Composite Asymmetric Dark Matter from Primordial Black Holes

TL;DR

The paper tackles the origin of both the baryon asymmetry and the dark-matter abundance within a composite ADM framework by leveraging PBH evaporation as a single source of CP-violating decays of heavy scalars. Through out-of-equilibrium, CP-violating decays of heavy scalars produced at the end of Hawking radiation, the model generates correlated asymmetries in SM baryons and dark baryons, with PBHs evaporating after the electroweak transition but before BBN to preserve cosmological consistency. The results indicate that heavy scalars with masses in $10^6$--$10^9\, ext{GeV}$ and PBH masses in $10^7$--$10^9\, ext{g}$ can reproduce the observed energy densities, predicting a DM mass in the range $0.1$--$100\, ext{GeV}$ depending on mass ratios and CP-violating parameters. This cogenesis scenario links baryon and DM without a need for portal-mediated number transfer, offers testable implications for long-lived particles at colliders and beam-dump experiments, and opens avenues for extensions to non-monochromatic PBH spectra and more detailed UV completions.

Abstract

We investigate a cogenesis scenario for composite asymmetric dark matter framework: a dark sector has a similar strong dynamics to quantum chromodynamics in the standard model, and the dark-sector counterpart of baryons is the dark matter candidate. The Hawking evaporation of primordial black holes plays the role of a source of heavy scalar particles whose $CP$-violating decay into quarks and dark quarks provides particle--anti-particle asymmetries in baryons and dark matter, respectively. Primordial black holes should evaporate after the electroweak phase transition and before the big-bang nucleosynthesis for explaining the baryon asymmetry of the Universe and for consistent cosmology. We find that this scenario explains the observed values for both baryon and dark matter energy densities when the heavy scalar particles have a mass of $10^6 \text{--} 10^9\, \mathrm{GeV}$ and the primordial black holes have masses of $10^7 \text{--} 10^9\,\mathrm{g}$.

Figures (4)

• Figure 1: The $M_\mathrm{BH}^\mathrm{in}$--$m_\mathcal{T}$ plot for the successful baryogenesis: we obtain the observed baryon energy density $\Omega_B h^2 = 0.022$ on black lines (different values of $\varepsilon_\mathcal{T}$ are written on each lines). The reheating temperature above the electroweak scale $T_\mathrm{EWPT} = 160 \, \mathrm{GeV}$ (the light-cyan region) requires the primordial $B-L$ asymmetry. The light-gray region is excluded by the late-time evaporation of PBHs (corresponding mass of $M_\mathrm{BH} \geq 10^9 \, \mathrm{g}$), and the pink shaded region is excluded by the strong depletion of the produced $\mathcal{T}$. There are several dots on the plot, which correspond to the reference points used in the following figures.
• Figure 2: (Left): The energy density ratio $\rho_{\mathcal{T}'}/\rho_{\mathcal{T}}$ at the reheating temperature as a function of $m_{\mathcal{T}'}/m_{\mathcal{T}}$ with fixed $m_\mathcal{T} = 10^6 \,\mathrm{GeV}$: different input PBH masses $M_\mathrm{BH}^\mathrm{in} = 10^7 \, \mathrm{g}$ (blue thick), $M_\mathrm{BH}^\mathrm{in} = 5 \times 10^7 \, \mathrm{g}$ (red dashed), and $M_\mathrm{BH}^\mathrm{in} = 3 \times 10^8 \, \mathrm{g}$ (green dotted). (Right): A schematic picture for the energy density ratios with different PBH mass. The black-dashed line depicts $m_{\mathcal{T}'}$ that is equal to the PBH temperature as a function of the PBH mass $M_\mathrm{BH}$.
• Figure 3: The DM mass prediction for the fixed parameters $(m_\mathcal{T}\,,M_\mathrm{BH}^\mathrm{in}\,,\varepsilon_\mathcal{T})$ from $0.1 \,\mathrm{GeV}$ to $100 \,\mathrm{GeV}$: the color-triplet mass of $m_\mathcal{T} = 10^6 \, \mathrm{GeV}$ is fixed and the initial PBH mass of $10^8 \, \mathrm{g}$ (left panel) and of $10^9 \, \mathrm{g}$ (right panel). $\varepsilon_\mathcal{T}$ is fixed to produce the correct relic abundance, $\Omega_B h^2 = 0.022$, for each $m_\mathcal{T}$ and $M_\mathrm{BH}^\mathrm{in}$. The values on each plot show the DM mass in GeV. The assumption that the dark photon is the lightest particle in the dark sector is no longer valid for DM masses below $100 \, \mathrm{MeV}$.
• Figure 4: Time evolution of $\rho_R$ (black) and $\rho_\mathrm{BH}$ (magenta). Different line types correspond to different $\beta / \beta_\mathrm{min}$. The gray-thick line represents $\rho_R$ in the absence of PBHs, which is proportional to $t^{-2}$. We take $M_\mathrm{BH} = 10^7 \, \mathrm{g}$.