Asymmetric Dark Matter (0901.4117v1)

Abstract: We consider a simple class of models in which the relic density of dark matter is determined by the baryon asymmetry of the universe. In these models a $B - L$ asymmetry generated at high temperatures is transfered to the dark matter, which is charged under $B - L$. The interactions that transfer the asymmetry decouple at temperatures above the dark matter mass, freezing in a dark matter asymmetry of order the baryon asymmetry. This explains the observed relation between the baryon and dark matter densities for dark matter mass in the range 5--15 GeV. The symmetric component of the dark matter can annihilate efficiently to light pseudoscalar Higgs particles $a$, or via $t$-channel exchange of new scalar doublets. The first possibility allows for $h^0 \to aa$ decays, while the second predicts a light charged Higgs-like scalar decaying to $\tau\nu$. Direct detection can arise from Higgs exchange in the first model, or a nonzero magnetic moment in the second. In supersymmetric models, the would-be LSP can decay into pairs of dark matter particles plus standard model particles, possibly with displaced vertices.

• The paper introduces an ADM model that connects dark matter relic density to baryon asymmetry through high-temperature B−L asymmetry transfer.
• The analysis predicts a dark matter mass range between 5 and 15 GeV and details novel annihilation channels for eliminating symmetric components.
• The study explores supersymmetric ADM models with distinctive collider signatures, including displaced vertex events from long-lived particle decays.

Asymmetric Dark Matter: A Detailed Exploration

The paper "Asymmetric Dark Matter" by David E. Kaplan, Markus A. Luty, and Kathryn M. Zurek introduces an intriguing model linking the relic density of dark matter to the baryon asymmetry of the universe. Unlike the traditional view where dark matter and baryon densities originate via distinct mechanisms, this model proposes that the cosmic coincidence of their similar densities arises from a shared origin. Central to this explanation is the transfer of a baryon-minus-lepton (B−L) asymmetry, generated at high temperatures, to dark matter particles carrying a B−L charge.

Key Features of Asymmetric Dark Matter

The paper elucidates a mechanism in which the dark matter density is fixed by the baryon asymmetry, independent of thermal freeze-out processes often associated with WIMPs. The proposed framework, termed Asymmetric Dark Matter (ADM), highlights the following critical elements:

• Transfer of Asymmetry: At high temperatures, a B−L asymmetry develops and equitably distributes between baryons and dark matter. This transfer depends on higher-dimensional effective interactions that fall out of equilibrium at temperatures above the electroweak scale, resulting in frozen asymmetries.
• Range of Dark Matter Mass: The authors predict the dark matter particle mass between 5 to 15 GeV, derived from the relation between baryonic and dark matter densities. This mass range is consistent with the electroweak scale and offers potential explanations for experimental observations such as those by the DAMA/LIBRA collaboration.
• Annihilation of Symmetric Components: To eliminate the symmetric portion of dark matter, annihilations can occur via light pseudoscalar Higgs particles or through t-channel exchanges of scalar doublets.
• Direct Detection Prospects: Models provide possibilities for direct dark matter detection through Higgs exchange or magnetic moment interactions.

Specific Models and Collider Phenomenology

The paper presents multiple explicit models to illustrate the ADM concept, emphasizing supersymmetry's role in these constructions. A notable example is the supersymmetric model wherein dark matter carries lepton number, facilitating collider signatures like displaced vertices from long-lived particle decays.

Key aspects discussed include:

• Supersymmetric Model: ADM models integrate naturally with supersymmetry, connecting to electroweak physics. In some instances, the lightest supersymmetric particle (LSP) decays into pairs of dark matter particles along with Standard Model particles, potentially exhibiting displaced vertices at colliders.
• Alternate Annihilation Channels: ADM models accommodate novel annihilation channels for symmetric dark matter components involving hidden sector fields or utilizing new dynamics such as those in hidden valley scenarios.

Implications and Future Directions

The work has significant theoretical and practical implications:

• Theoretical Insights: ADM provides a compelling framework challenging the traditional WIMP paradigm, suggesting a fundamentally different understanding of dark matter genesis linked to baryonic asymmetries.
• Experimental Motivations: The predicted mass range for dark matter motivates direct search strategies sensitive to lower masses. Potential collider signals arising from model-specific interactions could furnish new avenues for verification at current and future particle physics experiments.

Overall, the asymmetric dark matter model presents a cohesive framework that merits further exploration both in theoretical landscapes and experimental verifications. Future work may expand on the theoretical foundations, explore additional model constructions, and refine experimental search strategies to probe the existence and properties of ADM in the cosmic milieu.