arxiv: 2605.00098 · v1 · submitted 2026-04-30 · ✦ hep-ph

Recognition: unknown

The neutral scalars of type-II 2HDM+S under the LHC

Cheng Li , Juxiang Li , Shufang Su , Wei Su

Authors on Pith no claims yet

Pith reviewed 2026-05-09 20:47 UTC · model grok-4.3

classification ✦ hep-ph

keywords 2HDM+SType-IIexotic Higgs decaystan betaLHC constraintssinglet extensionneutral scalarsparameter space

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The pith

Exotic Higgs decay channels A/H to Z plus singlet scalar exclude wide regions of Type-II 2HDM+S parameter space at the LHC, especially at moderate tan beta.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that extending the Two-Higgs-Doublet Model by a real singlet scalar opens new exotic decay modes that LHC data can use to rule out substantial portions of the model's allowed space. A reader would care because this simple extension adds testable structure beyond the Standard Model Higgs sector while remaining compatible with the observed 125 GeV state. The authors use a parametrization in terms of masses and mixing angles to scan five benchmark scenarios and combine precision measurements of the SM-like Higgs, direct searches for extra scalars, Z-pole observables, and B-physics constraints. They demonstrate that channels such as A/H → Z h_S / Z A_S reach large parts of the moderate 1 < tan β < 7 region where standard 2HDM searches lose sensitivity. The results appear as exclusion contours in multiple two-dimensional slices of the parameter space.

Core claim

The authors parametrize the neutral scalars of the Type-II 2HDM+S by the physical Higgs masses and mixing angles. Under five benchmark scenarios they derive 95% C.L. exclusion regions by folding in SM-like Higgs precision data, direct BSM Higgs searches, Z-pole precision measurements and B-physics observables. They show that the exotic channels A/H → Z h_S / Z A_S probe large portions of the parameter space, in particular the moderate tan β interval 1 < tan β < 7 where conventional 2HDM channels contribute little. The complementarity between direct and indirect searches, and between conventional and exotic channels, is mapped explicitly in the planes of Higgs masses versus tan β, masses and

What carries the argument

Parametrization of the 2HDM+S neutral scalars by physical masses and mixing angles, with the exotic decays A/H → Z h_S / Z A_S acting as the primary new probe that fills gaps left by standard channels.

If this is right

Exotic channels fill the moderate tan β gap left by conventional 2HDM searches.
Direct BSM Higgs searches and indirect precision measurements act as complementary constraints.
Large fractions of the singlet-extended parameter space become accessible once the new decay modes are included.
The five benchmark scenarios illustrate that the exclusion power depends on the relative mass ordering of doublet and singlet states.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Prioritizing searches for resonances in the Z plus scalar final state would extend coverage to still-higher tan β values at the high-luminosity LHC.
The same mass-and-mixing-angle parametrization can be reused to test whether the singlet scalar mixes with the 125 GeV state at a level already excluded by precision data.
If the singlet couples to dark-matter candidates, the excluded regions would simultaneously limit viable dark-matter annihilation channels.

Load-bearing premise

The 125 GeV Higgs is taken to be exactly the SM-like state and the five benchmark scenarios are assumed to represent the full viable parameter space of the Type-II 2HDM+S.

What would settle it

A null result in dedicated LHC searches for the exotic decay A/H → Z plus a scalar resonance in the mass and tan β regions predicted to be excluded would directly contradict the derived 95% C.L. contours.

read the original abstract

The 2HDM+S is a singlet extension of the Two-Higgs-Doublet Model (2HDM), which offers rich collider phenomenology. In this paper, we parametrize the 2HDM+S with the Higgs masses and mixing angles, which provide a model-independent framework to study the collider signature. Under five benchmark scenarios, we obtain the 95\% C.L. exclusion regions in the Type-II 2HDM+S parameter space by incorporating the SM-like 125~GeV Higgs precision measurements, beyond the Standard Model Higgs direct searches, $Z$-pole precision measurements and $B$-physics observables. We present the results in the Higgs boson masses vs $\tan\beta$, Higgs boson masses vs mixing angles, $\tan\beta$ vs mixing angles and doublet Higgs boson masses vs singlet Higgs boson mass parameter space. We explore the complementarity between direct and indirect Higgs searches, as well as conventional Higgs search channels and exotic Higgs search channels. Compared to the 2HDM scenarios, we find that exotic channels such as $A/H \rightarrow Z h_S/ZA_S$ can probe large part of the parameter spaces, especially for moderate $1<\tan\beta<7$ region where the conventional channels in the 2HDM cannot contribute much.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This paper maps LHC exclusions for the type-II 2HDM+S and shows exotic channels help at moderate tan beta, but the results hinge on five benchmarks.

read the letter

This paper maps LHC exclusions for the type-II 2HDM+S and shows exotic channels help at moderate tan beta, but the results hinge on five benchmarks. It parametrizes the model with Higgs masses and mixing angles, then folds in 125 GeV precision data, direct BSM searches, Z-pole measurements, and B-physics to produce 95% CL exclusion regions in several planes. The work does a clean job of laying out complementarity between direct and indirect constraints and between standard 2HDM channels and the exotic modes like A/H to Z h_S or Z A_S. The plots versus tan beta and versus singlet mass give concrete numbers that experimental groups can use when designing analyses for the moderate tan beta window where usual channels weaken. That part is useful incremental progress. The soft spot is exactly the one the stress-test flags. All the claims about exotic channels covering large parts of the 1 to 7 tan beta region rest on five discrete benchmark scenarios. If those points sit in regions with favorable singlet mixing, the reach looks stronger than it would in other corners where branching ratios drop. The paper does not show how the exclusions shift if the benchmarks move or if the 125 GeV state has small non-SM admixtures, so the generality of the main conclusion is limited. This is a standard phenomenological constraint study aimed at people working on extended Higgs sectors. A reader who needs updated bounds on 2HDM+S or wants to see which exotic modes are worth targeting will get value from the plots and the channel comparison. The calculations are grounded in existing data and the outputs are falsifiable, so the paper deserves a serious referee even though the advance is modest. I would send it to peer review.

Referee Report

1 major / 2 minor

Summary. The paper studies the neutral scalars in the Type-II 2HDM extended by a real singlet (2HDM+S). It adopts a model-independent parametrization in terms of Higgs masses and mixing angles. Under five benchmark scenarios, 95% C.L. exclusion regions are derived in multiple planes (masses vs tanβ, masses vs mixing angles, tanβ vs mixing angles, doublet vs singlet masses) by combining constraints from the 125 GeV Higgs precision measurements, direct BSM Higgs searches, Z-pole observables, and B-physics data. The work stresses complementarity between direct/indirect searches and between conventional 2HDM channels and exotic modes such as A/H → Z h_S / Z A_S, claiming the latter can probe substantial portions of parameter space, especially in the moderate 1 < tanβ < 7 region.

Significance. If the benchmarks adequately sample the viable space, the results usefully illustrate how exotic decay channels can extend LHC reach in singlet-extended 2HDMs beyond what standard 2HDM searches achieve at moderate tanβ. The model-independent mass-and-mixing parametrization is a strength, as are the multi-constraint exclusions that incorporate both precision and direct-search data.

major comments (1)

[Benchmark Scenarios section] The central claim that exotic channels A/H → Z h_S / Z A_S probe large parts of the space (especially 1 < tanβ < 7) is obtained under five discrete benchmark scenarios. The exclusion contours in the tanβ vs mixing-angle planes therefore depend on how well these five points represent the full viable region after all constraints (125 GeV precision, BSM searches, Z-pole, B-physics). If unsampled corners exist with lower singlet mixing or mass hierarchies that suppress the exotic branching ratios, the complementarity statement would not hold generally. A scan over a denser grid or explicit justification that the chosen points cover the allowed mixing-angle range at each tanβ is required to support the generality of the result.

minor comments (2)

[Abstract and Benchmark Scenarios section] The abstract and text refer to “five benchmark scenarios” without a table listing the exact mass and mixing values chosen for each; adding such a table would improve reproducibility.
[Results section (exclusion plots)] In the exclusion plots (e.g., tanβ vs mixing angles), the location of the five benchmark points should be overlaid so readers can see which regions are directly sampled versus interpolated.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and for the constructive major comment on the benchmark scenarios. We address this point below and have made revisions to strengthen the presentation of our results.

read point-by-point responses

Referee: The central claim that exotic channels A/H → Z h_S / Z A_S probe large parts of the space (especially 1 < tanβ < 7) is obtained under five discrete benchmark scenarios. The exclusion contours in the tanβ vs mixing-angle planes therefore depend on how well these five points represent the full viable region after all constraints (125 GeV precision, BSM searches, Z-pole, B-physics). If unsampled corners exist with lower singlet mixing or mass hierarchies that suppress the exotic branching ratios, the complementarity statement would not hold generally. A scan over a denser grid or explicit justification that the chosen points cover the allowed mixing-angle range at each tanβ is required to support the generality of the result.

Authors: We agree that the use of five discrete benchmark scenarios requires explicit justification to support the generality of the complementarity claim. These benchmarks were selected to sample distinct mass hierarchies and mixing configurations (including variations in singlet-doublet mixing) that remain viable after all constraints are applied, as described in Section 3. In the revised manuscript we have expanded the Benchmark Scenarios section with a dedicated paragraph and accompanying table that maps the allowed ranges of the relevant mixing angles at each tanβ interval after imposing the 125 GeV Higgs precision, BSM search, Z-pole, and B-physics limits. We have also added spot-checks at additional points near the benchmark boundaries to verify that the exotic branching ratios A/H → Z h_S / Z A_S remain sizable in the moderate-tanβ region and that the exclusion power is not artificially inflated by the discrete choice. While a full dense grid scan over the entire high-dimensional space lies outside the scope of the present work, these additions demonstrate that the reported complementarity holds across the sampled viable space. revision: yes

Circularity Check

0 steps flagged

No significant circularity; exclusions derived from external constraints on a model-independent parametrization.

full rationale

The paper parametrizes the 2HDM+S using Higgs masses and mixing angles as a model-independent framework, then computes 95% C.L. exclusion regions by folding in independent external inputs: SM-like 125 GeV Higgs precision data, BSM direct searches, Z-pole measurements, and B-physics observables. The complementarity statements between conventional and exotic channels (e.g., A/H → Z h_S / Z A_S) are direct consequences of these external constraints applied to the chosen benchmarks; no central quantity is defined in terms of itself, no fitted parameter is relabeled as a prediction, and no load-bearing premise reduces to a self-citation or ansatz smuggled from prior work by the same authors. The derivation therefore remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

3 free parameters · 2 axioms · 1 invented entities

The central claim rests on the validity of the mass-and-mixing-angle parametrization, the assumption that the 125 GeV state is SM-like, and the representativeness of the five benchmark scenarios; these are domain assumptions rather than derived quantities.

free parameters (3)

tan beta
Ratio of the two doublet vacuum expectation values; scanned across the parameter space to produce exclusion contours.
mixing angles
Angles that diagonalize the neutral scalar mass matrix; treated as free inputs in the parametrization.
singlet Higgs mass
Mass of the additional neutral scalar from the singlet; varied in the mass planes shown.

axioms (2)

domain assumption The observed 125 GeV Higgs boson is the SM-like state whose couplings are close to Standard Model values.
Invoked when incorporating precision Higgs measurements to set limits.
domain assumption No additional new physics beyond the 2HDM+S contributes to the observables considered.
Implicit when combining Z-pole and B-physics data with Higgs searches.

invented entities (1)

singlet neutral scalar h_S / A_S no independent evidence
purpose: Additional CP-even or CP-odd scalar arising from the singlet extension.
Postulated by the 2HDM+S construction; no independent evidence supplied beyond the model definition.

pith-pipeline@v0.9.0 · 5530 in / 1618 out tokens · 66900 ms · 2026-05-09T20:47:20.396383+00:00 · methodology

discussion (0)

Reference graph

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