{"id":"21791256-0821-4842-966c-9a7e5d61f466","arxiv_id":"2508.12309","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":6.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":4,"one_line_summary":"In the Type-I 2HDM, light long-lived Higgs particles are forced into a narrow relation between mixing angle and tanβ, and FASER2 could probe the benchmark regions about a hundred times better than FASER.","lead":"The authors map out the allowed light scalar and pseudoscalar particle masses in a Type-I Two-Higgs-Doublet Model and show where those particles can be long-lived. They identify four benchmark scenarios that also match the measured W boson mass and compare how well the FASER and FASER2 detectors could find these particles.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claimed 'complete region' rests on the unverified approximation that light BSM Higgs oblique corrections are dominated by ΔS; if ΔT/ΔU contribute comparably, the simple alignment formulas and benchmark regions may shrink.","rationale":"The reader's weakest assumption correctly identifies the ΔS-versus-ΔT treatment of oblique parameters as the pivot for the completeness claim. My reading focuses on that single approximation as the most load-bearing condition: if it fails, the two closed-form relations for cos(β−α) are not faithful summaries of the constrained parameter space. Since the abstract gives no fit details, the claim remains unverified. I do not see a reason to move away from UNVERDICTED; the concern reinforces the reader's verdict rather than overturning it. I also note that the long-lived condition is an input to the FASER reach rather than a derived output, but that is secondary to the oblique-parameter issue.","tokens_in":959,"tokens_out":6225,"duration_ms":72405,"concrete_test":"Take one benchmark point satisfying the claimed relations with tanβ = 10, m_H = 25 GeV, m_A = 20 GeV, and m_H± = 300 GeV. Compute the full one-loop oblique parameters ΔS, ΔT, ΔU using a public tool such as 2HDMC or the formulas of Grimus et al., and test the point against the current 95% CL electroweak fit ellipse (e.g., GFitter). Repeat for the four proposed benchmark points. If any point falls outside the ellipse when ΔT is included, the ΔS-dominated approximation is not valid for the light-mass region and the claimed 'complete region' is incomplete.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central completeness statement depends on the abstract's assertion that for light H and A the global fit of oblique parameters is dominated by ΔS rather than ΔT. The formulas cos(β−α) ≃ 1/tanβ and cos(β−α) ≃ (1/tanβ)(2m_H^2 − m_h^2)/(m_H^2 − m_h^2) are presented as the result of imposing vacuum stability, perturbative unitarity, and current experimental bounds, but the abstract does not show how the complete region follows. If the full one-loop ΔT (or ΔU) is not numerically negligible in the benchmark mass and tanβ ranges, the electroweak-fit ellipse is rotated and rescaled, so the stated relations would not delimit the true allowed set. The phrase 'ΔS could be the main contribution' is itself weaker than a demonstrated dominance, and the completeness claim is only as strong as this approximation. In addition, the long-lived nature of H and A is an input condition for the FASER reach; if the h→H A or h→A A invisible decay constraints are not implemented at full LHC precision, the claimed allowed region could contain points already excluded by direct invisible-width measurements.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper analyzes the parameter space of the Type-I Two-Higgs-Doublet Model (2HDM) that allows for light long-lived scalar (H) and pseudoscalar (A) particles. It claims that, when imposing vacuum stability, perturbative unitarity, and current experimental bounds, the allowed region is summarized by simple approximate relations: cos(β−α) ≃ 1/tanβ for the light scalar H, and cos(β−α) ≃ (1/tanβ)(2m_H^2 − m_h^2)/(m_H^2 − m_h^2) for the light pseudoscalar A. The abstract further states that the dominant electroweak precision contribution for light BSM Higgs bosons is ΔS (unlike the heavy case where ΔT dominates), that invisible Higgs decay is the most important experimental constraint, and that four benchmark regions can simultaneously accommodate a light long-lived particle and explain the W boson mass anomaly. Finally, the paper projects FASER and FASER2 reaches, finding FASER2 improves sensitivity by about two orders of magnitude.","tokens_in":1229,"tokens_out":3600,"duration_ms":37793,"significance":"If the claims are fully substantiated, the paper would provide a compact analytic description of the allowed light-Higgs parameter space in Type-I 2HDM, which is a useful tool for designing LLP searches. The identification of invisible Higgs decay as the leading constraint and the quantitative FASER2 sensitivity projection are valuable and falsifiable predictions. The benchmark points that connect the LLP scenario to the W mass anomaly are also of interest. However, the manuscript as presented (essentially the abstract alone) does not supply the derivations, the exhaustive constraint list, the numerical verification of the ΔS-dominance approximation, or the detector-specific details behind the FASER reach; the significance is therefore conditional on those missing components being provided and verified.","major_comments":[{"comment":"The claim that for light BSM Higgs bosons 'ΔS could be the main contribution during the global fit of the oblique parameters' is not demonstrated. The subsequent alignment formulas cos(β−α) ≃ 1/tanβ and cos(β−α) ≃ (1/tanβ)(2m_H^2 − m_h^2)/(m_H^2 − m_h^2) are stated as outcomes of imposing theoretical and experimental constraints, but the abstract provides no derivation, no numerical check, and no estimate of the size of ΔT and ΔU in the relevant mass and tanβ ranges. Please provide an analytic argument or a numerical scan showing that the full oblique-parameter ellipse is well approximated by the ΔS-only contribution for the benchmark points, and quantify the error incurred by dropping ΔT and ΔU.","section":"Abstract"},{"comment":"The phrase 'complete region' is undefined. The abstract lists some constraints (vacuum stability, perturbative unitarity, current experimental bounds) but does not specify which experimental searches are included, which references are used, or how the completeness is established. A reader cannot assess whether additional direct Higgs searches, flavor observables, or electroweak precision observables would remove part of the claimed region. Please provide a table of all applied bounds with references, and show explicitly that the derived relation for cos(β−α) is the exact boundary of the allowed region rather than an approximate fit.","section":"Abstract"},{"comment":"The assertion that 'the invisible Higgs decay is the most important constraint' is not quantified. For each benchmark point, the partial widths for h→AA and h→HA (or any invisible decay of the 125 GeV Higgs) must be computed, and the resulting excluded regions from invisible Higgs searches must be shown. Without this, the four proposed benchmark regions could include points already excluded by LHC invisible-width measurements. Please present the relevant branching ratios and overlay the invisible-decay exclusion on the parameter-space plots.","section":"Abstract"},{"comment":"The long-lived nature of H and A is an input condition for the FASER reach, but the abstract does not specify the proper decay lengths, dominant decay modes, or production cross sections of the light scalars at the LHC for the benchmark points. The stated factor-of-100 improvement of FASER2 over FASER cannot be reproduced without these details. Please provide the benchmark particle properties, the assumed FASER/FASER2 geometry, and the acceptance calculations that lead to the sensitivity curves.","section":"Abstract"}],"minor_comments":[{"comment":"There is a typo in 'beyongd' (should be 'beyond').","section":"Abstract"},{"comment":"The acronym 'LLPs' is used without expanding it; please spell out 'long-lived particles' at first use.","section":"Abstract"},{"comment":"The phrase 'complete region' should be qualified, for example 'complete allowed region under the constraints specified in this work'.","section":"Abstract"},{"comment":"The notation 'FASER and FASER 2' is inconsistent; please use 'FASER' and 'FASER2' consistently.","section":"Abstract"},{"comment":"Please provide a reference for the W boson mass anomaly and state which experimental value is used.","section":"Abstract"}],"recommendation":"major_revision","confidential_remarks":"The submitted packet contains only the abstract; none of the derivations, tables, or figures referenced in the abstract are available in the manuscript text. If this is the full submission, it is far below the standard for a journal article. If the full text was omitted by mistake, the revision must include the complete derivations, a full constraint list, numerical validation of the ΔS-dominance assumption, and the benchmark specifications. The scientific question is timely and the proposed approximate formulas could be valuable, but the current form does not allow verification of the central completeness claim."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Here's my quick take. The abstract claims a complete map of the light H/A region in Type-I 2HDM, gives two simple alignment formulas, and says FASER2 gains ~100x over FASER. That is exactly the kind of concrete outcome a collider phenomenology paper should advertise: a checkable condition and a testable reach. The idea that invisible Higgs decay is the key constraint is also worth highlighting, and the W-mass benchmarks are a nice way to connect the LLP program to an actual discrepancy.\n\nWhat I cannot verify from the abstract is the completeness claim itself. The load-bearing piece is that ΔS dominates the oblique fit for light BSM Higgses. The abstract hedges with 'could be the main contribution,' which is not the same as showing it. If ΔT or ΔU enters at a comparable level in the relevant mass and tanβ range, the ellipse rotates, the simple cos(β−α) relations break down, and the 'complete region' label becomes an approximation rather than a boundary. The stress-test note is fair. The full paper will need to show the one-loop fit, not just assert the dominance.\n\nThere are also smaller gaps. The benchmarks are fitted to the W mass, which is legitimate, but the abstract does not report the uncertainty or the goodness of fit. The completeness depends on the constraint list being exhaustive; I can't audit that from the abstract. The long-lived nature of H and A is an input condition for the FASER reach, not a derived consequence. And since there are no references shown, I can't compare against prior 2HDM LLP scans to judge novelty.\n\nNone of this makes me want to block the paper. The question is well-posed, the formulas are a good organizing principle, and the FASER2 projection is directly useful. If the derivations hold up in the full text, this will be a reference for anyone searching for light scalars in Type-I 2HDM. My advice: send it to a serious referee with a request to see the ΔS vs ΔT calculation, the complete constraint list, and the fit quality for the W-mass benchmarks. That is the appropriate bar for a paper making a completeness claim.\n\nFor my own use: I wouldn't cite it from the abstract alone, but I'd bring it to a reading group once the full version is out.","headline":"Plausible and useful map of light H/A in Type-I 2HDM, but the 'complete region' rests on an unshown ΔS-dominance assumption that deserves a real referee.","tokens_in":1727,"tokens_out":2702,"would_cite":false,"duration_ms":28166,"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":"Light long-lived Higgs scalars in Type-I 2HDM are confined to two simple parameter relations.","keywords":["Type-I 2HDM","long-lived particles","light scalar","light pseudoscalar","oblique parameters","invisible Higgs decay","W boson mass anomaly","FASER2"],"falsifier":"A full one-loop oblique parameter computation for $m_H,m_A<m_h$ that finds $\\Delta T$ comparable to $\\Delta S$ would falsify the claimed relations. Alternatively, a direct search that excludes $h\\to$ invisible decays for all four benchmark points would falsify the claim that these points simultaneously explain the $W$ boson mass anomaly.","tokens_in":772,"feed_emoji":"🔭","tokens_out":7238,"duration_ms":69836,"temperature":0.7,"pith_summary":"This paper maps the full parameter space of the Type-I Two-Higgs-Doublet Model (2HDM), a two-doublet extension of the Standard Model, that can host light, long-lived scalar ($H$) and pseudoscalar ($A$) particles. Its central claim is that after vacuum stability, perturbative unitarity, and current experimental bounds are imposed, the allowed region collapses to two simple approximate relations: $\\cos(\\beta-\\alpha)\\simeq 1/\\tan\\beta$ for $H$, and $\\cos(\\beta-\\alpha)\\simeq \\frac{1}{\\tan\\beta}\\frac{2m_H^2-m_h^2}{m_H^2-m_h^2}$ for $A$. The reason is that for BSM Higgs bosons lighter than the observed 125 GeV Higgs, the oblique parameter $\\Delta S$ dominates the electroweak precision fit, in contrast to the heavy-mass case where $\\Delta T$ dominates. The paper identifies invisible Higgs decay as the most important constraint on this region, proposes four benchmark points that both yield long-lived particles and explain the $W$ boson mass anomaly, and shows that FASER2 would be roughly a hundred times more sensitive than FASER. A sympathetic reader should take away that the light-Higgs Type-I 2HDM parameter space is effectively an analytic band, not a broad multi-parameter scan.","feed_headline":"Light long-lived Higgs states pinned to two simple formulas.","feed_subtitle":"Type-I 2HDM scalars that could explain the W mass anomaly now have a narrow, testable parameter band.","key_machinery":"The carrying mechanism is the oblique parameter global fit, specifically the dominance of $\\Delta S$ over $\\Delta T$ for BSM Higgs bosons below the Standard Model Higgs mass. This dominance converts electroweak precision constraints into nearly single-variable bounds that pin $\\cos(\\beta-\\alpha)$ to the two analytic relations. The invisible Higgs decay constraint then supplies the sharpest cut on the remaining region. The long-lived nature of $H$ and $A$ follows from the suppressed couplings that this alignment-like limit enforces, and it is these displaced decays that FASER and FASER2 are designed to catch.","core_discovery":"The paper's central discovery is that the complete region of the Type-I 2HDM allowing light long-lived scalars is captured by two approximate formulas rather than a multi-dimensional scan. For the light CP-even scalar $H$, the alignment-breaking parameter $\\cos(\\beta-\\alpha)$ is forced to $\\simeq 1/\\tan\\beta$; for the lighter CP-odd $A$, it is forced to $\\simeq \\frac{1}{\\tan\\beta}\\frac{2m_H^2-m_h^2}{m_H^2-m_h^2}$. These relations emerge because at low BSM Higgs masses $\\Delta S$ dominates the oblique parameter global fit, opposite to the heavy-mass regime in which $\\Delta T$ dominates. The invisible Higgs decay $h\\to AA/HH$ is the most important constraint, and within the surviving region four benchmark parameter sets produce long-lived particles while simultaneously explaining the $W$ boson mass anomaly. The paper evaluates the FASER and FASER2 reaches for these benchmarks and finds FASER2 improves sensitivity by about two orders of magnitude.","pith_inferences":["If the $\\Delta S$-dominance logic holds, analogous alignment-like relations should appear in other extended Higgs sectors with light scalars, such as singlet extensions or 2HDM+$S$; testing those relations would be a natural follow-up.","The benchmark points that explain the $W$ mass anomaly are also within reach of LHC searches for $H\\to$ dilepton or diphoton signatures, which the paper does not examine; a null result there would tighten the region further.","A null FASER2 search would not by itself exclude the Type-I 2HDM light-pseudoscalar explanation of $W$ mass, since the LLP lifetime assumptions could be altered by small coupling changes, but it would disfavor the specific benchmark construction.","Because the relations are tan$\\beta$-dependent, BELLE II or a future Higgs factory measuring $h\\to$ invisible could effectively substitute for a dedicated LLP search at low masses."],"forward_implications":["The light-H/A parameter space is no longer a high-dimensional scan: any future search can compare against the analytic band set by $\\tan\\beta$ and $m_H$.","Invisible Higgs decay is the sharpest probe; a measured $h\\to$ invisible branching ratio close to current limits would exclude most of the long-lived region.","The four benchmark points tie the long-lived-particle program to the $W$ mass anomaly: if FASER2 sees these LLP signals, it simultaneously corroborates that anomaly's new-physics explanation.","FASER2's roughly hundredfold sensitivity gain over FASER makes it a decisive near-term test of the entire proposed region.","If the relations hold, future LLP searches in the Type-I 2HDM can be designed directly from the analytic formulas, avoiding blind scans over the full parameter space."],"supporting_citations":[],"fun_headline_variants":["Type-I 2HDM light LLPs: two formulas nail the whole parameter space","Two formulas map the entire light LLP region in Type-I 2HDM","Light long-lived scalars: two equations box in the whole Type-I 2HDM","Type-I 2HDM's light LLP region shrinks to two neat formulas","Light LLPs from Type-I 2HDM explain W mass anomaly with two formulas"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The 'complete region' stands on the assumption that for light BSM Higgs bosons the oblique parameter fit is dominated by $\\Delta S$ instead of $\\Delta T$; if that dominance fails, the two cosine relations no longer hold.","fun_headline_variants_meta":{"raw":{"variants":["Type-I 2HDM light LLPs: two formulas nail the whole parameter space","Two formulas map the entire light LLP region in Type-I 2HDM","Light long-lived scalars: two equations box in the whole Type-I 2HDM","Type-I 2HDM's light LLP region shrinks to two neat formulas","Light LLPs from Type-I 2HDM explain W mass anomaly with two formulas"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001022,"raw_usage":{"total_tokens":4352,"prompt_tokens":1028,"completion_tokens":3324,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":644,"completion_tokens_details":{"reasoning_tokens":3229}},"tokens_in":644,"tokens_out":3324,"duration_ms":24981,"temperature":1.0,"reasoning_tokens":3229,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T17:23:14.721929+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A full one-loop oblique parameter computation for $m_H,m_A<m_h$ that finds $\\Delta T$ comparable to $\\Delta S$ would falsify the claimed relations. Alternatively, a direct search that excludes $h\\to$ invisible decays for all four benchmark points would falsify the claim that these points simultaneously explain the $W$ boson mass anomaly.","supporting_citations":[],"review_version":2}