Asteroid-mass soliton as the dark matter-baryon coincidence solution

Abstract

Nontopological solitons formed during first-order phase transitions can serve as macroscopic dark matter candidates, with their stability ensured by a charge asymmetry traditionally assumed to originate from baryogenesis. Following this generic pattern, we demonstrate that solitogenesis after baryogenesis makes the solitons a coincident dark matter candidate, providing new explanations for the coincidence problem between baryon and dark matter energy densities. We derive a novel and robust conclusion: asteroid-mass coincident soliton dark matter is always accompanied by detectable gravitational waves observable by LISA, $μ$Ares, and Theia, providing a new candidate beyond primordial black holes in this mass window. Additionally, we propose a simple neutrino-ball scenario that addresses baryon asymmetry, dark matter, and neutrino masses, featuring new particles below the electroweak scale and correlated observable signals, including lensing, gravitational waves, and soliton evaporation or collisions.

Figures (3)

• Figure 1: Sketch of the paradigm. Both the baryon asymmetry ($Y_B$) and the hidden sector charge asymmetry ($Y_\chi$) are generated during the baryogenesis process, satisfying $Y_\chi/Y_B\sim\mathcal{O}(0.1-1)$. The SM particles penetrate into the true vacuum, yielding the observed BAU. The asymmetric dark particles inherited from baryogenesis are reflected by the bubble wall due to their large mass gap, consequently being trapped in the false vacuum to form soliton DM.
• Figure 2: The parameter space of coincident Fermi-ball DM. Left: $T_*$ and $M_{\rm fb}$ as functions of $(\alpha,\beta/H_*)$, with $c_\chi=0.5$ fixed. Right: $c_\chi$ as a function of $(M_{\rm fb},R_{\rm fb})$, with $\alpha=0.1$ fixed. The colored shaded regions indicate the constraints and projected detection regimes from lensing and GW experiments. See the text for details.
• Figure A1: The parameter space fixing $\lambda_{\phi}=0.18$, $\lambda_\eta=0.30$, and $\lambda_{\phi\eta}=1.2$. The neutrino-ball mass and GW frequency are plotted as black and blue contours, respectively. The orange, gray, green, and light blue regions represent the parameter space that the mass gap is insufficient to trap $\chi$'s in the false vacuum, the solitons are unstable against $\chi\to\phi\nu$ decay, the bubbles cannot nucleate, and the Yukawa Landau pole is below 100 TeV, respectively. See the text for details.