Additional Neutral Gauge Boson Research Articles

Z’ boson mass reach and model discrimination at muon colliders

We study the discrimination power of future multi-TeV muon colliders for a large set of models with extended gauge symmetries and additional neutral gauge bosons (“Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z'$$\\end{document}-models”). Our study is carried out using a χ2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\chi ^2$$\\end{document}-analysis of leptonic observables of s-channel scattering in effective Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z'$$\\end{document}-models. We make use of angular and chiral asymmetries induced in such models to find the discovery reach of a given muon collider setup in terms of the Z′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z'$$\\end{document} mass and to discriminate between the different scenarios. In this context, we discuss how polarized beams – should they become available at muon colliders – or polarization measurements can help in the discrimination. Our results show that typical muon collider setups which are currently under consideration can give a significantly higher reach compared to existing bounds and projections for high-luminosity LHC.

Searching for Z\u2032 bosons at the P2 experiment

The P2 experiment aims at high-precision measurements of the parity-violating asymmetry in elastic electron-proton and electron-12C scatterings with longitudinally polarized electrons. We discuss here the sensitivity of P2 to new physics mediated by an additional neutral gauge boson Z′ of a new U(1)′ gauge symmetry. If the charge assignment of the U(1)′ is chiral, i.e., left- and right-handed fermions have different charges under U(1)′, additional parity-violation is induced directly. On the other hand, if the U(1)′ has a non-chiral charge assignment, additional parity-violation can be induced via mass or kinetic Z-Z′ mixing. By comparing the P2 sensitivity to existing constraints, we show that in both cases P2 has discovery potential over a wide range of Z′ mass. In particular, for chiral models, the P2 experiment can probe gauge couplings at the order of 10−5 when the Z′ boson is light, and heavy Z′ bosons up to 79 (90) TeV in the proton (12C) mode. For non-chiral models with mass mixing, the P2 experiment is sensitive to mass mixing angles smaller than roughly 10−4, depending on model details and gauge coupling magnitude.

Type III seesaw for neutrino masses in U(1)B\u2212L model with multi-component dark matter

We propose a B − L gauged extension of the Standard Model where light neutrino masses arise from type III seesaw mechanism. Unlike the minimal B − L model with three right handed neutrinos having unit lepton number each, the model with three fermion triplets is however not anomaly free. We show that the leftover triangle anomalies can be cancelled by two neutral Dirac fermions having fractional B − L charges, both of which are naturally stable by virtue of a remnant ℤ2× {mathbb{Z}}_2^{prime } symmetry, naturally leading to a two component dark matter scenario without any ad-hoc symmetries. We constrain the model from all relevant phenomenological constraints including dark matter properties. Light neutrino mass and collider prospects are also discussed briefly. Due to additional neutral gauge bosons, the fermion triplets in type III seesaw can have enhanced production cross section in collider experiment.

Freezing-in dark matter through a heavy invisible Z′

We demonstrate that in a class of the $U(1)'$ extension of the Standard Model (SM), under which all the Standard Model matter fields are uncharged and the additional neutral gauge boson $Z'$ couples to a set of heavy nonstandard fermions, dark matter (DM) production mediated by $Z'$ can proceed through the generation of generalized Chern-Simons (GCS) couplings. The origin of the GCS terms is intimately connected to the cancellation of gauge anomalies. We show that the DM production cross section triggered by GCS couplings is sufficient even for an intermediate scale $Z'$ . A large range of DM and Z masses is then allowed for reasonably high reheating temperature ($T_\rh \gtrsim 10^{10}~\text{GeV}$). This type of scenario opens up a new paradigm for unified models. We also study the UV completion of such effective field theory constructions, augmenting it by a heavy fermionic spectrum. The latter, when integrated out, generates the GCS-like terms and provides a new portal to the dark sector. The presence of a number of derivative couplings in the GCS-like operators induces a high temperature dependence to the DM production rate. The mechanism has novel consequences and leads to a new reheating dependence of the relic abundance.

Hidden U(1) gauge symmetry realizing a neutrinophilic two-Higgs-doublet model with dark matter

We propose a neutrinophilic two-Higgs-doublet model with hidden local $U(1)$ symmetry, where active neutrinos are Dirac type, and a fermionic dark matter (DM) candidate is naturally induced as a result of remnant symmetry even after the spontaneous symmetry breaking. In addition, a physical Goldstone boson arises as a consequence of two types of gauge singlet bosons and contributes to the DM phenomenologies as well as an additional neutral gauge boson. Then, we analyze the relic density of DM within the safe range of direct detection searches and show the allowed region of dark matter mass.

Top-philic Z\u2032 forces at the LHC

Despite extensive searches for an additional neutral massive gauge boson at the LHC, a Z′ at the weak scale could still be present if its couplings to the first two generations of quarks are suppressed, in which case the production in hadron colliders relies on tree-level processes in association with heavy flavors or one-loop processes in association with a jet. We consider the low-energy effective theory of a top-philic Z′ and present possible UV completions. We clarify theoretical subtleties in evaluating the production of a top-philic Z′ at the LHC and examine carefully the treatment of ananomalous Z′ current in the low-energy effective theory. Recipes for properly computing the production rate in the Z′ + j channel are given. We discuss constraints from colliders and low-energy probes of new physics. As an application, we apply these considerations to models that use a weak-scale Z′ to explain possible violations of lepton universality in B meson decays, and show that the future running of a high luminosity LHC can potentially cover much of the remaining parameter space favored by this particular interpretation of the B physics anomaly.

Search for additional heavy neutral Higgs and gauge bosons in the ditau final state produced in 36 fb\u22121 of pp collisions at sqrt{s}=13 TeV with the ATLAS detector

A search for heavy neutral Higgs bosons and Z′ bosons is performed using a data sample corresponding to an integrated luminosity of 36.1 fb−1 from proton-proton collisions at sqrt{s}=13 TeV recorded by the ATLAS detector at the LHC during 2015 and 2016. The heavy resonance is assumed to decay to τ+τ− with at least one tau lepton decaying to final states with hadrons and a neutrino. The search is performed in the mass range of 0.2-2.25 TeV for Higgs bosons and 0.2-4.0 TeV for Z′ bosons. The data are in good agreement with the background predicted by the Standard Model. The results are interpreted in benchmark scenarios. In the context of the hMSSM scenario, the data exclude tan β > 1.0 for mA = 0.25 TeV and tan β > 42 for mA = 1.5 TeV at the 95% confidence level. For the Sequential Standard Model, ZSSM′ with mZ′ < 2.42 TeV is excluded at 95% confidence level, while ZNU′ with mZ ′ < 2.25 TeV is excluded for the non-universal G(221) model that exhibits enhanced couplings to third-generation fermions.

Lepton-flavor violatingBdecays in genericZ′models

LHCb has reported deviations from the Standard Model in $b\to s\mu^+\mu^-$ transitions for which a new neutral gauge boson is a prime candidate for an explanation. As this gauge boson has to couple in a flavour non-universal way to muons and electrons in order to explain $R_K$, it is interesting to examine the possibility that also lepton flavour is violated, especially in the light of the CMS excess in $h\to\tau^\pm\mu^\mp$. In this article, we investigate the perspectives to discover the lepton-flavour violating modes $B\to K^{(*)}\tau^\pm\mu^\mp$, $B_s\to \tau^\pm\mu^\mp$ and $B\to K^{(*)} \mu^\pm e^\mp$, $B_s\to \mu^\pm e^\mp$. For this purpose we consider a simplified model in which new-physics effects originate from an additional neutral gauge boson ($Z^\prime$) with generic couplings to quarks and leptons. The constraints from $\tau\to3\mu$, $\tau\to\mu\nu\bar{\nu}$, $\mu\to e\gamma$, $g_\mu-2$, semi-leptonic $b\to s\mu^+\mu^-$ decays, $B\to K^{(*)}\nu\nu$ and $B_s$--$\overline{B}_s$ mixing are examined. From these decays, we determine upper bounds on the decay rates of lepton flavour violating $B$ decays. $Br(B\to K\nu\nu)$ limits the branching ratios of LFV $B$ decays to be smaller than $8\times 10^{-5} (2\times 10^{-5})$ for vectorial (left-handed) lepton couplings. However, much stronger bounds can be obtained by a combined analysis of $B_s$--$\overline{B}_s$, $\tau\to3\mu$, $\tau\to\mu\nu\bar{\nu}$ and other rare decays. The bounds depend on the amount of fine-tuning among the contributions to $B_s$--$\overline{B}_s$ mixing. Allowing for a fine-tuning at the percent level we find upper bounds of the order of $10^{-6}$ for branching ratios into $\tau\mu$ final states, while $B_s\to \mu^\pm e^\mp$ is strongly suppressed and only $B\to K^{(*)} \mu^\pm e^\mp$ can be experimentally accessible (with a branching ratio of order $10^{-7}$).

Flavour dependent gauged radiative neutrino mass model

We propose a one-loop induced radiative neutrino mass model with anomaly free flavour dependent gauge symmetry: $\mu$ minus $\tau$ symmetry $U(1)_{\mu-\tau}$. A neutrino mass matrix satisfying current experimental data can be obtained by introducing a weak isospin singlet scalar boson that breaks $U(1)_{\mu-\tau}$ symmetry, an inert doublet scalar field, and three right-handed neutrinos in addition to the fields in the standard model. We find that a characteristic structure appears in the neutrino mass matrix: two-zero texture form which predicts three non-zero neutrino masses and three non-zero CP-phases from five well measured experimental inputs of two squared mass differences and three mixing angles. Furthermore, it is clarified that only the inverted mass hierarchy is allowed in our model. In a favored parameter set from the neutrino sector, the discrepancy in the muon anomalous magnetic moment between the experimental data and the the standard model prediction can be explained by the additional neutral gauge boson loop contribution with mass of order 100 MeV and new gauge coupling of order $10^{-3}$.

Scalar dark matter with CERN-LEP data andZ′search at the LHC in anU(1)′model

In the framework of an nonuniversal $U(1)'$ extension of the standard model, we propose an scalar candidate for cold dark matter which exhibits interactions with ordinary matter through Higgs and gauge bosons. Using limits from low energy observables, we find constraints on the new physics parameters of the model associated to the extra abelian symmetry, in particular, the mass of the additional neutral gauge boson $Z'$ and the new gauge coupling constant. We found that for the lower experimental limit $M_{Z'}=3$ TeV constrained by direct research at LHC, the ratio between the $U(1)'$ and $SU(2)_L$ gauge coupling constants is around $0.4$. Taking into account this limit and the observable relic density of the Universe, we search for new constraints on the mass of the dark matter particle of the model. We found that for a higgsphobic model, the mass of the scalar dark matter must be $M_{\sigma}=70$ GeV. We also found different kinematical threshold and resonances that enhance the dispersion of dark matter into ordinary matter for different regions of the space of parameters of the model, obtaining masses as low as $1.3$ GeV and as large as $125$ GeV with not allowed intermediate regions due to resonances.

Charged diboson production at the LHC in a four-site model with a composite Higgs boson

We investigate the scope of the LHC in probing the parameter space of a 4-site model supplemented by one composite Higgs state, assuming all past, current and future energy and luminosity stages of the CERN machine. We concentrate on the yield of charged di-boson production giving two opposite-charge different-flavour leptons and missing (transverse) energy, i.e., events induced via the subprocess $q\bar q\to e^+\nu_e \mu^-\bar\nu_\mu$ + ${\rm{c.c.}}$, which enables the production in the intermediate step of all additional neutral and charged gauge bosons belonging to the spectrum of this model, some of which in resonant topologies. We find this channel accessible over the background at all LHC configurations after a dedicated cut-based analysis. We finally compare the yield of the di-boson mode to that of Drell-Yan processes and establish that they have complementary strengths, one covering regions of parameter space precluded to the others and vice versa.

Phenomenology of a three-family model with gauge symmetry SU(3)c ⊗ SU(4)L ⊗ U(1)X

We study an extension of the gauge group SU(3)c ⊗ SU(2)L ⊗ U(1)Y of the standard model to the symmetry group SU(3)c ⊗ SU(4)L ⊗ U(1)X (3-4-1 for short). This extension provides an interesting attempt to answer the question of family replication in the sense that models for the electroweak interaction can be constructed so that anomaly cancellation is achieved by an interplay between generations, all of them under the condition that the number of families must be divisible by the number of colours of SU(3)c. This method of anomaly cancellation requires a family of quarks transforming differently from the other two, thus leading to tree-level flavour changing neutral currents (FCNC) transmitted by the two extra neutral gauge bosons Z′ and Z′′ predicted by the model. In a version of the 3-4-1 extension, which does not contain particles with exotic electric charges, we study the fermion mass spectrum and some aspects of the phenomenology of the neutral gauge boson sector. In particular, we impose limits on the Z − Z′ mixing angle and on the mass scale of the corresponding physical new neutral gauge boson Z2, and establish a lower bound on the mass of the additional new neutral gauge boson Z′′ ≡ Z3. For the analysis we use updated precision electroweak data at the Z-pole from the CERN LEP and SLAC Linear Collider, and atomic parity violation data. The mass scale of the additional new neutral gauge boson Z3 is constrained by using updated experimental inputs from neutral meson mixing in the analysis of the sources of FCNC in the model. The data constrain the Z − Z′ mixing angle to a very small value of , and the lower bounds on and are found to be of and , respectively.

Torsion discovery potential and its discrimination at CERN LHC

Torsion models constitute a well-known class of extended quantum gravity models. In this paper we study some phenomenological consequences of a torsion field interacting with fermions at LHC. A torsion field could appear as a new heavy state characterized by its mass and couplings to fermions. These new states will form a resonance decaying into difermions, as occurs in many extensions of the standard model, such as models predicting the existence of additional neutral gauge bosons, usually named Z{sup '}. Using the dielectron channel we evaluate the integrated luminosity needed for a 5{sigma} discovery as a function of the torsion mass, for different coupling values. We also calculate the luminosity needed to discriminate, with 95% C.L., the two possible different torsion natures. Finally, we show that the observed signal coming from the torsion field could be distinguished from a signal coming from a new neutral gauge boson, provided there is enough luminosity.

$SU(3)_c\otimes SU(4)_{\mathrm {L}}\otimes U(1)_X$ model for three families

An extension of the standard model to the local gauge group $SU(3)_c\otimes SU(4)_{\mathrm {L}}\otimes U(1)_X$ as a three-family model is presented. The model does not contain exotic electric charges and we obtain a consistent mass spectrum by introducing an anomaly-free discrete Z 2 symmetry. The neutral currents coupled to all neutral vector bosons in the model are studied. By using experimental results from the CERN LEP, SLAC Linear Collider and atomic parity violation data we constrain the mixing angle between two of the neutral currents in the model and the mass of the additional neutral gauge bosons to be $-0.0032\leq\sin\theta\leq 0.0031$ and $0.67 \hbox{TeV}\leq M_{Z_2} \leq 6.1$ TeV at $95 \%$ C.L., respectively.

CONSTRAINTS ON NEUTRAL BOSONS OF THESp(6)L⊗U(1)YMODEL

Lower limits are calculated on the mass of an additional neutral gauge boson, Z′, suggested by the Sp (6)L⊗ U (1)Ymodel, using direct search limits at hadron collider. We found that MZ′≥ 655 GeV . The production cross-section times branching ratio of Z′ decaying into dileptons in hadronic collisions, is found to be generation dependent and can be used to distinguish the model.

SU(3)c⊗SU(3)L⊗U(1)Xas anSU(6)⊗U(1)Xsubgroup

An extension of the standard model to the local gauge group ${\mathrm{SU}(3)}_{c}\ensuremath{\bigotimes}{\mathrm{SU}(3)}_{L}\ensuremath{\bigotimes}{U(1)}_{X}$ as a family independent model is presented. The mass scales, the gauge boson masses, and the masses for the spin 1/2 particles in the model are studied. The mass differences between the up and down quark sectors, between the quarks and leptons, and between the charged and neutral leptons in one family are analyzed. The existence of two Dirac neutrinos for each family, one light and one very heavy, is predicted. By using experimental results from CERN LEP, SLC and atomic parity violation we constrain the mixing angle between the two neutral currents and the mass of the additional neutral gauge boson to be $\ensuremath{-}0.00015&lt;~\mathrm{sin}\ensuremath{\theta}&lt;~0$ and $1.5 \mathrm{TeV}&lt;~{M}_{{Z}_{2}}$ at $95%$ C.L.

SU(3)c⊗SU(3)L⊗U(1)Xas anE6subgroup

An extension of the Standard Model to the local gauge group $SU(3)_c\otimes SU(3)_L\otimes U(1)_X$ which is a subgroup of the electroweak-strong unification group $E_6$ is analyzed. The mass scales, the gauge boson masses, and the masses for the spin 1/2 particles in the model are calculated. The mass differences between the up and down quark sectors, between the quarks and leptons, and between the charged and neutral leptons in one family are explained as a consequence of mixing of ordinary with exotic fermions implied by the model. By using experimental results we constrain the mixing angle between the two neutral currents and the mass of the additional neutral gauge boson to be $-0.0015 \leq \sin\theta \leq 0.0048$ and $600 GeV \leq M_{Z_2}$ at 95% CL. The existence of a Dirac neutrino for each family with a mass of the order of the electroweak mass scale is predicted.

Search for additional neutral gauge bosons

We have searched for a heavy neutral gauge boson, Z′, using the decay channel Z′ → ee. The data were collected with the DØ detector at the Fermilab Tevatron during the 1992–1993 p p collider run at s =1.8 TeV from an integrated luminosity of 15±1 pb −1. Limits are set on the cross section times brancing ratio for the process p p → Z′ → ee as a function of the Z′ mass. We exclude the existence of a Z′ of mass less than 490 GeV/c 2, assuming a Z′ with the same coupling strengths to quarks and leptons as the standard model Z boson.

Signals of new gauge bosons at futuree + e ? colliders

We analyze possible indirect signals of additional neutral gauge bosons at futuree + e − colliders, concentrating onSU(2) L ×U(1) y ×U(1) y , andSU(2) L ×SU(2) R ×U(1) effective theories. We develop a simple formalism to describe these effects and make a careful study of radiative corrections, in particular initial state radiation, which will be shown to have important implications. To make realistic estimates of the sensitivity to the new gauge boson effects, we use a model detector fore + e − annihilation at a center of mass energy of 500 GeV. Using a number of selected physical observables we then show that masses considerably higher than the total energy (up to a factor of 6) can be probed and that distinction between various theoretical models is possible.

Supersymmetry with spontaneous R-parity breaking in Z 0 decays: The case of an additional Z

Single production of SUSY particles in the decays of the Z 0 may proceed with large rates in models with spontaneously broken R-parity. We focus on the case where there is a lepton number symmetry as part of the gauge group. In the simplest of such models there is a single additional neutral gauge boson and the strength of R p -violating interactions is related with that of the new gauge force. We study the phenomenological implications of the model for Z 0 decays, including the study of the rates for single chargino production in Z 0 decays, i.e. Z 0→ ξ ± τ ±, as well as for the so-called Zen events, and find that they may be measurable at LEP. The first process, characteristics of spontaneously broken R-parity models, may proceed with a branching ratio as large as few × 10 −5 and should lead to a very clear signature. Zen events have a different origin than in the minimal SUSY standard model (MSSM). Their rates may also be enhanced with respect to MSSM. Our estimates of these rates take into account all of the relevant observational constraints, such as those that follow from neutrinophyics, from precise Z 0 property measurements, as well as SUSY particle searches at LEP.