Abstract
Assisted annihilation generates thermal sub-GeV dark matter through a novel annihilation between a pair of dark matter and standard-model-like states, called the "assister". We show that, depending on the mass hierarchy between the assister and dark matter, there can be either a suppression or a boost of the effective cross section. This augmentation enables the possibility of $\mathcal{O}(100)$ MeV scale dark matter with perturbative coupling that saturates the relic density estimates while being relatively insulated from cosmological constraints like big bang nucleosynthesis and cosmic microwave background.
Highlights
The landscape of particulate interpretation of dark matter (DM) is dominated by the weakly interacting massive particles (WIMPs) that can explain the astrophysically measured dark matter abundance
In a corner of parameter space of the theory, where the operators in the Lagrangian given in Eq (3) dominate over every other term and the mass hierarchy is given by mφ ∼ mA ≪ mS, the assisted annihilation mechanism is operative in setting the DM relic density
We show that when assister(s) are lighter than the DM a Boltzmann boost can significantly enhance assisted annihilation
Summary
The landscape of particulate interpretation of dark matter (DM) is dominated by the weakly interacting massive particles (WIMPs) that can explain the astrophysically measured dark matter abundance They have masses in the GeV scale with weak scale two-body annihilation cross sections driving their freeze-out in the early Universe. An Nð≥3Þ → 2 process driving thermal freeze-out can naturally lead to LDM [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23] This type of annihilation process can be relevant if (i) the two-body cross section is forbidden or strongly suppressed, (ii) densities of the annihilating species are appreciable, and (iii) the velocity of the interacting particles are low [24]. We find that the relative mass hierarchy of the assisters and the DM states together with the decay width of the assisters determine the viable windows for this scenario
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