Extra Gauge Bosons Research Articles

Mass bounds on new neutral gauge bosons in E6 models from SN 1987A data.

${\mathrm{E}}_{6}$ models contain right-handed neutrinos which, if light, should be emitted during stellar collapse. Their interactions with matter involve the exchange of an extra neutral gauge boson ${Z}^{\ensuremath{'}}$. We use data from SN 1987A to place bounds on the mass of this new gauge boson which in ${\mathrm{E}}_{6}$ models can be parametrized in terms of a mixing angle $\ensuremath{\theta}$. The limits obtained are, in general, much stronger than those from accelerator data and lie, except for a narrow band around $\ensuremath{\theta}=\ensuremath{-}14.48\ifmmode^\circ\else\textdegree\fi{}$, at the several TeV mass scale.

New constraints on extra gauge bosons

Recent W and Z boson mass measurements are used to constrain extended electroweak gauge models.

On the possibility of studying extra gauge Z′-Boson effects in e+e-→l+ - at TRISTANat TRISTAN

A new possibility is suggested in order to study in the process e+e-→l+- at energies below the standard Z-boson production threshold the effects coming from an extra neutral gauge boson Z′ in superstring-inspiredE6 models. It is shown that at energies \( \sqrt s \) ∼(50 ÷ 60) GeV the cross-section for relatively light Z′(MZ′≲2.5MZ) can have an interference dip absent in the standard model. The depth and energy coordinates of this dip depend on Z′-boson parameters. This information concerning the Z′-boson can be obtained by making use of TRISTAN, which is a high-luminosity set-up.

Higgs bosons and sleptons in an alternative left-right model.

The phenomenological structure of the combined Higgs-boson-slepton sector of the alternative left-right-supersymmetric model introduced by Ma is explored. Constraints upon and relations between Higgs-boson and slepton masses are derived and a tightly constrained mass spectrum is found. In general, one neutral Higgs boson is never heavier than 98 GeV, one neutral Higgs boson is always nearly degenerate in mass with the extra neutral gauge boson ${Z}_{2}^{0}$, and the charged Higgs boson can in principle be as light as 22 GeV. Further constraints require large ratios of Higgs vacuum expectation values, strongly favor the ${W}_{R}$ mass above \AA{}423 GeV, predict one Higgs-boson mass to be always very close to 98 GeV, and masses of the other Higgs bosons and the sleptons to be bounded from above and preferably not much above the $Z$ mass. In addition, the possibility of detecting light Higgs bosons at CERN LEP and the SLAC Linear Collider is briefly discussed.

Phenomenological mass limits on extra Z for someE 6 breaking patterns

We examine four distinctE6 symmetry-breaking patterns and find the lower limit for the extra neutral gauge boson mass and the Z-Z′ mixing angle in each case. The values determined are in general within the regions allowed by the low-energy experimental data.

Neutrino counting at the Z peak in extended electroweak models

The consequences of mixing between the standard model Z and a possible extra neutral gauge boson, Z', on neutrino counting at the Z peak are investigated. Our results are presented in the number of light neutrino generations ( V v ), and total Z width ( Γ z) plane. We find that a large range of values are possible, including the case where one of these quantities takes on its three-generation SM valur while the other does not. Z-Z′ mixing does not appear to be able to conceal a fourth generation of light neutrinos.

Implications from SN1987A on supersymmetric, left-right and E 6 particle masses

Current extensions of the standard model contain extra particles that, if light, should be emitted in the course of stellar collapse. Using data on SN1987A, we place bounds on the mass of the heavy particles that mediate their production and rescattering in the stellar medium. Taking into account the uncertainties in the parameters of the stellar core, we find the following conservative lower bounds. The quarks and selectrons of supersymmetric theories, as well as the extra neutral gauge bosons of left-right symmetric models and of a variety of E 6 superstring-inspired models, must all lie above the one TeV scale. One particular E 6 model, however, evades our constraints.

Stellar energy loss through e+e---> nu nu -bar in E6.

We calculate the energy loss due to neutrino-pair production in e{sup +}e{sup {minus}} annihilation in the superstring-inspired E{sub 6} model which has one extra low-energy neutral gauge boson. In addition, the contribution of the Higgs boson arising from a general low-energy superpotential has also been estimated. Within the context of existing neutral-current data we analyze our results.

Radiative zeros and extra neutral gauge bosons at lepton-hadron colliders.

We consider the process ${e}^{\ifmmode\pm\else\textpm\fi{}}$p\ensuremath{\rightarrow}${e}^{\ifmmode\pm\else\textpm\fi{}}$\ensuremath{\gamma}X. In the first section, we look for radiative zeros and find that they are absent in ${e}^{\mathrm{\ensuremath{-}}}$p collisions but possibly observable in ${e}^{+}$p collisions. In the second section we investigate the effects of the exchange of an extra neutral gauge boson on the process at hand. We find that, given appropriate cuts and using expected luminosities at the DESY ep collider HERA, a 2-standard-deviation effect could arise from a light neutral gauge boson. Z' masses up to \ensuremath{\sim}300 GeV/${c}^{2}$ could be probed at the 1-standard-deviation level.

Extra neutral gauge boson and the processes e+e--->ZiHa in a superstring-inspired model.

We discuss the processes ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${Z}_{i}$${H}_{a}$ (i=1,2; a=1,2,3) in a superstring-inspired model involving two Higgs-boson doublets and one singlet, and also an additional neutral gauge boson (${Z}_{E}$), at CERN LEP II and higher energies. Our main result is that, for ${Z}_{2}$ sitting on resonance at LEP II energy, the total cross section for the process ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${Z}_{1}$${H}_{2}$ is significantly large as compared with those for ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\ensuremath{\mu}}^{+}$${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$, ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${W}^{+}$${W}^{\mathrm{\ensuremath{-}}}$. For ${Z}_{2}$ at off resonance, the cross sections are almost the same as that for the standard model.

EXTRA NEUTRAL GAUGE BOSONS IN e+e−ANNIHILATION INTO HADRONS

The influence of an extra neutral E6 gauge boson of mass 140–300 GeV on the total cross section of e+e− annihilation into hadrons is studied at energies around the mass of the heavy neutral gauge boson.

Phenomenology of a technicolor model with softly broken flavor symmetry

We consider the phenomenology of a technicolor model with softly broken flavor symmetries. First we explore the breaking of the large gauge symmetries of this model and use e +e − scattering data to bound the VEV's responsible for the breaking. Next we examine the box diagrams responsible for quark and lepton masses in order to get a limit on the top quark mass. Finally, we consider contributions to FCNC effects arising from the extra gauge bosons and heavy fermions in this model. Because the flavor symmetry is softly broken, these are GIM-suppressed; they do, however, give additional limits on the model.

Limits on right-handed interactions from SN 1987A observations.

We consider the emission of light (${m}_{{\ensuremath{\nu}}_{R}}\phantom{\rule{0ex}{0ex}}\ensuremath{\lesssim}$ 10 MeV right-handed neutrinos from supernova 1987A via right-handed charged- and neutral-current interactions. By requiring that the neutronization process ${e}_{R}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{R}n$ does not carry away most of the energy that can be radiated by the supernova, ${E}_{T}\phantom{\rule{0ex}{0ex}}\ensuremath{\lesssim}\phantom{\rule{0ex}{0ex}}$ (4-5) \ifmmode\times\else\texttimes\fi{} ${10}^{53}$ ergs, we exclude the range of values for the right-handed $W$-boson mass, (3.7-6.7)${\mathrm{M}}_{{\mathrm{W}}_{\mathrm{L}}}$ \ensuremath{\le} ${\mathrm{M}}_{{\mathrm{W}}_{\mathrm{R}}}$ \ensuremath{\le} (280-500)${\mathrm{M}}_{{\mathrm{W}}_{\mathrm{L}}}$ for vanishing ${\mathrm{W}}_{\mathrm{L}}$ --- ${\mathrm{W}}_{\mathrm{R}}$ mixing parameter \ensuremath{\zeta}, and for \ensuremath{\zeta} \ensuremath{\ne} 0 we get (0.4-1.2) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}5}$ \ensuremath{\le} ${\left[{\ensuremath{\zeta}}^{2}\phantom{\rule{0ex}{0ex}}+\phantom{\rule{0ex}{0ex}}({M}_{{W}_{L}}^{4}\phantom{\rule{0ex}{0ex}}/\phantom{\rule{0ex}{0ex}}{M}_{{W}_{R}}^{4})\right]}^{\frac{1}{2}}\phantom{\rule{0ex}{0ex}}\ensuremath{\le}(0.02\ensuremath{-}0.07)$. For right-handed $W$ bosons heavier than 300 ${M}_{{W}_{L}}$, a significant ${\ensuremath{\nu}}_{R}$ emission may arise from the neutral-current-induced process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{R}{\ensuremath{\nu}}_{R}$, as well as $\mathrm{nn}\ensuremath{\rightarrow}\mathrm{nn}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ mediated by an extra gaugae boson $Z\ensuremath{'}$. In this case, for an appropriately defined effective mass ${M}_{N}$ for $Z\ensuremath{'}$, we find the excluded region $(2.4\ensuremath{-}4.3){M}_{{W}_{L}}<{M}_{N}<(30\ensuremath{-}85){M}_{{W}_{L}}$, mainly dependent on the core temperature and density profile.

EFFECTS OF AN EXTRA NEUTRAL E6 GAUGE BOSON IN e+e− ANNIHILATION INTO HADRONS

We calculate the influence of an extra neutral E6 gauge boson on the energy weighted and total cross sections in e+e− annihilation into hadrons. Longitudinal and azimuthal asymmetries are sensitive to the various extra U(1) factors and can show noticeable deviations from the standard model.

Phenomenology of a horizontal gauge boson in e+e- collisions.

The effects of an extra neutral gauge boson Z\ifmmode \tilde{}\else \~{}\fi{} predicted by the Sp(8)\ifmmode\times\else\texttimes\fi{}U(1) model, are studied both on and off the Z resonance in ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ collisions. Distinctive features are pointed out.

On the mass and mixings of the Z E

The experimental data on the neutral current couplings are used to derive lower bounds on the mass of Z E, the extra neutral gauge boson appearing in the minimal ‘beyond the standard model’ scenario favoured in superstring compactifications. This is based on the gauge group SU(3) c×SU(2) L×U(1) Y ×U(1) E. Taking sin 2 θ w =0.229, m W=80.76 GeV and m Z=91.59 GeV it is found that the mixing angle θ between Z and Z E must satisfy −0.136<sin θ<−0.007 corresponding to m Z E >152 GeV or, assuming E 6 unification m Z E >155 GeV.

Comparison of discovery limits for E6 neutral gauge bosons at future colliders.

We study and compare the phenomenology of extra ${\mathrm{E}}_{6}$ neutral gauge bosons at ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$, ep, and hadron colliders. Our purpose is to compare the discovery reach of the various colliders and see how they compare in studying the phenomenology of extra neutral gauge bosons. We find that of the future colliders, hadron colliders probe the highest mass scales for the existence of extra neutral gauge bosons although precision measurements at ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ colliders, the SLAC Linear Collider will put tight constraints on models predicting extra neutral gauge bosons. If deviations from the standard model are observed at ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ colliders at \ensuremath{\surd}As=${\mathrm{M}}_{\mathit{Z}}^{0}$, other measurements, especially those at the DESY ep collider HERA, will be necessary to unravel the physics. We also find that high-precision, low-energy neutral-current experiments will be competitive with ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ and ep colliders for detecting the presence of extra ${\mathrm{E}}_{6}$ neutral gauge bosons.

PRODUCTION AND DECAYS OF EXTRA GAUGE BOSONS IN A LEFT-RIGHT E6 SUPERSTRING MODEL

We examine the production and decays of extra gauge bosons Z2 and WR in a recently proposed left-right E6 superstring model with alternative assignments of the fermions in the 27 representation of E6. We find that either [Formula: see text] or [Formula: see text] decay modes may have a branching fraction as high as 6% and 13%, respectively. The bosonic decays of the Z2 are similar to those found in the minimal rank 5 E6 superstring model, except for a possible new [Formula: see text] mode. Allowed regions of Z2 mass versus the Z, Z′ mixing are determined from neutral current data.

PHENOMENOLOGICAL ASPECTS OF E6 SUPERSTRING-INSPIRED MODELS

The author discusses general problems of superstring - inspired models. These include some results on compactification, first problems for model building, and problems with supersymmetry breaking. A minimal model is described. This description focuses on generalities of the model, radiative breaking of the gauge symmetry, the particle spectrum, Gauginos and Higgs particles, and exotic color triplets (D-particles).

Extra neutral gauge bosons in electron-positron collisions at resonance.

A simple extension of the standard model to an SU(2${)}_{\mathrm{L}}$\ifmmode\times\else\texttimes\fi{}U(1${)}_{\mathrm{Y}}$\ifmmode\times\else\texttimes\fi{}U(1) gauge symmetry is considered. The symmetry is broken by vacuum expectation values of one doublet and one singlet scalar field, resulting in a second massive neutral gauge boson. Electron-positron collisions at this Z' resonance are calculated. Aside from the possibility of Z' decays into exotic fermions which fill out the irreducible representations of grand unified theories, there generally are important decay modes into ${W}^{+}$${W}^{\mathrm{\ensuremath{-}}}$ and ${Z}^{0}$${H}^{0}$ coming from mixing between the Z' and the Z of the standard model, even after imposing the constraints from experiment on the magnitude of the mixing angle.