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Can the new resonance at LHC be a CP-Odd Higgs boson?

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Damir Becirevic, Enrico Bertuzzo, Olcyr Sumensari, Renata Zukanovich Funchal

High Energy Physics - Phenomenology · Submitted 17 Dec 2015 · 42 references

Pith's verdict: A competent 2HDM scan that turns two fixed masses into windows for the other scalars — the windows are real but softer than the paper's phrasing suggests.

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arXiv ID1512.05623 (version 3)
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CitationDamir Becirevic, Enrico Bertuzzo, Olcyr Sumensari, Renata Zukanovich Funchal. "Can the new resonance at LHC be a CP-Odd Higgs boson?." arXiv:1512.05623 (2015). https://pith.science/paper/BB5OJBKR
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The paper

The paper claims

If the 750 GeV diphoton bump is a CP-odd Higgs, its partner scalars are squeezed into narrow mass windows.

The reading

The paper asks whether the excess of two-photon events near 750 GeV reported by ATLAS and CMS in December 2015 could be the CP-odd neutral Higgs boson $A$ of a two-Higgs-doublet model. The authors take the two masses that are known or claimed — $m_h = 125.7$ GeV for the observed Higgs and $m_A = 750$ GeV for the new state — and ask what the general consistency conditions of the model then force on the two remaining scalars, the charged $H^pm$ and the heavy CP-even $H$. Those conditions are that the scalar potential be bounded from below, that the electroweak vacuum be the global minimum, and that Higgs-Higgs scattering amplitudes stay within tree-level unitarity. Scanning the surviving parameter space, they find the two unknown masses are trapped between a lower and an upper edge, and that the mixing angle between the two CP-even states must stay close to the alignment limit. They then check that the surviving points are not killed by electroweak precision data or by leptonic and semileptonic $B$ decays. The appeal is that this is a cheap, testable picture: if the resonance is really a pseudoscalar, the charged and heavy neutral Higgses should sit in a band that the LHC can reach in the same run.

What carries the argument

The machinery is the standard reparameterisation of the two-Higgs-doublet scalar potential: the quartic couplings $lambda_{1..5}$ are rewritten in terms of the physical masses $m_h$, $m_H$, $m_A$, $m_{H^pm}$, the mixing angles $alpha$ and $beta$, and the soft-breaking mass parameter $M^2 = m_{12}^2/(sinbeta cosbeta)$. That rewriting turns the abstract conditions — bounded-from-below inequalities on the $lambda$'s, a global-minimum condition involving $m_{12}^2$, and the unitarity bounds on the $S$-wave partial waves of Higgs-Higgs scattering — into concrete cuts on the mass plane, which a flat random scan then carves out. The same couplings then feed the pseudoscalar decay widths to fermions, photons and $Zgamma$, the charged-Higgs decays to $t bar b$ and $tau nu$, and the effective scalar and pseudoscalar Wilson coefficients $g_S$, $g_P$ that shift $B to D tau nu$ and $B to tau nu$.

Extended reading notes

Core claim

The central claim is that fixing $m_h = 125.7(4)$ GeV and $m_A = 750(30)$ GeV inside a generic CP-conserving two-Higgs-doublet model, and imposing the potential's boundedness, vacuum stability and tree-level unitarity, leaves a parameter space in which the other two scalars are bounded on both sides: roughly $400$ GeV $lesssim m_{H^pm} lesssim 1$ TeV and $200$ GeV $lesssim m_H lesssim 1$ TeV. The scan also concentrates on small $tanbeta$ (most points below 5, essentially none above 15), on $|cos(beta-alpha)| lesssim 0.3$ — so the 125 GeV state couples to $W$ and $Z$ almost as in the Standard Model — and on the soft $Z_2$-breaking mass in the range $|M| in (200, 800)$ GeV. The authors further report that the pseudoscalar width is dominated by $A to tbar t$ and can be as large as about 40 GeV at $tanbeta = 1$, which is the sort of broad resonance the ATLAS fit preferred. Finally they check the surviving points against the $S$, $T$, $U$ parameters using the Gfitter covariance matrix, and against $B(B to tau nu_tau)$, $R_D$ and $B(B_s to mu^+ mu^-)$, finding no exclusion of the small-$tanbeta$ region they favour, with $B_s to mu^+ mu^-$ only cutting away $tanbeta lesssim 0.7$.

Load-bearing premise

The quoted mass windows are read off a flat random scan whose prior ranges were chosen by hand, with the upper edges sitting near the scan ceiling and no stated number of sampled points or statistical interpretation, so the bounds reflect the scan setup as much as the theory.

Editorial extensions

If this is right

  • If the 750 GeV state is the pseudoscalar, the charged Higgs should lie between about 400 GeV and 1 TeV, which puts it within reach of the same LHC run that produced the excess.
  • The heavy CP-even scalar $H$ should lie between about 200 GeV and 1 TeV, and its couplings to $W$ and $Z$ should be suppressed relative to the 125 GeV state by $|cos(beta-alpha)| lesssim 0.3$.
  • The pseudoscalar should be broad for small $tanbeta$ — up to roughly 40 GeV at $tanbeta = 1$ — with the width essentially saturated by $A to tbar t$.
  • In the Type II model, $B to tau nu$ and $R_D$ should begin to depart visibly from their Standard Model values only at moderate-to-large $tanbeta$, beyond the region the scan prefers.
  • Very small $tanbeta$ below about 0.7 is excluded by $B_s to mu^+ mu^-$ regardless of which Yukawa assignment is chosen, because that constraint runs through the top-quark coupling.

Reading between the lines

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

  • The upper edges of the quoted windows sit close to the 1.5 TeV ceiling imposed on the scan itself, so a reader should treat the '1 TeV' numbers as scan-geometry statements as much as theory statements; widening the prior volume would move them.
  • Because the pseudoscalar's gluon-fusion production in a pure two-Higgs-doublet model is generally too small to reproduce the reported rate, the spectrum argument and the rate argument are somewhat independent: the mass windows could survive even if the diphoton excess turns out to need extra fermions, and conversely a confirmed excess rate would not by itself confirm the pseudoscalar interpretatio
  • A cleaner discriminator than the mass windows would be the shape of the diphoton line: the large width the authors derive at small $tanbeta$ predicts a broad bump, while a narrow resonance would push the interpretation toward larger $tanbeta$ and correspondingly different $B to tau nu$ and $R_D$ expectations.
  • The alignment result $|cos(beta-alpha)| lesssim 0.3$ suggests that precision Higgs-coupling measurements at the 125 GeV state, rather than direct searches, may be the fastest way to falsify the scenario.
Original abstract

A plausible explanation of the recent experimental indication of a resonance in the two-photon spectrum at LHC is that it corresponds to the CP-odd Higgs boson. We explore such a possibility in a generic framework of the two Higgs doublet models (2HDM), and combine $m_A \approx 750$GeV with the known $m_h =125.7(4)$~GeV to show that the charged Higgs boson and the other CP-even scalar masses become bounded from bellow and from above. We show that this possibility is also consistent with the electroweak precision data and the low energy observables, which we test in a few leptonic and semileptonic decay modes.

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, 3,122 input tokens.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.17 · human participants 0.02 · controlled comparison 0.05 · randomized assignment 0.01 · states quantitative result 0.86 · compares with prior results 0.18 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v3. Results and the main claim are underlined; .

A plausible explanation of the recent experimental indication of a resonance in the two-photon spectrum at LHC is that it corresponds to the CP-odd Higgs boson. We explore such a possibility in a generic framework of the two Higgs doublet models (2HDM), and combine $m_A \approx 750$GeV with the known $m_h =125.7(4)$~GeV to show that the charged Higgs boson and the other CP-even scalar masses become bounded from bellow and from above. We show that this possibility is also consistent with the electroweak precision data and the low energy observables, which we test in a few leptonic and semileptonic decay modes.

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 plausible explanation of the recent experimental indication of a resonance in the two-photon spectrum at LHC is that it corresponds to the CP-odd Higgs boson. background 0.86 0.09 0.40 hedged possibility 0.97
s1 We explore such a possibility in a generic framework of the two Higgs doublet models (2HDM), and combine $m_A \approx 750$GeV with the known $m_h =125.7(4)$~GeV to show that the charged Higgs boson and the other CP-even scalar masses become bounded from bellow and from above. contribution 0.74 0.94 0.20 asserted 0.96
s2 We show that this possibility is also consistent with the electroweak precision data and the low energy observables, which we test in a few leptonic and semileptonic decay modes. result 0.96 0.92 0.28 asserted 0.59

What kind of paper the classifier reports this is: theoretical result 0.99 · evidence from proof or derivation 0.50.

What was examined, and what was not

sources read
  • arXiv listing abstract v3
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. Result of the scan of the parameter space as indicated in the text and after imposing constraints given in Eqs. (7–10). To better appreciate the effects of fixing mA = 750(30) GeV, we also made the scan of parameters without fixing mA = 750(30) GeV, shown in the plots by brighter points. 3 Including fermions As it is well known, in order to avoid the tree level flavor changing neutral currents (FCNC), one imposes that the fermions of definite charge and chirality couple to a specific Higgs doublet. In this way one distinguishes various types of 2HDM: In Type I models all fermions…
Figure 2. Partial decay widths as functions of tan β for all four types of 2HDM considered in this paper. Full decay width is depicted by the dashed curve and it is most often indistinguishable from Γ(A → tt¯). mode is largely dominant and essentially saturates the width of the CP-odd Higgs boson, Γ(A), the results of which are given in Tab. 3 for four different values of tan β. Since the experimenters are searching for the A → τ τ mode, in the same table we also give the values of B(A → τ τ ) for all four types of 2HDM considered here. It is worth emphasizing that for small values of tan β…
Figure 3. Allowed region by the S, T and U parameters at 99% CL. we used the latest Gfitter values for the best fit, uncertainties and covariance matrix [31], ∆S SM = 0.05 ± 0.11, ∆T SM = 0.09 ± 0.13, ∆U SM = 0.01 ± 0.11, V =   1 0.90 −0.59 0.90 1 −0.83 −0.59 −0.83 1   , (21) composing the χ 2 function as χ 2 = X i,j (Xi − X SM i )(σ 2 ) −1 ij (Xj − X SM j ), (22) with Xi = ∆S, ∆T, ∆U and the covariance matrix σ 2 ij ≡ σiVijσj , in which (σ1, σ2, σ3) = (0.11, 0.13, 0.11). In
Figure 4. B(B → τντ ) and RD are computed in the Type II 2HDM using mH± = 400 GeV and mH± = 1 TeV, and it is compared to the experimental values (gray bands) at 2σ-level. Central experimental values are depicted by the full horizontal lines. The band showing deviation from the Standard Model for large values of tan β, in both plots, corresponds to mH± = 400 GeV. The hatched stripes, instead, correspond to low tan β . 0.7, excluded by B(Bs → µ +µ −). Type gS gP I − m` m2 H± (md − mu) cot2 β m` m2 H± (md + mu) cot2 β II − m` m2 H± (mu + md tan2 β) − m` m2 H± (mu − md tan2 β) X m` m2 H± (md −…
Figure 5. In the left plot we superpose the results of Sec. 5 and the scan of allowed points presented in

Figures reproduced from arXiv:1512.05623 by the authors.

References
How the literature uses it

67 arXiv papers cite this in 75 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 · 27 sentences without a confident label

Compares with it 2 papers
  • ([ref]) over the same ranges considered in [ref] (contrary to this reference we have nevertheless assumed alignment limit).

    Dark Matter Phenomenology of SM and Enlarged Higgs Sectors Extended with Vector Like Leptons · EWPT Constraints · 0.81

  • Since the SM Higgs remains the only source of spontaneous EWSB, this scenario is intrinsically different from models where the neutral component of an $SU(2)_L$ doublet is responsible for the diphoton excess [ref] , as well as from left-right symmetric approaches to the diphoton excess [ref] or Georgi-Machacek models [ref] , in which an EW triplet acquires a vev, and from extensions of $SU(2)_L$ [ref] .

    Diphotons from an Electroweak Triplet-Singlet · Introduction · 0.81

Cites it as background 44 papers

What it cites · 12 sentences without a confident label

Uses data or values from 7 papers
  • In order to compute the related bounds on the spectrum, we used the latest Gfitter values for the best fit, uncertainties and covariance matrix [ref] ,

    The global electroweak fit at NNLO and prospects for the LHC and ILC · Electroweak Precision Tests · 0.94

  • By averaging the values obtained by BaBar [ref] and Belle [ref] , we have $B(B→τν_τ)=1.44(32) ×10^-4$, which we then combine with $f_B =188(6)$ MeV [ref] , and $V_ub=3.6(1)×10^-3$ as obtained from the global fit by UTfit and CKM-fitter [ref] , to conclude that for all types of 2HDM considered here the resulting value for $B(B→τν_τ)_2HDM$ is consistent with experiment and is practically indistinguishable from the Standard Model predictions.

    Current status of the Standard Model CKM fit and constraints on $\Delta F=2$ New Physics · Low energy physics observables · 0.99

  • By averaging the values obtained by BaBar [ref] and Belle [ref] , we have $B(B→τν_τ)=1.44(32) ×10^-4$, which we then combine with $f_B =188(6)$ MeV [ref] , and $V_ub=3.6(1)×10^-3$ as obtained from the global fit by UTfit and CKM-fitter [ref] , to conclude that for all types of 2HDM considered here the resulting value for $B(B→τν_τ)_2HDM$ is consistent with experiment and is practically indistinguishable from the Standard Model predictions.

    Evidence of B-->tau nu decays with hadronic B tags · Low energy physics observables · 0.99

Cites as support 1 paper
Cites as background 6 papers
  • [ref] ), [equation] where $Φ_1$ and $Φ_2$ are the two complex scalar $SU(2)$ doublets with hypercharge $Y=+1$.

    Theory and phenomenology of two-Higgs-doublet models · General Constraints on 2HDM and the Spectrum of Higgses · 0.90

  • More general, in terms of Yukawa couplings, is the so called Type III 2HDM in which the couplings to fermions are all to be fixed by the data [ref] which is often impractical because of too many free parameters so that one has to resort to additional assumptions such as minimal flavor violation (MFV) [ref] , the natural flavor conservation [ref] , or the aligned 2HDM [ref] where the minimal flavor violation is ensured by assuming proportionality between the matrices of Yukawa couplings to the two Higgs doublets.

    B->tau nu in multi-Higgs models with MFV · Including fermions · 0.93

  • More general, in terms of Yukawa couplings, is the so called Type III 2HDM in which the couplings to fermions are all to be fixed by the data [ref] which is often impractical because of too many free parameters so that one has to resort to additional assumptions such as minimal flavor violation (MFV) [ref] , the natural flavor conservation [ref] , or the aligned 2HDM [ref] where the minimal flavor violation is ensured by assuming proportionality between the matrices of Yukawa couplings to the two Higgs doublets.

    Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model · Including fermions · 0.93

Discussion

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