Triple Gauge Boson Vertices Research Articles

Fermionic UV models for neutral triple gauge boson vertices

Searches for anomalous neutral triple gauge boson couplings (NTGCs) provide important tests for the gauge structure of the standard model. In SMEFT (“standard model effective field theory”) NTGCs appear only at the level of dimension-8 operators. While the phenomenology of these operators has been discussed extensively in the literature, renormalizable UV models that can generate these operators are scarce. In this work, we study a variety of extensions of the SM with heavy fermions and calculate their matching to d = 8 NTGC operators. We point out that the complete matching of UV models requires four different CP-conserving d = 8 operators and that the single CPC d = 8 operator, most commonly used by the experimental collaborations, does not describe all possible NTGC form factors. Despite stringent experimental constraints on NTGCs, limits on the scale of UV models are relatively weak, because their contributions are doubly suppressed (being d = 8 and 1-loop). We suggest a series of benchmark UV scenarios suitable for interpreting searches for NTGCs in the upcoming LHC runs, obtain their current limits and provide estimates for the expected sensitivity of the high-luminosity LHC.

Impact of dimension-eight SMEFT operators in the electroweak precision observables and triple gauge couplings analysis in universal SMEFT

We perform a complete study of the electroweak precision observables and electroweak gauge boson pair production in terms of the SMEFT up to ${\cal O}(1/\Lambda^4)$ under the assumption of universal, C and P conserving new physics. We show that the analysis of data from those two sectors allows us to obtain closed constraints in the relevant parameter space in this scenario. In particular we find that the Large Hadron Collider data can independently constrain the Wilson coefficients of the dimension-six and -eight operators directly contributing to the triple gauge boson vertices. Our results show that the impact of dimension-eight operators in the study of triple gauge couplings is small.

Probing model-independent limits on W+W−γ triple gauge boson vertex at the LHeC and the FCC-he

We study the cross-section of production of a single W− boson in association with a neutrino through the process . Additionally, we obtain limits on the anomalous couplings Δκγ and λγ of the W+W−γ vertex at the Large Hadron electron Collider (LHeC) and the future circular collider hadron-electron (FCC-he). The impact of the polarized beam due to the electron is also analyzed. Our best limits for Δκγ and λγ at the 95% C.L. are: Δκγ = ±0.0017, (unpolarized electron beam) and , (polarized electron beam) identifying the W− boson through the hadronic decay channel. In addition, the collision is one of the clean, pure and simple processes to probe the W+W−γ coupling without the complications of QCD backgrounds.

Electroweak sector under scrutiny: A combined analysis of LHC and electroweak precision data

We perform a comprehensive study of the Higgs couplings, gauge-boson couplings to fermions and triple gauge boson vertices. We work in the framework of effective theories including the effects of the dimension-six operators contributing to these observables. We determine the presently allowed range for the coefficients of these operators via a 20 parameter global fit to the electroweak precision data, as well as electroweak diboson and Higgs production data from LHC Run 1 and 2. We quantify the improvement on the determination of the 20 Wilson coefficients by the inclusion of the Run 2 results. In particular we present a novel analysis of the ATLAS Run 2 36.1 $\rm fb^{-1}$ data on the transverse mass distribution of $W^+W^-$ and $W^\pm Z$ in the leptonic channel which allow for stronger tests of the triple gauge boson vertices. We discuss the discrete (quasi)-degeneracies existing in the parameter space of operator coefficients relevant for the Higgs couplings to fermions and gauge bosons. In particular we show how the inclusion of the incipient $tH$ data can break those degeneracies in the determination of the top-Higgs coupling. We also discuss and quantify the effect of keeping the terms quadratic in the Wilson coefficients in the analysis and we show the importance of the Higgs data to constrain some of the operators that modify the triple gauge boson couplings in the linear regime.

Effective Lagrangian approach to the EWSB sector

In a model independent framework, the effects of new physics at the electroweak scale can be parametrized in terms of an effective Lagrangian expansion. Assuming the SU(2)LxU(1)Y gauge symmetry is linearly realized, the expansion at the lowest order span dimension–six operators built from the observed Standard model (SM) particles, in addition to a light scalar doublet. After a proper choice of the operator basis we present a global fit to all the updated available data related to the electroweak symmetry breaking sector: triple gauge boson vertex (TGV) collider measurements, electroweak precision tests and Higgs searches. In this framework modifications of the interactions of the Higgs field to the electroweak gauge bosons are related to anomalous TGV's, and given the current experimental precision, we show that the analysis of the latest Higgs boson data at the LHC and Tevatron gives rise to strong bounds on TGV's that are complementary to those from direct TGV measurements. Interestingly, we present how this correlated pattern of deviations from the SM predictions could be different for theories based on a non–linear realization of the SU(2)LxU(1)Y symmetry, characteristic of for instance composite Higgs models. Furthermore, anomalous TGV signals expected at first order in the non–linear realization may appear only at higher orders of the linear one, and viceversa. Their study could lead to hints on the nature of the observed boson.

Heavy fermion nondecoupling effects in triple gauge boson vertices

Within a spontaneously broken gauge group we carefully analyse and calculate triple gauge boson vertices dominated by triangle one-loop Feynman diagrams involving heavy fermions compared to external momenta and gauge boson masses. We perform our calculation strictly in four dimensions and derive a general formula for the off-shell, one-particle irreducible (1PI) effective vertex which satisfies the relevant Ward Identities and the Goldstone boson equivalence theorem. Our goal is to search for non-decoupling heavy fermion effects highlighting their synergy with gauge chiral anomalies. Particularly in the Standard Model, we find that when the arbitrary anomaly parameters are fixed by gauge invariance and/or Bose symmetry, the heavy fermion contribution cancels its anomaly contribution leaving behind anomaly and mass independent contributions from the light fermions. We apply these results in calculating the corresponding CP-invariant one-loop induced corrections to triple gauge boson vertices in the SM, minimal $Z'$models as well as their extensions with a fourth fermion generation, and compare with experimental data.

New physics contribution to neutral trilinear gauge boson couplings

We study the one loop new physics effects to the CP even triple neutral gauge boson vertices $\gamma^\star \gamma Z$, $\gamma^\star Z Z$, $Z^\star Z \gamma$ and $Z^\star Z Z$ in the context of Little Higgs models. We compute the contribution of the additional fermions in Littles Higgs model in the framework of direct product groups where $[SU(2)\times U(1)]^2 $ gauge symmetry is embedded in SU(5) global symmetry and also in the framework of simple group where $SU(N)\times U(1)$ gauge symmetry breaks down to $SU(2)_L\times U(1)$. We calculate the contribution of the fermions to these couplings when $T$ parity is invoked. In addition, we re-examine the MSSM contribution at the chosen point of SPS1a' and compare with the SM and Little Higgs models.

Probing anomalous triple gauge boson vertex in photon induced processes using proton taggers

In these proceedings, we present the sensitivity to the anomalous triple gauge boson vertex WWγ that can be achieved using forward proton taggers in ATLAS. The sensitivity can be in general improved with respect to LEP and the Tevatron results, especially for the Δ κ γ parameter.

Multigauge-boson vertices and chiral Lagrangian parameters in Higgsless models with ideal fermion delocalization

Higgsless models with fermions whose SU(2) properties are "ideally delocalized," such that the fermion's probability distribution is appropriately related to the W boson wavefunction, have been shown to minimize deviations in precision electroweak parameters. As contributions to the S parameter vanish to leading order, current constraints on these models arise from limits on deviations in multi-gauge-boson vertices. We compute the form of the triple and quartic gauge boson vertices in these models and show that these constraints provide lower bounds only of order a few hundred GeV on the masses of the lightest KK resonances. Higgsless models with ideal fermion delocalization provide an example of extended electroweak gauge interactions with suppressed couplings of fermions to extra gauge-bosons, and these are the only models for which triple-gauge-vertex measurements provide meaningful constraints. We relate the multi-gauge couplings to parameters of the electroweak chiral Lagrangian, and the parameters obtained in these SU(2) x SU(2) models apply equally to the corresponding five dimensional gauge theory models of QCD. We also discuss the collider phenomenology of the KK resonances in models with ideal delocalization. These resonances are found to be fermiophobic, therefore traditional direct collider searches are not sensitive to them and measurements of gauge-boson scattering will be needed to find them.

Precision measurements of electroweak gauge boson parameters at LEP

Over ten years after the start-up of LEP and four years after the completion of the energy scans around the Z resonance the analyses of the Z parameters by the four experiments Aleph, Delphi and L3 are final and the Opal results are very close to final. The analyses of the polarisation of τ leptons and measurements of the production rates and forward-backward asymmetries in the heavy flavour sector are approaching their finalisation. Recent data taking nearly doubled the statistics of W ± pair events available at Lep and lead to significantly improved preliminary measurements of the W ± pair production cross section, the W mass and branching fractions as well as improved limits on non-standard couplings at the triple gauge boson vertices. Altogether, in combination with measurements of the weak mixing angle at the SLC and the top quark mass at the Tevatron, these results provide stringent test of the Standard Model of the electroweak interaction and constrain its last missing parameter, the mass of the Higgs boson.

Evaluation ofS,T, U parameters, triple gauge boson vertices and some oblique corrections in extraU(1) superstring inspired model

Explicit evaluation of the following parameters has been carried out in the extraU (1) superstring inspired model: (i) As Mz2 varies from 555 GeV to 620 GeV and (m t) CDF = 175.6 ± 5.7 GeV (Table 1): (a) SNew varies from -0.100 ± 0.089 to -0.130 ± 0.090, (b) TNew varies from -0.098 ± 0.097 to -0.129 ± 0.098, (c) UNew varies from -0.229 ± 0.177 to -0.253 ± 0.206, (d) Τz varies from 2.487 ± 0.027 to 2.486 ± 0.027, (e) ALR varies from 0.0125 ± 0.0003 to 0.0126 ± 0.0003, (f) A FB b remains constant at 0.0080 ± 0.0007. Almost identical values are obtained for (m t)D0 = 169 GeV (see table 2). (ii) Triple gauge boson vertices (TGV) contributions: AsMz 2 varies from 555 GeV to 620 GeV and (m t) CDF = 175.6 ±5.7 GeV. (a)√s = 500 GeV, asymptotic case: $$\overline f _1^{Z_1 } $$ varies from -0.301 to -0.179; $$\overline f _{3|Z_1 }^{Z_1 } $$ varies from -0.622 to -0.379; $$f_5^{Z_1 } $$ varies from +0.0061 to 0.0056; $$\overline f _{3|Z_1 }^{\gamma _1 } $$ varies from -3.691 to -2.186. $$\overline f _z^{Z_2 } $$ varies from +0.270 to +0.118; $$\overline f _3^{Z_2 } $$ varies from +0.552 to 0.238; $$f_5^{Z_2 } $$ varies from +0.0004 to +0.0002; $$\overline f _{3|Z_2 }^{\gamma _1 } $$ remains constant at -0.110. (b)√s = 700 GeV, asymptotic case: $$\overline f _1^{Z_1 } $$ varies from -0.297 to -0.176; $$\overline f _3^{Z_1 } $$ varies from -0.609 to -0.370; $$\overline f _5^{Z_1 } $$ varies from -0.0082 to -0.0078; $$\overline f _{3|Z_1 }^{\gamma _1 } $$ varies from -3.680 to -2.171.√s = 700 GeV, nonasymptotic case: $$\overline f _1^{Z_2 } $$ varies from -0.173 to -0.299; $$\overline f _3^{Z_2 } $$ varies from-0.343 to -0.591; $$f_5^{Z_2 } $$ varies from -0.005 to -0.011; $$\overline f _{3|Z_2 }^{\gamma _1 } $$ remains constant at -0.110. The pattern of form factors values for√s = 1000, 1200 GeV is almost identical to that of√s= 700 GeV. Further the values of the form factors for (m t)D0 (=169 GeV) follow identical pattern as that of (m t) CDF form factors values (see tables 5, 6, 9, 10). We conclude that the values of all the form factors with the exception of these of $$f_5^{Z_1 } $$ , $$f_5^{Z_2 } $$ are comparable or larger than theS, T values and therefore the TGV contributions are important while deciding the use of extraU (1) model for doing physics beyond standard model.

NLO QCD corrections and triple gauge boson vertices at the NLC

We study NLO QCD corrections as relevant to hadronic W decay in W pair production at a future 500 GeV electron-positron linac, with particular emphasis on the determination of triple gauge boson vertices. We find that hard gluon bremstrahlung may mimic signatures of anomalous triple gauge boson vertices in certain distributions. The size of these effects can strongly depend on the polarisation of the initial electron positron beams.

Two-loop large Higgs mass corrections to electroweak gauge boson quartic couplings

The two-loop corrections to the electroweak gauge boson quartic couplings, growing quadratically with the Higgs boson mass, are calculated in the Standard Model in the limit of large Higgs mass. The corrections to WWWW, WWZZ and ZZZZ four-vertices are found to be an order of magnitude larger than the two-loop m H 2 corrections to light fermion and triple gauge boson vertices. For a heavy Higgs boson with a mass around 1 TeV the corrections are at the several percent level and in principle could be observed experimentally.

Di-Boson production at hadron colliders with general triple gauge boson couplings. Analytic expressions of helicity amplitudes and cross-sections

We discuss the tests of general Triple Gauge Boson Vertices (TGV) through bosonic pair production at present and future hadron colliders. All bosonic final states are reviewed via the tree level quark-antiquark annihilation sub-processes. The full analytic expressions of the helicity amplitudes and cross-sections are given. These expressions should be useful in any attempt to disentangle the effects of the most general non standard WWV(V = γ,Z) vertices including 14 free parameters. We investigate the sensitivity of the invariant mass and transverse momentum distributions to the full set of anomalous couplings including final state polarization structures. We particularly consider these features at the projected CERN Large Hadron Collider (LHC) energy scale.

Measurement of the W-pair cross section in e+e− collisions at 172 GeV

Abstract The e+e−→W+W− cross section is measured in a data sample collected by ALEPH at a mean centre-of-mass energy of 172.09 GeV, corresponding to an integrated luminosity of 10.65 pb−1. Cross sections are given for the three topologies, fully leptonic, semi-leptonic and hadronic of a W-pair decay. Under the assumption that no other decay modes are present, the W-pair cross section is measured to be 11.7±1.2 (stat.) ±0.3 (syst.) pb . The existence of the triple gauge boson vertex of the Standard Model is clearly preferred by the data. The decay branching ratio of the W boson into hadrons is measured to be B(W→hadrons) =67.7±3.1 (stat.) ±0.7 (syst.) % , allowing a determination of the CKM matrix element |Vcs|=0.98±0.14(stat.)±0.03(syst.).

The fermion-loop scheme for finite-width effects in e+et- annihilation into four fermions

We describe the gauge-invariant treatment of the finite-width effects of W and Z bosons in the fermion-loop scheme and its application to the six-fermion (LEP2) processes e t- e + → four fermions, with massless external fermions. The fermion-loop scheme consists in including all fertnionic one-loop corrections in tree-level amplitudes and resumming the self-energies. We give explicit results for the unrenormalized fermionic one-loop contributions to the gauge-boson self-energies and the triple gauge-boson vertices, and perform the renormalization in a gauge invariant way by introducing complex pole positions and running couplings. A simple effective Born prescription is presented, which allows for a relatively straightforward implementation of the fermion-loop scheme in LEP1 and LEP2 processes. We apply this prescription to typical LEP2 processes, i.e. e t-e + → μ t- ν μu d, e t-e + → s cu d , and e t-e + → e t- ν er d , and give numerical comparisons with other gauge-invariance-preserving schemes in the energy range of LEP2, NLC and beyond.

Effects of the electroweak symmetry breaking sector in rare B and K decays

The effects of the electroweak symmetry breaking sector in rare $B$ and $K$ decays are considered in the presence of new strong dynamics at a large energy scale. In the context of the low energy effective lagrangian of the symmetry breaking sector, we focus on the contributions that are not constrained by bounds on oblique corrections or anomalous triple gauge boson vertices. We find that these have very little effect in $b\to s\gamma$, but potentially large contributions appear in $b\to s\ell^+\ell^-$ and $b\to s\nu\bar\nu$ as well as in $b\to s g$ processes. Deviations from the standard model in rare $K$ decays such as $K^+\to\pi^+\nu\bar\nu$ and $K_L\to\pi^0\nu\bar\nu$ are shown to be correlated with the ones in the $B$ modes. The distinct resulting pattern of deviations from the standard model in rare decays is a characteristic feature of a strongly interacting electroweak symmetry breaking sector.

Non-decoupling effects of heavy particles in triple gauge boson vertices

Non-decoupling effects of heavy particles present in beyond-the-standard models are studied for the triple gauge boson vertices γW + W − and Z 0 W + W −. We show from a general argument that the non-decoupling effects are described by four independent parameters, in comparison with the three parameters S, T and U in the oblique corrections. These four parameters of the effective triple gauge boson vertices are computed in two beyond-the-standard models. We also study the relation of the four parameters to the S, T, U parameters, relying on an operator analysis.

Triple Gauge-Boson Vertices and New Physics

Triple Gauge-Boson Vertices and New Physics

Electroweak chiral Lagrangian and new precision measurements.

A revised and complete list of the electroweak chiral lagrangian operators up to dimension-four is provided. The connection of these operators to the $S$, $T$ and $U$ parameters and the parameters describing the triple gauge boson vertices $WW\gamma$ and $WWZ$ is made, and the size of these parameters from new heavy physics is estimated using a one flavor-doublet model of heavy fermions. The coefficients of the chiral lagrangian operators are also computed in this model.