Astrophysical Signatures of Secluded Dark Matter (0810.1502v2)

Abstract: We analyze the indirect astrophysical signatures of secluded models of WIMP dark matter, characterized by a weak-scale rate for annihilation into light MeV-scale mediators which are metastable to decay into Standard Model states. Such scenarios allow a significant enhancement of the annihilation cross section in the galactic halo relative to its value at freeze-out, particularly when the mediator is light enough for this process to proceed through radiative capture to a metastable `WIMP-onium' bound state. For MeV-scale vector mediators charged under a hidden U(1)' gauge group, the enhanced annihilation rate leads predominantly to a sizable excess positron flux, even in the absence of astrophysical boost factors.

• The paper demonstrates that secluded dark matter models enhance WIMP annihilation via metastable WIMP-onium bound states, providing a natural explanation for observed cosmic ray positron excesses.
• The analysis quantifies an enhancement factor near 100 driven by long-range interactions from light U(1)' mediators, highlighting significant astrophysical implications.
• The findings offer practical insights for indirect detection methods and future experimental strategies by correlating theoretical predictions with cosmic ray data.

Astrophysical Signatures of Secluded Dark Matter

The paper presents an investigation into the indirect astrophysical signatures associated with secluded models of Weakly Interacting Massive Particle (WIMP) dark matter. This research explores scenarios where WIMPs, characterized by weak-scale annihilation rates into light MeV-scale mediators, manifest significant enhancements in their annihilation cross-sections within the galactic halo compared to their values at cosmological freeze-out.

The primary focus is on scenarios where these mediators belong to a hidden U(1)$'$ gauge group. These mediators can enable a sufficient rate enhancement through processes such as radiative capture into a metastable 'WIMP-onium' bound state. The paper is particularly relevant in the context of excess positron fluxes observed in cosmic ray experiments, which traditional dark matter models struggle to explain.

Key Findings

1. Secluded Dark Matter Models: The models are characterized by the annihilation of WIMPs into metastable mediators, which eventually decay into Standard Model (SM) particles. Importantly, these models predict very weak direct interactions with SM particles, making direct detection challenging and placing emphasis on indirect detection methods.
2. Enhanced Annihilation Rates: The analysis reveals that conditions can facilitate enhanced annihilation rates in the galactic halo. When the mediator is sufficiently light, the recombination process through WIMP-onium bound states leads to significant amplification of the annihilation cross-section, independent of traditional astrophysical boost factors.
3. Numerical Enhancements: The paper provides quantitative expressions for the enhancement factors, suggesting possible enhancements by factors of around 100 due to the recombination process. These enhancements are notably because of long-range interactions mediated by the light U(1)$'$ vector mediators, providing a natural explanation for the observed positron excess without relying on speculative local density increases.

Theoretical and Practical Implications

The theoretical implications of this work are substantial. It introduces a mechanism to naturally explain the enhanced annihilation signals that have been reported as positron excesses in cosmic rays. This mechanism and its reliance on obscure annihilation channels open new avenues for dark matter research, particularly those that encourage looking beyond traditional frameworks that might have overlooked such secluded interactions.

On the practical side, the paper influences the interpretation of current and future data from cosmic ray observations and gamma-ray telescopes. It provides theoretical predictions that can guide the design of experiments and the interpretation of results in the search for dark matter signatures.

Future Directions

The results suggest promising directions for future research:

• Further theoretical exploration into secluded dark matter models with different mediator types and their potential observable signatures.
• Detailed modeling of galactic propagation effects on observable positron flux, to refine predictions and compare with data from new-generation cosmic ray detectors.
• Developing experimental techniques and detection strategies tailored to identifying the indirect signatures predicted by these secluded models.

In summary, this paper adds significant depth to our understanding of how secluded dark matter can reveal itself through astrophysical observations, offering a compelling framework that aligns well with both theoretical constructs and empirical data. As the field advances, it will be crucial to continue this line of inquiry to either validate the secluded WIMP paradigm or refine our understanding of dark matter in the universe.