Gauge Boson Self-interactions Research Articles

Studies on dimension-eight genuine Quartic Boson Coupling operators

Vector Boson Scattering (VBS) processes provide a great source of information on the structure of the Quartic Gauge Boson Couplings (QGCs). The Standard Model allows self interactions of the charged vector gauge bosons, although vertices with neutral-only bosons are forbidden. In this paper we use Monte Carlo samples containing VBS events with two Z-bosons in association with two jets, and we present preliminary studies for the setting of constraints on anomalous quartic couplings. In these studies we investigate typical kinematic variables and we classify them according to their sensitivity to aQGC effects. Finally, we evaluate the cross-section enhancement by each one of the dimension-eight QGC operators in the ZZjj channel.

Analysis of the anomalous quartic WWWW couplings at the LHeC and the FCC-he

The quartic gauge boson couplings that identify the strengths of the gauge boson self-interactions are exactly determined by the non-Abelian gauge nature of the Standard Model. The examination of these couplings at $ep$ collisions with high center-of-mass energy and high integrated luminosity provides an important opportunity to test the validity of the Standard Model and the existence of new physics beyond the Standard Model. The quartic gauge boson couplings can contribute directly to multi-boson production at colliders. Therefore, we examine the potential of the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ at the Large Hadron Electron Collider and the Future Circular Collider-hadron electron to study non-standard $WWWW$ couplings in a model independent way by means of the effective Lagrangian approach. We present an investigation on measuring $W^{+}W^{-}$ production in pure leptonic and semileptonic decay channels. In addition, we calculate the sensitivity limits at $95\%$ Confidence Level on the anomalous $\frac{f_{M0}}{\Lambda^{4}}$, $\frac{f_{M1}}{\Lambda^{4}}$, $\frac{f_{M7}}{\Lambda^{4}}$, $\frac{f_{S0}}{\Lambda^{4}}$, $\frac{f_{S1}}{\Lambda^{4}}$, $\frac{f_{T0}}{\Lambda^{4}}$, $\frac{f_{T1}}{\Lambda^{4}}$ and $\frac{f_{T2}}{\Lambda^{4}}$ couplings obtained by dimension-8 operators through the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ for the Large Hadron Electron Collider and the Future Circular Hadron Electron Collider's different center-of-mass energies and integrated luminosities. Our results show that with the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ at the Large Hadron Electron Collider and the Future Circular Collider-hadron electron the sensitivity estimated on the anomalous $WWWW$ couplings can be importantly strengthened.

Model independent study for the anomalous quartic WWγγ couplings at future electron-proton colliders

The Large Hadron Electron Collider and the Future Circular Collider-hadron electron with high center-of-mass energy and luminosity allow to better understand the Standard Model and to examine new physics beyond the Standard Model in the electroweak sector. Multi-boson processes permit for a measurement of the gauge boson self-interactions of the Standard Model that can be used to determine the anomalous gauge boson couplings. For this purpose, we present a study of the process ep→νeγγj at the Large Hadron Electron Collider with center-of-mass energies of 1.30, 1.98 TeV and at the Future Circular Collider-hadron electron with center-of-mass energies of 7.07, 10 TeV to interpret the anomalous quartic WWγγ gauge couplings using a model independent way in the framework of effective field theory. We obtain the sensitivity limits at 95% Confidence Level on 13 different anomalous couplings arising from dimension-8 operators. The best limit in fMi/Λ4 (i=0,1,2,3,4,5,7) parameters is obtained for fM2/Λ4 parameter while the best sensitivity derived on fTi/Λ4 (i=0,1,2,5,6,7) parameters is obtained for fT5/Λ4. In addition, this study is the first report on the anomalous quartic couplings determined by effective Lagrangians at ep colliders.

WWγ production at hadron colliders with NLO QCD+EW corrections and parton shower effects

production in proton–proton collision provides a window to the mechanism of electroweak symmetry breaking and a direct accessment to triple and quartic gauge couplings. Precision study of gauge boson self-interactions may also provide evidence of existence of new physics beyond the standard model. In this paper, we study the production at the LHC and future higher energy proton–proton colliders at the QCD+EW NLO including parton shower effects. We find that the contributions from the photon-induced (i.e. qγ- and γγ-initiated) channels are non-negligible since the photon luminosity can be enhanced significantly with the increment of colliding energy, and the large real jet emission QCD and EW corrections can be depressed sufficiently by applying the jet veto event selection scheme. Moreover, we also investigate the theoretical errors arising from the PDF uncertainty and the factorization/renormalization scale dependence.

Measurement of fiducial and differential W^+W^- production cross-sections at sqrt{s}=13\xa0TeV with the ATLAS detector

A measurement of fiducial and differential cross-sections for W^+W^- production in proton–proton collisions at sqrt{s}=13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 36.1 hbox {fb}^{-1} is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as WWrightarrow e^{pm }nu mu ^{mp }nu . To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory.

Production of vector resonances at the LHC via WZ-scattering: a unitarized EChL analysis

In the present work we study the production of vector resonances at the LHC by means of the vector boson scattering WZ → WZ and explore the sensitivities to these resonances for the expected future LHC luminosities. We are assuming that these vector resonances are generated dynamically from the self interactions of the longitudinal gauge bosons, WL and ZL, and work under the framework of the electroweak chiral Lagrangian to describe in a model independent way the supposedly strong dynamics of these modes. The properties of the vector resonances, mass, width and couplings to the W and Z gauge bosons are derived from the inverse amplitude method approach. We implement all these features into a single model, the IAM-MC, adapted for MonteCarlo, built in a Lagrangian language in terms of the electroweak chiral Lagrangian and a chiral Lagrangian for the vector resonances, which mimics the resonant behavior of the IAM and provides unitary amplitudes. The model has been implemented in MadGraph, allowing us to perform a realistic study of the signal versus background events at the LHC. In particular, we have focused our study on the pp → WZjj type of events, discussing first on the potential of the hadronic and semileptonic channels of the final WZ, and next exploring in more detail the most clear signals. These are provided by the leptonic decays of the gauge bosons, leading to a final state with ℓ1+ℓ1−ℓ2+νjj, ℓ = e, μ, having a very distinctive signature, and showing clearly the emergence of the resonances with masses in the range of 1.5–2.5 TeV, which we have explored.

Ferromagnetic properties of charged vector boson condensate

Bose-Einstein condensation of W bosons in the early universe is studied. It is shown that, in the broken phase of the standard electroweak theory, the condensed W bosons form a ferromagnetic state with aligned spins. In this case the primeval plasma may be spontaneously magnetizedinside macroscopically large domains and form magnetic fields which may be the seeds for the observed today galactic and intergalactic fields.However, in a modified theory, e.g. in a theory with stronger quartic self interactions of gauge bosons e.g. due to a smaller value of the weak mixing angle, antiferromagnetic condensation is possible. In the latter case W bosons form scalar condensate with macroscopically large electric charge density i.e. with a large average value of the bilinear product of W-vector fields but with microscopically small averagevalue of the field itself.

Anisotropic trispectrum of curvature perturbations induced by primordial non-Abelian vector fields

Motivated by the interest in models of the early universe where statistical isotropy is broken and can be revealed in cosmological observations, we consider an SU(2) theory of gauge interactions in a single scalar field inflationary scenario. We calculate the trispectrum of curvature perturbations, as a natural follow up to a previous paper of ours, where we studied the bispectrum in the same kind of models. The choice of a non-Abelian set-up turns out to be very convenient: on one hand, gauge boson self-interactions can be very interesting being responsible for extra non-trivial terms (naturally absent in the Abelian case) appearing in the cosmological correlation functions; on the other hand, its results can be easily reduced to the U(1) case. As expected from the presence of the vector bosons, preferred spatial directions arise and the trispectrum reveals anisotropic signatures. We evaluate its amplitude τNL, which receives contributions both from scalar and vector fields, and verify that, in a large subset of its parameter space, the latter contributions can be larger than the former. We carry out a shape analysis of the trispectrum; in particular we discuss, with some examples, how the anisotropy parameters appearing in the analytic expression of the trispectrum can modulate its profile and we show that the amplitude of the anisotropic part of the trispectrum can be of the same order of magnitude as the isotropic part.

Addendum to “Off-shell structure of the anomalousZandγself-couplings”

We point out that the lowest dimension operators that preserve $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ gauge invariance and induce gauge boson self-interactions affecting only the neutral gauge bosons are just two $\mathrm{dim}=8$ operators. If these operators constitute the only new physics source, there will then exist only two independent anomalous couplings affecting Z and $\ensuremath{\gamma}:$ i.e., one $\mathrm{CP}$ conserving and one $\mathrm{CP}$ violating. On this basis, we give the corresponding relations among the $ZZZ,$ $\mathrm{ZZ}\ensuremath{\gamma},$ and $\ensuremath{\gamma}\ensuremath{\gamma}Z$ couplings used up to now in the analyses of experimental data. A reanalysis taking these relations into account should produce much more stringent constraints on the anomalous couplings.

Probing neutral gauge boson self-interactions in ZZ production at hadron colliders

A detailed analysis of ZZ production at the upgraded Fermilab Tevatron and the CERN Large Hadron Collider is presented for general ZZZ and ZZ\gamma couplings. Deviations from the Standard Model gauge theory structure for each of these can be parameterized in terms of two form factors which are severely restricted by unitarity at high energy. Achievable limits on these couplings are shown to be a dramatic improvement over the limits currently obtained by e^+e^- experiments.

ANOMALOUS HIGGS COUPLINGS

We review the effects of new effective interactions on Higgs-boson phenomenology. New physics in the electroweak bosonic sector is expected to induce additional interactions between the Higgs doublet field and the electroweak gauge bosons, leading to anomalous Higgs couplings as well as anomalous gauge-boson self-interactions. Using a linearly realized SU (2)L× U (1)Y invariant effective Lagrangian to describe the bosonic sector of the Standard Model, we review the effects of the new effective interactions on the Higgs-boson production rates and decay modes. We summarize the results from searches for the new Higgs signatures induced by the anomalous interactions in order to constrain the scale of new physics, in particular at CERN LEP and Fermilab Tevatron colliders.

TWO- AND THREE-VECTOR-BOSON PRODUCTION IN e+e- COLLISIONS WITHIN THE BESS MODEL

The BESS model is the Higgsless alternative to the standard model of electroweak interaction with nonlinear realized spontaneous symmetry breaking. Since it is nonrenormalizable, new couplings (not existing in the SM) are induced at each loop order. On the basis of the one-loop induced gauge boson self-couplings we calculated the cross sections for the two- and three-gauge-boson production processes in e+e- collisions. Measurements of these cross sections in a planned e+e- linear collider at [Formula: see text] (NLC) will supply a good empirical test of the gauge boson self-interactions and thus should enable us to discriminate between the SM and the BESS model.

Equivalence of Hamiltonian and Lagrangian path integral quantization: Effective gauge theories.

The equivalence of correct Hamiltonian and naive Lagrangian (Faddeev-Popov) path integral quantization (Matthews's theorem) is proven for gauge theories with arbitrary effective interaction terms. Effective gauge-boson self-interactions and effective interactions with scalar and fermion fields are considered. This result becomes extended to effective gauge theories with higher derivatives of the fields.

Non-standard gauge-boson self-interactions within a gauge invariant model

We examine dimension-six extensions of the standard electroweak Lagrangian which are invariant under localSU(2) L ×U(1) Y -transformations. The dimensionfour trilinear and quadrilinear effective interactions of the vector bosons with one another are found to coincide with the vector boson interactions previously derived from globalSU(2) weak isospin symmetry broken by electromagnetism. Supplementing the model by a well-known dimension-six single-parameter quadrupole interaction leads to the most general vector boson self-couplings that can be obtained by addition of dimension-six terms to the standard Lagrangian. We examine in some detail anotherSU(2) L ×U(1) Y -symmetric interaction which containsW 3 B mixing and modifies both vector boson self-couplings and fermionic interactions. Independently of being strongly constrained by the LEP 1 data, the addition of this interaction to the above-mentioned non-standard ones does not change the form of the trilinear and quadrilinear non-standard self-couplings of the vector bosons. Therefore, while being interesting in itself with respect to LEP 1 physics, this term is irrelevant with respect to the phenomenology of the vector-boson self-interactions.

Consistency and current algebras of a non-Abelian chiral gauge theory in four dimensions.

We present a gauge-symmetric reformulation of anomalous gauge theories and study the symmetry structures of an $\mathrm{SU}(N)$ chiral gauge model in four dimensions. The gauge symmetry is made manifest via the introduction of the Wess-Zumino term, but turns out to be spontaneously broken; correspondingly, the gauge bosons become massive and some nonstandard self-interactions of gauge bosons arise. While the total gauge current, consisting of both fermion and unphysical Wess-Zumino fields, is anomaly free, the gauge anomalies and the Schwinger terms reappear in the fermion chiral currents and are related through the underlying gauge symmetry. Canonical reasoning is given to establish their connection.

Complete determination of gauge boson self-interactions in the bess model

The electroweak gauge theory with nonlinearly realized SSB (BESS model), which is the Higgs-less alternative to the SM, is defined by a nonrenormalizable lagrangian. Consequently, new interactions emerge at each loop order. We calculate these (quantum-induced) contributions to both cubic and quartic gauge boson self-interactions and observe a striking difference between the two cases: while the induced three-boson couplings remain of the pure Yang-Mills type, this is not the case with the quartic ones. Furthermore, it is shown that the resulting interaction strengths are sizably different from the SM ones, if the “hidden symmetry” parameter λ 2 is not small. These deviations from the SM may lead to interesting phenomenological implications, e.g. in W + W − or WZ production.

Strongly interacting gauge boson sector in an electroweak theory with “hidden” gauge symmetry

We consider an SU(2) × U(1) gauge theory with nonlinearly realized spontaneous symmetry breaking as a model for electroweak interactions in which no physical Higgs particle occurs. It contains a further triplet of heavy vector fields (in addition to the ordinary gauge bosons W μ and Y μ). The theory is nonrenormalizable and therefore new interactions are generated at each loop level. We construct invariant new effective terms representing such interactions and calculate the 1-loop induced parameters corresponding to some of those terms. In particular, we determine the 1-loop induced cubic self-interactions of gauge bosons (light and heavy ones). We show that they are of Yang-Mills type and do not lead to anomalous magnetic or electric moments. They should show up as a considerable breaking of fermion-gauge boson coupling universality.

Phenomenological implications of an electroweak theory without Higgs

An alternative to the standard electroweak gauge theory is considered which does not involve the physical Higgs particle, but contains heavy vector boson resonances manifesting the strong gauge boson self-interactions. We investigate phenomenological implications of such a theory and demonstrate that processes including heavy quarks (in particular heavy quark pair production and asymmetry in e +e − annihilation) constitute a good testing ground for experimentally discriminating this theory from the SM at energies available at present or within the near future.