{"id":"181905fd-6c78-46d8-8c5e-c4ce7978facd","arxiv_id":"1908.10809","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":3.0,"correctness_risk":"low","formal_verification":"none","parameter_count":4,"one_line_summary":"Current LHC data leave substantial room for singlet and inert doublet scalar extensions, and scalar-to-scalar decay signatures with rates up to tens of picobarns remain unexplored.","lead":"This conference paper surveys what LHC data currently say about three simple extensions of the Standard Model Higgs sector: a real singlet, an inert doublet that provides a dark matter candidate, and a two-singlet model with exotic scalar-to-scalar decays. It is a compact status map for deciding which new collider searches are worth running.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"O(60 pb) two-real-scalar rates rest on a private ScannerS build with no independent recast or cross-check; BP4's 125 GeV scalar-to-4b rate should be reproduced publicly before endorsing it.","rationale":"The reader's weakest_assumption names exactly this dependency on external tools and the private ScannerS build, and I agree. This is not an accusation of error; the paper is honestly reporting prior work, and the companion paper [76] may well contain the needed details. But a proceedings paper that encourages dedicated experimental searches rests on the findability and reproducibility of its central rate maps. The proposed test is cheap and decisive: a public reproduction of BP4 with public tools. If it passes, the conditional can be lifted; if it fails, the headline rate is not supported. Since the reader already conditioned the verdict on these items and I find no additional internal contradiction or reason for rejection, my stress-test leaves the reader's CONDITIONAL verdict unchanged.","tokens_in":13089,"tokens_out":6447,"duration_ms":71323,"concrete_test":"Independently reproduce the BP4 benchmark (M3 = 125 GeV) using a public version of ScannerS or another two-real-singlet implementation; generate a UFO model and compute pp -> h3 -> h1h1 -> 4b at 13 TeV with MadGraph5_aMC@NLO, using the same HiggsBounds-5.4.0 and HiggsSignals-2.3.0 versions quoted in the paper. Apply a recast of the ATLAS/CMS searches for 125 GeV scalars decaying to two lighter scalars in the 4b channel over the M1 10-60 GeV range, and also compare the total inclusive production cross section with the claimed 60 pb upper point. If the O(60 pb) point is excluded, or if its computed rate drops below the stated value by more than the expected theory uncertainty, the Section 4 claim needs revision.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section 4's central claim is that pp -> h3 -> h1h1 (and related chains) can reach O(60 pb) at the 13 TeV LHC 'while still complying with all current theoretical and experimental bounds.' The load-bearing support for this claim is not in this paper: the benchmark planes and rate maps are imported from the companion paper [76], and the text states that 'results have been obtained using a private version of the ScannerS framework.' There is no public model file, no independent cross-section normalization check, no recast of the relevant multi-b-jet searches, and no uncertainty estimate. In BP4, M3 = 125 GeV, so an O(60 pb) rate means the 125 GeV state must decay almost exclusively to the light scalars and be produced near the full inclusive 13 TeV Higgs production rate; any small correction in kappa_125, BR, or the production-mode sum, or any limitation in how HiggsBounds/HiggsSignals treated the 4b final state, could push these points against existing exclusions. The paper itself flags exactly this kind of issue for the IDM VBF recast in Section 3.1 ('This emphasizes the importance of comparing fully simulated samples...'), but no equivalent caveat or cross-check is supplied for the Section 4 rates. Thus the multi-picobarn 'new signature' recommendation is not independently established; it inherits the reliability of a private tool and the companion paper.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This proceedings contribution surveys constraints on three extended scalar sectors: the real singlet extension, the inert doublet model (IDM), and the two-real-singlet extension. The author updates the singlet model parameter space using HiggsBounds, HiggsSignals, the W-boson mass, and perturbativity constraints; recasts VBF and monojet searches for the IDM; reports CLIC projection significances for IDM scalar pair production; and presents benchmark rates for scalar-to-scalar decays pp -> h3 -> h1h2 and pp -> ha -> hbhb in the two-real-singlet model, including a BP4 point with pp -> h3 -> h1h1 rates up to about 60 pb at the 13 TeV LHC, claimed to satisfy all current theoretical and experimental bounds. The paper recommends dedicated experimental searches for these signatures.","tokens_in":13391,"tokens_out":4035,"duration_ms":45848,"significance":"The paper is a compact status report and a useful motivator for new LHC searches. Its strengths include the use of publicly available tools (HiggsBounds, HiggsSignals, 2HDMC, micrOmegas), the explicit caveats attached to the IDM VBF recast, and the CLIC projection results drawn from dedicated simulations. If the Section 4 rates are correct, they identify an uncovered signature with multi-picobarn production rates, which would be a genuinely useful experimental target. However, the central quantitative claim is not independently established in this manuscript: the benchmark planes and rate maps are imported from the companion paper [76] and computed with a private version of ScannerS, with no independent cross-check, no recast of the relevant multi-b-jet searches, and no uncertainty estimate. The paper's strongest recommendation therefore inherits the reliability of an external, non-public implementation.","major_comments":[{"comment":"The O(60 pb) rate for pp -> h3 -> h1h1 is the load-bearing quantitative claim of the paper, but it is not supported within this manuscript. The text states that \"results have been obtained using a private version of the ScannerS framework,\" and the benchmark rates are taken from the companion paper [76] without independent verification. Since BP4 has M3 = 125 GeV, a 60 pb rate requires near-SM h3 production and near-unity h3 -> h1h1 branching; small corrections in kappa_125, in the branching ratio, or in the treatment of the 4b final state by HiggsBounds/HiggsSignals could all change the conclusion. The authors should provide an independent cross-check, for example a public model file, a comparison of the cross-section normalization with an established tool, and a recast of existing multi-b resonance searches, or should explicitly re-label the claim as an inherited result from [76] with the associated uncertainty.","section":"Section 4, Figure 6 (BP4)"},{"comment":"The IDM viability conclusion depends on the VBF recast, which the author correctly describes as a leading-order calculation with a K-factor and hand-estimated missing transverse energy. The caveat is stated, but its practical impact is not quantified. Since the surviving region labelled \"Allowed by Dark Matter + VBF Constr.\" in Figure 4 is defined by this approximate recast, the paper should state an estimated uncertainty on the recast boundary or identify which parts of the surviving parameter space are robust to a 10-20% change in the signal efficiency or to offshell/interference effects.","section":"Section 3.1, Figure 4"},{"comment":"The claim that scalar-to-scalar decays with all final-state scalars different from 125 GeV \"have not yet been fully explored\" is too strong without a more systematic check of existing searches. The paper mentions only the ATLAS WWWW search [79] as covering a small region of the h3 -> h2h2 plane, but does not discuss constraints from existing 4b, bbtautau, or bbll resonance searches that can be sensitive to the benchmark final states. Please specify which existing searches have been explicitly checked for BPs 1, 3, 4, and 5, and why they do not exclude the high-rate regions shown in Figure 6.","section":"Section 4, text after Eq. (4.4)"}],"minor_comments":[{"comment":"There are several typographical errors, including \"goverend\" in Section 3.2, \"signatures has been\" in Section 4, and \"Mh & Mh/2\" in the caption of Figure 4; these should be corrected to read \"governed,\" \"signatures have been,\" and \"MH & Mh/2,\" respectively.","section":"General"},{"comment":"The axis label \"M_H + mA\" should be \"MA + MH\", and the notation \"S+B/S = S/sqrt(S+B)\" is not defined explicitly in the text; please add a sentence defining the significance variable used in the plots.","section":"Figure 5"},{"comment":"Several references are given only as arXiv identifiers without journal or proceedings information (for example [30], [61], [62], and [79]); adding full citation details would improve the manuscript's usability.","section":"References"},{"comment":"The left and right panels of Figure 3 are reproduced from other works and are not described in enough detail for the reader to understand the scan ranges or the meaning of the grey and red points; please expand the caption or refer more explicitly to the defining equations and parameter ranges.","section":"Figure 3"}],"recommendation":"major_revision","confidential_remarks":"This is a proceedings-style paper whose main new quantitative claim, the O(60 pb) scalar-to-scalar rate, is delegated to a companion paper and a private code version. I would advise the editor that acceptance should be conditioned on the authors either clearly framing Section 4 as a summary of [76] with no new verification, or adding a verification element such as a public model file, an independent cross-check, and a recast of multi-b searches. The IDM VBF recast uncertainty should also be quantified before the viability claim is taken at face value."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThis is a LHCP2019 proceedings note by Tania Robens, not a fresh research paper. It does two useful things: it updates the real-singlet exclusion maps with the 2019 ATLAS/CMS di-Higgs combination limits, and it lays out the current status of the inert doublet model, including a VBF recast from her group's earlier work. The part that will get attention is Section 4: in the two-real-scalar model, scalar-to-scalar production like pp -> h3 -> h1h2 can reach O(60 pb) at 13 TeV 'while still complying with all current theoretical and experimental bounds.' That is a striking number and a good hook for experimentalists.\n\nCredit where due: the paper is honest and clearly written. It says explicitly which figures are taken from prior papers, and it flags that the IDM VBF limit is based on an LO recast with a K-factor and hand-estimated missing transverse energy, recommending fully simulated samples. That is the right level of transparency.\n\nThe soft spot is the same one the stress-test note hits. The 60 pb rate claim is not supported inside this paper. The text says only that results came from a private version of ScannerS and refers you to the companion paper [76]. For BP4, where M3 = 125 GeV, an O(60 pb) rate means the 125 GeV state is produced almost as often as the SM Higgs and decays almost entirely to lighter scalars, not to SM fermions. That is a strong statement. It could easily be wrong if kappa_125, the branching ratios, or the treatment of 4b final states in HiggsBounds/HiggsSignals shift by even a few percent. The paper is appropriately cautious about the IDM recast but applies no equivalent caution here.\n\nI would not call that fatal. For a proceedings write-up, it is acceptable to point to a companion paper for details, and the models themselves are not novel claims of this paper. But if this were a regular journal submission, I would ask for either an independent check of the Section 4 rates or an explicit sentence saying they are preliminary and need full-simulation cross-checks.\n\nWho is this for? Experimental colleagues who want a quick map of what is still allowed in the singlet and inert doublet models, and a pointer to possible new search channels. They can read it in twenty minutes. It does not replace the original papers.\n\nRecommendation: yes, send it to a serious referee if it reaches a journal; the updates are small but the claims are concrete and a referee will keep the author honest about the Section 4 uncertainty.","headline":"Useful proceedings summary of singlet and inert doublet constraints; the standout 60 pb scalar-to-scalar rates are imported from the companion paper and deserve a cross-check.","tokens_in":14038,"tokens_out":2834,"would_cite":false,"duration_ms":30361,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"A simple two-real-scalar extension of the Standard Model could produce scalar-to-scalar decays at rates up to about 60 pb at the 13 TeV LHC while evading all current constraints, a gap that dedicated searches should close.","keywords":["extended scalar sectors","Higgs boson","LHC searches","Inert Doublet Model","scalar singlet extension","scalar-to-scalar decays","future e+e- colliders","dark matter candidate"],"falsifier":"A dedicated ATLAS or CMS search for $p p \\to h_3 \\to h_1 h_2$ and $p p \\to h_a \\to h_b h_b$ in final states with four or six b-jets, using the Run 2 dataset, would settle the central claim: predicted rates of tens of picobarns would be visible, while the absence of an excess would exclude the benchmark regions where those rates are quoted.","tokens_in":12780,"feed_emoji":"⚛️","tokens_out":7824,"duration_ms":75985,"temperature":0.7,"pith_summary":"This short report maps what current and future collider limits say about three simple extensions of the Standard Model's scalar sector: adding one real singlet scalar, adding an inert second doublet, and adding two real singlet scalars. The paper compiles the parameter-space regions that survive theoretical constraints and existing experimental searches, and it points to where those searches miss viable possibilities. The central point is that the two-real-scalar model can produce scalar-to-scalar decays such as $p p \\to h_3 \\to h_1 h_2$ and $p p \\to h_a \\to h_b h_b$ at rates of order tens of picobarns at the 13 TeV LHC, with no current search targeting exactly these final states. The author encourages dedicated experimental searches using the existing Run 2 dataset and argues that future $e^+e^-$ colliders could probe the inert doublet model down to production cross sections near one femtobarn.","feed_headline":"Unexplored scalar-to-scalar decays may reach 60 pb at the 13 TeV LHC","feed_subtitle":"These rates would be high enough that the existing Run 2 data should already contain such events if the model is right.","key_machinery":"The load-bearing object is the scalar potential of the two-real-scalar model with a $Z_2\\otimes Z_2'$ symmetry. After the doublet and the two singlet fields take vacuum expectation values and mix, the three neutral mass eigenstates $h_1,h_2,h_3$ couple to Standard Model particles through rescaling factors $\\kappa_i$, with orthogonality enforcing $\\sum_i \\kappa_i^2 = 1$; the measured 125 GeV scalar must have $|\\kappa_{125}| \\gtrsim 0.96$. The new signatures come from the trilinear scalar couplings among these eigenstates, which allow a heavier state to decay into two lighter ones, $h_3 \\to h_1 h_2$ or $h_a \\to h_b h_b$, with the light scalars subsequently decaying into Standard Model particles, typically $b\\bar{b}$ pairs. For the inert doublet model, the same exact $Z_2$ symmetry that provides the dark matter candidate forces all collider signatures to end in electroweak gauge bosons plus missing energy.","core_discovery":"The paper's central claim is that the most promising unprobed corner of the extended scalar sector is not the already-searched resonant or Higgs-pair channels but scalar-to-scalar decays between non-SM scalars. In the $Z_2\\otimes Z_2'$ two-real-scalar model, three neutral scalars mix and couple to Standard Model particles through rescaling factors that must satisfy an orthogonality relation; the measured 125 GeV scalar has a near-unity rescaling factor, yet the other two scalars can still be produced at the LHC and decay into each other. Companion benchmark scans give production rates up to approximately 60 pb for $p p \\to h_3 \\to h_1 h_2$ and $p p \\to h_a \\to h_b h_b$ at 13 TeV while satisfying perturbative unitarity, boundedness, Higgs signal-rate measurements, and current search limits. For the singlet extension and the inert doublet model, the paper concludes that viable parameter regions remain, with the inert doublet model requiring modified search strategies such as lower missing transverse energy cuts rather than entirely new final states.","pith_inferences":["If the scalar-to-scalar production rates are as large as reported, the main obstacle is the absence of a dedicated search rather than luminosity; even a small signal efficiency would make these events visible in the accumulated Run 2 data.","The same asymmetric-decay mechanism could appear in other multi-scalar models, so a model-independent search for $h_a \\to h_b h_b$ with four or six b-jets might be broadly useful beyond this specific benchmark model.","Lowering missing-transverse-energy thresholds in multi-lepton analyses could open up the inert doublet model's parameter space, and likely also other dark-sector scenarios with compressed mass spectra, a direct testable consequence of the recast discussion in the paper."],"forward_implications":["If the two-real-scalar model is realized, Run 2 data should already contain multi-b-jet events from scalar-to-scalar decays, with the largest benchmark rates reaching tens of picobarns.","The singlet extension's allowed parameter space is dominated by Higgs signal-rate measurements and direct heavy-scalar searches up to masses around 1 TeV, with the W-boson mass and coupling perturbativity cutting in at higher masses.","The inert doublet model survives all current constraints but has not been directly tested by the LHC experiments; recasts of vector-boson-fusion and monojet searches exclude only part of its parameter space, mainly the region where the dark-matter scalar is slightly off shell.","At a future $e^+e^-$ collider, lepton-plus-missing-energy final states could reveal the inert doublet model for dark scalar masses below roughly 500 GeV, with the semi-leptonic channel extending the reach toward 1 TeV.","Scalar-to-scalar signatures with final states different from the 125 GeV Higgs should be included in future search menus, since simple counting implies the existing dataset already has enough collisions to contain them if the predicted rates are correct."],"supporting_citations":[{"why":"Companion paper that defines the two-real-scalar model, its benchmark planes, and the maximal scalar-to-scalar rates quoted here.","marker":"[76]"},{"why":"Survey of constraints on extended scalar sectors that supplies the generic scans and the inert doublet model region maps used throughout.","marker":"[20]"},{"why":"Recast of vector-boson-fusion and monojet searches that limits the inert doublet model's parameter region in the mass-coupling plane.","marker":"[34]"},{"why":"Proposes inert doublet model benchmark points for e+e- colliders and supplies production cross-section estimates.","marker":"[33]"},{"why":"Dedicated simulation study giving the significance estimates and roughly one-femtobarn discovery threshold quoted for future e+e- colliders.","marker":"[59]"},{"why":"CMS combination of Higgs-pair searches used as the comparison limit for the singlet model's $h_2 \\to h_1 h_1$ rate.","marker":"[28]"},{"why":"ATLAS combination of Higgs-pair searches used as the comparison limit for the singlet model's $h_2 \\to h_1 h_1$ rate.","marker":"[29]"},{"why":"W-boson mass precision calculation that provides a dominant constraint for heavier singlet-like scalars.","marker":"[21]"},{"why":"CMS search for invisible Higgs decays through vector-boson fusion, the basis for the inert doublet model recast.","marker":"[56]"}],"fun_headline_variants":["Scalar-to-scalar decays: new LHC search channel up to 60 pb","Extended scalars: cascade decays offer untested LHC reach","New scalar decay modes may be visible in LHC data","Untested scalar cascade decays could reach 60 pb at LHC"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The paper's maps of which parameter points survive rely on the reliability of the computer tools and search re-interpretations used to enforce constraints; in particular, one inert-doublet exclusion comes from a leading-order recast with an estimated missing-energy cut, and the two-real-scalar rates were imported from a companion paper using a private scanner with no independent cross-check here.","fun_headline_variants_meta":{"raw":{"variants":["Scalar-to-scalar decays: new LHC search channel up to 60 pb","Extended scalars: cascade decays offer untested LHC reach","New scalar decay modes may be visible in LHC data","Untested scalar cascade decays could reach 60 pb at LHC"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000592,"raw_usage":{"total_tokens":2720,"prompt_tokens":834,"completion_tokens":1886,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":450,"completion_tokens_details":{"reasoning_tokens":1809}},"tokens_in":450,"tokens_out":1886,"duration_ms":14995,"temperature":1.0,"reasoning_tokens":1809,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T10:35:40.840282+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A dedicated ATLAS or CMS search for $p p \\to h_3 \\to h_1 h_2$ and $p p \\to h_a \\to h_b h_b$ in final states with four or six b-jets, using the Run 2 dataset, would settle the central claim: predicted rates of tens of picobarns would be visible, while the absence of an excess would exclude the benchmark regions where those rates are quoted.","supporting_citations":[],"review_version":1}