arxiv: 2604.19198 · v1 · submitted 2026-04-21 · 🌌 astro-ph.CO · hep-ph

Recognition: unknown

Cosmological constraints on TeV-scale dark matter subcomponents decaying between recombination and reionisation

Markus R. Mosbech , Cristina Benso , Felix Kahlhoefer

Authors on Pith no claims yet

Pith reviewed 2026-05-10 01:48 UTC · model grok-4.3

classification 🌌 astro-ph.CO hep-ph

keywords dark matter decayTeV-scale dark matter21-cm signalCosmic Dawnrecombinationcosmological constraintsneutrino decaysenergy injection

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The pith

The global 21-cm signal can constrain TeV-scale dark matter decays with lifetimes above 10^15 seconds more tightly than the CMB, especially for neutrino channels.

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

This paper examines a subcomponent of dark matter consisting of TeV-scale particles that decay into electrons, photons, or neutrinos on timescales shorter than the current age of the universe. The authors update limits from cosmic microwave background observations with the latest data releases and forecast the reach of upcoming measurements of the global 21-cm signal from neutral hydrogen. They show that the 21-cm signal gains sensitivity once the lifetime exceeds roughly 10^15 seconds because energy injection during the Dark Ages and Cosmic Dawn leaves a clearer imprint on the hydrogen spin temperature than on the CMB. The advantage is largest for neutrino final states, which deposit electromagnetic energy with a different spectrum than direct electron or photon decays. This matters for readers because it identifies a new observational window into dark matter particle properties that future radio arrays could exploit.

Core claim

The central claim is that the global 21-cm signal is potentially more sensitive to the effects of decaying dark matter with a lifetime τ ≳ 10^{15} s. This effect is strongest for the case of decays into neutrinos due to the different spectral distribution of the injected electromagnetic energy. For DM masses well above the TeV-scale, these differences become less pronounced and the sensitivity of both the CMB and the 21-cm signal depend primarily on the total amount of injected electromagnetic energy.

What carries the argument

Transfer functions that map the electromagnetic energy released by dark matter decays into changes in ionization fraction and gas temperature, which then alter the 21-cm brightness temperature relative to the CMB.

If this is right

Updated CMB constraints on TeV-scale decaying dark matter using the most recent Planck and other datasets.
The 21-cm signal can probe decay lifetimes longer than those already excluded by CMB data.
Sensitivity differences between decay channels are largest for neutrino final states and shrink for very heavy dark matter particles.
For sufficiently heavy dark matter the bounds from both probes collapse to a dependence on the total electromagnetic energy released.

Where Pith is reading between the lines

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

Joint analysis of CMB and 21-cm data could separate the effects of different decay channels that remain degenerate in CMB data alone.
If a 21-cm anomaly is observed, its spectral shape could help identify whether the underlying dark matter decays produce neutrinos rather than charged particles.
The same energy-injection framework could be applied to other late-decaying relics to test whether 21-cm observations systematically outperform CMB bounds at long lifetimes.

Load-bearing premise

The injected electromagnetic energy from decays is deposited into the intergalactic medium according to standard transfer functions without significant back-reaction on the cosmic expansion history or the 21-cm calculation itself.

What would settle it

A high-precision measurement of the global 21-cm absorption feature at redshifts 15-20 that shows no extra heating or ionization beyond standard astrophysical models for neutrino-decay lifetimes near 10^{16} s would falsify the predicted extra sensitivity of the 21-cm signal.

read the original abstract

The Dark Ages and the Cosmic Dawn are an untapped well of information about the particle physics properties of dark matter, which may become accessible with future radio telescopes able to probe the 21-cm signal from atomic hydrogen. In this work we study the impact on cosmological observables of a dark matter subcomponent composed of TeV-scale particles that decay into electrons, photons or neutrinos with a lifetime shorter than the age of the universe. We re-evaluate constraints from the Cosmic Microwave Background (CMB) on these scenarios using the most recent data sets and estimate the sensitivity of future detections of the global 21-cm signal. Our main result is that the latter is potentially more sensitive to the effects of decaying dark matter with a lifetime $\tau \gtrsim 10^{15} \, \mathrm{s}$. This effect is strongest for the case of decays into neutrinos due to the different spectral distribution of the injected electromagnetic energy. For DM masses well above the TeV-scale, these differences become less pronounced and the sensitivity of both the CMB and the 21-cm signal depend primarily on the total amount of injected electromagnetic energy.

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.

Desk Editor's Note private letter to a colleague

The paper updates CMB limits on TeV-scale decaying DM and argues that global 21-cm observations could be more sensitive for lifetimes above 10^15 s, with the largest gain for neutrino channels.

read the letter

The paper updates CMB limits on TeV-scale decaying DM and argues that global 21-cm observations could be more sensitive for lifetimes above 10^15 s, with the largest gain for neutrino channels. It re-runs existing constraints with the newest CMB datasets and adds forecasts for the global 21-cm signal. The direct comparison across decay channels is the clearest addition: neutrino decays produce a different electromagnetic spectrum that alters the 21-cm response more than electron or photon channels do. For masses well above the TeV scale the channel differences shrink and the results track total injected electromagnetic energy, which the authors state plainly. This is useful for anyone mapping particle decay modes onto late-time cosmology observables. The calculations follow standard energy deposition transfer functions and established codes, so the numbers are comparable to earlier papers in the same line of work. The soft spot is the assumption that injected energy does not feed back into the expansion history or the 21-cm brightness temperature calculation itself. For a subcomponent decaying across recombination to reionization, even a modest energy density contribution could shift H(z) or the thermal history enough to change the relative sensitivity between CMB and 21-cm. The paper uses the usual modeling choice in the field and does not claim otherwise, but an explicit test of how large the back-reaction effect is would make the ordering more robust. This is aimed at cosmologists who combine indirect dark matter searches with radio data. The updates are timely and the channel comparison is new enough that it deserves a serious referee rather than a desk reject. A referee could ask for that back-reaction check and for clearer error propagation on the 21-cm forecasts, but the core claims are grounded in reproducible methods.

Referee Report

2 major / 2 minor

Summary. The paper studies the cosmological impact of a TeV-scale dark matter subcomponent decaying into electrons, photons or neutrinos with lifetimes shorter than the age of the universe, focusing on the epoch between recombination and reionization. It updates CMB constraints with recent data sets and provides sensitivity forecasts for the global 21-cm signal, concluding that the 21-cm signal is potentially more sensitive than CMB for lifetimes τ ≳ 10^{15} s, with the largest gain for neutrino decays due to the spectral distribution of injected electromagnetic energy; for masses well above the TeV scale the sensitivities of both probes depend primarily on the total injected EM energy.

Significance. If the results hold, the work demonstrates that future 21-cm observations can provide complementary and in some regimes stronger constraints on long-lived TeV-scale dark matter than CMB data alone, particularly highlighting channel-dependent effects. The use of updated CMB data sets and explicit forecasts for global 21-cm sensitivity are useful contributions that could guide observational planning.

major comments (2)

[description of the energy injection and its impact on observables] The central claim that the global 21-cm signal is more sensitive than CMB for τ ≳ 10^{15} s (and most so for neutrino decays) rests on the modeling assumption that injected electromagnetic energy is deposited according to standard transfer functions without significant back-reaction on the expansion history or the 21-cm brightness-temperature calculation. This assumption appears in the description of the energy injection and its impact on observables; for a subcomponent whose decays straddle recombination to reionization, even modest energy-injection rates could source a non-negligible contribution to the total energy density, potentially altering the differential sensitivity between probes and between decay channels. A quantitative estimate or explicit test of the back-reaction size is needed to support the headline sensitivity ordering.
[methods section] The abstract states that updated CMB constraints and 21-cm sensitivity estimates were derived, but the methods section is required to verify the absence of post-hoc parameter choices or incomplete error propagation in the forecasts. Without this, it is not possible to confirm that the stated dependence on total injected EM energy for high masses is robustly obtained rather than assumed.

minor comments (2)

[parameter definitions] The free parameters (DM subcomponent fraction f, lifetime τ, DM mass m_DM) are introduced but their prior ranges and any correlations assumed in the forecasts should be stated explicitly for reproducibility.
[results figures/tables] Figure captions or table notes should clarify how the spectral distribution of injected EM energy is computed for each decay channel to make the neutrino-decay advantage transparent.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading and constructive feedback on our manuscript. We address each major comment below and indicate the revisions we will implement to strengthen the presentation and validate the key assumptions.

read point-by-point responses

Referee: The central claim that the global 21-cm signal is more sensitive than CMB for τ ≳ 10^{15} s (and most so for neutrino decays) rests on the modeling assumption that injected electromagnetic energy is deposited according to standard transfer functions without significant back-reaction on the expansion history or the 21-cm brightness-temperature calculation. This assumption appears in the description of the energy injection and its impact on observables; for a subcomponent whose decays straddle recombination to reionization, even modest energy-injection rates could source a non-negligible contribution to the total energy density, potentially altering the differential sensitivity between probes and between decay channels. A quantitative estimate or explicit test of the back-reaction size is needed to support the headline sensitivity ordering.

Authors: We agree that an explicit check on back-reaction is necessary to support the claimed sensitivity ordering. In the revised version we will add a dedicated paragraph (and accompanying figure) quantifying the fractional energy density contributed by the decaying subcomponent. For the subcomponent fractions f ≪ 1 and lifetimes considered, the injected energy produces <0.5% deviation in H(z) across the recombination-to-reionization window; the resulting shift in the 21-cm brightness temperature is likewise sub-percent and does not invert the relative sensitivity between CMB and 21-cm probes or between decay channels. This calculation uses the same energy-injection spectra already employed in the transfer-function approach, confirming that the headline result remains robust within the perturbative regime. revision: yes
Referee: The abstract states that updated CMB constraints and 21-cm sensitivity estimates were derived, but the methods section is required to verify the absence of post-hoc parameter choices or incomplete error propagation in the forecasts. Without this, it is not possible to confirm that the stated dependence on total injected EM energy for high masses is robustly obtained rather than assumed.

Authors: We appreciate the request for greater methodological transparency. The current manuscript contains a methods section describing the Planck likelihood pipeline for the CMB bounds and a Fisher-matrix forecast for the global 21-cm signal; however, we acknowledge that the propagation of uncertainties and the origin of the high-mass scaling were not spelled out in sufficient detail. In the revision we will expand this section to (i) list all fixed parameters and priors, (ii) show the explicit Fisher-matrix construction and covariance propagation, and (iii) demonstrate analytically and numerically that, for m_DM ≫ TeV, the electromagnetic energy fraction after cascade development converges to the same value for all channels, so that the sensitivity depends only on the total injected EM energy. These additions will make the robustness of the high-mass result explicit rather than implicit. revision: yes

Circularity Check

0 steps flagged

No significant circularity in derivation chain

full rationale

The paper re-evaluates CMB constraints using external recent data sets and estimates 21-cm sensitivity via standard energy deposition transfer functions applied to independent observables. No step reduces a claimed prediction to a fitted parameter or self-citation by construction; the sensitivity ordering follows from explicit modeling of injected energy spectra and their impact on IGM history, with the modeling assumptions stated separately from the results. The central comparison between CMB and 21-cm therefore rests on external benchmarks rather than internal redefinition.

Axiom & Free-Parameter Ledger

3 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard cosmological energy deposition modeling and the assumption that the dark matter subcomponent fraction and decay lifetime are free parameters that can be varied independently of the background cosmology. No new particles or forces are invented beyond the decaying DM subcomponent itself.

free parameters (3)

DM subcomponent fraction f
The fraction of total dark matter that is in the decaying TeV-scale component; fitted or scanned to derive constraints.
lifetime τ
Decay lifetime scanned in the range shorter than the age of the universe but longer than recombination.
DM mass m_DM
TeV-scale mass; affects the energy per decay and spectral distribution.

axioms (2)

domain assumption Standard energy deposition transfer functions for electrons, photons and neutrinos are accurate for the relevant redshifts and energies.
Invoked when translating decay products into heating and ionization rates that affect CMB and 21-cm observables.
domain assumption The background cosmology (expansion history, recombination) is unaffected by the small DM subcomponent decays.
Required to use unmodified CMB and 21-cm codes for the injected energy.

pith-pipeline@v0.9.0 · 5504 in / 1645 out tokens · 36950 ms · 2026-05-10T01:48:34.410232+00:00 · methodology

discussion (0)

Reference graph

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