The impact of gamma-ray propagation effects on indirect dark matter searches

summary

The gist

The gist: The full treatments of propagation effects, including inverse Compton scattering, can significantly alter observed gamma-ray fluxes from WIMP annihilation by up to a factor of three orders

In short

The study investigated how gamma-ray fluxes from dark matter annihilation are altered by propagation effects during their journey to Earth. By including secondary processes like inverse Compton scattering alongside pair production, researchers found that for heavy WIMPs and distant sources, these effects can change the observed gamma-ray flux by up to three orders of magnitude. This means current dark matter constraints might be less stringent than previously thought.

Key concepts

WIMP Annihilation: Weakly Interacting Massive Particles (WIMPs) are a leading dark matter candidate. When two WIMPs collide, they annihilate into other particles, which create cascades of secondary products, including high-energy gamma rays that travel across the universe.
Pair Production: This is a primary attenuation mechanism where gamma rays interact with background photons, such as the Cosmic Microwave Background (CMB) or Extragalactic Background Light (EBL), to create electron-positron pairs. These charged leptons then contribute to further energy loss during propagation.
Inverse Compton Scattering: This process occurs when secondary electrons and positrons created by pair production scatter off background photons, gaining energy in the process. This transfers energy back into the background radiation, effectively regenerating high-energy gamma rays that would otherwise be attenuated.

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This episode discusses

The paper

The impact of gamma-ray propagation effects on indirect dark matter searches · Read on arXiv

Ignacio Martínez López, Rafael Alves Batista, Miguel A. Sánchez-Conde, Antonio Juan Rubio-Monterob

Universidad Autónoma de Madrid · Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) · Instituto de Física Teórica, Instituto de Física Teórica Universidad Autónoma de Madrid · Sorbonne Université

In this work, we investigate dark matter (DM) detection in the context of weakly interacting massive particles (WIMPs). Upon annihilation, WIMPs generate cascades of secondary particles through various channels, many of which culminate in the production of gamma rays. As these gamma rays travel toward Earth, their spectra are reshaped by interactions with the intervening medium. While current models typically account for attenuation via pair production on the extragalactic background light, they often neglect the fate of the resulting electrons and positrons, specifically subsequent inverse Compton scattering of these secondary particles, which can regenerate high-energy gamma rays. Here, we revisit the predicted gamma-ray fluxes from WIMP annihilation by performing a more detailed treatment of propagation effects. We show that for distant sources and annihilation channels such as τ+τ-, the full treatments can significantly alter the observed gamma-ray flux, by up to a factor of three orders of magnitude for heavy WIMPs. This has an impact on current dark matter limits derived without taking into account propagation effects, depending on the considered WIMP mass and annihilation channel. Our study demonstrates the importance of a detailed propagation treatment for indirect dark matter searches, and the need to account for such effects in order to obtain accurate, more reliable dark matter signal predictions and exclusion limits.

DOI: 10.1088/1475-7516/2026/10/042

Transcript

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

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: Today's paper: "The impact of gamma-ray propagation effects on indirect dark matter searches".

Jocelyn: The gist: The full treatments of propagation effects, including inverse Compton scattering,

Vera: First, who's behind it and why it matters.

Paper summary: Vera: We just covered that the paper looks at WIMP annihilation signals and how propagation effects, specifically inverse Compton scattering, can dramatically alter the predicted gamma-ray fluxes.

Jocelyn: The authors are investigating this by performing a more detailed treatment of these propagation effects instead of just relying on standard pair production models.

Subrahmanyan: They use a combined framework called CosmiXs and CRPropa to model this, where CosmiXs generates the prompt spectra from the DM annihilation, and CRPropa simulates how those particles interact during transit.

Vera: CRPropa is described as a Monte Carlo simulation designed to track high energy astrophysical messengers like cosmic rays, neutrinos, electrons, and gamma rays >

Jocelyn: They use a one-dimensional mode to treat the interactions and energy loss processes while ignoring magnetic field effects during the simulation >

Subrahmanyan: The paper shows that for higher WIMP masses, specifically when mchi is around one hundred TeV and propagation distances are over one hundred Mpc, these differences become substantial > <ref:2603.20409#pg1>

Vera: In fact, for leptonic channels like tau plus tau, the flux ratios between simulations with and without inverse Compton scattering can reach values as high as one hundred three in the lower energy regime > <ref:2603.20409#pg1>

Jocelyn: The results suggest that while a more detailed treatment doesn't change the main dark matter observable which is the velocity averaged annihilation cross section much, it definitely shifts things for specific signals >

Subrahmanyan: It means that if you only look at gamma rays, you need this more complex propagation treatment to get a real picture of what might be happening with heavy WIMPs >

Vera: So if you're setting limits on WIMP properties, the way you model the journey of those gamma rays is really important, as shown in "The impact of gamma-ray propagation effects on indirect dark matter searches"

Conclusion: Jocelyn: So putting it all together, this paper by Martínez López et al. says that accounting for inverse Compton scattering is essential when you're interpreting indirect dark matter detection limits.

Vera: It essentially shows that these propagation effects can partially relax constraints that were considered very stringent before >

Subrahmanyan: Incorporating these effects will be key to getting more precise and reliable limits on WIMP properties using gamma-ray data from instruments like Fermi-LAT and future ones like CTAO >

Jocelyn: The study confirms that accurate modeling of gamma-ray propagation is essential when interpreting indirect dark matter detection limits, especially for channels like tau plus tau where the shifts in the velocity averaged DM cross section constraints approach factors of zero point four for the highest masses considered >

Vera: It's about properly accounting for propagation effects in indirect DM searches, and that's what makes this work on "The impact of gamma-ray propagation effects on indirect dark matter searches" important to read >

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