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arxiv: 2606.24865 · v1 · pith:ECWEU3KAnew · submitted 2026-06-23 · ✦ hep-ph

Probing Invisible Fermions in B to D^(*)ell X_(inv) via Angular Observables

Lipika Kolay , Soumitra Nandi , Shantanu Sahoo This is my paper

Pith reviewed 2026-06-25 23:04 UTC · model grok-4.3

classification ✦ hep-ph
keywords B decaysinvisible fermionsangular observablessemileptonic decaysdark sectorsterile neutrinosweak effective theoryangular distributions
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The pith

Massive invisible fermions induce distinctive modifications in angular distributions of B to D* lepton invisible decays.

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

The paper establishes that semileptonic B decays involving an invisible fermion produce angular distributions that depend on the fermion's mass. Observables sensitive to this mass enable discrimination between different new physics scenarios. Angular structures further allow separation of left-handed and right-handed interactions between the lepton and the dark sector. A reader would care because these decays offer a window into light dark particles that might otherwise be hard to detect directly.

Core claim

Within a general weak effective theory framework, a massive invisible fermion in the decay B → D* ℓ X_inv induces distinctive modifications in the angular distributions. Observables with enhanced sensitivity to the invisible particle mass allow clear discrimination of such scenarios, while angular structures differentiate left- and right-handed lepton-dark-sector currents.

What carries the argument

Angular observables in the decay B → D* ℓ X_inv that are sensitive to the mass of the invisible fermion and the chirality of the currents.

Load-bearing premise

The invisible particle behaves as a massive fermion whose effects are fully captured by a general weak effective theory without additional light degrees of freedom altering the angular distributions.

What would settle it

Measurement of angular distributions in B → D* ℓ X_inv decays that fail to exhibit the predicted mass-dependent patterns or chirality distinctions for any assumed fermion mass.

Figures

Figures reproduced from arXiv: 2606.24865 by Lipika Kolay, Shantanu Sahoo, Soumitra Nandi.

Figure 1
Figure 1. Figure 1: FIG. 1. Schematic diagram of the decay plane of [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. The [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
read the original abstract

Semileptonic decays $B \to D^{*} \ell X_{\text{inv}}$ provide a sensitive probe of light invisible particles, such as sterile neutrinos or dark-sector fermions. Within a general weak effective theory framework, we show that a massive invisible fermion induces distinctive modifications in the angular distributions. We identify observables with enhanced sensitivity to the invisible particle mass, allowing a clear discrimination of such scenarios, and highlight angular structures that differentiate left- and right-handed lepton-dark-sector currents.

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 / 2 minor

Summary. The paper claims that in the decay B → D* ℓ X_inv, a massive invisible fermion within a general weak effective theory framework induces distinctive modifications to the angular distributions. It identifies observables with enhanced sensitivity to the invisible particle mass that allow discrimination between scenarios and differentiation between left- and right-handed lepton-dark-sector currents.

Significance. If the results hold, this provides a useful extension of EFT analyses to massive invisible particles in semileptonic B decays, potentially guiding experimental searches at Belle II and LHCb by leveraging angular information for better sensitivity and chirality discrimination beyond total rates.

minor comments (2)
  1. The abstract and introduction would benefit from a brief statement of the mass range considered for the invisible fermion to contextualize the numerical sensitivity studies.
  2. Notation section: clarify the precise definition of the four-fermion operators involving the invisible fermion early in the text for readers unfamiliar with the general weak EFT setup.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of our work and for recommending minor revision. No specific major comments were provided in the report.

Circularity Check

0 steps flagged

No significant circularity; forward EFT calculation

full rationale

The paper constructs four-fermion operators in a general weak effective theory for B → D* ℓ X_inv with a massive invisible fermion, then computes angular distributions by phase-space integration. This is a standard forward theoretical prediction with no parameter fitting to the target observables, no self-definitional loops, and no load-bearing self-citations that reduce the central claim to prior unverified inputs by the same authors. The scope explicitly limits to the EFT without additional light degrees of freedom, making the derivation self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 1 invented entities

The central claim rests on the applicability of a general weak effective theory to the decay and on the assumption that the invisible particle is a single massive fermion with chiral couplings to leptons.

free parameters (1)
  • mass of invisible fermion
    The mass enters the kinematics and angular distributions as a free parameter that the observables are designed to constrain.
axioms (1)
  • domain assumption General weak effective theory framework captures the relevant interactions
    Explicitly invoked in the abstract as the setting for the calculation.
invented entities (1)
  • invisible fermion no independent evidence
    purpose: To produce the claimed modifications in angular distributions
    The paper treats it as a hypothetical particle whose effects are being probed rather than derived from first principles.

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discussion (0)

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Reference graph

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