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The Minimal Scalar-Stealth Top Interpretation of the Diphoton Excess

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Wei Chao, Ran Huo, Jiang-Hao Yu

High Energy Physics - Phenomenology · Submitted 17 Dec 2015 · 67 references

Pith's verdict: A competent, derivative entry in the December 2015 diphoton wave whose one genuinely checkable prediction — the fixed digluon-to-diphoton ratio — is also the part that constrains it.

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arXiv ID1512.05738 (version 2)
Pith IDJXW6R525, Pith's permanent record of this paper and its review
CitationJiang-Hao Yu, Ran Huo, Wei Chao. "The Minimal Scalar-Stealth Top Interpretation of the Diphoton Excess." arXiv:1512.05738 (2015). https://pith.science/paper/JXW6R525
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The paper

The paper claims

A 750 GeV scalar plus a light hidden top could account for the diphoton bump without tripping any other LHC search.

The reading

In late 2015 both ATLAS and CMS saw a small excess of high-mass diphoton events near 750 GeV, and this paper asks what kind of new particle could produce it without also producing jets, weak bosons, or missing energy at rates the LHC had already excluded. The authors' answer is deliberately minimal: one new neutral scalar $S$ at 750 GeV, produced by gluon fusion and decaying to two photons through a loop of a new vector-like top quark $T$. The obstacle is that LHC searches push ordinary vector-like quarks up to roughly 700–900 GeV, and a top that heavy would need a Yukawa coupling outside the perturbative regime to make enough photons. Their way around it is to make $T$ odd under a parity and nearly degenerate with a dark-matter particle, so that its decays produce too little visible energy to be caught by the existing top-plus-missing-energy searches; such a quark is called a stealth top. With masses around 400–500 GeV and couplings of order 0.5–1.5, they find the diphoton rate can reach the observed 5–10 fb while the dijet rate stays an order of magnitude below its bound.

What carries the argument

The load-bearing object is the loop amplitude $A_{1/2}(154)$ for a fermion of mass $154$ in the $S$-$154$-$154$ and $S$-photon-photon vertices, together with the resulting fixed ratio $154$. That ratio is what makes the paper's argument work: it converts the diphoton measurement into a prediction for the dijet channel, and the prediction comes out safely small. The second piece of machinery is the stealth window, $154$, a near-degeneracy between the vector-like top and a dark-matter partner that suppresses the visible energy in top-plus-missing-energy events and lets the top sit below the usual 700–900 GeV vector-like quark bound. The authors check this window by reinterpreting an ATLAS stop search and, within a top-flavored dark-matter completion, by computing relic density and direct-detection rates.

Extended reading notes

Core claim

The paper claims that a singlet scalar $S$ of 750 GeV coupled to a stealth vector-like top can reproduce $13$ TeV diphoton rates of $5$–$10$ fb while satisfying the $8$ TeV diphoton bound of $1.32$ fb and the dijet limits. The mechanism is that the same top loop generates both the $Sgg$ and $Sgg$-to-photon couplings, so the two rates are locked in a fixed ratio $154$; the authors compute $154$, i.e. $154$ is $148.8$, meaning the digluon width dominates and the diphoton branching ratio sits near $0.7$ percent. Because the production cross section scales with the digluon width, a light top with a modest Yukawa coupling supplies enough gluon fusion to reach the observed rate, and the accompanying dijet rate falls roughly an order of magnitude below the $8$ TeV bound. The authors extend the single-top setup to a second model with an additional vector-like doublet, which triples the loop content and so reaches the same rate with a smaller coupling.

Load-bearing premise

Everything rests on the stealth window: the new top must sit within about 180 GeV of a dark-matter particle so that its decays leave too little visible energy to be excluded, and that window is only verified inside one particular dark-matter model.

Editorial extensions

If this is right

  • A stealth top in the 400–500 GeV range with coupling 0.5–1.5 would give a diphoton signal that persists at 13 TeV with roughly the same rate, since the gluon-luminosity rescaling from 8 to 13 TeV is about 4.7 and matches the observed ratio.
  • The same parameter space predicts a dijet rate near 200 fb, an order of magnitude below the 8 TeV bound, so the model survives even if dijet searches tighten.
  • Because the scalar couples to ordinary matter only through a small mixing with the Standard Model Higgs, the $WW$, $ZZ$, and $hh$ rates stay suppressed for mixing angles below roughly $10^{-2}$.
  • If the dark-matter partner is heavier than half the scalar mass or couples negligibly to $S$, the total width stays narrow and dominated by digluon, keeping the diphoton branching ratio predictable.

Reading between the lines

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

  • The whole construction lives or dies with the diphoton excess itself; a resonance that fades in more 13 TeV data would leave the stealth-top fit with nothing to explain, though the model would remain a valid low-mass vector-like quark scenario.
  • The stealth window is checked inside a single dark-matter completion, so a reader could reasonably ask whether other completions force a larger mass splitting and thereby close the window.
  • Because the digluon width dominates the total width, the model predicts a very narrow scalar, which is a sharper and more distinctive signature than the diphoton rate alone.
  • The same loop that makes the diphoton rate also generates $Z\gamma$ and $ZZ$ couplings at fixed relative strengths, giving a further handle that a future analysis could use to separate this model from competing explanations.
Original abstract

A resonance near 750 GeV has been observed at both the ATLAS and CMS experiments in its diphoton decay channel. We propose a possible interpretation based on a simplified model: a 750 GeV singlet scalar resonance, and a minimal stealth vector quark are introduced. At the LHC, the scalar is produced through gluon fusion, and subsequently decays to diphoton final state. The light stealth quarks could enhance the diphoton rate significantly, while still keeping other channels below the current LHC search limits. We find that the stealth quarks around 400 ~ 500 GeV with its coupling to scalar around 0.5 ~ 1.5 could explain the diphoton excess, and avoid current di-jet constraints. We also comment on other potential signatures of this stealth model.

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-1.13.0 via TypeSafe API, question bank abstract-p1-20260923, 2026-09-23: 1 request, 4,904 input tokens.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.22 · human participants 0.01 · controlled comparison 0.05 · randomized assignment 0.01 · states quantitative result 0.95 · compares with prior results 0.38 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

A resonance near 750 GeV has been observed at both the ATLAS and CMS experiments in its diphoton decay channel. We propose a possible interpretation based on a simplified model: a 750 GeV singlet scalar resonance, and a minimal stealth vector quark are introduced. At the LHC, the scalar is produced through gluon fusion, and subsequently decays to diphoton final state. The light stealth quarks could enhance the diphoton rate significantly, while still keeping other channels below the current LHC search limits. We find that the stealth quarks around 400 ~ 500 GeV with its coupling to scalar around 0.5 ~ 1.5 could explain the diphoton excess, and avoid current di-jet constraints. We also comment on other potential signatures of this stealth model.

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 A resonance near 750 GeV has been observed at both the ATLAS and CMS experiments in its diphoton decay channel. background 0.99 0.07 0.04 asserted 1.00
s1 We propose a possible interpretation based on a simplified model: a 750 GeV singlet scalar resonance, and a minimal stealth vector quark are introduced. contribution 0.77 0.85 0.15 hedged possibility 0.95
s2 At the LHC, the scalar is produced through gluon fusion, and subsequently decays to diphoton final state. method 0.93 0.26 0.04 asserted 0.99
s3 The light stealth quarks could enhance the diphoton rate significantly, while still keeping other channels below the current LHC search limits. interpretation 0.55 0.41 0.19 hedged possibility 1.00
s4 We find that the stealth quarks around 400 ~ 500 GeV with its coupling to scalar around 0.5 ~ 1.5 could explain the diphoton excess, and avoid current di-jet constraints. result 0.98 0.93 0.81 asserted 0.95
s5 We also comment on other potential signatures of this stealth model. future work 0.58 0.56 0.03 unclear 0.90

What kind of paper the classifier reports this is: theoretical result 0.97 · evidence from argument 0.51.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
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. FIG. 1: We show the parameter contour (
Figure 2. FIG. 2: The signal favored region
Figure 3. FIG. 3: Production cross section times branching diphoton ratio as the function of the VL top
Figure 4. FIG. 4: Constraints on the model from the LHC Run-1 in the dijet channel: the cyan region has

Figures reproduced from arXiv:1512.05738 by the authors.

References
How the literature uses it

64 arXiv papers cite this in 70 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 · 21 sentences without a confident label

Contests it 1 paper
Uses its data or values 1 paper
Compares with it 1 paper
  • For the case $ψ$ being only slightly heavier than $χ$, the dijet will be very soft and $m_ψ=400 GeV$ will be compatible with the LHC direct searches of VL quarks, which is similar to the case of the stealth supersymmetry [ref] and stealth top model [ref] . ],

    Symmetries Behind the 750 GeV Diphoton Excess · Diphoton excess · 0.90

Cites it as background 46 papers

What it cites · 16 sentences without a confident label

Uses the method or tool of 1 paper
  • For model II which has nontrivial $SU(2)_L$ doublet, the only precision measurement constraint is the tri-gauge coupling, which can be universally calculated by [ref] and generate a Wilson coefficient of $1/6gϵ^abcW^aμ_ρW^bν_μW^cρ_ν$, but the constraints should be weak.

    How to use the Standard Model effective field theory · Model Constraints · 0.83

Uses data or values from 4 papers
Compares with 2 papers
Cites as support 1 paper
Cites as background 38 papers
  • This could be an argument against the reality of the diphoton excess, meaning nothing but a statistical fluctuations; but if taken seriously, it put strong constraint on the implied model building [ref] [ Refs. [ref] on this subject appeared at the same time as this work.].

    A 750 GeV Dark Pion: Cousin of a Dark G-parity-odd WIMP · Introduction · 0.85

  • This could be an argument against the reality of the diphoton excess, meaning nothing but a statistical fluctuations; but if taken seriously, it put strong constraint on the implied model building [ref] [ Refs. [ref] on this subject appeared at the same time as this work.].

    Phenomenology of a 750 GeV Singlet · Introduction · 0.85

  • This could be an argument against the reality of the diphoton excess, meaning nothing but a statistical fluctuations; but if taken seriously, it put strong constraint on the implied model building [ref] [ Refs. [ref] on this subject appeared at the same time as this work.].

    On a possible large width 750 GeV diphoton resonance at ATLAS and CMS · Introduction · 0.85

Discussion

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