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arxiv: 2606.09596 · v1 · pith:DOJFABCAnew · submitted 2026-06-08 · ✦ hep-ph

Lifting Effective-Field-Theory Degeneracies in Semileptonic Heavy-Baryon Decays

Hindi Zouhair This is my paper

Pith reviewed 2026-06-27 16:04 UTC · model grok-4.3

classification ✦ hep-ph
keywords effective field theorysemileptonic decaysheavy baryonslepton flavor universalitytau polarizationnew physicsLambda_b to Lambda_c
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0 comments X

The pith

Tau polarization in Lambda_b to Lambda_c tau nu lifts effective field theory degeneracies unresolved by R(D) and R(D*) data.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper performs an effective field theory analysis of semileptonic heavy baryon decays to probe possible lepton flavor universality violation in b to c tau transitions. It uses lattice QCD helicity form factors with full covariance to propagate solutions that fit meson data into the baryonic observables R_Lambda_c, tau polarization P_tau, and forward-backward asymmetry A_FB. The central finding is that tau polarization supplies the leading sensitivity to distinguish among these solutions. Scalar-containing directions produce large shifts in polarization together with low-q^2 deformations in the normalized spectrum, while vector and tensor directions stay near the Standard Model point. Baryonic polarization and differential observables therefore supply independent information on the Lorentz structure of any new physics.

Core claim

In an effective field theory analysis of Lambda_b to Lambda_c tau nu_bar using lattice QCD helicity form factors, propagating meson-compatible solutions into the baryonic observable space shows that tau polarization provides the leading source of sensitivity for lifting EFT degeneracies that remain unresolved in current measurements of R(D) and R(D*). Vector-like and tensor-like solutions remain clustered near the Standard Model prediction, whereas scalar-containing directions produce large polarization displacements and characteristic low-q^2 deformations of the normalized differential spectrum. A covariance-aware analysis demonstrates that baryonic polarization and differential observables

What carries the argument

Propagation of meson-compatible EFT solutions into baryonic observables R_Lambda_c, P_tau and A_FB, using lattice QCD helicity form factors with covariance propagation, where P_tau supplies the dominant distinguishing power.

If this is right

  • Scalar-containing EFT solutions produce large displacements in tau polarization P_tau.
  • These solutions also generate characteristic deformations in the normalized differential spectrum at low q^2.
  • Vector-like and tensor-like solutions cluster near the Standard Model prediction in the baryonic observables.
  • Polarization and differential observables supply complementary and independent information on the Lorentz structure.
  • Future measurements of P_tau and the low-q^2 spectrum at LHCb can test semitauonic flavor anomalies.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Prioritizing tau polarization measurements in baryon decays at LHCb could separate scalar from non-scalar explanations of the anomalies.
  • Applying the same propagation method to other heavy baryon modes would test whether operator mixing remains negligible across channels.
  • The low-q^2 spectral deformations offer an observable signature that can be checked independently of overall rate ratios.

Load-bearing premise

Meson-compatible effective field theory solutions apply directly to baryonic decays without additional baryon-specific constraints or operator mixing that would change the degeneracy structure.

What would settle it

A measurement of P_tau in Lambda_b to Lambda_c tau nu that remains consistent with the Standard Model prediction while R(D) and R(D*) show deviations would show that scalar directions are not realized or that the direct propagation step fails.

Figures

Figures reproduced from arXiv: 2606.09596 by Hindi Zouhair.

Figure 1
Figure 1. Figure 1: constitutes the central result of this work and demonstrates explicitly how baryonic observables lift the approximate EFT degeneracies that remain unresolved in mesonic analyses of b → c τν¯τ transitions. The displayed points correspond to EFT parameter configurations that satisfy the mesonic acceptance cri￾terion defined in Eqs. (1)–(2), using the experimen￾tally measured values of R(D) and R(D∗ ) at the … view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Covariance-aware separation of meson-compatible [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Differential deformation of the normalized semilep [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Differential phase-space sensitivity to EFT-induced [PITH_FULL_IMAGE:figures/full_fig_p009_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. spectral-deformation fingerprint of meson-compatible [PITH_FULL_IMAGE:figures/full_fig_p010_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Projected EFT discrimination power as a function of the attainable precision on [PITH_FULL_IMAGE:figures/full_fig_p012_6.png] view at source ↗
read the original abstract

Semileptonic heavy-baryon decays provide a sensitive probe of the helicity structure underlying possible lepton-flavor universality violation in $b\to c\,\tau\bar\nu_\tau$ transitions. We perform an effective-field-theory analysis of $\Lambda_b\to\Lambda_c\tau\bar\nu_\tau$ and related baryonic modes using lattice-QCD helicity form factors with full covariance propagation. Propagating meson-compatible EFT solutions into the baryonic observable space$(R_{\Lambda_c},\,P_\tau,\,A_{\rm FB})$, we show that tau polarization provides the leading source of sensitivity for lifting EFT degeneracies that remain unresolved in current measurements of $R(D)$ and $R(D^\ast)$. Vector-like and tensor-like solutions remain clustered near theStandard-Model prediction, whereas scalar-containing directions produce large polarization displacements and characteristic low-$q^2$ deformations of the normalized differential spectrum. A covariance-aware analysis demonstrates that baryonic polarization and differential observables provide complementary and independent information on the Lorentz structure of semileptonic new physics. $P_\tau(\Lambda_b\to\Lambda_c\tau\bar\nu_\tau)$ and the low-$q^2$ spectrum as particularly powerful probes for future tests of semitauonic flavor anomalies at LHCb and future flavor facilities.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 4 minor

Summary. The manuscript performs an effective-field-theory analysis of semileptonic heavy-baryon decays Λ_b → Λ_c τ ν_τ (and related modes) using lattice-QCD helicity form factors with full covariance propagation. It propagates meson-compatible EFT Wilson-coefficient solutions into the baryonic observable space (R_Λc, P_τ, A_FB) and shows that tau polarization supplies the dominant sensitivity for lifting degeneracies that persist in current R(D) and R(D*) measurements; vector- and tensor-like directions remain near the SM while scalar-containing directions produce large P_τ displacements and low-q² spectral deformations.

Significance. If the central results hold, the work supplies concrete, falsifiable predictions for polarization and differential observables that are complementary to meson data and directly testable at LHCb and future facilities. The explicit use of lattice helicity form factors together with covariance propagation is a methodological strength that improves the robustness of the degeneracy-lifting claims relative to analyses that treat form-factor uncertainties less systematically.

minor comments (4)
  1. [Abstract] Abstract, final sentence: the clause beginning 'A covariance-aware analysis demonstrates...' is grammatically incomplete and should be rephrased for clarity.
  2. [§4.2] §4.2, around Eq. (18): the definition of the normalized differential spectrum dΓ/dq² / Γ should be stated explicitly so that the reported low-q² deformations can be reproduced without ambiguity.
  3. [Table 2] Table 2: the caption does not specify whether the quoted uncertainties include only statistical or also systematic lattice errors; this affects the interpretation of the P_τ sensitivity.
  4. [Figure 4] Figure 4: the color coding for the different EFT directions (vector, scalar, tensor) is not described in the caption or legend, making the clustering near the SM difficult to verify visually.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive assessment of our work, the recognition of its methodological strengths, and the recommendation for minor revision. No major comments are listed in the report, so we have no specific points requiring point-by-point rebuttal. We will address any minor editorial or presentational suggestions in the revised manuscript.

Circularity Check

0 steps flagged

No significant circularity; derivation uses external inputs for new predictions

full rationale

The paper takes EFT solutions fitted to meson data (R(D), R(D*)) as external inputs and propagates them through independent lattice-QCD helicity form factors to compute baryonic observables (R_Lambda_c, P_tau, A_FB). This produces new predictions about which directions lift degeneracies, without any step reducing by construction to the meson inputs or to a self-citation. No self-definitional, fitted-input-renamed-as-prediction, or ansatz-smuggled patterns appear. The central claim remains independent of the meson fits once the form-factor computation is performed.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The analysis rests on standard EFT operator basis and external lattice-QCD inputs; no new particles or forces are introduced.

free parameters (1)
  • EFT Wilson coefficients
    Coefficients for scalar, vector, and tensor operators are constrained by meson data and then propagated.
axioms (2)
  • domain assumption Lattice-QCD helicity form factors with full covariance accurately describe the baryonic transitions
    Used as the primary input for all observable predictions.
  • domain assumption The effective-field-theory framework remains valid across meson and baryon systems without additional operator mixing
    Required to propagate meson solutions directly to baryonic observables.

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discussion (0)

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Reference graph

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    (12) and (13)

    Vector and axial-vector helicity amplitudes The vector and axial-vector helicity amplitudes are defined in Eqs. (12) and (13). The helicity amplitudes are obtained by contracting the hadronic matrix elements with the polarization vectors of the off-shellW∗ boson in the dilepton rest frame. ForλΛc = + 1 2 they read H V + 1 2 ,0 = s λ(q2) q2 (mΛb +m Λc)f +(...

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    Angular-coefficient decomposition All differential decay rates, polarization observables, and angular asymmetries discussed in the main text are constructed from bilinear combinations of the helicity amplitudes listed above. The EFT sensitivity of the observables therefore originates from interference among vector, axial, scalar, and tensor helicity struc...