Searching for heavy vector bosons Z^′, predicted in models inspired by Grand Unification Theories, is among the challenging objectives of the LHC. The ATLAS and CMS collaborations have looked for Z^′ bosons assuming that they can decay only into Standard Model channels, and have set exclusion limits by investigating dilepton, dijet and, to a smaller extent, top-antitop final states. In this work we explore possible loopholes in these Z^′ searches, by studying supersymmetric as well as leptophobic scenarios. We demonstrate the existence of realizations in which the Z^′ boson automatically evades the typical bounds derived from the analyses of the Drell-Yan invariant-mass spectrum. Dileptonic final states can in contrast only originate from supersymmetric Z^′ decays and are thus accompanied by additional effects. This feature is analyzed in the context of judiciously chosen bench-mark configurations, for which visible signals could be expected in future LHC data with a 4σ − 7σ significance. Our results should hence motivate an extension of the current Z^′ search program to account for supersymmetric and leptophobic models.

We investigate the production of vector-like quarks with charge 5/3 at the LHC and their subsequent decays into new singly or doubly charged bosons plus a heavy quark (top or bottom). In particular, we explore final states with same-sign di-leptons (electron or muon pairs), with the leptons coming from the decay of the new bosons and, in the case of production of singly charged bosons, from top quarks as well. These processes are predicted by classes of models based on extensions of the gauge group of the Standard Model, such as the 331 Model, where the electroweak symmetry is described by SU(3)_L × U(1)_X, X being a new abelian charge. For this purpose, a CMS search for vector-like partners with charge 5/3 decaying into Wt is recast to obtain model-independent bounds and projected reaches at future luminosity stages of the LHC. The results are then interpreted as mass bounds for the new particles predicted in the 331 Model and as a constraint on the scale of its spontaneous symmetry breaking. The complete set of model-independent results are provided as recast efficiencies, to allow for reinterpretation in different scenarios.

The top-quark mass is a parameter of paramount importance in particle physics, playing a crucial role in the electroweak precision tests and in the stability of the Standard Model vacuum. I will discuss the main strategies to extract the top-quark mass at the LHC and the interpretation of the measurements in terms of well-posed top-mass definitions, taking particular care about renormalon ambiguities, progress in Monte Carlo event generators for top physics and theoretical uncertainties.

I study the phenomenology of heavy neutral bosons \(Z'\), predicted in GUT-inspired U(1)\('\) models, at the Large Hadron Collider. In particular, I investigate possible signatures due to \(Z'\) decays into supersymmetric particles, such as chargino, neutralino, and sneutrino pairs, leading to final states with charged leptons and missing energy. The analysis is carried out at \(\sqrt{s}=14\) TeV, for a few representative points of the parameter space of the Minimal Supersymmetric Standard Model, suitably modified to accommodate the extra \(Z'\) boson and consistent with the discovery of a Higgs-like boson with mass around 125 GeV. Results are presented for several observables and compared with those obtained for direct \(Z'\) decays into lepton pairs, as well as direct production of supersymmetric particles. For the sake of comparison, \(Z'\) phenomenology in an effective supersymmetric extension of the Sequential Standard Model is also discussed.

EPJ Web of Conferences, open-access proceedings in physics and related sciences