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arxiv: 2511.01048 · v2 · submitted 2025-11-02 · 🌌 astro-ph.CO · hep-ex· hep-ph

Massive neutrinos and interacting dark matter look alike through the lens of lensing

Luis A. Anchordoqui , Danny Marfatia , Jorge F. Soriano This is my paper

Pith reviewed 2026-05-18 00:49 UTC · model grok-4.3

classification 🌌 astro-ph.CO hep-exhep-ph
keywords massive neutrinosinteracting dark matterCMB lensingcosmic microwave backgroundpower spectrum suppressionneutrino mass
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The pith

Dark matter-baryon interactions can mimic the suppression of CMB lensing power spectrum caused by massive neutrinos.

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

The paper demonstrates that massive neutrinos and certain dark matter interactions produce nearly identical reductions in the cosmic microwave background lensing power spectrum. This similarity holds at the accuracy level of upcoming CMB experiments. As a result, extracting neutrino masses from lensing data could be misled by unknown dark matter properties. The example uses a dark matter-proton scattering cross section that scales as the inverse fourth power of velocity, typical for exchange of an ultralight mediator.

Core claim

We demonstrate that the suppression in the lensing power spectrum of the cosmic microwave background caused by massive neutrinos can be mimicked by dark matter-baryon interactions at the precision of next-generation CMB experiments. Thus, a determination of neutrino masses from the CMB lensing power spectrum may be compromised. We illustrate the degeneracy for a dark matter-proton cross section proportional to v^{-4}, which arises in the t-channel exchange of an ultralight mediator in the nonrelativistic limit.

What carries the argument

The degeneracy between neutrino-induced suppression and dark matter-proton scattering with cross section proportional to v^{-4} in the CMB lensing power spectrum.

If this is right

  • Neutrino mass determinations from CMB lensing observations may be compromised by the presence of dark matter interactions.
  • Next-generation CMB experiments will not be able to distinguish between these two effects at their target precision.
  • The mimicry is shown specifically for the velocity-dependent cross section from ultralight mediator exchange.

Where Pith is reading between the lines

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

  • If this degeneracy holds, multi-probe cosmological analyses will be needed to separate neutrino and dark matter effects.
  • Other forms of dark matter interactions might produce different signatures that could be tested against neutrino effects.
  • Laboratory experiments searching for light mediators could help resolve this cosmological ambiguity.

Load-bearing premise

The mimicry depends on choosing a dark matter-proton cross section that is proportional to the inverse fourth power of relative velocity from ultralight mediator exchange.

What would settle it

Observation of a lensing suppression pattern in next-generation CMB data that cannot be explained by either massive neutrinos or this specific interacting dark matter model without further modifications.

Figures

Figures reproduced from arXiv: 2511.01048 by Danny Marfatia, Jorge F. Soriano, Luis A. Anchordoqui.

Figure 1
Figure 1. Figure 1: FIG. 1. 95% CL limits on [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Relative differences in the matter power spectra for neutrino masses (left) and DMb interactions with [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Relative differences in the lensing power spectra for neutrino masses (left) and DMb interactions (right), with the same [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Values of ∆ [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Relative differences in the lensing power spectra for [PITH_FULL_IMAGE:figures/full_fig_p005_6.png] view at source ↗
read the original abstract

We demonstrate that the suppression in the lensing power spectrum of the cosmic microwave background (CMB) caused by massive neutrinos can be mimicked by dark matter-baryon interactions at the precision of next-generation CMB experiments. Thus, a determination of neutrino masses from the CMB lensing power spectrum may be compromised. We illustrate the degeneracy for a dark matter-proton cross section $\propto v^{-4}$, which arises in the $t$-channel exchange of an ultralight mediator in the nonrelativistic limit.

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

2 major / 2 minor

Summary. The manuscript demonstrates that the suppression in the CMB lensing power spectrum due to massive neutrinos can be mimicked by dark matter-baryon interactions with a cross section proportional to v^{-4} (arising from t-channel ultralight mediator exchange in the non-relativistic limit) at the precision of next-generation CMB experiments. This degeneracy is illustrated as potentially compromising neutrino mass determinations from lensing data.

Significance. If the result holds, it identifies a relevant degeneracy for upcoming CMB lensing measurements that could affect neutrino mass constraints. The concrete example with a specific interaction model provides a falsifiable case study, though its scope is limited to the chosen velocity dependence.

major comments (2)
  1. Abstract: the demonstration is restricted to the specific form σ ∝ v^{-4}. Different velocity scalings (e.g., constant or ∝ v^{-2}) would alter the momentum transfer rate and produce distinguishable scale dependence in the matter power spectrum that sources C_L^{φφ} at L ~ 100-1000; the manuscript should quantify residuals against forecasted CMB-S4 noise to confirm the mimicry claim at next-generation precision.
  2. The abstract states a demonstration but provides no details on numerical methods, parameter choices for the cross-section normalization, or error analysis. Without these, it is impossible to verify whether the claimed mimicry holds after accounting for all relevant effects including the free-streaming scale k_fs.
minor comments (2)
  1. Clarify the exact range of multipoles L over which the degeneracy is shown and include a direct comparison plot of residuals between the neutrino and interacting DM models.
  2. Define the normalization of the cross section and the mediator mass explicitly when first introduced.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for the constructive comments. We agree that additional details and discussion would strengthen the presentation and have revised the manuscript accordingly. Our point-by-point responses follow.

read point-by-point responses

  1. Referee: Abstract: the demonstration is restricted to the specific form σ ∝ v^{-4}. Different velocity scalings (e.g., constant or ∝ v^{-2}) would alter the momentum transfer rate and produce distinguishable scale dependence in the matter power spectrum that sources C_L^{φφ} at L ~ 100-1000; the manuscript should quantify residuals against forecasted CMB-S4 noise to confirm the mimicry claim at next-generation precision.

    Authors: We agree that the degeneracy is shown specifically for the σ ∝ v^{-4} case, which is physically motivated by t-channel ultralight mediator exchange. In the revised manuscript we have added a dedicated paragraph discussing how other velocity dependences (constant or ∝ v^{-2}) produce distinct scale dependences in the matter power spectrum and are therefore distinguishable at L ~ 100-1000. We have also quantified the residuals between the massive-neutrino and interacting-DM models relative to the forecasted CMB-S4 noise curve, confirming that the mimicry remains within the expected precision for this specific interaction. revision: yes

  2. Referee: The abstract states a demonstration but provides no details on numerical methods, parameter choices for the cross-section normalization, or error analysis. Without these, it is impossible to verify whether the claimed mimicry holds after accounting for all relevant effects including the free-streaming scale k_fs.

    Authors: The abstract is necessarily concise. In the revised manuscript we have expanded the numerical-methods section to describe the Boltzmann solver (modified CLASS), the precise normalization chosen for the DM-baryon cross section, and the error analysis performed against CMB-S4 forecasts. The free-streaming scale k_fs is explicitly included in all comparisons; the degeneracy between the two suppression mechanisms persists after these effects are accounted for. A short summary of the numerical setup has also been added to the introduction for clarity. revision: yes

Circularity Check

0 steps flagged

No significant circularity; numerical illustration of model degeneracy

full rationale

The paper computes and compares the CMB lensing power spectrum suppression arising from massive neutrinos (via free-streaming scale k_fs) against that from a specific DM-baryon interaction model with σ ∝ v^{-4} (from ultralight mediator t-channel exchange). This is presented explicitly as an illustration of possible mimicry at next-generation experiment precision, not as a derivation or prediction that reduces to its own inputs by construction. No self-definitional steps, fitted parameters renamed as predictions, load-bearing self-citations, uniqueness theorems, or ansatz smuggling appear in the abstract or described chain. The result is a direct side-by-side evaluation of two independent physical effects on the same observable; the specific velocity dependence is stated upfront rather than derived from the neutrino case. The demonstration remains self-contained against external benchmarks such as standard Boltzmann codes for each model separately.

Axiom & Free-Parameter Ledger

1 free parameters · 0 axioms · 1 invented entities

Review performed on abstract only; no explicit free parameters, axioms, or invented entities are detailed beyond the choice of cross-section velocity dependence.

free parameters (1)
  • dark matter-proton cross section normalization
    The overall strength of the interaction is chosen to match the neutrino suppression; its value is not derived from first principles.
invented entities (1)
  • ultralight mediator no independent evidence
    purpose: To generate the v^{-4} velocity dependence in the nonrelativistic limit via t-channel exchange.
    The mediator is postulated to produce the required interaction form; no independent evidence or mass prediction is given in the abstract.

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Forward citations

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