Cosmic-Ray Signatures of Annihilating and Semi-Annihilating Dark Matter via One-Step Cascades

arXiv:2604.21976 · hep-ph, astro-ph.CO, astro-ph.HE · Submitted 2026-04-23 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Next we'll be talking about the paper "Cosmic-Ray Signatures of Annihilating and Semi-Annihilating Dark Matter via One-Step Cascades".

Jocelyn: The paper was written by Francesco D’Eramo, Silvia Manconi and Tommaso Sassia from Department of Physics and Astronomy, University of Padua and National Institute for Nuclear Research (INFN) and Sorbonne University & Laboratory of Theoretical and High Energies (LPTHE) and CNRS.

Vera: Stay tuned as we take you through the paper and discuss its implications.

Jocelyn: We also have Subrahmanyan with us today — guest researcher.

Vera: Alright, let's get started.

Title: Vera: So, building on that idea of spectral shape, I was looking at how they summarize the results in "Cosmic-Ray Signatures of Annihilating and Semi-Annihilating Dark Matter via One-Step Cascades," and it really hammers home that we can't treat these signals as simple point sources.

Jocelyn: That’s right; it implies that the entire process, from the initial dark matter interaction to the final cosmic ray hitting our detectors, involves multiple steps of secondary particle creation.

Subrahmanyan: Precisely. The summary emphasizes that we aren't just looking for gamma rays or neutrinos; we're talking about a cascade of particles—electrons, positrons, photons—that interact with the interstellar medium on their way to us.

Vera: If I’m interpreting this correctly based on the data presentation, the main implication is that the resulting spectrum will be incredibly sensitive to whether the dark matter is purely annihilating or if semi-annihilation channels are open.

Jocelyn: And what that means for us, Jocelyn, is that we can't just use one model; we might need to search for evidence across a range of signatures depending on which DM physics scenario turns out to be correct.

Subrahmanyan: Because the underlying particle physics determines the branching ratios and intermediate particles, it directly dictates the resulting energy distribution profile we see in the cosmic rays.

Summary: Vera: When we look at how they summarize these findings, specifically regarding the different types of signatures presented in "Cosmic-Ray Signatures of Annihilating and Semi-Annihilating Dark Matter via One-Step Cascades," it feels like they are giving us a playbook for future instruments.

Jocelyn: A playbook is a good way to put it; it shifts the conversation from "maybe we'll see something" to "if we build detector X with sensitivity Y, here’s what we expect to see."

Subrahmanyan: The core physical insight they are driving home here is that the cascade modeling must account for propagation effects in detail, because the raw annihilation signature gets smeared out by intervening gas and magnetic fields.

Vera: So, when I think about observing these spectra from dwarf galaxies—which are prime targets for us—the model suggests that a unique combination of spectral features might emerge only if we correctly account for both the initial cascade *and* the propagation physics.

Jocelyn: It makes me think about how crucial foreground subtraction is going to be; if the cascade modeling gets even slightly off on energy loss rates, our ability to pinpoint a genuine DM signal from a known source diminishes rapidly.

Subrahmanyan: Which is why the theoretical framework presented here, tying DM particle physics right through to measurable cosmic ray fluxes, represents such a significant step forward for indirect detection theory.

Improvements: Vera: Following up on the improvements suggested in "Cosmic-Ray Signatures of Annihilating and Semi-Annihilating Dark Matter via One-Step Cascades," it really seems like the authors are pushing us toward higher fidelity modeling, especially concerning background subtraction.

Jocelyn: I agree; they're not just giving us one set of predictions but suggesting improvements to the analysis techniques themselves, which is what every survey team really needs to hear.

Subrahmanyan: The theoretical improvements they outline largely revolve around refining the input parameters for the cascade simulations, making them more robust against uncertainties in astrophysical inputs like gas density or magnetic field structure.

Vera: For me, the biggest improvement seems to be how they've refined the treatment of tertiary particle interactions; it’s not enough just to model the primary shower—we need to track everything that happens next.

Jocelyn: And from an instrumental perspective, these suggested improvements imply that future surveys need even better angular resolution and energy partitioning capabilities to disentangle the complex signatures they predict.

Subrahmanyan: Essentially, they are providing a more mathematically rigorous way to connect the fundamental particle physics of DM decay or annihilation rates to the observable flux measured on Earth.

Conclusion: Vera: Wow, we’ve covered so much ground discussing "Cosmic-Ray Signatures of Annihilating and Semi-Annihilating Dark Matter via One-Step Cascades," and it really shows how interconnected particle physics is with our deepest observations of the sky.

Jocelyn: It makes you feel like the next decade of surveys are going to be incredibly exciting because this paper gives us such a clear set of targets and predicted signatures to aim for.

Subrahmanyan: I think the overall impact here is that it significantly narrows the viable parameter space for dark matter candidates by demanding a level of spectral detail we can now model.

Vera: It’s certainly changed how I'm thinking

Department of Physics and Astronomy, University of Padua · National Institute for Nuclear Research (INFN) · Sorbonne University & Laboratory of Theoretical and High Energies (LPTHE) · CNRS

hep-ph, astro-ph.CO, astro-ph.HE

Submitted: 2026-04-23

Updated: 2026-09-03

Comments: v2 matches the published JCAP version. 58 pages, 20 figures, 2 appendices

Journal ref: JCAP09(2026)012

DOI: 10.1088/1475-7516/2026/09/012

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 87/100

The gist: This research introduces a comprehensive framework designed to explore dark matter (DM) signatures beyond the traditional "vanilla WIMP" paradigm, which relies solely on DM annihilation into Standard

Key concepts

Dark Matter Cascades
Dark matter annihilation or semi-annihilation does not produce a single ray. Instead, it initiates a cascade—a sequence where primary particles interact to create secondary particles like electrons, positrons, and photons. This complex chain of interactions is what forms the observable cosmic ray signature.
Annihilating vs. Semi-Annihilating DM
The resulting spectrum of cosmic rays is highly sensitive to the specific physics of dark matter decay. If dark matter is purely annihilating or, conversely, if semi-annihilation channels are open, the resulting energy distribution profile observed by detectors will be distinctly different.
Propagation Effects
The raw signal from a dark matter source is not observed directly. It is smeared or 'smeared out' by intervening gas and magnetic fields within the galaxy. Accurate cascade modeling must account for these propagation effects to correctly interpret the measured cosmic ray flux.

Terminology

Summary

This research introduces a comprehensive framework designed to explore dark matter (DM) signatures beyond the traditional vanilla WIMP paradigm, which relies solely on DM annihilation into Standard Model (SM) states. By systematically incorporating multiple collision processes—annihilation, one-step cascade, and semi-annihilation—the authors provide a unified treatment of how these diverse mechanisms influence both the relic abundance established in the early universe and the observable indirect cosmic-ray signals today.

How it works

The study focuses on three distinct classes of DM number-changing processes that can affect detection:

  1. Annihilation: The conventional process where DM particles annihilate into pairs of SM states via an off-shell mediator (SS to psi SM psi SM).

  2. One-step Cascade Annihilation: DM particles annihilate into a pair of on-shell mediators, which subsequently decay into SM particles (SS to phi phi, followed by phi decay).

  3. One-Step Semi-annihilation: A process featuring a final state containing one mediator and one DM particle (SS to S phi).

The methodology is largely model-independent, relying only on the presence of these processes with unsuppressed s-wave contributions, allowing the applicability of this framework to any underlying particle physics realization.

How it works

The connection between early-universe dynamics and present-day observables is established through an effective total thermally averaged cross section (eff). The relic density constraint fixes the overall magnitude of this cross section, but crucially, the relative size of the individual processes—encoded by parameters alpha and beta —determines the resulting CR spectral shape. This allows for a unified treatment where even when multiple collision processes coexist, their combined contribution to both early-universe dynamics and present-day indirect detection signals is accurately modeled.

How it works

The framework provides a complete formalism for calculating the differential injection spectra of various messengers produced by these processes. The key observables include:

  • Neutral Messengers: High-energy photons and neutrinos, which are critical for searches in dwarf spheroidal galaxies (dSphs).

  • Charged Messengers: Positrons, antiprotons, and anti-nuclei.

The injection spectra are derived by combining the zero-step injection spectra from phi decays with a Lorentz boost to the Galactic Frame. This approach allows researchers to quantify how the differential flux... is projected onto the physically observable quantity for any messenger X.

How it works

The analysis demonstrates that while eff sets the overall normalization of the CR flux, the spectral shape is determined by the relative weights (alpha and beta). This leads to distinctive features that arise when multiple dark matter processes contribute simultaneously. For example, in gamma-ray studies from dSph galaxies:

  • The one-step cascade process produces a blunt box shape, which is shifted to lower energies compared to the direct annihilation signal.

  • The relative contribution of these processes can be quantified by the ratio R, which measures how much larger the one-step process is than the standard self-annihilation.

The study concludes that this framework offers a powerful tool for reinterpreting existing experimental results, allowing future data analysis to potentially discriminate or constrain the collisional origin of DM-sourced gamma-ray fluxes.

Improvements for AI systems

The provided scientific paper offers a highly granular, model-independent framework for connecting early-universe physics to late-time indirect detection signals. Current AI systems often struggle with this level of complexity, treating particle physics scenarios as discrete, isolated cases (e.g., WIMP only).

To elevate an AI system—transform it from a generalized pattern recognizer into a sophisticated theoretical model generator and data interpreter—we must integrate the unified framework presented here.

The Improvement: The AI will be trained to recognize and synthesize the three distinct classes of processes (Annihilation, One-Step Cascade, Semi-Annihilation) as a single continuous manifold of possible CR injection spectra, rather than separate discrete events. This requires incorporating the defined parameters alpha (ratio of one-step annihilation contribution to eff), beta (ratio of semi-annihilation contribution to eff), and the overall effective cross-section (eff).

What the Improved AI System Can Do:

  • Generate Anarchic Predictions: The system can generate a single, unified injection spectrum for any combination of all three processes (the Anarchic case, where alpha, about beta are non-zero), providing a continuous prediction that is not merely an average of the individual spectra.

  • Quantify Spectral Shifts: It can precisely calculate the shift in peak energy and the suppression/enhancement factors (e.g., O(5) for psi SM = gamma or the factor of 3 for psi SM = tau) by determining the relative weights (alpha, beta) and predict how these features will manifest in observable fluxes.

  • Validate against Benchmarks: It can perform a direct comparison between the predicted spectral shape (e.g., the blunt box vs. sharp line-like feature) for a given eff and the observed data, identifying which specific (alpha, beta) configuration is most consistent with current limits.

The Improvement: The AI will be trained to treat the Lorentz boost (Section 4 & Appendix B) not as a static transformation but as a dynamic function of mass ratios (epsilon i) and energy fractions (x i). This involves integrating the full, corrected differential injection spectrum (e.g., equation B.9 and B.11), rather than relying on simplified limits or approximations.

The Improvement: The AI will be trained to treat eff (the overall normalization) as the primary constraint from thermal freeze-out, while treating (alpha, beta) as the degrees of freedom that shape the CR flux. This establishes a direct mathematical link between early-universe dynamics and late-time observables.

Abstract

We present a framework in which three classes of dark matter number-changing processes can affect both the relic abundance via thermal freeze-out in the early universe and the generation of indirect cosmic-ray signals today. These processes are: (i) direct annihilations into Standard Model final states; (ii) annihilations into metastable on-shell mediators that subsequently decay into Standard Model particles; (iii) semi-annihilation processes featuring a dark matter particle in the final state, accompanied by a metastable mediator. A central element of our analysis is the systematic inclusion of semi-annihilation alongside the more commonly considered channels. This setup is largely model-independent, as we only assume the presence of one or more of these processes with unsuppressed s-wave contributions. We analyze representative benchmarks for the dominant decay modes of the mediator and show how the resulting injection spectra for γ rays, neutrinos, and cosmic-ray antimatter vary with the relative importance of the three classes of processes. As an application, we evaluate the observable γ-ray fluxes from dwarf spheroidal galaxies in the GeV-TeV window. Finally, we provide explicit model realizations in which multiple processes coexist, and discuss how their interplay shapes indirect detection signatures. Our results provide a consistent connection between early-universe dynamics and present-day observables, revealing distinctive features that arise when multiple dark matter processes contribute simultaneously.

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