{"id":"d1866bc7-c774-4b57-8b7c-8c07eeaa24e2","arxiv_id":"2507.18295","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Updated LHC limits on vector leptoquark masses and couplings from a combined recast of pair, single, indirect, and interference production in dimuon-dijet data.","lead":"Vector leptoquarks are hypothetical particles that some theories use to explain puzzling flavor measurements. This paper re-derives their LHC exclusion limits by adding indirect production, its interference with Standard Model processes, and QCD-QED pair production, finding notably stronger or sometimes weaker limits depending on the particle's quantum numbers.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"V2/eV2 exclusion limits are drawn using an EFT approximation below the mass range where the paper validates it, so the central 'all relevant production mechanisms' claim is not uniformly supported.","rationale":"The reader's weakest_assumption already identifies the V2/eV2 EFT issue, and my reading agrees that it is the single most load-bearing concern. The paper's own self-report in Sec. IVF and footnote 2 confirms that the full-theory interference cannot be evaluated with the available pipeline, so an EFT is substituted; the validation in Fig. 7 is only for U1 and eU1, and it indicates a matching scale around 3-4 TeV, while the V2/eV2 plots extend down to 2 TeV. Because indirect production and interference dominate the high-coupling region of the exclusion limits, an unquantified EFT error there can move the contours. This is an internal limitation, not a disagreement with community consensus, and the authors are honest about it. I considered the photon-PDF uncertainty in Table III as an alternative concern, but the authors explicitly flag that uncertainty and quote a wide eU1 range, whereas the EFT issue affects a larger fraction of the new exclusion plots and is not covered by any cross-check. The recommended verdict remains what the reader gave: the paper should be accepted with the conditional caveat that the V2/eV2 low-mass limits be validated or restricted once the full-theory computation is available.","tokens_in":20340,"tokens_out":6075,"duration_ms":66649,"concrete_test":"For a benchmark point such as V2 with xRL20,12 nonzero, compute the full-theory q qbar -> mu+ mu- amplitude with the t-channel V2 propagator at M_V2 = 2, 2.5, and 3 TeV using an independent implementation (manual helicity amplitudes, FeynArts/FormCalc, or a corrected UFO model), and compare the resulting IP+II cross sections with the EFT prediction used in Figs. 4(i). If the fractional difference exceeds roughly 10% at any mass below 3 TeV, recompute the V2 and eV2 exclusion contours in that region using the full-theory amplitude; if the 95% CL boundary shifts by more than 10% in the coupling coordinate, replace the asterisked limits or explicitly restrict the low-mass part of those panels.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most load-bearing concern attaches to the V2 and eV2 exclusion limits in Figs. 4(g)-(l) and 5(h)-(n), which carry asterisks indicating that the indirect-production and interference contributions were computed in an effective-operator approximation. As Sec. IVF and footnote 2 state, the full-theory interference cannot be evaluated in MadGraph with the FeynRules models, so the authors integrate out the t-channel vLQ and use the dimension-6 operators of Table IV. This approximation is valid only when M_lq is much larger than the typical partonic center-of-mass energy, and the paper's own Fig. 7 shows that for U1 and eU1 the EFT and full theory agree only for M_lq roughly above 3-4 TeV, with matching shifting even higher for higher-generation quarks. Yet the V2/eV2 exclusion contours are presented down to 2 TeV, and no direct full-theory cross-check is shown for these species because the full-theory amplitude is exactly what failed. Since IP and II dominate the high-coupling tails of the limits, an uncontrolled EFT error below the matching scale can shift the 95% CL boundaries. The paper is transparent about the workaround, but the central claim of updated limits accounting for all relevant production mechanisms is not uniformly supported for V2 and eV2.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents updated LHC exclusion limits on vector leptoquarks (U1, eU1, V2, eV2, U3) by recasting existing ATLAS and CMS searches in dimuon-plus-jets and high-mass dimuon channels. The authors combine four production mechanisms: pair production (PP), single production (SP), t-channel indirect production (IP), and indirect interference with the SM Drell-Yan background (II). They report model-independent mass limits in Table III, coupling exclusions in the mass-coupling plane in Figs. 4 and 6, two-coupling exclusions in Fig. 5, and a comparison of the full vLQ theory with an effective-operator description in Fig. 7. A distinctive feature is the inclusion of QCD-QED mixed pair production, which shifts mass limits appreciably for highly charged species, and the use of the dimuon tail to constrain couplings at large mass. For V2 and eV2, the IP and II contributions are computed in an effective-operator approximation because the full-theory interference evaluation in MadGraph fails with the authors' FeynRules models; this is stated transparently in Sec. IVF and footnote 2.","tokens_in":20658,"tokens_out":3413,"duration_ms":40704,"significance":"If the results are taken at face value, the paper provides the most complete current recast of LHC limits for vector leptoquarks, systematically combining all leading production channels and validating the dimuon-tail limits against the recent CMS non-resonant search. The explicit treatment of interference sign and the demonstration that QCD-QED mixed pair production strengthens model-independent mass limits for high-charge species are useful and clearly presented. The paper is also commendably transparent about its main technical limitation, the effective-operator workaround for V2/eV2. However, because that approximation is validated only in a mass range that does not cover the full extent of the presented contours, the central claim that the limits account for all relevant production mechanisms is not uniformly supported.","major_comments":[{"comment":"The V2 and eV2 IP and II contributions are obtained by integrating out the t-channel leptoquark and using the dimension-six operators of Table IV, as stated in Sec. IVF and footnote 2. The paper's own validation in Fig. 7 is performed only for U1 and eU1, and it shows that the full theory and the EFT agree only for M_lq ≳ 3-4 TeV. The V2/eV2 exclusion contours, however, are presented down to 2 TeV (and to 1 TeV in some panels, e.g., the lower edge of the PP-only comparison), with no full-theory cross-check for these species. Since IP and II dominate the high-coupling tails of the limits, the V2/eV2 boundaries below roughly 3-4 TeV rest on an unvalidated approximation; if the EFT overestimates or underestimates the interference there, the excluded regions would shift. I recommend either computing the full-theory IP and II for V2/eV2 with an independent matrix-element implementation or analytic expressions for benchmark masses, or restricting the asterisked IP*/II* contours and the associated exclusion statements to the validated mass range and showing only PP+SP below it.","section":null}],"minor_comments":[{"comment":"The table heading says 'model-independent mass exclusion limits on various sLQ models', but the table lists vLQ species; this should be corrected to vLQ.","section":"Table III"},{"comment":"The caption states that the exclusion limits from the effective-operator approach and the full theory are compared, but it does not mention that the comparison is shown only for U1 and eU1; please state explicitly that no full-theory validation is shown for V2 and eV2.","section":"Fig. 7"},{"comment":"The sentence 'This would give us a reasonable estimation of the exclusion limits for those vLQs, especially when they couple to the first and second generation quarks, for M_lq ≳ 3-4 TeV' should be reconciled with the figure ranges; the contours extend well below 3 TeV, so the reader cannot tell which parts of the curves are claimed to be reliable.","section":"Sec. IVF"},{"comment":"The notation 'Nobs(M_lq)/Lexp = sigma_obs(M_lq) x epsilon_exp(M_lq)' should clarify that sigma_obs is the observed upper limit on the cross section times efficiency and that the equality with the sum over topologies holds at the boundary; the current presentation is slightly ambiguous.","section":"Eq. (6)"},{"comment":"The text following Eq. (2) defines the barred quantities as evaluated at x=1, but it does not explicitly state whether a common coupling x is assumed for all contributing couplings in the PP expressions; please clarify the convention, especially for channels in which different couplings enter.","section":"Sec. II"},{"comment":"The format of the table columns is confusing: each row lists 'x Limit' three times without clear column headers. Please restructure the table so that each coupling and its extrapolated limit are labeled unambiguously.","section":"Table V"}],"recommendation":"major_revision","confidential_remarks":"The only blocking issue is the EFT approximation for V2/eV2 below the validated matching scale. The authors are transparent about the limitation, and the rest of the analysis appears technically sound, so I would not reject the paper on this basis; I would request that the V2/eV2 full-theory interference be computed at least for benchmark points, or that the contours be restricted to the validated mass range."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The short version: this is a useful and mostly careful recasting paper. It updates vector leptoquark exclusion limits by combining pair, single, indirect, and interference production for all five vLQ species that give dilepton-plus-jets final states. The genuinely new pieces are the QCD-QED mixed pair production channel, which shifts model-independent mass bounds by up to several hundred GeV for high-charge species, and the per-species sign table for interference with Drell-Yan. The paper also validates its EFT description against the full theory in the high-mass regime.\n\nWhat is done well: the U1, eU1, and U3 limits are built from a clear sum of leading-order channels with validated cut efficiencies, and the dimuon-tail results agree with the dedicated CMS non-resonant search. The interference signs for each species are concrete and easy to check. Table III is a clean update of model-independent mass limits.\n\nSoft spots, in proportion: the V2 and eV2 exclusion curves in Figs. 4(g)-(l) and 5(h)-(n) are computed with an effective-operator approximation for indirect production and interference, because the full-theory interference fails in MadGraph. That is stated plainly in Sec. IVF and footnote 2, but the paper's own Fig. 7 shows the EFT matches the full theory only for masses around 3-4 TeV and above, while the limits are drawn down to 2 TeV. So the \"all relevant production mechanisms\" claim is not uniformly supported in that lower-mass range. The authors call it a \"reasonable estimation,\" which is fair, but the caveat should survive into the published version. Minor second point: the photon-PDF uncertainty for the QCD-QED pair production is flagged but not propagated; they quote a wide range for eU1 and defer the full PDF study. That is a known limitation, not a hidden one.\n\nCitation pattern is fine; the paper builds on the authors' own TooLQit framework and scalar-LQ recasting, which is normal and acknowledged.\n\nWho gets value: anyone interpreting LHC dilepton limits in leptoquark models, especially for B-anomaly model building. It deserves a serious referee; the V2/eV2 EFT range should be probed or the contours restricted to the validated mass region, but the core of the paper is solid.\n\nRecommendation: send it to review, with attention to the V2/eV2 EFT caveat and the photon-PDF uncertainty.","headline":"Useful vLQ recasting with genuinely new QCD-QED pair production and per-species interference results, but the V2/eV2 exclusion curves rest on an EFT stand-in below the mass range where the paper validates it.","tokens_in":21151,"tokens_out":1877,"would_cite":true,"duration_ms":19206,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper argues that LHC limits on vector leptoquark masses and couplings strengthen substantially when single production, indirect t-channel exchange, and its interference with Standard Model Drell-Yan are added to pair production, and…","keywords":["vector leptoquarks","LHC exclusion limits","pair production","single production","indirect production","Drell-Yan interference","QCD-QED mixed production","effective field theory"],"falsifier":"Compute the $V_2$ and $\\tilde V_2$ indirect and interference cross sections with the full t-channel propagator, without integrating the leptoquark out, at masses of 2, 2.5, and 3 TeV for first-generation couplings, and compare the resulting 95% CL exclusion contours with the EFT-based curves; a shift larger than the analysis's stated uncertainties would move the claimed excluded regions.","tokens_in":20158,"feed_emoji":"⚛️","tokens_out":12730,"duration_ms":119099,"temperature":0.7,"pith_summary":"Vector leptoquarks are hypothetical colour-triplet bosons that couple a quark to a lepton, and their pair-production searches are usually taken as the model-independent way to bound their masses. This paper argues that the true LHC exclusion reach is considerably better, because several production modes all feed the same dimuon-plus-jets final state: pair production, single production, indirect t-channel exchange, and the interference of that exchange with the Standard Model Drell-Yan process. The interference can add to or subtract from the Standard Model background depending on the leptoquark's quantum numbers, so the improvement over pair-production-only limits is not uniform. The paper also shows that QCD-QED mixed pair production raises the model-independent mass limits, noticeably for highly charged species, and that an effective-operator description agrees with the full theory for leptoquark masses above roughly 3-4 TeV. If the paper is right, current LHC data already exclude vector leptoquarks over a wider mass-coupling region than the existing literature claims.","feed_headline":"Pair, single, and indirect channels tighten leptoquark mass limits","feed_subtitle":"Adding t-channel exchange and Drell-Yan interference shifts 95% CL exclusions by hundreds of GeV.","key_machinery":"The argument is carried by a bookkeeping scheme that classifies every contribution to the dimuon-plus-jets final state by its order in $\\alpha_s$, $\\alpha_e$, and the leptoquark coupling $x$, so that the pair-production cross section is written as $\\sigma_{PP}=\\sigma^{200}+\\sigma^{110}+\\sigma^{020}+x^2(\\sigma^{101}+\\sigma^{011})+x^4\\sigma^{002}$, with the QCD-QED mixed term $\\sigma^{110}$ coming from gluon-photon fusion and carrying the model-independent mass-shift effect. Single production is split into two-body and three-body contributions, and the nonresonant contribution is split into indirect production and its interference with the Standard Model Drell-Yan background. The other load-bearing object is the effective-operator description obtained by integrating out the t-channel leptoquark, which turns the indirect and interference amplitudes into four-fermion operators and is used to obtain the $V_2$ and $\\tilde V_2$ exclusion curves. The sign of the interference term, which is determined by the chiral structure of the leptoquark Yukawa coupling, decides whether the combined signal exceeds or falls below the pair-production-only expectation.","core_discovery":"The central claim, stated in the paper's own terms, is that a systematic combination of all vLQ production mechanisms that yield dimuon-plus-dijet events gives markedly stronger 95% CL exclusion limits in the mass-coupling plane than the pair-production-only analyses that dominate the literature, and that including the QCD-QED mixed pair-production channel shifts the model-independent mass limits by hundreds of GeV for high-charge species. The five species considered are $U_1$, $\\tilde U_1$, $V_2$, $\\tilde V_2$, and $U_3$. The interference of indirect production with Standard Model Drell-Yan can be constructive or destructive: for example, $U_1$ and $V_2$ with $L$-$R$-type couplings subtract from the background, while $\\tilde U_1$ and certain $V_2$ couplings add to it, so the size of the limit improvement depends on the species and on the chirality of the coupling. In the high-mass regime the indirect and interference contributions dominate, and the limits obtained by integrating out the t-channel leptoquark coincide with the full-theory limits for $M_{\\rm LQ}\\gtrsim 3$-$4$ TeV for couplings to first- and second-generation quarks. At large coupling $x\\simeq\\sqrt{4\\pi}$ the extrapolated maximum mass exclusions reach tens of TeV for several couplings.","pith_inferences":["If the EFT matching scale is a genuine validity boundary, then the $V_2$ and $\\tilde V_2$ exclusion curves below about 3-4 TeV should be recomputed with the full t-channel propagator before being used for model-building; the paper identifies this limitation but does not fully resolve it.","The same count-every-topology logic should transfer to other coloured mediators with dilepton-plus-jets signatures; the sign of their interference with Standard Model Drell-Yan would determine whether combined searches improve or degrade the limit.","The reported sensitivity of the QCD-QED mass shift to the photon PDF suggests that a better-determined photon PDF, or a PDF set that includes data-driven constraints, would either confirm or shrink the improved limits; this can be tested with existing LHC data.","The tens-of-TeV extrapolated limits at $x\\simeq\\sqrt{4\\pi}$ should be interpreted with a dedicated perturbative-unitarity check per coupling; without it those numbers are kinematic bounds rather than rigorous exclusions."],"forward_implications":["Nominal model-independent 95% CL mass limits rise by up to a few hundred GeV once QCD-QED mixed pair production is included; the largest shifts occur for the highest-charge species, with photon-PDF uncertainties quoted as large as or larger than the shift.","Because indirect production and its interference fall off more slowly with mass than resonant production, the high-mass dimuon tail sets coupling limits out to several TeV; extrapolating the coupling to the perturbative boundary $x\\simeq\\sqrt{4\\pi}$ gives maximum mass exclusions of tens of TeV for some couplings.","The direction of the improvement is set by the interference sign: destructively interfering species such as $U_1$ and $V_2$ gain most from the dimuon-tail analysis, while constructively interfering species such as $\\tilde U_1$ keep the direct-search limits as the stronger constraint.","For first- and second-generation quark couplings the effective-operator and full-theory exclusions agree once $M_{\\rm LQ}\\gtrsim 3$-$4$ TeV, so the EFT-based curves are reliable in that high-mass region; the matching mass moves higher for third-generation couplings."],"supporting_citations":[{"why":"Provides the observed dimuon-plus-dijet event counts and selection-cut definitions used for recasting all production topologies.","marker":"[58]"},{"why":"Establishes the combined-signal method (PP+SP+IP+II) for scalar leptoquarks that this paper extends to vector leptoquarks.","marker":"[29]"},{"why":"Defines the single-production counting and the subtraction of overlapping two-body and three-body contributions used here.","marker":"[36]"},{"why":"Supplies the chi-squared method for extracting limits from the high-mass dimuon invariant-mass tail including interference.","marker":"[37]"},{"why":"Provides the high-mass dimuon invariant-mass spectrum from which the 2-sigma coupling limits are derived.","marker":"[68]"},{"why":"Supplies the leptoquark model files used for Monte Carlo event generation and the package that will incorporate the updated limits.","marker":"[55]"},{"why":"Gives the published t-channel leptoquark exchange limits that the paper's dimuon-based limits are checked against.","marker":"[69]"},{"why":"Catalogues the vLQ species, quantum numbers, and interactions that define the model space.","marker":"[8]"}],"fun_headline_variants":["Leptoquark limits tighten with Drell-Yan interference","Combined channels sharpen LHC leptoquark exclusion bounds","QCD-QED mixed pair production shifts leptoquark mass limits","Indirect leptoquark production and interference refine LHC exclusions","Tighter leptoquark mass exclusions from full LHC production set"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the effective-operator approximation used for the $V_2$ and $\\tilde V_2$ indirect and interference contributions is accurate down to the lowest masses at which limits are drawn (about 2 TeV), even though the paper's own comparison shows the EFT and the full theory agree only around 3-4 TeV for first- and second-generation couplings.","fun_headline_variants_meta":{"raw":{"variants":["Leptoquark limits tighten with Drell-Yan interference","Combined channels sharpen LHC leptoquark exclusion bounds","QCD-QED mixed pair production shifts leptoquark mass limits","Indirect leptoquark production and interference refine LHC exclusions","Tighter leptoquark mass exclusions from full LHC production set"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000236,"raw_usage":{"total_tokens":1522,"prompt_tokens":983,"completion_tokens":539,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":599,"completion_tokens_details":{"reasoning_tokens":450}},"tokens_in":599,"tokens_out":539,"duration_ms":5866,"temperature":1.0,"reasoning_tokens":450,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T18:15:40.218166+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Compute the $V_2$ and $\\tilde V_2$ indirect and interference cross sections with the full t-channel propagator, without integrating the leptoquark out, at masses of 2, 2.5, and 3 TeV for first-generation couplings, and compare the resulting 95% CL exclusion contours with the EFT-based curves; a shift larger than the analysis's stated uncertainties would move the claimed excluded regions.","supporting_citations":[{"cited_title":"Fresh look at the lhc limits on scalar leptoquarks,","cited_arxiv_id":null,"evidence_quote":"Provides the observed dimuon-plus-dijet event counts and selection-cut definitions used for recasting all production topologies."},{"cited_title":"LHC Study of Third-Generation Scalar Leptoquarks with Machine-Learned Likelihoods","cited_arxiv_id":"2309.05407","evidence_quote":"Establishes the combined-signal method (PP+SP+IP+II) for scalar leptoquarks that this paper extends to vector leptoquarks."}],"review_version":2}