Asymmetric Dark Matter: Theories, Signatures, and Constraints

TL;DR

Asymmetric Dark Matter (ADM) proposes a shared origin for the dark and baryon asymmetries, explaining the observed density ratio $\rho_{DM}/\rho_B \approx 5$ via a DM number excess tied to the baryon asymmetry and predicting $m_X$ in the GeV–TeV range depending on the model. The review categorizes ADM scenarios into two main mechanisms for sharing or generating asymmetries—sphaleron transfers and higher-dimension/renormalizable operators, and two broad generation pathways—cogenesis and darkogenesis—including Affleck-Dine dynamics and electroweak or spontaneous baryogenesis analogues. It further discusses how the symmetric DM component is eliminated through annihilations (with heavy mediators or dark forces), the role of hidden sectors and self-interactions, and the possibility of late-time wash-out via oscillations. The paper surveys a broad phenomenology, linking cosmological constraints (CMB), astrophysical objects (neutron stars, the Sun, white dwarfs), indirect/direct detection experiments, and collider signatures, highlighting how ADM shapes experimental strategies and where future tests may be most informative.

Abstract

We review theories of Asymmetric Dark Matter (ADM), their cosmological implications and detection. While there are many models of ADM in the literature, our review of existing models will center on highlighting the few common features and important mechanisms for generation and transfer of the matter-anti-matter asymmetry between dark and visible sectors. We also survey ADM hidden sectors, the calculation of the relic abundance for ADM, and how the DM asymmetry may be erased at late times through oscillations. We consider cosmological constraints on ADM from the cosmic microwave background, neutron stars, the Sun, and brown and white dwarves. Lastly, we review indirect and direct detection methods for ADM, collider signatures, and constraints.

Figures (12)

• Figure 1: left: $\rho_{DM}/\rho_B$ versus the DM mass to DM-number violation decoupling temperature ratio, $m_X/T_D$. This plot is designed to illustrate how Boltzmann statistics with $m_X/T_D > 1$ can suppress the DM energy density, giving rise to the observed $\rho_{DM}/\rho_B$ even for heavy DM mass. For decoupling of DM number violation at 200 GeV, the DM must be at least 2 TeV. From Buckley:2010ui. right: In the absence of a large DM density suppression from a large DM to decoupling temperature ratio, cancellations in the sphaleron conserved quantities $B-L$ and $B-3 D$ can be used to achieve the correct density. The dashed, solid and dot-dashed (red, blue, green) lines correspond to $\Omega_{DM}/\Omega_B = (1,5,25)$, with $m_X/T_D = 0.25$ and DM mass $m_X = 200$ GeV. From Kribs:2009fy.
• Figure 2: A schematic of higher dimension ADM models Kaplan:2009ag. The $x$-axis represents the inaccessibility of the sector (the visible or dark sector) and the $y$-axis its energy, with the set-up inspired by Hidden Valley models Strassler:2006im. The mediator of the higher dimension operator, ${\cal O}_D {\cal O}_{B-L}$, presents a barrier between the two sectors. At high temperatures the barrier is effectively removed though high energy interactions, allowing the $B-L$ and $D$ number to be shared between the two sectors. At low temperatures, the barrier effectively freezes in the asymmetry between the two sectors.
• Figure 3: A schematic of leptogenesis ADM models. Out-of-equilibrium and CP violating decays of a sterile neutrino into both the SM and DM sectors give rise to an asymmetry in both sectors. From Falkowski:2011xh.
• Figure 4: Schematic of darkogenesis models. Darkogenesis makes use of dynamics in the dark sector (with a dark Higgs and dark sphalerons) to generate a dark asymmetry that is then transferred to the baryons via a connector sector. Figure from Shelton:2010ta.
• Figure 5: Typical processes for removing the thermal symmetric (in $X$ and $\bar{X}$) abundance. $X-\bar{X}$ can annihilate to light force mediators $\phi$ (whether they be scalar or vector), or through a heavier state directly to SM $f \bar{f}$.