{"id":"63ed6a99-14f0-4985-b9d7-f40eb25a3348","arxiv_id":"1908.06244","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Assuming b to u and b to c transitions share the same vector new physics, the paper predicts branching ratios, ratios, asymmetries, and polarizations for B_s to (K,K*) tau nu and B to pi tau nu.","lead":"This paper predicts how often B_s and B mesons decay into a kaon or pion plus a tau lepton and neutrino, assuming the same new physics pattern seen in other B meson decays. It provides ratios and polarization observables that could distinguish two vector new physics scenarios.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"P_tau discrimination between V_L and \\tilde V_L is not supported by the paper's own Table III: for B_s->K tau nu the \\tilde V_L band lies entirely inside the SM band.","rationale":"The paper is a standard EFT phenomenology study with an explicitly stated model-dependent assumption; that assumption is a limitation, not an internal error, so it is not the most load-bearing flaw. The strongest claim, that P_tau(q^2) can easily differentiate V_L and \\tilde V_L, is contradicted by the paper's own Table III: the \\tilde V_L integrated P_tau range for B_s->K tau nu is fully contained in the SM range, and the other modes show large overlap. The paper offers no quantitative measure of discrimination power. A concrete computation of binned P_tau envelopes would settle whether the claim survives. Eq. (1)'s c-quark fields in a b->u Lagrangian also need an erratum, but this is likely typographical. I agree with the reader's CONDITIONAL verdict; the paper should either provide a quantitative separation analysis or soften the \"easily differentiate\" claim, but the branching-ratio predictions and NP parameter scan remain useful.","tokens_in":9612,"tokens_out":12252,"duration_ms":121541,"concrete_test":"Using the same random scan and inputs that produced Table III and Fig. 4, recompute the 1 sigma envelopes of P^tau(q^2) for the V_L scenario (identical to SM) and the \\tilde V_L scenario, bin by bin in q^2. Compute the overlap fraction of the two envelopes in each bin. If for B_s->K tau nu the \\tilde V_L envelope is contained in the SM envelope in all bins, as the integrated Table III suggests, then the statement that P^tau can easily differentiate V_L and \\tilde V_L is unsupported. A stronger check is to fold in a projected experimental uncertainty (for example, 5% per bin) and evaluate the statistical separation (chi-square or CL_s) between the two hypotheses, reporting the q^2 range where separation reaches 2 sigma.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central discriminator claim in Section III.B is that \"the measurement of P^tau(q^2) can easily differentiate V_L and \\tilde V_L NP contributions.\" Because V_L does not affect tau polarization, the V_L prediction is the SM band. The paper's own numbers do not support an easy separation. Table III gives the integrated \\langle P^tau\\rangle ranges for \\tilde V_L: [-0.026, 0.217] (B_s->K tau nu), [0.249, 0.513] (B_s->K* tau nu), and [0.117, 0.315] (B->pi tau nu). The SM 1 sigma ranges from Table II are [-0.035, 0.279], [0.458, 0.603], and [0.195, 0.385], respectively. For B_s->K tau nu the \\tilde V_L band is a subset of the SM band, so any integrated measurement consistent with SM is also consistent with \\tilde V_L. For the other two modes the overlap is substantial. The q^2-dependent plots (Fig. 4) may separate in some bins, but no quantitative separation test or experimental sensitivity estimate is provided. Additionally, Eq. (1) is labelled b->u but contains c-quark fields in the operators, which is a formal inconsistency; even if typographical, it leaves the central Lagrangian ambiguous. The load-bearing concern is the unsupported \"easily differentiate\" claim, not the explicitly admitted model-dependent assumption.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper studies the semileptonic decays B_s -> (K,K*) tau nu and B -> pi tau nu in an effective field theory with vector new physics (NP) couplings V_L and tilde V_L. The authors impose 2 sigma constraints from RD, RD*, RJ/psi, and R_l^pi to obtain allowed ranges for these couplings, using an explicitly stated assumption that b -> u and b -> c transitions share a common NP pattern. They then compute branching fractions, ratios R, forward-backward asymmetries, tau polarization, and convexity parameters for the target modes in the SM and in the presence of V_L and tilde V_L. The central claim is that these modes can probe the NP implied by the B anomalies, and that the tau polarization P_tau(q^2) can distinguish the V_L and tilde V_L scenarios.","tokens_in":9881,"tokens_out":2640,"duration_ms":26856,"significance":"If the underlying model-dependent assumption is accepted, the paper provides a straightforward extension of the standard EFT analysis to a set of decay modes that are experimentally accessible at LHCb and Belle II. The numerical results for integrated and q^2-dependent observables, especially the tau polarization and convexity parameter, are potentially useful predictions. The authors correctly propagate existing constraints and clearly separate SM and NP expectations. However, the significance is limited by the explicitly acknowledged b -> u / b -> c equality, which is not derived or tested, and by the absence of any quantitative sensitivity estimate for the claimed discriminating power of P_tau. The paper does not ship code or machine-checked proofs, but the calculation follows standard, reproducible EFT machinery.","major_comments":[{"comment":"The effective Lagrangian is labeled as the b -> u transition but contains c-quark fields in every operator (e.g., \\bar c_L \\gamma^\\mu b_L). This is a formal inconsistency in the central definition of the theory. If it is a typographical error, the fields should be u quarks; if not, the relation of this Lagrangian to the b -> u decays studied in the paper and to the b -> c constraints used for the fit is unclear. The authors must correct this and confirm that all subsequent expressions use the intended quark fields.","section":"Section II.A, Eq. (1)"},{"comment":"The claim that \"the measurement of P^tau(q^2) can easily differentiate V_L and tilde V_L NP contributions\" is not supported by the paper's own integrated results. Since V_L does not alter tau polarization, the V_L prediction for P_tau is the SM band. Table III shows that the tilde V_L integrated range for B_s -> K tau nu is [-0.026, 0.217], while the SM 1 sigma range is [-0.035, 0.279]; the tilde V_L band is a strict subset of the SM band. For B_s -> K* tau nu and B -> pi tau nu the overlap is also large. The q^2-dependent plots in Fig. 4 show some separation in certain bins, but no quantitative separation test or experimental sensitivity estimate is provided. The authors should either soften the \"easily differentiate\" claim or add a quantitative discrimination study, such as chi^2 or expected exclusion power with realistic uncertainties.","section":"Section III.B, first bullet; Table III; Fig. 4"},{"comment":"The entire NP parameter space for the target modes relies on the \"strict model dependent assumption\" that b -> u and b -> c transitions have the same NP Wilson coefficients V_L and tilde V_L. This assumption is explicitly admitted, but it is load-bearing: without it, the RD, RD*, and RJ/psi constraints cannot be transferred to B_s -> (K,K*) tau nu and B -> pi tau nu. The paper should state more prominently in the conclusions that all predictions are conditional on this equality, and ideally investigate how the allowed ranges change under modest violations of the assumption (for example, allowing separate b -> u and b -> c coefficients). Without such a stability check, the central prediction is only as strong as the untested assumption.","section":"Section I and abstract; Section III.B"}],"minor_comments":[{"comment":"The experimental value for B(B -> tau nu) is quoted as (1.09 ± 2.4) × 10^-4; the uncertainty likely should be 0.24 rather than 2.4, and the notation should be fixed.","section":"Table I"},{"comment":"The word \"psudoscalar\" appears to be a typo for \"pseudoscalar\".","section":"Section II.A"},{"comment":"The figures contain duplicated panels in Fig. 2 and some labels are not legible in the printed version; the authors should ensure each panel is uniquely labeled and referenced in the text.","section":"Section III, figures"},{"comment":"The ratio R is defined generically, but the normalization mode is later specified as l = mu. It would be clearer to define R with the muon mode explicitly in Eq. (2).","section":"Section II.A, Eq. (2)"},{"comment":"The text states a \"combined deviation of 3.78 sigma\" for RD and RD* but the table lists RD and RD* separately without showing the combined uncertainty; a reference to the source of the combined significance would be helpful.","section":"Section I, Table I"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the scope of the journal and the calculation is straightforward EFT, but the central discriminative claim is contradicted by the paper's own integrated numbers. The manuscript also contains a formal inconsistency in Eq. (1) that must be resolved. I recommend major revision rather than rejection because the issues are fixable: correcting the typo, softening or quantifying the P_tau discrimination claim, and clarifying the conditional nature of the b -> u / b -> c assumption."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"First thing you should know: this is a modest but legitimate extension of an earlier EFT analysis. The genuinely new bits are the first integrated tau-polarization and convexity predictions for B_s->(K,K*)tau nu and B->pi tau nu, plus the correlated V_L / tilde V_L constraints propagated from RD, RD*, RJ/psi, and R_l^pi under an explicitly admitted b->u/b->c common-NP assumption. The machinery is standard and mostly inherited from their previous paper [20], which is fine.\n\nWhat it does well: SM predictions are laid out clearly, the scan over CKM and form-factor inputs is described, and they are upfront about the model-dependence of the main premise. The q^2 plots give a useful visual sense of where NP could show up in these modes.\n\nThe soft spots, in order of seriousness. First, the headline discriminator claim -- that measuring P^tau(q^2) would \"easily differentiate\" V_L from tilde V_L -- is not supported by their own Table III. For B_s->K tau nu the tilde V_L band is entirely inside the SM 1-sigma band, and for the other two modes the overlap is substantial. The q^2-dependent plots in Fig. 4 may separate in some bins, but no quantitative separation test or sensitivity estimate is provided. That claim should be softened or backed with a bin-level analysis.\n\nSecond, Eq. (1) is labeled b->u but the operators contain c-quark fields. Likely a typo from the b->c version, but it leaves the central Lagrangian ambiguous and must be fixed.\n\nThird, the b->u/b->c equality is a strong assumption. They call it \"strict model dependent\" in the abstract, so it is not hidden, but the NP bands for the target decays follow only if that equality holds. A reader who doesn't buy the assumption is left with much weaker statements.\n\nMinor: no code or complete input tables are shipped, so the scan is not independently reproducible. The reference list is a bit dated for 2019, but that is normal for this subfield.\n\nOverall, this is a citable, useful phenomenology note for people working on B anomalies, and it deserves a serious referee. The central calculation is probably right; the discriminator claim is the main thing that needs revision.","headline":"Useful extension of an existing EFT analysis with first predictions for new tau observables, but the headline discriminator claim is not supported by the paper's own tables.","tokens_in":10475,"tokens_out":2064,"would_cite":true,"duration_ms":19837,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["14.40.Nd","13.20.He","13.20.-v"],"model":"deepseek-v4-flash","headline":"The paper claims that under a common new-physics pattern for $b\\to u$ and $b\\to c$ transitions, the $\\tau$ modes $B_s\\to(K,K^*)\\tau\\nu$ and $B\\to\\pi\\tau\\nu$ deviate from the Standard Model, and measuring $P^\\tau(q^2)$ can tell $V_L$ and…","keywords":["B meson decays","semileptonic decays","tau polarization","lepton flavor universality","b to u transitions","b to c transitions","effective field theory","new physics"],"falsifier":"Measure the $q^2$-dependent tau longitudinal polarization $P^\\tau(q^2)$ in $B\\to\\pi\\tau\\nu$ or $B_s\\to K\\tau\\nu$: $\\tilde{V}_L$ pushes it outside the Standard-Model band, while $V_L$ leaves it inside. A high-statistics measurement matching the Standard Model would rule out $\\tilde{V}_L$; one that misses both predicted bands would falsify the shared-pattern assumption.","tokens_in":9336,"feed_emoji":"⚛️","tokens_out":11120,"duration_ms":93795,"temperature":0.7,"pith_summary":"This paper claims that known hints of lepton-flavor non-universality in $b\\to c$ and $b\\to u$ semileptonic $B$ decays, if they have a common origin, make concrete predictions for $\\tau$ modes that have not yet been measured: $B_s\\to K\\tau\\nu$, $B_s\\to K^*\\tau\\nu$, and $B\\to\\pi\\tau\\nu$. Using an effective field theory with two vector-type new-physics couplings, $V_L$ and $\\tilde{V}_L$, the authors fit the allowed parameter space from $R_D$, $R_{D^*}$, $R_{J/\\psi}$, and $R_\\pi^l$ at $2\\sigma$ and propagate it to these decays. They find that $V_L$ shifts the branching ratios and ratios $R(q^2)$ upward, while $\\tilde{V}_L$ also shifts the tau longitudinal polarization $P^\\tau(q^2)$; they state that measuring $P^\\tau(q^2)$ can easily differentiate the two couplings. The paper also reports averaged polarization and convexity values for the first time for these modes. A sympathetic reader would care because these are complementary observables that could confirm or reject the common new-physics explanation of the $B$ anomalies.","feed_headline":"One tau-polarization curve separates two new-physics couplings","feed_subtitle":"If b→u and b→c anomalies share a cause, three tau-modes should deviate, and P^τ tells which coupling is real.","key_machinery":"The engine of the paper is the effective Lagrangian for $b\\to u\\,\\ell\\nu$ transitions with vector-type new-physics couplings, Eq. (1), which introduces the Wilson coefficients $V_L$, $V_R$, $\\tilde{V}_L$, and $\\tilde{V}_R$; only $V_L$ and $\\tilde{V}_L$ are kept. The analysis combines this with the standard machinery of three-body semileptonic decay distributions for a pseudoscalar or vector meson final state, producing the $q^2$-dependent differential branching ratio, the ratio of branching ratios $R=B(B_q\\to M\\tau\\nu)/B(B_q\\to M\\ell\\nu)$, the forward-backward asymmetry $A_{FB}^\\ell$, the charged-lepton polarization $P^\\ell$, and the convexity $C_F^\\ell$. A $2\\sigma$ scan over the measured $R_D$, $R_{D^*}$, $R_{J/\\psi}$, and $R_\\pi^l$ maps out the allowed $V_L$ and $\\tilde{V}_L$ regions, which are then propagated into the three $\\tau$ modes. The discriminative step is that $V_L$ and $\\tilde{V}_L$ produce nearly identical rate predictions but different $P^\\tau(q^2)$, so polarization acts as the distinguishing observable.","core_discovery":"The central claim is that the $b\\to u$ transitions $B_s\\to (K,K^*)\\tau\\nu$ and $B\\to\\pi\\tau\\nu$ are not just bystanders in the flavor anomalies: under the assumption that $b\\to u$ and $b\\to c$ decays share the same new-physics pattern, the existing $R_D$, $R_{D^*}$, $R_{J/\\psi}$, and $R_\\pi^l$ constraints force the Wilson coefficients $V_L$ and $\\tilde{V}_L$ into ranges that produce visible deviations from the Standard Model in the $\\tau$ modes. In the $V_L$ scenario, the differential branching ratio and $R(q^2)$ deviate while angular observables $A_{FB}^\\tau$, $P^\\tau$, and $C_F^\\tau$ stay SM-like; in the $\\tilde{V}_L$ scenario the same rate observables deviate and, additionally, $P^\\tau(q^2)$ shifts. The paper's explicit conclusion is that a measurement of $P^\\tau(q^2)$ can easily differentiate $V_L$ and $\\tilde{V}_L$ new-physics contributions.","pith_inferences":["If measurements later show $P^\\tau(q^2)$ tracking the Standard Model while rates deviate, that would single out $V_L$ and effectively exclude the right-handed-neutrino vector coupling in this setup.","The same scan could be extended to other $b\\to u$ tau modes, such as baryonic or excited-meson final states, where the $V_L$/$\\tilde{V}_L$ rate degeneracy may be broken differently.","If independent fits of the $b\\to u$ and $b\\to c$ sectors disagree, that would signal that the common-pattern assumption is too strong and that new physics distinguishes the two transitions."],"forward_implications":["With $V_L$ constrained by the anomalies, the $q^2$-dependent branching ratios and $R(q^2)$ for $B_s\\to K\\tau\\nu$, $B_s\\to K^*\\tau\\nu$, and $B\\to\\pi\\tau\\nu$ rise above their Standard-Model bands.","With $\\tilde{V}_L$, the same rate observables deviate and the averaged tau polarization changes, for example $\\langle P^\\tau\\rangle=[-0.026,0.217]$ for $B_s\\to K\\tau\\nu$ within the allowed $2\\sigma$ range.","A measurement of $P^\\tau(q^2)$ can distinguish $V_L$ from $\\tilde{V}_L$, since only the right-handed-neutrino coupling shifts the polarization.","These three modes complement $R_D$, $R_{D^*}$, and $R_{J/\\psi}$ as independent tests of the same new physics."],"supporting_citations":[{"why":"Provides the measured $R_D$ and $R_{D^*}$ world averages whose $2\\sigma$ constraints bound $V_L$ and $\\tilde{V}_L$.","marker":"[12–16]"},{"why":"Provides the measured $R_{J/\\psi}$ ratio used as an additional constraint in the scan.","marker":"[17]"},{"why":"Provides the world-average $R_\\pi^l$ input used to constrain the $b\\to u$ sector.","marker":"[11]"},{"why":"Provides the effective Lagrangian with vector-type new-physics couplings that defines $V_L$ and $\\tilde{V}_L$.","marker":"[19]"},{"why":"Provides the three-body differential decay distributions and observable definitions for $B\\to(P,V)\\ell\\nu$ used in the calculations.","marker":"[20]"},{"why":"Supplies the Standard-Model $R_D$ predictions that define the anomaly baseline for the $b\\to c$ sector.","marker":"[1–4]"},{"why":"Supplies the Standard-Model $R_{D^*}$ predictions used as the benchmark in the fit.","marker":"[5–8]"},{"why":"Supplies the Standard-Model $R_{J/\\psi}$ range used to compare with the measured value.","marker":"[9]"}],"fun_headline_variants":["Tau polarization pinpoints new physics in B_s and B decays","Pτ measurement resolves vector coupling ambiguity in B→τν","Angular observable Pτ breaks new physics degeneracy","One tau polarization curve separates new physics scenarios","B_s and B tau decays: polarization distinguishes NP couplings"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the $b\\to u$ and $b\\to c$ decay sectors share the same new-physics pattern; if the two sectors are not aligned, the predicted $V_L$ and $\\tilde{V}_L$ bands for $B_s\\to(K,K^*)\\tau\\nu$ and $B\\to\\pi\\tau\\nu$ do not follow from the fitted anomalies.","fun_headline_variants_meta":{"raw":{"variants":["Tau polarization pinpoints new physics in B_s and B decays","Pτ measurement resolves vector coupling ambiguity in B→τν","Angular observable Pτ breaks new physics degeneracy","One tau polarization curve separates new physics scenarios","B_s and B tau decays: polarization distinguishes NP couplings"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000731,"raw_usage":{"total_tokens":3266,"prompt_tokens":933,"completion_tokens":2333,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":549,"completion_tokens_details":{"reasoning_tokens":2253}},"tokens_in":549,"tokens_out":2333,"duration_ms":19315,"temperature":1.0,"reasoning_tokens":2253,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T12:52:27.490371+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the $q^2$-dependent tau longitudinal polarization $P^\\tau(q^2)$ in $B\\to\\pi\\tau\\nu$ or $B_s\\to K\\tau\\nu$: $\\tilde{V}_L$ pushes it outside the Standard-Model band, while $V_L$ leaves it inside. A high-statistics measurement matching the Standard Model would rule out $\\tilde{V}_L$; one that misses both predicted bands would falsify the shared-pattern assumption.","supporting_citations":[{"cited_title":"Patrignani et al","cited_arxiv_id":null,"evidence_quote":"Provides the world-average $R_\\pi^l$ input used to constrain the $b\\to u$ sector."},{"cited_title":"Dutta, A","cited_arxiv_id":null,"evidence_quote":"Provides the effective Lagrangian with vector-type new-physics couplings that defines $V_L$ and $\\tilde{V}_L$."},{"cited_title":"Rajeev and R","cited_arxiv_id":null,"evidence_quote":"Provides the three-body differential decay distributions and observable definitions for $B\\to(P,V)\\ell\\nu$ used in the calculations."}],"review_version":1}