{"id":"3f8b53a8-12b2-4da6-8d50-21866719713b","arxiv_id":"1908.06243","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Using vector and scalar new physics couplings fit to R_D and R_D*, the authors predict B_s to D_s tau nu observables and find tau polarization distinguishes two vector scenarios.","lead":"A physics paper predicts new observable signatures in the decay B_s to D_s tau nu under the assumption that recent B meson anomalies come from new physics. It finds that tau polarization could distinguish two new physics scenarios, making this channel a useful future test.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The scalar exclusion claim is not established: the Fig. 1 scan only explores real Wilson coefficients, so complex phases could allow scalar NP to survive the B_c→τν bound.","rationale":"The reader's weakest_assumption identifies the same load-bearing issue: the paper does not state that the NP Wilson coefficients are real, yet Fig. 1 scans only real coefficient pairs. I find this concern genuinely load-bearing for the paper's headline scalar-exclusion claim, because that claim depends entirely on the scanned parameter space. Complex phases introduce new interference paths in B_c→τν that could allow scalar coefficients to satisfy the 30% branching-ratio bound while still fitting R_D and R_D*. The reader's CONDITIONAL verdict already accounts for this by flagging the unstated real-coupling assumption, so I do not propose changing the verdict. The internal R_J/ψ discrepancy (abstract says >2σ, introduction says 1.3σ) and the absence of numerical details are noted but are presentation issues rather than the central logical soft spot. My proposed test directly probes the region of parameter space the paper omits and would settle whether the scalar exclusion is a real result or an artifact of the real-plane scan.","tokens_in":3810,"tokens_out":6495,"duration_ms":72708,"concrete_test":"Re-run the Fig. 1 scan with complex couplings: sample |S_L|,|S_R| in [0,2] and phases in [0,2π), impose R_D and R_D* in their 1σ ranges and BR(B_c→τν)≤0.30 using the same lattice form factors and the expressions from Ref. [17]. If any nonzero-volume region in the complex (S_L,S_R) plane survives all constraints, the conclusion must be weakened from 'scalar NP couplings are ruled out' to 'the real scalar couplings sampled in Fig. 1 are excluded.' If no region survives, the concern is settled and the original conclusion stands.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section IV concludes 'only vector type NP couplings satisfy the B(B_c→τν) constraint whereas the scalar type NP couplings are ruled out.' The support for this conclusion is the parameter scan in Fig. 1. The axes are labeled with the coefficient pairs (V_L,V_R), (~V_L,~V_R), (S_L,S_R), (~S_L,~S_R), so the scan is over real, two-dimensional coefficient planes. The effective Lagrangian (1) does not restrict the Wilson coefficients to be real, and the text never states such a restriction. For complex coefficients, the decay amplitudes contain interference terms that are not captured by scanning real coefficient pairs. In particular, in B_c→τν the scalar operators S_L and S_R both contribute to the same scalar hadronic current; with independent phases their contributions and the SM amplitude can interfere destructively. The real-plane scan therefore does not cover the EFT parameter space relevant to the B_c bound. As a result, the unqualified statement that scalar NP couplings are ruled out is stronger than the shown calculation supports. The separate claim that P_τ(q^2) distinguishes the (V_L,V_R) and (~V_L,~V_R) scenarios is less exposed to this issue, but it too would need a complex-phase check before the paper can claim full coverage.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper studies the semileptonic decay B_s -> D_s tau nu as a probe of the b -> c tau nu transitions that underlie the R_D and R_D* anomalies. Using an effective Lagrangian with vector and scalar new-physics Wilson coefficients, the authors impose 1 sigma constraints from the measured R_D and R_D* ratios and from B(B_c -> tau nu) <= 30%, then scan four two-coupling scenarios: (V_L,V_R), (V~_L,V~_R), (S_L,S_R), and (S~_L,S~_R). They predict the differential branching ratio, R(q^2), the forward-backward asymmetry, the tau polarization fraction, and the convexity parameter for B_s -> D_s tau nu, and they conclude that only vector-type couplings survive the B_c -> tau nu constraint while scalar-type couplings are ruled out. They also propose P_tau(q^2) as a discriminator between the (V_L,V_R) and (V~_L,V~_R) scenarios.","tokens_in":4032,"tokens_out":7469,"duration_ms":78164,"significance":"If the central claim holds, the paper strengthens vector-type new-physics explanations of the R_D and R_D* anomalies and identifies an observable that can distinguish left- and right-handed neutrino scenarios. A notable strength is that the B_s -> D_s tau nu observables are predictions, not inputs to the fit, so the exercise is a genuine forward test and not circular. The use of lattice QCD form factors from Ref. [14] and the consistent extension of the companion formalism [17] are also positive features. The significance is, however, conditional: the main exclusion statement depends on an unstated assumption that the Wilson coefficients are real, and the paper provides little of the underlying decay-rate machinery, so the robustness of the conclusion cannot be fully assessed from the manuscript alone.","major_comments":[{"comment":"The conclusion that scalar NP couplings are ruled out relies on the scans in Fig. 1, whose axes are the real two-dimensional planes (S_L,S_R) and (S~_L,S~_R). Equation (1) does not restrict the Wilson coefficients to be real, and the text nowhere states such a restriction. For complex coefficients, the scalar contributions to B_c -> tau nu can interfere with the SM amplitude and with each other with independent phases, so destructive interference can reduce the branching ratio below the 30% bound even for large |S_L| and |S_R|. The real-plane scan therefore does not cover the EFT parameter space relevant to the bound, and the unqualified statement that scalar couplings are ruled out is stronger than the shown calculation supports. The authors should either state and justify the real-coefficient assumption or extend the scan to complex phases, or provide an analytic argument that phases cannot relax the bound.","section":"Section IV and Fig. 1"},{"comment":"The paper does not display the explicit expressions for dGamma/dq^2, the angular observables, or the B_c -> tau nu branching ratio in terms of the Wilson coefficients; all of these are imported from Refs. [17,18]. Since the central claim of Section IV is that the B_c -> tau nu constraint excludes scalar couplings, at least the B_c -> tau nu decay-rate formula and the definition of the 30% bound should be shown, so that the exclusion and the allowed ranges in Table II can be checked from the material in this paper alone.","section":"Sections II and III"},{"comment":"Equation (2) defines R(q^2) as B(B_s -> D_s tau nu)/B(B_s -> D_s l nu), which is a q^2-independent ratio of total branching fractions, yet the text and Fig. 2 treat R(q^2) as a q^2-dependent observable. The intended quantity is presumably the differential ratio [dGamma_tau/dq^2]/[dGamma_l/dq^2], with the total ratio obtained by integrating numerator and denominator separately. This definition should be corrected, since R(q^2) is one of the main predicted quantities.","section":"Section II, Eq. (2)"},{"comment":"The statement that 'only vector type NP couplings satisfy the B(B_c -> tau nu) constraint' is broader than the scenarios actually scanned. Only four isolated two-coupling pairs are considered at a time; simultaneous vector and scalar couplings, or mixtures of left- and right-handed neutrino operators, are not examined. The conclusion should be qualified to the pair scenarios studied unless a general argument is provided that no mixed scenario can satisfy all constraints.","section":"Section IV"}],"minor_comments":[{"comment":"The abstract states that the R_J/psi measurement is 'more than 2 sigma' away from the standard model, while Section I reports '1.3 sigma'. These numbers should be harmonized, since the R_J/psi anomaly is cited as motivation.","section":"Abstract and Section I"},{"comment":"The caption does not indicate which sub-panels correspond to which NP scenario or what the shaded regions and contours represent; the figure should be self-explanatory with labeled panels and a legend.","section":"Fig. 1 caption"},{"comment":"The first column is labeled 'B%' without a subscript; for clarity it should read B(B_s -> D_s tau nu) in percent or otherwise identify the mode explicitly.","section":"Table II"},{"comment":"The convexity parameter C_F(q^2) is written as a second derivative with respect to cos theta but the evaluation point is not specified; the standard definition evaluates at cos theta = 0, and this should be stated.","section":"Section II, Eq. (2)"}],"recommendation":"major_revision","confidential_remarks":"The paper is very short and depends heavily on the companion reference [17] for its formalism; the editor may wish to consider whether a standalone letter is appropriate without including at least the central decay-rate formulas. The abstract/introduction discrepancy on R_J/psi should be corrected. I do not see grounds for concern about novelty disclosure or citation practice."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a decent, short application of the authors' earlier effective-Lagrangian framework to B_s→D_s τν, and it gives a genuinely useful observable—τ polarization—to separate the (V_L,V_R) and (~V_L,~V_R) scenarios. The forward predictions for branching ratios and polarization are the real content, and they are not circular: the B_s→D_s τν observables are never fed back into the fit to R_D and R_D*. That part holds up.\n\nThe soft spot is the conclusion. The text says scalar NP couplings are ruled out by the B(B_c→τν) constraint, but the support is a scan over real two-dimensional planes for (S_L,S_R) and (~S_L,~S_R). The effective Lagrangian (1) does not set the Wilson coefficients to real numbers, and the paper never states that restriction. With complex phases, scalar and SM amplitudes can interfere destructively in B_c→τν, so the real-plane scan does not exclude scalar NP. The claim needs to be restricted to real coefficients, or the scan needs to be repeated over phases. This is a load-bearing flaw for the conclusion, not a minor typo.\n\nAlso, the paper does not show its decay-rate formulas—it points to Ref. [17]—and gives no numerical code or tables of form factor inputs. That makes independent verification needlessly hard. The abstract says R_J/ψ is more than 2σ from SM; the introduction says 1.3σ. One of them is wrong; that kind of inconsistency in a short paper is annoying and should have been caught.\n\nOn balance: the vector-scenario predictions and the P_τ discriminating power are likely correct and useful to the semileptonic B community. The scalar exclusion, as stated, is not established. This paper deserves a serious referee, but the referee should send it back for a clear statement about the reality assumption and a softened or properly qualified scalar conclusion. I'd put it in a reading group if you want to discuss how parameter scans can overstate exclusions, but I wouldn't cite it in its current form.","headline":"Useful complementary predictions for B_s→D_s τν, but the scalar-operator exclusion is overclaimed because the parameter scan ignores complex phases.","tokens_in":4619,"tokens_out":2284,"would_cite":false,"duration_ms":23249,"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":"If scalar new-physics couplings are ruled out by the $B_c \\to \\tau \\nu$ bound, the $\\tau$ polarization in $B_s \\to D_s \\tau \\nu$ decays becomes the observable that separates the two surviving vector scenarios.","keywords":["lepton flavor universality","B_s to D_s tau nu decay","R_D anomaly","semileptonic B decays","effective Lagrangian","tau polarization","B_c to tau nu constraint"],"falsifier":"Compute $\\mathcal{B}(B_c \\to \\tau \\nu)$ as a function of a complex phase for a scalar coupling, say $S_L = |S_L| e^{i\\phi}$, using points that fit $R_D$ and $R_{D^*}$ at $1\\sigma$; if any such point predicts $\\mathcal{B}(B_c \\to \\tau \\nu)$ below $30\\%$, the paper's central exclusion of scalar new physics is falsified.","tokens_in":3560,"feed_emoji":"⚛️","tokens_out":8176,"duration_ms":70178,"temperature":0.7,"pith_summary":"This paper studies whether new physics invoked to explain the $R_D$ and $R_{D^*}$ anomalies, which disagree with the standard model at about $4.1\\sigma$, also shows up in the related $B_s \\to D_s \\tau \\nu$ decay. Using a model-independent effective Lagrangian with vector and scalar couplings, it finds that scalar new-physics couplings are excluded by the upper bound on $\\mathcal{B}(B_c \\to \\tau \\nu)$, while vector couplings survive. It then predicts the branching ratio, $R_{D_s}$, forward-backward asymmetry, $\\tau$ polarization, and convexity parameter for $B_s \\to D_s \\tau \\nu$ in the surviving scenarios. The payoff is that the $q^2$-dependent $\\tau$ polarization cleanly separates the two vector scenarios, so this decay mode can serve as a test bed for the lepton-flavor-universality anomalies.","feed_headline":"Only vector new physics survives the B_c to tau nu bound","feed_subtitle":"Tau polarization in B_s to D_s tau nu can tell which vector scenario is real.","key_machinery":"The machinery is an effective Lagrangian for the $b \\to c \\tau \\nu$ transition that adds to the standard-model operator eight new-physics Wilson coefficients: vector couplings $V_L$, $V_R$, $\\tilde{V}_L$, $\\tilde{V}_R$ and scalar couplings $S_L$, $S_R$, $\\tilde{S}_L$, $\\tilde{S}_R$. The argument is driven by two constraints: the measured $R_D$ and $R_{D^*}$ restrict the allowed coupling planes, and the $\\mathcal{B}(B_c \\to \\tau \\nu) \\le 30\\%$ bound eliminates the scalar planes. The $B_s \\to D_s$ form factors enter from lattice QCD, and from the resulting amplitudes the paper computes $q^2$-dependent observables including the $\\tau$ polarization that distinguishes the surviving vector scenarios.","core_discovery":"The central claim is that after imposing the $1\\sigma$ $R_D$ and $R_{D^*}$ measurements along with the LEP constraint $\\mathcal{B}(B_c \\to \\tau \\nu) \\le 30\\%$, only the vector new-physics couplings $(V_L, V_R)$ and $(\\tilde{V}_L, \\tilde{V}_R)$ are allowed; the scalar couplings $(S_L, S_R)$ and $(\\tilde{S}_L, \\tilde{S}_R)$ are ruled out. Within the surviving vector scenarios, the differential branching fraction and $R_{D_s}(q^2)$ deviate noticeably from the standard model, and the $\\tau$ polarization fraction $P_\\tau(q^2)$ takes different ranges in the two scenarios, making it the discriminating observable.","pith_inferences":["The exclusion of scalar couplings is derived on real coupling planes; allowing complex phases could change the interference with the standard model in $B_c \\to \\tau \\nu$ and possibly reopen the scalar window.","The same effective-Lagrangian observables could be adapted to other $b \\to c \\tau \\nu$ modes, such as $B_c \\to J/\\psi \\, \\tau \\nu$ or $\\Lambda_b \\to \\Lambda_c \\tau \\nu$, where polarization measurements might sharpen the same discrimination.","If the $\\mathcal{B}(B_c \\to \\tau \\nu)$ bound is later strengthened, the surviving vector parameter space will shrink; if it relaxes, the scalar scenarios deserve another look.","A dedicated experimental extraction of $P_\\tau(q^2)$ in $B_s \\to D_s \\tau \\nu$, rather than an integrated rate alone, would be the most direct test of the paper's proposed separation."],"forward_implications":["Scalar new-physics explanations of the $R_D$ and $R_{D^*}$ anomalies are excluded unless they also satisfy the $B_c \\to \\tau \\nu$ bound, redirecting model building toward vector couplings.","A measurement of the $B_s \\to D_s \\tau \\nu$ branching ratio and $R_{D_s}$ in the quoted ranges would signal new physics at a level distinguishable from the standard model.","The $\\tau$ polarization $P_\\tau(q^2)$, predicted in $[0.234, 0.403]$ for $(V_L, V_R)$ and $[0.064, 0.276]$ for $(\\tilde{V}_L, \\tilde{V}_R)$, offers a way to tell the two vector scenarios apart.","The $q^2$-dependent shapes of $R_{D_s}$ and the differential branching ratio provide additional handles that do not rely only on total branching fractions."],"supporting_citations":[{"why":"Experimental measurements of $R_D$ and $R_{D^*}$ that define the $4.1\\sigma$ anomaly and supply the $1\\sigma$ constraints on the new-physics parameter space.","marker":"[7–12]"},{"why":"Lattice QCD determination of the $B_s \\to D_s$ form factors used to compute all decay observables in this channel.","marker":"[14]"},{"why":"Sets up the effective Lagrangian basis for $b \\to c \\ell \\nu$ transitions with new-physics couplings.","marker":"[15]"},{"why":"Extends and validates the operator basis including scalar and tensor structures used in the analysis.","marker":"[16]"},{"why":"Companion paper establishing the observable definitions and the calculation framework the present predictions rely on.","marker":"[17]"},{"why":"Provides the LEP-based constraint $\\mathcal{B}(B_c \\to \\tau \\nu) \\le 30\\%$ that rules out the scalar new-physics couplings.","marker":"[18]"}],"fun_headline_variants":["Tau polarization picks vector over scalar in B_s decay","Vector new physics only survivor after B_c bound","R_D anomalies leave only vector couplings for B_s to D_s tau nu","Tau polarization distinguishes surviving vector scenarios"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The paper assumes the new-physics couplings are real, so its conclusion that scalar couplings are ruled out could fail if complex phases let those couplings interfere with the standard model differently in $B_c \\to \\tau \\nu$.","fun_headline_variants_meta":{"raw":{"variants":["Tau polarization picks vector over scalar in B_s decay","Vector new physics only survivor after B_c bound","R_D anomalies leave only vector couplings for B_s to D_s tau nu","Tau polarization distinguishes surviving vector scenarios"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000533,"raw_usage":{"total_tokens":2567,"prompt_tokens":953,"completion_tokens":1614,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":569,"completion_tokens_details":{"reasoning_tokens":1549}},"tokens_in":569,"tokens_out":1614,"duration_ms":9886,"temperature":1.0,"reasoning_tokens":1549,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T12:51:59.775010+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Compute $\\mathcal{B}(B_c \\to \\tau \\nu)$ as a function of a complex phase for a scalar coupling, say $S_L = |S_L| e^{i\\phi}$, using points that fit $R_D$ and $R_{D^*}$ at $1\\sigma$; if any such point predicts $\\mathcal{B}(B_c \\to \\tau \\nu)$ below $30\\%$, the paper's central exclusion of scalar new physics is falsified.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Lattice QCD determination of the $B_s \\to D_s$ form factors used to compute all decay observables in this channel."},{"cited_title":"Cirigliano, J","cited_arxiv_id":null,"evidence_quote":"Sets up the effective Lagrangian basis for $b \\to c \\ell \\nu$ transitions with new-physics couplings."},{"cited_title":"Bhattacharya, V","cited_arxiv_id":null,"evidence_quote":"Extends and validates the operator basis including scalar and tensor structures used in the analysis."},{"cited_title":"Dutta and N","cited_arxiv_id":null,"evidence_quote":"Companion paper establishing the observable definitions and the calculation framework the present predictions rely on."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the LEP-based constraint $\\mathcal{B}(B_c \\to \\tau \\nu) \\le 30\\%$ that rules out the scalar new-physics couplings."}],"review_version":1}