Abstract
We study the collider phenomenology of a neutral gauge boson Z′ arising in minimal but anomalous U(1) extensions of the Standard Model (SM). To retain gauge invariance of physical observables, we consider cancellation of gauge anomalies through the Green-Schwarz mechanism. We categorize a wide class of U(1) extensions in terms of the new U(1) charges of the left-handed quarks and leptons and the Higgs doublet. We derive constraints on some benchmark models using electroweak precision constraints and the latest 13 TeV LHC dilepton and dijet resonance search data. We calculate the decay rates of the exotic and rare one-loop Z′ decays to ZZ and Z-photon modes, which are the unique signatures of our framework. If observed, these decays could hint at anomaly cancellation through the Green-Schwarz mechanism. We also discuss the possible observation of such signatures at the LHC and at future ILC colliders.
Highlights
Together with choosing particular relations between the gauge charges of the chiral fermions such that the anomalies cancel [1]
We study the collider phenomenology of a neutral gauge boson Z arising in minimal but anomalous U(1) extensions of the Standard Model (SM)
In [5] the authors conclude that such an effective action and its phenomenological consequences cannot determine the nature of the high-scale physics
Summary
We review how the GS mechanism [3] can be used to generate a lowenergy effective action which is anomaly free — for a more formal review of gauge anomalies, see [15,16,17,18]. The second and third parts of eq (2.2), LPQ and LGCS, are called the Peccei-Quinn (PQ) and the generalized Chern-Simons (GCS) terms respectively These two classes of terms, as described above, are chosen such that they remove all gauge anomalies. From the LPQ terms we see that this theory contains vertices including axion and gauge bosons of the form AZZ, AZ Z , Aγγ, AW +W − (the coupling to gluons is zero). The LGCS part generates the new tree-level vertices ZZγ, ZZ γ, Z Z γ, which are not present in traditional anomaly-free U(1)-extensions [1] As described above, these new terms serve, in practice, as counter-terms for anomalous amplitudes, as for example the standard triangle-fermion amplitude. The GCS terms remain unsuppressed even at low energies, see eq (2.5)
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