Bound-state formation for thermal relic dark matter and unitarity

Abstract

We show that the relic abundance of thermal dark matter annihilating via a long-range interaction, is significantly affected by the formation and decay of dark matter bound states in the early universe, if the dark matter mass is above a few TeV. We determine the coupling required to obtain the observed dark matter density, taking into account both the direct 2-to-2 annihilations and the formation of bound states, and provide an analytical fit. We argue that the unitarity limit on the inelastic cross-section is realized only if dark matter annihilates via a long-range interaction, and we determine the upper bound on the mass of thermal-relic dark matter to be about 197 (139) TeV for (non)-self-conjugate dark matter.ArXiv ePrint: 1407.7874

Effects of bound states on dark matter annihilation

“…We also note that Refs. [8,9] tried to sum over all the energy levels (n ≥ 1) but concluded it yields a factor of π 2 =6 compared to the ground state case. However, they used the recombination cross section equation (75.6) in [3] that only applies for n ¼ 1 and also underestimated the enhancement.…”

Asymmetric dark matter: residual annihilations and self-interactions

“…S ann and S BSF depend only on the ratio α D /v rel in the Coulomb approximation [60,61], which is satisfactory during freeze-out [44] (for a caveat, see [62] and Sec. 7.2).…”

Dynamical generation of the weak and Dark Matter scales from strong interactions

“…Their annihilation cross section is estimated to be σv ∼ g 4 TC /4πM 2 , around the unitarity bound [34,35]. By performing a naive rescaling of the QCD non-relativistic pp cross section, σ pp v ∼ 100/m 2 p , we estimate that the cosmological thermal relic abundance of a technibaryon equals the total DM abundance if its mass is loosely around m B ∼ 200 TeV.…”

“…The lightest techni-baryon is stable and is a natural DM candidate; if it is a thermal relic, the observed DM abundance is reproduced for m B ≈ 100 TeV [34,35].…”