Electroweak couplings and LHC constraints on alternative Z′ models in E6

Abstract

We report the most general expression for the chiral charges of a [Formula: see text] gauge boson coming from an [Formula: see text] unification model, as a function of the electroweak parameters and the charges of the [Formula: see text] factors in the chain of subgroups. These charges are valid for an arbitrary Higgs sector and only depend on the branching rules of the [Formula: see text] fundamental representation and the corresponding rules for the fermionic representations of their subgroups. By assuming [Formula: see text] unification, the renormalization group equations (RGE) allow us to calculate the electroweak parameters at low energies for most of the chains of subgroups in [Formula: see text]. From RGE and unitary conditions, we show that at low energies there must be a mixing between the gauge boson of the standard model hypercharge and the [Formula: see text]. From this, it is possible to delimit the preferred region in the parameter space for a breaking pattern in [Formula: see text]. In general, without unification, it is not viable to determine this region; however, for some models and under certain assumptions, it is possible to limit the corresponding parameter space. By using the most recent upper limits on the cross-section of extra gauge vector bosons [Formula: see text] decaying into dileptons from the ATLAS data at 13 TeV with accumulated luminosities of 36.1 fb[Formula: see text] and 13.3 fb[Formula: see text], we report the 95% C.L. lower limits on the [Formula: see text] mass for the typical [Formula: see text] benchmark models. We also show the contours in the 95% C.L. of the [Formula: see text] mass bounds for the entire parameter space of [Formula: see text].