Probing triple-gauge couplings in anomalous gauge theories at hadron and lepton colliders

Kavli Affiliate: Carlos Wagner
| Summary:
Gauge anomalous quantum field theories are inconsistent as full UV theories since they lead to the breaking of Lorentz invariance or Unitarity, as well as non-renormalizability. It is well known, however, that they can be interpreted as effective field theories (EFT) with a cut-off. The latter cannot be made arbitrarily large and it is related to the energy scale at which additional fermions with suitable gauge charges enter, rendering the full model anomaly-free. A nondecoupling effect that remains in the EFT is the appearance of anomalous loop-induced triple-gauge couplings, encapsulating information from the full UV theory. In this work we take as an example an Abelian gauge symmetry $U(1)’_μ$ under which $2^nd$-generation leptons are axially charged, leading to an EFT that consists of the Standard Model (SM) with an additional massive $Z’$ gauge boson. As a consequence, there are triple gauge couplings involving the $Z’$ and Electroweak SM gauge bosons via mixed gauge anomalies. We study the possibility of probing these loop suppressed anomalous couplings at hadron and lepton colliders, with $Z’$-lepton couplings allowed by current experimental bounds, finding that due to the large SM backgrounds and small signal, the HL-LHC is incapable of this task. The 100 TeV $pp$ collider at $mathcalL=20~mathrm ab^-1$ on the other hand could probe anomalous couplings for $m_Z’in[150,800]~mathrmGeV$ and obtain discovery significances for $m_Z’in[230,330]~mathrmGeV$. Lepton colliders are also well suited for probing these anomalous couplings. In particular we show that a muon collider running at the $Z’$-resonance and an electron-positron collider such as CLIC with $sqrts=3~rm TeV$ can be complimentary in probing the anomalous couplings for $m_Z’in[100,700]~rm GeV$, with CLIC sensitive to discovery for $m_Z’in[125,225]~rm GeV$.
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