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arxiv: 2511.13606 · v3 · submitted 2025-11-17 · ✦ hep-ph

Probing Dark Sector Particles Coupling to Neutrinos with Double Beta Decay

Noor-Ines Boudjema , Frank F. Deppisch , Antonio Herrero-Brocal , Chayan Majumdar , Supriya Senapati This is my paper

Pith reviewed 2026-05-17 22:01 UTC · model grok-4.3

classification ✦ hep-ph
keywords double beta decayMajoron-like scalarneutrino couplingsdark sectorspectral distortionsoff-shell productioncosmological constraints
0
0 comments X p. Extension

The pith

Double beta decay experiments can probe scalar particles coupled to neutrinos with couplings as small as 2×10^{-6}.

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

This paper explores how a massive scalar particle, similar to a Majoron and coupled to neutrinos possibly with dark sector fermions, would alter the electron spectrum observed in two-neutrino double beta decay. On-shell production of the scalar below the decay energy and off-shell production for higher masses both create distinct distortions compared to the standard process. The authors derive the sensitivity of current and future experiments to these effects and show that upcoming detectors could reach couplings of |a_ν| ≈ 2×10^{-6} for sub-MeV scalars while still constraining heavier scalars. This uses the large 2νββ datasets already being collected in neutrinoless double beta decay searches, offering a laboratory complement to cosmological limits on such particles.

Core claim

On- and off-shell production of a massive Majoron-like scalar coupled to neutrinos produces characteristic distortions in the double beta decay electron spectrum. Future experiments can therefore probe scalar-neutrino couplings of |a_ν| ≈ 2×10^{-6} for sub-MeV scalars and remain sensitive to off-shell production above the Q-value of double beta isotopes.

What carries the argument

Characteristic distortions in the emitted electron energy spectrum from on-shell and off-shell scalar production in the double beta decay process.

If this is right

  • Future double beta decay experiments can set limits on scalar-neutrino couplings at |a_ν| ≈ 2×10^{-6} for sub-MeV particles.
  • Sensitivity persists for scalar masses above the isotope Q-value via off-shell production.
  • The large statistics from 2νββ events collected in neutrinoless double beta decay searches enable this probe without new hardware.
  • The resulting bounds can be compared directly to cosmological constraints on the same particles.

Where Pith is reading between the lines

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

  • This approach could link laboratory searches for light scalars to models of neutrino self-interactions or dark matter mediators.
  • Similar spectral analyses might be applied to other rare processes involving neutrinos to search for light dark sector states.
  • Tighter limits from non-observation would constrain neutrino-dark sector models and affect interpretations of neutrino mass mechanisms.

Load-bearing premise

The spectral distortions from scalar production can be cleanly separated from standard two-neutrino double beta decay backgrounds and detector effects.

What would settle it

A high-statistics measurement of the double beta decay electron spectrum in a future experiment that matches the pure two-neutrino prediction without the predicted distortions at |a_ν| = 2×10^{-6} would falsify the projected sensitivity.

Figures

Figures reproduced from arXiv: 2511.13606 by Antonio Herrero-Brocal, Chayan Majumdar, Frank F. Deppisch, Noor-Ines Boudjema, Supriya Senapati.

Figure 1
Figure 1. Figure 1: FIG. 1: Feynman diagrams for neutrinoless double beta decay with scalar Majoron(-like) emission [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: Total decay width of the scalar particle [PITH_FULL_IMAGE:figures/full_fig_p012_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: Differential distribution [PITH_FULL_IMAGE:figures/full_fig_p019_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: As Fig. 3, but showing [PITH_FULL_IMAGE:figures/full_fig_p021_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5: Differential distribution [PITH_FULL_IMAGE:figures/full_fig_p022_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6: Upper limit on (products of) couplings from cosmological (DM thermal relic, collisional [PITH_FULL_IMAGE:figures/full_fig_p026_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7: Estimated upper limits and sensitivity on the coupling [PITH_FULL_IMAGE:figures/full_fig_p032_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8: Modification of the upper limit on [PITH_FULL_IMAGE:figures/full_fig_p034_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: FIG. 9: As Fig. 8, but for [PITH_FULL_IMAGE:figures/full_fig_p035_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: FIG. 10: Summary of double beta decay sensitivities as discussed in Sec. VI compared with the [PITH_FULL_IMAGE:figures/full_fig_p037_10.png] view at source ↗
read the original abstract

Motivated by the observation of non-zero neutrino masses and the potential for discovering physics beyond the Standard Model, numerous experiments are actively searching for neutrinoless double beta $(0\nu\beta\beta)$ decay. In all of these searches, a substantial amount of data on two-neutrino double beta $(2\nu\beta \beta)$ decay has been collected. In this work, we explore the sensitivity of current and future double beta decay experiments to a massive Majoron-like scalar particle coupled to neutrinos and potentially dark sector fermions, and compare their reach to the relevant cosmological constraints. On- and off-shell production of such a scalar leads to characteristic distortions in the emitted electron spectrum. We investigate how these distortions manifest in current and future double beta decay experiments, deriving the sensitivity to such a scenario. We project the reach of future experiments which can probe scalar-neutrino couplings of $|a_\nu| \approx 2\times 10^{-6}$ for sub-MeV scalar particles and remain sensitive to off-shell production above the Q-value of double beta isotopes.

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

1 major / 2 minor

Summary. The manuscript explores using spectral distortions in the summed-electron energy spectrum from two-neutrino double beta decay to probe a massive Majoron-like scalar particle coupled to neutrinos (and possibly dark sector fermions). On- and off-shell scalar production modifies the phase-space factor via the scalar propagator and neutrino-scalar vertex; the authors derive sensitivities for current and future 0νββ experiments and project a reach of |a_ν| ≈ 2×10^{-6} for sub-MeV scalars while remaining sensitive to off-shell production above the Q-value, comparing these limits to cosmological constraints.

Significance. If the projected sensitivities hold under realistic conditions, the work would demonstrate a new, data-driven probe of neutrino-dark sector couplings that exploits existing large 2νββ datasets from 0νββ searches. This could complement cosmological bounds on light scalars and provide falsifiable predictions for spectral shapes in multiple isotopes.

major comments (1)
  1. [Sensitivity derivation and results (abstract and associated sections)] The central projection of |a_ν| ≈ 2×10^{-6} (abstract) rests on the claim that on-shell and off-shell contributions produce identifiable distortions relative to pure 2νββ. The manuscript does not appear to marginalize over 5–10% shape uncertainties in the 2νββ background or 1–2% variations in energy resolution; without this, the quoted reach is an upper bound on ideal sensitivity rather than a realistic experimental projection. This assumption is load-bearing for the main result.
minor comments (2)
  1. [Theoretical framework] Clarify the precise definition of the coupling |a_ν| and its relation to the scalar propagator in the differential rate formula.
  2. [Experimental sensitivity] Add explicit discussion of how the analysis would be performed in a real experiment, including background modeling and statistical methods.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the constructive feedback. We address the major comment below and describe the revisions we intend to implement.

read point-by-point responses

  1. Referee: [Sensitivity derivation and results (abstract and associated sections)] The central projection of |a_ν| ≈ 2×10^{-6} (abstract) rests on the claim that on-shell and off-shell contributions produce identifiable distortions relative to pure 2νββ. The manuscript does not appear to marginalize over 5–10% shape uncertainties in the 2νββ background or 1–2% variations in energy resolution; without this, the quoted reach is an upper bound on ideal sensitivity rather than a realistic experimental projection. This assumption is load-bearing for the main result.

    Authors: We agree with the referee that a realistic projection must account for systematic uncertainties in the 2νββ background shape and detector energy resolution. The present analysis derives the sensitivity under the assumption of perfect knowledge of the standard 2νββ spectrum and ideal resolution in order to isolate the characteristic distortions produced by the scalar propagator and vertex. We acknowledge that this yields an idealized upper limit on the reach. In the revised manuscript we will incorporate these effects by (i) introducing nuisance parameters that allow 5–10% variations in the 2νββ spectral shape and (ii) convolving all theoretical spectra with a realistic energy-resolution function that includes 1–2% smearing. The resulting likelihood analysis will be used to obtain updated, more conservative sensitivity contours. We will revise the abstract, the sensitivity sections, and the associated figures to reflect the new projections while preserving the comparison to cosmological bounds. revision: yes

Circularity Check

0 steps flagged

No significant circularity in sensitivity derivation

full rationale

The paper derives projected reach for |a_ν| by computing on-shell and off-shell scalar contributions to the summed-electron spectrum in double beta decay, using modified phase-space factors relative to standard 2νββ. No quoted equations or steps reduce the central projection to a fitted input renamed as prediction, self-definition, or load-bearing self-citation chain. The calculation relies on standard particle-physics modeling of propagators, vertices, and detector response, remaining self-contained against external benchmarks such as known 2νββ spectra and cosmological limits. This matches the default expectation of an honest non-finding.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 1 invented entities

The central claim rests on the postulated existence of a new scalar field with neutrino couplings, standard assumptions about decay kinematics and detector response, and the ability to distinguish new physics signals from backgrounds.

free parameters (2)
  • scalar mass m_φ
    Mass is scanned across regimes (sub-MeV and above Q-value) to map sensitivity; not fitted to data but chosen to explore phenomenology.
  • coupling strength |a_ν|
    This is the target parameter whose experimental reach is projected rather than a fitted value.
axioms (2)
  • domain assumption The scalar is a Majoron-like particle with a specific effective coupling to neutrinos
    Assumed interaction form used to calculate on- and off-shell production rates.
  • domain assumption Spectral distortions are distinguishable from standard 2νββ decay and experimental backgrounds
    Required for the sensitivity derivation to hold in practice.
invented entities (1)
  • Massive Majoron-like scalar particle no independent evidence
    purpose: Mediator of new interactions between neutrinos and a possible dark sector
    Hypothetical particle introduced to explore beyond-Standard-Model effects; no independent evidence or specific mass prediction is provided.

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