The Self-Organized Criticality of Dark Matter in the Early Universe

Abstract

We propose a new mechanism for dark matter freeze-out that results in the self-organized criticality in dark matter production, wherein the final relic abundance is independent of initial inputs, in analogy to scale invariance in other realms of non-equilibrium physics. The dynamic of self-organized is triggered through a semi-annihilation process $\chi \phi \to \phi \phi$ in the premise of the instability of dark partner $\phi$, where $\chi$ is the dark matter candidate. The relic abundance can be analytically ascertained when the dark partner is slightly heavier than the dark matter, which permits a substantially heavy dark matter mass without violating unitarity bounds. We demonstrate that this process provides a bridge between the freeze-in and freeze-out mechanisms, and that the intricate dynamics of self-organized criticality can be actualized in a thermal dark sector bath.