The interference effects between an extra neutral spin-1 Z -boson and the Standard Model background in the Drell-Yan channel at the LHC are studied in detail. The final state with two oppositely charged leptons is considered. The interference contribution to the new physics signal, currently not fully taken into account by experimental collaborations in Z -searches and in the interpretation of the results, can be substantial. It may affect limits or discovery prospects of Z at the LHC. As the Z -boson interference is model-dependent, a proper treatment would a priori require a dedicated experimental analysis for each particular model. Doing so could potentially improve the sensitivity to new physics, but would require significantly more experimental effort.At the same time, it is shown that one can define an invariant mass window, valid for a wide range of models, for which the contribution of the model-dependent interference to the Beyond the Standard Model signal is reduced to O(10%), comparable to the level of the combined uncertainty from parton densities and higher order corrections. This quasi-model-independent "magic cut" does not scale with the mass of the Z -boson and is approximately constant over a large range of masses. Such control of the interference effects relies on not-too-small branching ratios of Z to leptons (typically of at least a few percent) which can be suppressed, however, by additional new decay channels of the Z ; a small width-to-mass ratio alone does not guarantee the interference to be small over an arbitrary kinematic range. Under the general assumption that these new decay channels of Z are not dominant, one can perform quasi-model-independent analyses, preserving the current scheme used by the experimental collaborations for the Z -boson search using the suggested invariant mass window cut.

We study confining gauge theories with fermions vectorial under the SM that produce a Higgs doublet as a Nambu-Goldstone boson. The vacuum misalignment required to break the electro-weak symmetry is induced by an elementary Higgs doublet with Yukawa couplings to the new fermions. The physical Higgs is a linear combination of elementary and composite Higgses while the SM fermions remain elementary. The full theory is renormalizable and the SM Yukawa couplings are generated from the ones of the elementary Higgs allowing to eliminate all flavour problems but with interesting effects for Electric Dipole Moments of SM particles. We also discuss how ideas on the relaxation of the electro-weak scale could be realised within this framework. 1 arXiv:1609.07122v2 [hep-ph]

Interference effects are widely neglected in searches for new physics. This is the case in recent publications on searches for W 0 bosons using leptonic final states. We examine the effects of interference on distributions frequently used to determine mass limits for possible W 0 bosons and show that there are important qualitative effects on the behavior of the new physics signal. There are two main consequences. First, exclusion limits where interferences effects have not been considered are likely to have been overestimated. Second, presenting experimental results as a function of a transverse mass cut rather than in terms of the contribution of new physics to the total cross section would be more informative. 1 W 0 bosons arise less frequently than Z 0 bosons as the extension needs to contain a SUð2Þ factor, while for the latter a simple Uð1Þ factor is sufficient. For a recent review on Z 0 scenarios, see [1].

The Large Hadron Collider experiments are probing the evolution of the strong coupling αs up to the TeV scale. We show how the ratio of 3-to 2-jets cross sections is affected by the presence of new physics and argue that it can be used to place a model-independent bound on new particles carrying QCD color charge. The current data potentially constrains such states to be heavier than a few hundred GeVs.

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