Vector-boson Self-couplings Research Articles

Beyond the standard model: Working group report

This report summarises the activities of the working group on ‘Physics beyond the Standard Model’. The results of investigations in incorporatingR-parity in grand unification, the possibility of a light charged Higgs boson in extension of MSSM and radiative generation of neutral vector boson self-couplings within the MSSM are described. Also given is an account of activities in neutrino physics, namely a proposal for a study of the atmospheric muon anomaly in deep underground mines, a field theoretic study of neutrino oscillations and a mechanism to generate appropriate masses of three active plus one sterile neutrino species.

Corrections to oblique parameters induced by anomalous vector boson couplings

We study quadratically divergent radiative corrections to the oblique parameters at LEP1 induced by non-standard vector boson self-couplings. We work in the Stueckelberg formalism and regulate the divergences through a gauge-invariant higher derivative scheme. Using consistency arguments together with the data we find a limit on the anomalous magnetic moment Delta kappa of the W-boson, |Delta kappa| <= 0.26.

Loop effects of exotic leptons on vector-boson pair production ate+e−colliders

We study quantum effects of exotic heavy leptons on the production of two vector bosons in e^+e^- annihilation. We present closed analytic expressions for vector-boson self-couplings and differential cross sections, within the framework of two favourable new-physics scenarios: (i) the fourth-generation Majorana-neutrino model and (ii) an E_6-inspired model with sequential mirror isodoublets. We constrain these models by requiring that their contributions to the oblique electroweak parameters be compatible with a recent global fit to high-precision data. We then systematically analyze the loop-induced deviations in the LEP2 cross section of e^+e^- -> W^+W^- predicted by the models thus confined.

ϵb constraints on self-couplings of vector bosons

We analyze the constraints on possible anomalous contributions to the W + W − Z vertex coming from non-universal radiative corrections to the Z → b b width. We parametrize these corrections in terms of ϵ b and use the LEP data to establish the allowed values for the anomalous triple couplings. We examine all CP conserving effective operators that exhibit SU(2) L × U(1) Y gauge invariance and do not give any tree level contribution to the present experimental observables. For some of these operators our constraints are comparable with the bounds coming from a global fit of the oblique parameters, which evidences the increasing relevance of the precise measurement of the b-quark parameters at LEP for the search of new physics.

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.

Formal connections between the vector boson self-couplings and the Lorentz invariance of the S-matrix

It is recalled that when constructing Lorentz invariant effective lagrangians involving massive vector bosons, some care should be generally taken at the quantum level, in order to ensure the Lorentz invariance of the physical quantities. In the case of globally invariant dimension-4 operators, we show that the formal requirement of the Lorentz invariance of the S -matrix selects uniquely the Yang-Mills type couplings. We discuss also the dimension-6 gauge invariant quadrupole type operators in the context of deviations from the standard model, and show that they lead to relativistically non -invariant observabls through loop corrections.

Bounds on BESS model parameters from vector-boson production ine + e ? collisions

The BESS model is the Higgs-less alternative to the standard model of electroweak interaction, based on nonlinearly 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 vector-boson self-couplings we study the two- and three-vector-boson-production processes in $e^+e^-$ collisions at $\sqrt{s}=500 GeV$, the expected energy of the next $ e^+e^-$ linear collider (NLC). Assuming that NLC results will agree with the SM predictions within given accuracy we identify the bounds for the free parameters of the BESS model.

Quartic divergences and vector boson self-couplings

We study the radiative corrections to the ρ parameter induced by non-standard three and four vector boson self-couplings. The demand of the absence of quartically divergent terms to a limitation of the possible allowed terms, corresponding to hidden directions in coupling constant space.

The self-couplings of vector bosons: does LEP-1 obviate LEP-2?

Theories beyond the standard model (“meta-theories”) are severely constrained by the current body of data and must necessarily respect the standard gauge symmetry. We analyze the constraints on two generic types of meta-theory, in which fundamental scalar do or do not exist. The novel low-energy effects can be comprehensively described by grafting onto the standard lagrangian new operators that - in the sense of a Taylor expansion - form a complete set. Completeness calls for consideration of previously discarded operators, and for a thorough exploitation of the equations of motion. We illustrate the current strictures by focusing on the allowed range of departures from the most crucial, untested, precise standard prediction: the size and structure of the triple gauge-boson vertices. We conclude that their direct measurement at LEP-2, while phenomenologically very interesting, is, alas, unlikely to provide new information.

Vector-boson self-couplings in an electroweak theory with heavy gauge boson triplets

We consider a nonlinear version of the electroweak standard model which contains no physical Higgs particle but, instead, a further triplet of (heavy) vector bosons. The theory is nonrenormalizable and, therefore, new types of interactions are induced at each loop order. We calculate the one-loop induced self-interactions of the different (light and/or heavy) gauge bosons and show that they are of a very specific (namely Yang-Mills-like) type.

Anomalous vector-boson self-interactions

We study the possibility that vector-boson self-couplings may differ from their standard model values. We find that known constraints from loop effects and from unitary already imply that such deviations are of order 10 −2 or less. Consequently, even if the correct model differs from the standard model and even if the energy scale of new physics is as low as 1 TeV, a direct observation of anomalous couplings is very imporabable in the LEP-200 and Tevatron experiments.

Loop corrections to the ϱ-parameter; the magnetic moment of the W± and e+e−→W+W−

Abstract Vector-boson loop corrections to the ϱ -parameter are considered for vector-boson self-interactions following from global SU(2) WI broken by electromagnetism. Minimizing the degree of divergence of the ϱ -parameter restricts the free trilinear vector-boson self-couplings to a single one, the anomalous magnetic dipole moment, κ , of the W +- . The analysis of e + e − → W + W − shows that this process is well suited for accurately determining this remaining free parameter, κ .

Nongauge interactions of vector bosons and rare K decays.

We study the effect of nonstandard vector-boson couplings on the rare decay modes of K mesons. Our results show that as long as the Glashow-Iliopoulos-Maiani mechanism is operative, experimental results on rare K decays do not produce any constraints on nonstandard self-couplings of vector bosons.

Two-loop large Higgs mass corrections to vector-boson self-couplings

The two-loop corrections to the three-vector-boson vertices are calculated in the limit of large Higgs mass. Corrections growing quadratically with the Higgs mass appear in the anomalous magnetic moment of the charged vector boson and the corresponding W 0W +W − coupling. Also the weak coupling constant in the W 0W +W − vertex receives a correction compared to the coupling in μ-decay. The results suggest a breakdown of perturbation theory for a Higgs mass of 3.4 TeV and larger.