Phases of cannibal dark matter

Abstract

A hidden sector with a mass gap undergoes an epoch of cannibalism if number changing interactions are active when the temperature drops below the mass of the lightest hidden particle. During cannibalism, the hidden sector temperature decreases only logarithmically with the scale factor. We consider the possibility that dark matter resides in a hidden sector that underwent cannibalism, and has relic density set by the freeze-out of two-to-two annihilations. We identify three novel phases, depending on the behavior of the hidden sector when dark matter freezes out. During the cannibal phase, dark matter annihilations decouple while the hidden sector is cannibalizing. During the chemical phase, only two-to-two interactions are active and the total number of hidden particles is conserved. During the one way phase, the dark matter annihilation products decay out of equilibrium, suppressing the production of dark matter from inverse annihilations. We map out the distinct phenomenology of each phase, which includes a boosted dark matter annihilation rate, new relativistic degrees of freedom, warm dark matter, and observable distortions to the spectrum of the cosmic microwave background.

Direct detection and complementary constraints for sub-GeV dark matter

“…Similarly we do not rely on λ hs for the thermalisation of the SM with the dark sector, yielding conservative limits from BBN. We also assume the trilinear coupling A s to be small, so that the 3 → 2 annihilation rate of singlet scalars is negligible and no phase of 'cannibalism' [62] occurs after freeze-out, again leading to conservative bounds.…”

Fourth Exception in the Calculation of Relic Abundances

“…[5], we assume DM begins in thermal equilibrium, has its number diluted through 2-to-2 annihilations, and has a temperature that tracks the photon temperature (for studies that relax at least one of these assumptions see for example Refs. [14][15][16][17][18][19][20][21][22][23][24][25][26][27]). We consider the presence of two states charged under the symmetry that stabilizes DM: χ and ψ, where m χ < m ψ and χ is DM.…”

Classification of dark pion multiplets as dark matter candidates and collider phenomenology

“…Second, multiplets of dark pions allow for explanations of the dark matter abundance that fall outside the standard paradigm of thermal freeze out of Weakly Interacting Massive Particles (WIMP) [8][9][10]. Strongly Interacting Massive Particles (SIMP) [11], in which 3 → 2 processes determine the DM relic abundance, is a well-known example of this, but dark pions also naturally accommodate more exotic mechanisms such as Codecaying Dark Matter [12][13][14] and ELDER Dark Matter [15]. Such scenarios are typically far less constrained by direct detection than WIMPs.…”