Asymmetric Two-Component Scalar FIMP Dark Matter

Abstract

We propose a two-component asymmetric feebly interacting massive particle (FIMP) dark matter (DM) model in which both DM candidates are complex scalar fields. The model is an extension of the standard model (SM) by two scalar DM components and a heavy scalar mediator, stabilized by a $\mathbb{Z}_2 \times \mathbb{Z}_2'$ symmetry. DM is produced via the freeze-in mechanism through the Higgs portal, while the CP-violating decay of the heavy mediator generates an asymmetry in the first component, which is partially transferred to the second component via quartic interactions. By solving the Boltzmann equations numerically, we compute the relic density and perform a detailed scan over the parameter space. The observed relic density $\Omega_{\text{DM}} h^2 = 0.12 \pm 0.001$ is successfully reproduced for benchmark parameters $m_{\phi_1}=0.1$~GeV, $m_{\phi_2}=0.5$~GeV, $M_S=100$~GeV, and $\mu_{12}=3\times10^{-9}$, with the second component contributing only about $5\%$ to the total abundance. We also examine phenomenological constraints. The DM self-interaction cross section lies orders of magnitude below the Bullet cluster bound ($\sigma/m < 0.47$~cm$^2$/g) and the more stringent double radio relic limit ($\sigma/m < 0.22$~cm$^2$/g). The invisible Higgs decay branching ratio is $\sim 6\times10^{-18}$, well below the LHC upper limit, and direct detection prospects are negligible due to the small Higgs portal couplings. Our model establishes a novel connection between two-component DM, the freeze-in mechanism, and DM asymmetry.