Electroweak Gauge Model Research Articles

Weak charges in SU(5)L × U(1)Y gauge models

Abstract Within the framework of a renormalizable SU(5)L × U(1)Y electro-weak gauge model with no exotic electric charges, we obtain all the neutral weak charge operators and their quantization, once the diagonalization of the neutral boson mass matrix is properly performed. Our results open up the path to a rich and promising phenomenological outcome. All the Standard Model phenomenology is recovered by simply decoupling the latter’s scale (vSM = 246 GeV) from the higher scale (V ∼ 10 TeV) specific to our new electro-weak unification.

RealisticSU(3)c⊗SU(3)L⊗U(1)Xmodel with a type II Dirac neutrino seesaw mechanism

Here we propose a realistic $\mathrm{SU(3)_c \otimes SU(3)_L \otimes U(1)_X}$ electroweak gauge model with enlarged Higgs sector. The scheme allows for the natural implementation of a type II seesaw mechanism for Dirac neutrinos, while charged lepton and quark masses are reproduced in a natural way thanks to the presence of new scalars. The new $\mathrm{SU(3)_c \otimes SU(3)_L \otimes U(1)_X}$ energy scale characterizing neutrino mass generation could be accessible to the current LHC experiments.

Charged fermion masses with Yukawa coupling strength universality

We consider the problem of the ordinary charged fermion mass patterns in the framework of a version of the 3-3-1 electroweak gauge model which includes charged heavy leptons. The masses of the top and the bottom quarks are given at the tree level. All the other charged fermion get their masses at the one loop level. The Yukawa coupling strength can be universal. The model is compatible with a mechanism for neutrino mass generation proposed by other authors.

Pathways to Naturally Small Neutrino Masses

In the minimal standard electroweak gauge model, there is an effective dimension-five operator which generates neutrino masses, and it has only three tree-level realizations. One is the canonical seesaw mechanism with a right-handed neutrino. Another is having a heavy Higgs triplet as recently proposed. The third is to have a heavy Majorana fermion triplet, an example of which is presented here in the context of supersymmetric $\mathrm{SU}(5)$ grand unification. The three generic one-loop realizations of this operator are also discussed.

Neutrino Masses and Leptogenesis with Heavy Higgs Triplets

A simple and economical extension of the minimal standard electroweak gauge model (without right-handed neutrinos) by the addition of two heavy Higgs scalar triplets would have two significant advantages. Naturally small Majorana neutrino masses would become possible, as well as leptogenesis in the early universe which gets converted at the electroweak phase transition into the present observed baryon asymmetry.

Decay of Z into two light Higgs bosons.

If the standard electroweak gauge model is extended to include two or more Higgs doublets, there may be a neutral Higgs boson h which is light (with a mass of say 10 GeV) but the hZZ coupling is suppressed so that it has so far escaped experimental detection. However, the effective hhZZ coupling is generally unsuppressed; hence, the decay of Z into two light Higgs bosons plus a fermion-antifermion pair may have an observable branching fraction, especially if h decays invisibly as, for example, in the recently proposed doublet Majoron model.

Scalar mass bounds in two supersymmetric extended electroweak gauge models

In two recently proposed supersymmetric extended electroweak gauge models, the reduced Higgs sector at the 100 GeV energy scale consists of only two doublets, but they have quartic scalar couplings different from those of the minimal supersymmetric standard model. In the SU(2)*SU(2)*U(1) model, there is an absolute upper bound of about 145 GeV on the mass of the lightest neutral scalar boson. In the SU(3)*U(1) model, there is only a parameter-dependent upper bound which formally goes to infinity in a particular limit.

New supersymmetric option for two Higgs doublets.

If the standard electroweak gauge model is embedded in a larger theory which is supersymmetric and the latter breaks down to the former at some mass scale, then the reduced Higgs potential at the electroweak mass scale may differ from that of the well-known minimal supersymmetric extension. Specifically, if the larger theory is based on $\rm {SU(2)_L \times SU(2)_R \times U(1)}$, an interesting alternative exists for two Higgs doublets.

New supersymmetric electroweak gauge model with natural baryon-number conservation

Baryon number ( B) is automatically conserved in the standard SU(2) × U(1) electroweak gauge model, but not in its supersymmetric extension where it must be imposed as an extra condition. This undesirable feature is avoided in the conventional left-right supersymmetric extension, but then flavor-changing neutral currents (FCNC) are not naturally suppressed. A new version is proposed with automatic B conservation as well as FCNC suppression except for u quarks through scalar exchange which then makes possible the decay t → c + Higgs boson.

SIMPSON’S 17 keV NEUTRINO IN MINIMALLY EXTENDED SU(2)L×U(1) ELECTROWEAK MODELS

It is shown that the standard SU(2) L× U(1) electroweak gauge model extended so as to incorporate a single right-handed neutrino singlet and a second Higgs doublet, supplemented with the singlet majoron hypothesis, can accommodate Simpson’s 17 keV neutrino in a rather unique way. A number of interesting phenomenological consequences follow from such a scheme, which are discussed.

New constraints on extra gauge bosons

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

Radiative corrections to W,Z masses and constraints on new Z bosons.

We explore the implications of the recent $W$- and $Z$-boson-mass measurements at the SLAC Linear Collider, CERN LEP, and Fermilab Tevatron, and also the $\ensuremath{\mu}$ pair and total hadronic cross sections measured at KEK TRISTAN. A detailed comparison is made between the ${M}_{W}$ and ${M}_{Z}$ data and standard-model predictions including radiative corrections. These measurements also constrain extended electroweak gauge models. We place model-dependent upper bounds on the mass of a second neutral gauge boson from ${M}_{W}$ and ${M}_{Z}$ data, and set lower bounds on the ${Z}^{\ensuremath{'}}$ mass from direct production searches at the Collider Detector at Fermilab (CDF). We analyze the effects of $Z\ensuremath{-}{Z}^{\ensuremath{'}}$ mixing on the $Z$ width, leptonic branching ratio, and peak cross section at ${e}^{+}{e}^{\ensuremath{-}}$ colliders. We find that a second $Z$ cannot account for the increase in total hadronic and decrease in $\ensuremath{\mu}$-pair cross sections observed at KEK TRISTAN and simultaneously satisfy the CDF ${Z}^{\ensuremath{'}}$ search limits.

Asymmetric left-right model for generating radiative quark and lepton masses.

The conventional SU(2){sub {ital L}}{times}SU(2){sub {ital R}}{times}U(1) electroweak gauge model is extended to include two heavy singlet quarks and one heavy singlet lepton. The scalar sector consists of two (2,1,1/2) doublets, two (1,2,1/2) doublets, one (2,1,3/2) doublet, one (1,2,3/2) doublet, as well as one (1,3,1) triplet. Realistic radiative masses for all light quarks and leptons are obtained. A {ital Z}{sub 2} discrete symmetry serves to distinguish the electron (or muon) and its neutrino from the other leptons.

Radiative quark and lepton masses

Realistic radiative quark and lepton masses for the first two generations can be obtained in the context of the standard SU(2) × U(1) electroweak gauge model, extended to include a fourth generation and four extra Higgs-boson doublets together with a Z 4 discrete symmetry which is softly broken down to Z 2.

One-loop-induced fermion masses and exotic interactions in a standard-model context.

The standard SU(2)\ifmmode\times\else\texttimes\fi{}U(1) electroweak gauge model is extended to include a fourth generation of quarks and leptons as well as four extra Higgs-boson doublets. With the implementation of a ${Z}_{4}$ discrete symmetry, which is softly broken down to ${Z}_{2}$, realistic radiative quark and lepton masses for the first two generations can be obtained. Assuming that the third and fourth lepton generations are odd under the unbroken ${Z}_{2}$, we discuss a number of interesting phenomenological consequences such as a longer $\ensuremath{\tau}$ lifetime and some possible anomalous $\ensuremath{\tau}$ interactions. We also single out some processes involving fourth-generation quarks and leptons which cannot be confused experimentally with those of the standard model.

Radiative hierarchy of Majorana neutrino masses

The standard SU (2) L×U (1) electroweak gauge model is extended to include a fourth generation of leptons as well as some extra Higgs bosons, transforming nontrivially under a discrete Z 3 symmetry, such that a radiative hierarchy of Majorana neutrino masses can be obtained without the addition of any neutral lepton singlet.

Radiative quark and lepton masses through soft supersymmetry breaking.

A supersymmetric extension of the standard strong and electroweak gauge model has the property that light quarks and leptons acquire radiative masses as the result of the breaking of a chiral symmetry by soft supersymmetry-breaking terms. This radiative mechanism is then extended to include all known quarks and leptons in the context of a supersymmetric SU(3)\ifmmode\times\else\texttimes\fi{}SU(2)\ifmmode\times\else\texttimes\fi{}U(1)\ifmmode\times\else\texttimes\fi{}U(1)' gauge model based on ${\mathrm{E}}_{6}$ particle content as the possible low-energy limit of a superstring theory.

Radiative quark and lepton masses induced by a fourth generation.

Realistic radiative quark and lepton masses for the first two generations, as well as mixing for all three, can be obtained in the context of the standard SU(2)\ensuremath{\bigotimes}U(1) electroweak gauge model. The required additional ingredients are a fourth generation and some extra Higgs-boson doublets together with a singlet, as well as a spontaneously broken ${Z}_{4}$ discrete symmetry.

Gauge-boson mass shifts for extended Higgs sectors.

We calculate the one-loop radiative corrections to gauge-boson masses in SU(2${)}_{\mathrm{L}}$\ifmmode\times\else\texttimes\fi{}U(1${)}_{\mathrm{Y}}$ electroweak gauge models with an extended Higgs sector in an on-shell renormalization scheme. Current gauge-boson mass measurements restrict certain Higgs-boson masses to lie below the unitarity bound. Future precise measurements of the Z-boson mass can significantly reduce this limit. We also compare our results to previous calculations for the shift in the \ensuremath{\rho} parameter.

LOWER BOUND ON NEUTRINO MASSES IN LEFT-RIGHT ELECTROWEAK GAUGE MODELS

Although Dirac neutrino masses are generally not calculable in SU (2)L× SU (2)R× U (1) electroweak gauge models, they can be bounded from below under certain naturalness assumptions. The generic result is [Formula: see text], where ζ and m1, m2 are the mixing angle and mass eigenvalues of WL, WR.