Dark matter and antimatter
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Dark Matter and Antimatter: Exploring the Connections
Antimatter as a Candidate for Dark Matter
Antimatter Macroscopic Dark Matter
Antimatter macroscopic dark matter (macros) represents a class of dark matter candidates that interact with ordinary matter primarily through annihilation with large cross-sections. Observations from terrestrial, astrophysical, and cosmological sources have constrained some of the parameter space for these anti-macros, but a significant portion, especially for nuclear-dense objects, remains unexplored .
Antimatter Cosmic Rays from Dark Matter Annihilation
Recent studies have utilized N-body simulations to calculate the fluxes of positrons and antiprotons resulting from dark matter annihilation. These simulations reveal that uncertainties in the fluxes mainly arise from fluctuations in the local dark matter density. Despite these uncertainties, the predicted antimatter fluxes are significantly lower than current measurements, suggesting that dark matter annihilation is not a major source of cosmic-ray antimatter .
Matter-Antimatter Asymmetry and Dark Matter
Observational Evidence and Theoretical Frameworks
The observed matter-antimatter asymmetry in the universe is a well-documented phenomenon. This asymmetry, which leads to the remnant matter density we observe today, is believed to have originated from processes in the early universe. Theoretical models, such as baryogenesis, attempt to explain this asymmetry and often link it to dark matter. For instance, some models propose that the same mechanisms responsible for generating the baryon asymmetry also produce dark matter .
Torsion and Matter-Antimatter Imbalance
One proposed scenario involves the Einstein-Cartan-Sciama-Kibble theory of gravity, which extends general relativity to include the intrinsic spin of matter. In this framework, spacetime torsion produced by spin leads to different decay rates for fermions and antifermions. This difference could have caused heavy fermions in the early universe to decay predominantly into normal matter, while their antiparticles decayed into hidden antimatter, potentially forming dark matter .
New Mechanisms for Asymmetry and Dark Matter
Another proposed mechanism involves the interference of tree-level diagrams, where the imaginary part of the Breit-Wigner propagator for an unstable mediator plays a crucial role. This model, which extends the Standard Model with additional particles, suggests that the real part of the neutral component of an inert doublet could serve as a cold dark matter candidate. The evolutions of dark matter relic density and baryon asymmetry are closely related in this scenario .
Experimental Probes and Constraints
Antiproton Interactions with Axion-like Dark Matter
Experiments on trapped antiprotons have provided new insights into the possible interactions between antimatter and dark matter. These experiments place direct constraints on the interaction of ultralight axion-like particles with antiprotons, significantly improving the sensitivity compared to previous astrophysical bounds. Such matter-antimatter asymmetric couplings could potentially link dark matter to the baryon asymmetry in the universe .
Cosmic-Ray Antiprotons and Dark Matter Signals
Global fits of cosmic-ray fluxes, particularly antiprotons measured by AMS-02, have been used to search for dark matter signals. While previous studies hinted at a possible dark matter signal, systematic uncertainties and correlations in the data need to be carefully considered. Recent analyses show that while cross-section uncertainties have a minor effect, data correlations can significantly impact the constraints on propagation models and the significance of potential dark matter signals .
Conclusion
The relationship between dark matter and antimatter is a complex and multifaceted area of research. While antimatter macroscopic dark matter remains a viable candidate, significant portions of its parameter space are yet to be explored. Theoretical models linking matter-antimatter asymmetry to dark matter provide intriguing possibilities, and experimental probes continue to refine our understanding of these interactions. As research progresses, the connections between dark matter and antimatter may offer deeper insights into the fundamental nature of our universe.
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