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

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 of magnitude for heavy WIMPs

Dark Matter Signals and Detection

Weakly interacting massive particles (WIMPs) are a leading candidate for dark matter, and their annihilation produces cascades of secondary particles that include gamma rays The differential flux of gamma rays from DM annihilation is given by Eq. 2.1, which depends on the velocity-averaged annihilation cross section and the astrophysical J-factor The astrophysical J-factor captures the dependence on the astrophysical distribution of DM along the line of sight, reflecting the square of the DM density integrated over volume

Propagation Effects Modeling

The paper investigates how gamma rays are reshaped by interactions with intervening media during their journey from a distant source to Earth The primary attenuation mechanism is pair production via interactions with background photons, such as the CMB, EBL and CRB These produced charged leptons can subsequently undergo inverse Compton scattering, which transfers energy back to background photons, forming an electromagnetic cascade The likelihood of such interactions is quantified through the inverse of the mean free path (λ−1), which represents the probability per unit of distance that a photon interacts with the background fields

Detailed Simulation Framework

The authors employ a combined framework using CosmiXs and CRPropa to model propagation effects, where CosmiXs generates prompt spectra from DM annihilation and CRPropa simulates interactions during transit CRPropa is a Monte Carlo simulation framework designed to track high-energy astrophysical messengers, including cosmic rays, neutrinos, electrons, and gamma rays They use the 1D mode to treat interactions and energy-loss processes while neglecting magnetic field effects Simulations were run with initial energies extending up to 120 TeV for DM particle masses consistent with supersymmetric models

Impact on Constraints

The analysis shows that including both pair production and inverse Compton scattering modifies the predictions for DM annihilations signals in the gamma-ray energy range For higher WIMP masses (e.g., mχ ≃ 100 TeV) and propagation distances exceeding 100 Mpc, the impact becomes substantial, with flux ratios between simulations with and without inverse Compton scattering reaching values as high as 103 in the lower-energy regime The results suggest that a more detailed treatment of propagation does not lead to substantial changes in the main DM observable, namely the velocity-averaged annihilation cross section However, for leptonic channels like τ+τ−, significant differences are observed, particularly for gamma rays arriving at Earth with energies below 1 TeV

Conclusions and Outlook

The study demonstrates that accounting for inverse Compton scattering is essential when interpreting indirect DM detection limits The findings imply that propagation effects can partially relax constraints previously considered stringent, potentially reopening portions of the WIMP parameter space Incorporating such effects will be key to obtaining more precise and reliable limits on WIMP properties using gamma-ray data collected by current instruments like Fermi-LAT and upcoming ones like CTAO Future work could extend this approach by including additional annihilation channels and exploring the role of magnetic fields in shaping the secondary emission The study highlights the potentially important role of inverse Compton scattering of secondary electrons by background photons – a phenomenon often neglected – which can lead to systematic biases in both the predicted spectra and the derived constraints on DM properties The results confirm that accurate modelling of gamma-ray propagation is essential when interpreting indirect DM detection limits The shifts in the velocityaveraged DM cross-section constraints for the τ+τ− channel approach factors of ∼ 0.4 for the highest masses considered, confirming that accurate modelling of gamma-ray propagation is essential when interpreting indirect DM detection limits The overall study highlights the importance of properly accounting for propagation effects in indirect DM searches

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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 of magnitude for heavy WIMPs

Conclusions and Outlook

The study demonstrates that accounting for inverse Compton scattering is essential when interpreting indirect DM detection limits The findings imply that propagation effects can partially relax constraints previously considered stringent, potentially reopening portions of the WIMP parameter space Incorporating such effects will be key to obtaining more precise and reliable limits on WIMP properties using gamma-ray data collected by current instruments like Fermi-LAT and upcoming ones like CTAO The study highlights the importance of properly accounting for propagation effects in indirect DM searches The results confirm that accurate modelling of gamma-ray propagation is essential when interpreting indirect DM detection limits

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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 of magnitude for heavy WIMPs

Dark Matter Signals and Detection

Weakly interacting massive particles (WIMPs) are a leading candidate for dark matter, and their annihilation produces cascades of secondary particles that include gamma rays The differential flux of gamma rays from DM annihilation is given by Eq. 2.

1. Improved WIMP detection limits by incorporating secondary particle regeneration: The AI system can now derive flux ratios that directly translate into modifications of the exclusion limits on ⟨σv⟩, as shown in Figure 7, which demonstrates how including inverse Compton scattering can partially relax constraints previously considered stringent.

2. Enhanced spectral shape prediction for high-energy gamma rays: The system can now model the full propagation history by simulating electromagnetic cascades resulting from DM annihilation, allowing it to predict spectra that show enhanced fluxes at lower energies and a corresponding depletion in the high-energy domain due to inverse Compton scattering.

3. Mass-dependent sensitivity analysis for observational constraints: The improved AI can perform a detailed exploration of energy windows, as illustrated in Figure 8, showing how constraints derived from observatories sensitive to ∼ 1–100 GeV energies (e.g., Fermi-LAT) show strong sensitivity to high DM masses for this specific cluster.

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.