REVIEW
750 GeV diphoton resonance in a top and bottom seesaw model
High Energy Physics - Phenomenology · Submitted 17 Dec 2015 · 37 references
Pith's verdict: A clean, narrow fit of an existing composite-scalar sector to the 750 GeV bump; the gauge-fixed diboson ratios are the durable part, the tuned scan and the assumed charged-scalar mass hierarchy are the soft parts.
T0 · AI review
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Referee report
The paper
The paper claims
A composite scalar built from bottom partners is offered as the 750 GeV diphoton resonance, produced by gluon fusion and decaying to two photons through light charged scalars.
The reading
What carries the argument
The load-bearing object is the composite singlet scalar $S_{N2} sim ar{omega}_L omega_R$, one of six bound states that the effective four-fermion interactions of the model generate below the compositeness scale. Two features make it work as a diphoton resonance. First, its coupling to vector-like quarks is not proportional to their masses, so the $S_{N2}gg$ and $S_{N2}gammagamma$ effective couplings can be large while the partner mass stays above the electroweak-precision bound of about 3 TeV. Second, the trilinear couplings $lambda_{Cij} mu' S_{Ni} S^{+}_{Cj} S^{-}_{Cj}$ let light charged scalars run in the diphoton loop, and their electric charge and multiplicity compensate for the small $Q_omega = -1/3$ charge of the bottom partner. The partial widths in Eqs. (15) and (16), built from the standard fermion and scalar loop form factors $A_{1/2}$ and $A_0$, carry the quantitative argument.
Extended reading notes
Core claim
The paper argues that a neutral composite singlet $S_{N2}$, bound from vector-like bottom partners $omega$, can reproduce the observed 750 GeV diphoton rate without conflicting with existing LHC searches. Production proceeds by gluon fusion, with the $omega$ loop supplying the $S_{N2}gg$ coupling; decay to two photons is supplied jointly by the $omega$ loop and by loops of light charged composite scalars $S^{pm}_{C1,2}$. Because the bottom partner's mixing with the bottom quark can be small, the resonance avoids a large $tar t$ or $b ar b$ branching fraction and survives the dijet and top-resonance limits. Scanning $375~{rm GeV} leq m_{S^{pm}_C} leq 2~{rm TeV}$, $3~{rm TeV} leq m_omega leq 10~{rm TeV}$ and $1 leq y_{N2}, lambda_{C2} leq 4pi$, the authors find that the excess is explained in the $2sigma$ range of the combined rate $sigma^{750}_{gammagamma} = (4.4 pm 1.1)~{rm fb}$ provided the charged scalars are lighter than about 750 GeV, the trilinear coupling satisfies $lambda_{C2} gtrsim 1.1$, and the bottom-partner Yukawa satisfies $y_{N2} gtrsim 1.24$. The most restrictive constraints in the scan come from the 8 TeV diphoton and dijet measurements, the latter bounding the total width to roughly below 1 GeV.
Load-bearing premise
The whole fit rests on the fermion-bubble estimates of the composite couplings in Eqs. (8) and (10), and the authors themselves note that when the compositeness scale is far above the low-energy scale this approximation may not be accurate and full one-loop renormalisation group equations would be needed, so a substantial shift in the true low-energy couplings would move or erase the viable region.
Editorial extensions
If this is right
- The decays of the resonance into $gammagamma$, $Zgamma$ and $ZZ$ are tied together by gauge symmetry in the fixed ratio $1 : 2s_W^2/c_W^2 : s_W^4/c_W^4$, so a measurement of any two channels tests the picture.
- Associate production $q ar{q}$ or $e^+e^- to S_{N2}(to gammagamma)gamma$ gives a distinctive three-hard-photon final state, proposed as a target for future LHC and ILC running.
- Pair production of the bottom partner opens the cascade $pp to omega ar{omega} to S_{N2} b, S_{N2} ar{b} to 2b + 4gamma$, a multi-photon signature the authors propose for a future 100 TeV hadron collider.
- The viable region is bounded from above by perturbativity of the trilinear coupling and from below by the requirement that the charged scalars be light enough to lift the diphoton rate.
Reading between the lines
- The predicted $Zgamma$ and $ZZ$ lines at 750 GeV are the cheapest near-term discriminant: any resonance that fits the diphoton bump while badly violating the $1 : 2s_W^2/c_W^2 : s_W^4/c_W^4$ ratio would rule this particular composite-singlet assignment out, independent of details of the strong sector.
- Because the same strong dynamics that binds $S_{N2}$ also binds the top-partner states held at 5 TeV in this analysis, a dedicated search for the heavier neutral singlet in the $tar t$ channel would probe the sibling of the resonance rather than the resonance itself.
- The construction shares its production-and-decay logic with other vector-like-fermion explanations of the same excess, so the distinguishing question is not the diphoton rate but which accompanying channel — $Zgamma$, three photons, or the $2b+4gamma$ cascade — appears first.
Original abstract
The top/bottom seesaw model, which extends the top seesaw in order to accomodate a 125 GeV Higgs boson, predicts vector-like top/bottom partners and these partners can be bounded to form several neutral and charged singlet composite scalars by some new strong dynamics. In this letter, we use such a singlet scalar to interpret the 750 GeV diphoton reseanance. This singlet scalar is dominantly produced through the gluon fusion process induced by the partners and its diphoton decay is induced by both the partners and the charged singlet scalars. We show that this scenario can readily account for the observed 750 GeV diphoton signal under the current LHC constraints. Further, this scenario predicts some other phenomenology, such as a strong correlation between the decays to $\gamma\gamma$, $Z \gamma$ and $ZZ$, a three-photon singal from the associate production of a singlet scalar and a photon, as well as some signals from the partner cascade decays. These signals may jointly allow for a test of this framework in future LHC and ILC experiments.
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.
The abstract, sentence by sentence
The top/bottom seesaw model, which extends the top seesaw in order to accomodate a 125 GeV Higgs boson, predicts vector-like top/bottom partners and these partners can be bounded to form several neutral and charged singlet composite scalars by some new strong dynamics. In this letter, we use such a singlet scalar to interpret the 750 GeV diphoton reseanance. This singlet scalar is dominantly produced through the gluon fusion process induced by the partners and its diphoton decay is induced by both the partners and the charged singlet scalars. We show that this scenario can readily account for the observed 750 GeV diphoton signal under the current LHC constraints. Further, this scenario predicts some other phenomenology, such as a strong correlation between the decays to $\gamma\gamma$, $Z \gamma$ and $ZZ$, a three-photon singal from the associate production of a singlet scalar and a photon, as well as some signals from the partner cascade decays. These signals may jointly allow for a test of this framework in future LHC and ILC experiments.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The top/bottom seesaw model, which extends the top seesaw in order to accomodate a 125 GeV Higgs boson, predicts vector-like top/bottom partners and these partners can be bounded to form several neutral and charged singlet composite scalars by some new strong dynamics. | background 1.00 | 0.10 | 0.04 | asserted 0.82 |
| s1 | In this letter, we use such a singlet scalar to interpret the 750 GeV diphoton reseanance. | contribution 0.96 | 0.84 | 0.11 | asserted 0.97 |
| s2 | This singlet scalar is dominantly produced through the gluon fusion process induced by the partners and its diphoton decay is induced by both the partners and the charged singlet scalars. | method 0.83 | 0.54 | 0.05 | asserted 1.00 |
| s3 | We show that this scenario can readily account for the observed 750 GeV diphoton signal under the current LHC constraints. | result 0.94 | 0.90 | 0.77 | asserted 0.84 |
| s4 | Further, this scenario predicts some other phenomenology, such as a strong correlation between the decays to $\gamma\gamma$, $Z \gamma$ and $ZZ$, a three-photon singal from the associate production of a singlet scalar and a photon, as well as some signals from the partner cascade decays. | result 0.65 | 0.75 | 0.07 | asserted 0.94 |
| s5 | These signals may jointly allow for a test of this framework in future LHC and ILC experiments. | future work 0.90 | 0.23 | 0.11 | hedged possibility 1.00 |
What was examined, and what was not
- arXiv listing abstract v4
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
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- R cross-paper relations
Figures
Figures reproduced from arXiv:1512.05585 by the authors.
References
How the literature uses it
70 arXiv papers cite this in 75 sentences
Papers citing it · 20 sentences without a confident label
Cites it as background 54 papers
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A lot of studies have been done here [ref] .
The Fourth Generation Quark and the 750 GeV Diphoton Excess · Introduction · 0.97
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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.].
The Minimal Scalar-Stealth Top Interpretation of the Diphoton Excess · Introduction · 0.85
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This toy model has been studied by several groups, see Refs. [ref] .
New Forces and the 750 GeV Resonance · Introduction · 0.85
What it cites · 9 sentences without a confident label
Uses data or values from 3 papers
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(3) The ATLAS [ref] and CMS [ref] searches for a resonance decaying to $γγ$ at $√(s)=8$ TeV give a $95%$ CL upper limit on the production cross section: [equation]
Search for high-mass diphoton resonances in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector · Numerical Calculations and Results · 0.96
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(2) The ATLAS [ref] and CMS [ref] searches for a scalar resonance decaying to $VV(V=W,Z)$ at $√(s)=8$ TeV with the full data set, combining all relevant $Z$ and $W$ decay channels, give a $95%$ CL upper limit on the production of the resonance decaying to $ZZ$, [equation]
Search for an additional, heavy Higgs boson in the $H\rightarrow ZZ$ decay channel at $\sqrt{s}$ = 8 TeV in $pp$ collision data with the ATLAS detector · Numerical Calculations and Results · 0.99
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When interpreting the excess in terms of the production rate of the resonance $X$, based on the expected and observed exclusion limits, the CMS and ATLAS experiments at 13 TeV LHC approximately give [ref] [equation] Combined with the 8 TeV data [ref] , the diphoton excess contributing to the combined production rate is given by [ref] [equation]
Knocking on New Physics' door with a Scalar Resonance · INTRODUCTION · 0.95
Cites as background 3 papers
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Several explanations have been proposed for such an excess [ref] .
Knocking on New Physics' door with a Scalar Resonance · INTRODUCTION · 0.98
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Several explanations have been proposed for such an excess [ref] .
What is the gamma gamma resonance at 750 GeV? · INTRODUCTION · 0.98
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Several explanations have been proposed for such an excess [ref] .
The QCD Axion from Aligned Axions and Diphoton Excess · INTRODUCTION · 0.98
Discussion
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