Constraining Light Dark Matter with Diffuse X-Ray and Gamma-Ray Observations

Abstract: We present constraints on decaying and annihilating dark matter (DM) in the 4 keV to 10 GeV mass range, using published results from the satellites HEAO-1, INTEGRAL, COMPTEL, EGRET, and the Fermi Gamma-ray Space Telescope. We derive analytic expressions for the gamma-ray spectra from various DM decay modes, and find lifetime constraints in the range 10^24-10^28 sec, depending on the DM mass and decay mode. We map these constraints onto the parameter space for a variety of models, including a hidden photino that is part of a kinetically mixed hidden sector, a gravitino with R-parity violating decays, a sterile neutrino, DM with a dipole moment, and a dark pion. The indirect constraints on sterile-neutrino and hidden-photino DM are found to be more powerful than other experimental or astrophysical probes in some parts of parameter space. While our focus is on decaying DM, we also present constraints on DM annihilation to electron-positron pairs. We find that if the annihilation is p-wave suppressed, the galactic diffuse constraints are, depending on the DM mass and velocity at recombination, more powerful than the constraints from the Cosmic Microwave Background.

• The paper derives robust lifetime constraints (10^24-10^28 s) on light dark matter by analyzing diffuse X-ray and gamma-ray emissions.
• It uses satellite data from HEAO-1, INTEGRAL, COMPTEL, EGRET, and Fermi to assess diverse dark matter decay and annihilation models.
• The results outperform previous indirect probes, providing vital benchmarks for future astrophysical dark matter searches.

Constraining Light Dark Matter with Diffuse X-Ray and Gamma-Ray Observations

The study undertaken by the authors aims to provide comprehensive constraints on the properties of light dark matter (LDM), particularly in the mass range between a few keV and 10 GeV, through the analysis of diffuse X-ray and gamma-ray observations. In this exploration, data from several prominent satellites, including HEAO-1, INTEGRAL, COMPTEL, EGRET, and the Fermi Gamma-ray Space Telescope, are utilized to evaluate gamma-ray spectra derived from diverse dark matter decay modes. The findings impose lifetime constraints for dark matter in the range of $10^{24}-10^{28}$ seconds, contingent upon the dark matter mass and the specific decay mode under discussion.

Summary of Numerical Results

The paper elucidates the constraints on both decaying and annihilating dark matter, represented through various models such as a hidden photino involved in a kinetically mixed hidden sector, a gravitino undergoing R-parity violating decays, a sterile neutrino, and dark matter with a dipole moment or a dark pion. Notably, the indirect constraints achieved via diffuse planet-background gamma-ray measurements, surpass other experimental or astrophysical probes in certain model parameter spaces, particularly for sterile-neutrino and hidden-photino dark matter.

The study places emphasis on decaying dark matter, additionally delineating constraints on dark matter annihilation processes to electron-positron pairs, particularly when there is $p$-wave suppression. Under these circumstances, subject to the dark matter mass and its velocity during recombination, the constraints derived from galactic diffuse gamma-ray observations are demonstrated to be more stringent than those obtained from Cosmic Microwave Background analyses. This insight is crucial, especially in scenarios where the annihilation cross-section is velocity-dependent.

Theoretical and Practical Implications

The theoretical implications of this research are significant, presenting a robust framework for evaluating dark matter decay channels within the astrophysical and cosmological context. Practically, the constraints set by this study provide valuable benchmarks for future hunt in understanding the elusive nature of dark matter and thereby directly shape the approaches and analytical techniques employed in both current and forthcoming observational astrophysics research.

The constraints from this study also emphasize the necessity for dedicated spectral analysis tools and methodologies that capitalize on the spectral resolution and sensitivity of existing and upcoming X-ray and gamma-ray observational facilities. Advancements in these areas could enhance the precision of these bounds, potentially revealing more about the fundamental properties of dark matter candidates, such as their decay lifetimes and interaction cross-sections.

Future Prospects

Looking ahead, this paper lays foundational work that could greatly benefit from more data, improved detector technology, and possibly new observatories tailored to X-ray and gamma-ray spectroscopy. There is significant potential for refining these constraints through optimized signal searches and refined background modeling, improving the current limits’ sensitivity and further constraining or potentially detecting new dark matter signatures.

By expanding on detailed analyses of satellite data in combing different approaches to increase signal-to-noise ratios and mitigate background noise, future explorations may open novel observational channels for light dark matter, thereby enhancing our understanding of one of the most profound components of the universe.

The authors’ contributions to constraining dark matter characteristics using diffuse atmospheric measurements reinforce the invaluable role astrophysical data plays in probing high-energy particle physics questions and underline an area ripe for innovative analytical and experimental pursuits.