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Register a new userAn emergent $Z^prime$ from the Higgs shadow
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We show in this work how a sub-100 GeV $Z$ in a $U(1)$ extension of the Standard Model (SM) can emerge through Higgs mediated channels at the Large Hadron Collider (LHC). The light $Z$ has minimal interaction with the SM sector as well as vanishing kinetic mixing with $Z$ boson which allows it to be light and below the SM gauge boson masses. Interestingly such a light $Z$ is very difficult to observe in the standard production modes. We show that it is possible to observe such a gauge boson via scalar mediators that are responsible for the symmetry breaking mechanism of the model. The model also provides a dark matter candidate whose compatibility with the observed relic density is established due to the light $Z$. We also comment on other interesting possibilities such a light $Z$ may present for other observables.
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The Higgs mechanism well describes the electroweak symmetry breaking in nature. We consider a possibility that the microscopic origin of the Higgs field is UV physics of QCD. We construct a UV complete model of a higher dimensional Yang-Mills theory as a deformation of a deconstructed (2,0) theory in six dimensions, and couple the top and bottom (s)quarks to it. We see that the Higgs fields appear as magnetic degrees of freedom. The model can naturally explain the masses of the Higgs boson and the top quark. The rho meson-like resonances with masses such as 1 TeV are predicted.
We study the phenomenology of simplified $Z^prime$ models with a global $U(2)^3$ flavour symmetry in the quark sector, broken solely by the Standard Model Yukawa couplings. This flavour symmetry, known as less-minimal flavour violation, protects $Delta F=2$ processes from dangerously large new physics (NP) effects, and at the same time provides a free complex phase in $bto s$ transitions, allowing for an explanation of the hints for additional direct CP violation in kaon decays ($epsilon^prime/epsilon$) and in hadronic $B$-decays ($Bto Kpi$ puzzle). Furthermore, once the couplings of the $Z^prime$ boson to the leptons are included, it is possible to address the intriguing hints for NP (above the 5$,sigma$ level) in $bto s ell^+ell^-$ transitions. Taking into account all flavour observables in a global fit, we find that $epsilon^prime/epsilon$, the $Bto Kpi$ puzzle and $bto s ell^+ell^-$ data can be explained simultaneously. Sizeable CP violation in $bto s ell^+ell^-$ observables, in particular $A_8$, is predicted, which can be tested in the near future, and an explanation of the $Bto Kpi$ and $epsilon^prime/epsilon$ puzzles leads to effects in di-jet tails at the LHC, that are not far below the current limits. Once $bto s ell^+ell^-$ is included, cancellations in di-muon tails, possibly by a second $Z^prime$, are required by LHC data.
We consider right-handed neutrino pair production in generic $Z^prime$ models. We propose a new, model-independent analysis using final states containing a pair of same-sign muons. A key aspect of this analysis is the reconstruction of the RH neutrino mass, which leads to a significantly improved sensitivity. Within the $U(1)_{(B-L)_{3}}$ model, we find that at the HL-LHC it will be possible to probe RH neutrino masses in the range $0.2lesssim M_{N_R} lesssim 1.1,$TeV.
We examine current collider constraints on some simple $Z^prime$ models that fit neutral current $B-$anomalies, including constraints coming from measurements of Standard Model (SM) signatures at the LHC. The `MDM simplified model is not constrained by the SM measurements but {em is} strongly constrained by a 139 fb$^{-1}$ 13 TeV ATLAS di-muon search. Constraints upon the `MUM simplified model are much weaker. A combination of the current $B_s$ mixing constraint and ATLAS $Z^prime$ search implies $M_{Z^prime}>1.2$ TeV in the Third Family Hypercharge Model example case. LHC SM measurements rule out a portion of the parameter space of the model for $M_{Z^prime}<1.5$ TeV.
The $Z$-portal is one of most popular and well-explored scenarios of dark matter (DM). To avoid the strong constraints coming from dilepton resonance searches at the LHC and direct detection of DM, it is usually required that in addition to being leptophobic, the $Z$ is axially coupled to either the (fermionic) DM or the standard model (SM) quarks. The first possibility has been extensively studied both in the context of simplified model and UV complete scenarios. However, the studies on the second possibiliy are largely confined to simplified models only. Here, we construct the minimal UV completion of these models satisfying both the criteria of leptophobia and purely axial $Z-$quark coupling. The anomaly cancellation conditions demand highly non-trivial structures, not only in the dark sector, but also in the Higgs sector.
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