Precision measurement constraints on the 4-Site model & the effect of interference in searches for new physics

Abstract

This work is divided in two parts.The first part presents a careful computation of Electroweak Precision Tests constraints on the 4-Site model, and the resulting limits on fermion couplings. The new heavy W and Zbosons present in this model can couple significantly to Standard Model fermions.Previous computations of these quantities were performed using an approximation that is here shown to have a more restricted validity domain as what was originally thought.The second part of the discussion is about searches of extra W and Z bosons as predicted in some extensions of the Standard Model (such as the 4-Site model) in the Drell-Yanchannels.The interference between the new physics and the Standard Model is commonly neglected in the interpretation of experimental searches. The importance of this effect isinvestigated in detail. The quantitative error in exclusion bounds due to neglecting the interference may be small, but important qualitative features are missed when using thisapproximation.It is important to be aware of the effect of interference in order to make sure wrong statements and bad conclusions are avoided, and to guarantee that analyses do stay within thedomain of validity of the approximations they rely o