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 $\psi$ that serves as the DM candidate, an auxiliary Dirac fermion $\chi$, a real scalar mediator $\phi$, and a heavier real scalar $S$, all stabilized by a $Z_2\times Z_2^{\mathrm{\prime }}$ discrete symmetry. The DM asymmetry is generated through the CP-violating out-of-equilibrium decays of the mediator $\phi$, while the heavier scalar $S$ plays a dual role: it generates the physical CP-violating phase required for the asymmetry through its interference with $\phi$, 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 $Y_{\mathrm{\Sigma }}$, and identify the scaling relations $Y_{-}^{\mathrm{\infty }}\propto {\mu }^2\epsilon \mathrm{/}{m}_{\phi }$ and ${\mathrm{\Omega }}_{\mathrm{D}\mathrm{M}}{h}^2\propto m_{\psi }{\mu }^2\epsilon \mathrm{/}{m}_{\phi }$, which we verify numerically. The observed relic abundance ${\mathrm{\Omega }}_{\mathrm{D}\mathrm{M}}{h}^2\simeq 0.12$ is naturally reproduced for a wide range of parameters; in particular, for $\epsilon ={10}^{-6}$ and $m_{\phi }=200$~GeV, the correct relic density is obtained for $\mu \approx 2.7\times {10}^{-9}$~GeV and $m_{\psi }\approx 40$~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.