from the unpolarized differential cross section for the process dū →W Ϫ ␥ by appropriate convolution with a set of simple polynomials depending only on the center-of-mass angle. One of these observables allows for the direct determination of the anomalous coupling usually denoted by ⌬, without any simplifying assumptions, and without relying on the presence of a radiation zero. The other two observables impose two sum rules on the remaining three anomalous couplings. The inclusion of the structure functions is discussed in detail for both pp and pp colliders. We show that, whilst for pp experiments this can be accomplished straightforwardly, in the pp case one has to resort to somewhat more elaborate techniques, such as the binning of events according to their longitudinal momenta. ͓S0556-2821͑99͒01523-4͔

The dependence of the differential cross section for on-shell W-pair production on the anomalous trilinear gauge couplings invariant under C and P is examined. It is shown that the contributions of the anomalous magnetic moments of the W boson due to the photon and the Z can be individually projected out by means of two appropriately constructed polynomials. The remaining four anomalous couplings are shown to satisfy a set of model-independent sum rules. Specific models which predict special relations among the anomalous couplings are then studied, in particular, the composite model of Brodsky and Hiller and linear and non-linear effective Lagrangian approaches. The relations predicted by these models, when combined with the aforementioned sum rules, give rise to definite predictions, particular to each model. These predictions can be used, at least in principle, in order to exclude or constrain such models. Finally, we present an elementary discussion of the statistical properties of the proposed observables.

We show that in the framework of the pinch technique the universal part of the parameter can be meaningfully de ned, beyond one loop. The universal part so obtained satis es the crucial requirements of gauge-independence, niteness, and process-independence, even when subleading contributions of the top quark are included. The mechanism which enforces the aforementioned properties is explained in detail, and several subtle eld theoretical issues are discussed.