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Signatures of the anomalous $Z\gamma$ and ZZ production at the lepton and hadron Colliders

High Energy Physics - Phenomenology · Submitted 19 Oct 1999 · 21 references

Pith's verdict: The factor-i fix to the ZγV vertices is a real service to the field; the sensitivity tables are illustrations, and the h3 = −f5 relation is not checkable here because the loop derivation sits in an unpublished companion.

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arXiv IDhep-ph/9910395 (version 5)
Pith IDGI7KURSA, Pith's permanent record of this paper and its review
CitationF.M. Renard, G.J. Gounaris, J. Layssac. "Signatures of the anomalous $Z\gamma$ and ZZ production at the lepton and hadron Colliders." arXiv:hep-ph/9910395 (1999). https://pith.science/paper/GI7KURSA
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Referee report
The paper

The paper claims

The standard parametrization of the neutral triple-gauge vertices (ZZZ, ZZ$gamma$, Z$gamma$$gamma$) is missing a factor of $i$, and putting it back makes the effective Lagrangian hermitian and reverses which new-physics terms interfere with

The reading

The paper's central move is a correction, not a discovery claim: the widely used 1987 parametrization of the vertices where two on-shell neutral gauge bosons meet an off-shell Z or photon omits a factor of $i$. Without it the associated effective Lagrangian is antihermitian, and the practical consequence is that CP-conserving new-physics amplitudes were being treated as the ones that add incoherently while CP-violating ones were treated as the ones that interfere. Restoring the factor swaps those roles, so every limit extracted in the regime where interference dominates carries the wrong sign. Beyond the bookkeeping, the authors rederive the Standard Model and new-physics helicity amplitudes for $fbar f o ZZ$ and $fbar f o Zgamma$ with all conventions fixed, then project how strongly each of the ten neutral couplings could be pinned down at LEP2, at a 500 GeV linear collider, at the Tevatron and at the LHC. A heavy-fermion loop model is used as a guide to what pattern of couplings is plausible: only $f_5$ and $h_3$ are generated at one loop, and they satisfy $h^Z_3 = -f^gamma_5$, a relation that is independent of the heavy fermion's couplings.

What carries the argument

The load-bearing object is the corrected vertex function: $Gamma^{alpha beta mu}_{ZZV}$ carrying the two CP-odd couplings $f^V_4, f^V_5$ and $Gamma^{alpha beta mu}_{Zgamma V}$ carrying $h^V_1$ through $h^V_4$, with the inserted factor of $i$ in the second. Translated through the equations of motion into contact $fbar f ZZ$ and $fbar f Zgamma$ interactions, these vertices generate the new-physics helicity amplitudes that are added to the Standard Model fermion-exchange amplitudes. The amplitude-level statement that CP-conserving couplings give real terms and CP-violating ones purely imaginary terms is what converts a sign convention into an experimentally visible interference pattern in angular distributions and in the left-right polarization asymmetry.

Extended reading notes

Core claim

The paper argues that the general $V_1V_2V_3$ vertex for two on-shell neutral bosons and one off-shell $Z$ or photon requires an extra factor of $i$ in the $Zgamma V$ sector relative to the standard reference form, so that the effective Lagrangian generating the $ZZZ$, $ZZgamma$ and $Zgammagamma$ vertices is hermitian. The authors state that with the old convention the interference pattern of CP-conserving and CP-violating new-physics amplitudes with the Standard Model was reversed, and that while existing experimental limits are barely affected because they are dominated by the quadratic term, increasing accuracy would eventually produce non-intuitive results. On that corrected basis they give the new-physics helicity amplitudes for $fbar f o ZZ$ and $fbar f o Zgamma$, note that CP-conserving couplings give real amplitudes that interfere linearly with the Standard Model while CP-violating ones give imaginary amplitudes that enter only quadratically, and collect one-standard-deviation sensitivity estimates for each coupling at LEP2, a 500 GeV linear collider, the Tevatron and the LHC. The heavy-fermion toy model supplies the testable prediction $h^Z_3 = -f^gamma_5$ together with the vanishing of $h^Z_4$ and $h^gamma_4$.

Load-bearing premise

The sensitivity numbers quoted for each coupling rest on assumed rather than derived experimental inputs: a LEP2 luminosity of 150 inverse picobarns with a factor-two selection loss, a linear-collider sample of 100 inverse femtobarns with one percent accuracy, and a claim of negligible background for $Zgamma$ at large angles.

Editorial extensions

If this is right

  • Any fit to $Zgamma$ production data that assumed the old convention and sat in the interference-dominated regime should be re-examined for a sign flip in the extracted CP-conserving couplings.
  • At a 500 GeV linear collider with polarized beams, the left-right asymmetry $A_{LR}$ departs from its Standard Model values of about 0.28 for $ZZ$ and 0.14 for $Zgamma$ in a way that differs sharply between photon-type and Z-type couplings, giving a handle for separating them.
  • If the heavy-fermion loop picture is right, measuring $h^Z_3$ and $f^gamma_5$ should return equal magnitudes and opposite signs, while $h^Z_4$ and $h^gamma_4$ should come out consistent with zero.
  • Because no neutral triple-gauge vertex arises from dimension-six operators in the linear representation, observing any of these couplings would point either to enhanced higher-dimensional operators or to a nearby new-physics scale.
  • Sensitivity to the dimension-eight couplings $h^V_2$ and $h^V_4$ grows faster with energy than to the dimension-six ones, so they should be bounded more tightly at the same collider.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The sign correction is the kind of error that is invisible until interference terms matter, which suggests the same convention should be checked in the charged triple-gauge literature where interference is already large.
  • The proposal to quote limits in narrow bins of subprocess invariant mass, rather than with multiplicative form factors, would make collider comparisons meaningful but also would require each experiment to publish a correlated set of limits rather than a single number.
  • If $h^Z_3 = -f^gamma_5$ holds, a global fit imposing it halves the number of free parameters in the CP-conserving sector, which would tighten the remaining bounds more than the naive gain from one fewer parameter.
  • The one-loop estimate of order $10^{-3}$ for these couplings at a few-hundred-GeV fermion mass implies that observability at LEP2 or the Tevatron needs an enhancement factor of order $10^2$, so a null result there constrains strongly interacting new-physics sectors more than weakly coupled ones.
Original abstract

The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ \gamma$ and $Z\gamma \gamma$ vertices, is critically examined. Their signatures and the possibilities to study them, through ZZ and $Z\gamma$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. Experimental limits obtained or expected on each coupling are collected. A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 4,300 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.02 · states limitation 0.18 · human participants 0.01 · controlled comparison 0.05 · randomized assignment 0.01 · states quantitative result 0.09 · compares with prior results 0.31 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v5. Results and the main claim are underlined; .

The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ \gamma$ and $Z\gamma \gamma$ vertices, is critically examined. Their signatures and the possibilities to study them, through ZZ and $Z\gamma$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. Experimental limits obtained or expected on each coupling are collected. A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ \gamma$ and $Z\gamma \gamma$ vertices, is critically examined. contribution 0.84 0.61 0.07 hedged possibility 0.58
s1 Their signatures and the possibilities to study them, through ZZ and $Z\gamma$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. contribution 0.96 0.70 0.06 asserted 0.75
s2 Experimental limits obtained or expected on each coupling are collected. contribution 0.58 0.23 0.09 asserted 0.94
s3 A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. method 0.99 0.77 0.04 asserted 0.95
s4 In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure. interpretation 0.47 0.55 0.29 asserted 0.66

What kind of paper the classifier reports this is: review 0.88 · evidence from literature 0.64.

What was examined, and what was not

sources read
  • arXiv listing abstract v5
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Feynman rule for the general V1V2V3 vertex. 18
Figure 2. Standard and anomalous contributions to the unpolarized
Figure 3. Standard and anomalous contributions to the unpolarized
Figure 4. Standard and anomalous contributions to unpolarized
Figure 5. Standard and anomalous contributions to unpolarized
Figure 6. Standard and anomalous contributions to Left-Right asy
Figure 7. Standard and anomalous contributions to Left-Right asy
Figure 8. Standard and anomalous contributions to the
Figure 9. Standard and anomalous contributions to the

Figures reproduced from arXiv:hep-ph/9910395 by the authors.

References
How the literature uses it

32 arXiv papers cite this in 76 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 40 sentences without a confident label

Contests it 2 papers
  • On the other hand, our $_4^$ bound in Eq.[ref] is much weaker than the ATLAS bounds on $(h_4^, h_4^Z)$, by a large factor of $∼32$, because the conventional nTGC form factor formulae are incompatible with the gauge-invariant SMEFT formulation of dimension-8 (including spontaneous electroweak gauge symmetry breaking), as we explain in Appendix [ref] and Table [ref].We emphasize that the existing ATLAS result [ref] used the conventional on-shell nTGC formula of the vertex $ZV^*$ [ref] for analyzing the $νν̅$ channel, which caused a significant underestimate of the sensitivity to $_3^$ by about $60%$.

    Probing Neutral Triple Gauge Couplings with $Z^* \gamma\, (\nu \bar \nu \gamma)$ Production at Hadron Colliders · . Probing nTGCs with $Z^*(νν̅)$ Production at Hadron Colliders · contest 0.87

  • [For the toy model [ref] states that the NTGC scales as $m_Z^2/M_F^2$, which is obviously not the correct scaling for a coupling generated from $d=8$ operators.

    Fermionic UV models for neutral triple gauge boson vertices · Introduction · contest 0.90

Uses its method or tool 1 paper
Compares with it 3 papers
Cites it as support 2 papers
Cites it as background 13 papers

Discussion

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