Even SIMP miracles are possible

TL;DR

This paper explores alternative mechanisms for dark matter freeze-out involving bound states and even-numbered interactions, expanding the theoretical landscape beyond traditional odd-numbered annihilation processes.

Contribution

It introduces the concept that bound states enable successful dark matter freeze-out through even-numbered interactions, broadening the scope of viable dark matter models.

Findings

Bound states can facilitate dark matter freeze-out via even-numbered interactions.

Formation of bound states can catalyze odd-numbered annihilation processes.

Theoretical models include confining sectors, glueball dark matter, and strongly interacting scalar theories.

Abstract

Strongly interacting massive particles $\pi$ have been advocated as prominent dark matter candidates when they regulate their relic abundance through odd-numbered $3 \pi \to2\pi$ annihilation. We show that successful freeze-out may also be achieved through even-numbered interactions $X X \to \pi \pi $ once bound states $X$ among the particles of the low-energy spectrum exist. In addition, $X$-formation hosts the potential of also catalyzing odd-numbered $3 \pi \to2\pi$ annihilation processes, turning them into effective two-body processes $\pi X \to \pi\pi$. Bound states are often a natural consequence of strongly interacting theories. We calculate the dark matter freeze-out and comment on the cosmic viability and possible extensions. Candidate theories can encompass confining sectors without a mass gap, glueball dark matter, or $\phi^3$ and $\phi^4$ theories with strong Yukawa or self-interactions.