Freeze-in Asymmetric Dark Matter with a Dual-Role Scalar: CP Violation and Symmetric-Component Depletion

We present a minimal, predictive scenario for asymmetric fermionic dark matter (DM) generated through freeze-in. The standard model (SM) is extended by a Dirac fermion $ψ$ that serves as the DM candidate, an auxiliary Dirac fermion $χ$, a real scalar mediator $φ$, and a heavier real scalar $S$, all stabilized by a $Z_2 \times Z_2'$ discrete symmetry. The DM asymmetry is generated through the CP-violating out-of-equilibrium decays of the mediator $φ$, while the heavier scalar $S$ plays a dual role: it generates the physical CP-violating phase required for the asymmetry through its interference with $φ$, and it mediates the annihilation of the symmetric component of the DM population. We solve the coupled Boltzmann equations for the asymmetric yield $Y_-$ and the total yield $Y_Σ$, and identify the scaling relations $Y_-^\infty \propto μ^2 \varepsilon / m_φ$ and $Ω_{\rm DM} h^2 \propto m_ψ\, μ^2 \varepsilon / m_φ$, which we verify numerically. The observed relic abundance $Ω_{\rm DM} h^2 \simeq 0.12$ is naturally reproduced for a wide range of parameters; in particular, for $\varepsilon = 10^{-6}$ and $m_φ= 200$~GeV, the correct relic density is obtained for $μ\approx 2.7 \times 10^{-9}$~GeV and $m_ψ\approx 40$~GeV. We further confront the model with current experimental constraints, including direct detection, indirect detection, collider searches, and DM self-interactions, and show that the predicted signals lie far below the sensitivity of current experiments. This scenario provides a self-consistent and testable realization of asymmetric fermionic DM within the freeze-in framework.

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Authors

S. Peyman Zakeri

Published

Oct 3, 2026

Paper type

preprint

Source

Arxiv