Dark Parton Shower Effects for Cosmic Ray Boosted Dark Matter

We investigate the dark parton shower effects in the direct detection of cosmic-ray boosted dark matter (CRDM), focusing on a dark photon-mediated model with fermionic dark matter-electron interactions. Utilizing a Monte Carlo framework to incorporate the Sudakov form factors and kinematic dipole recoil schemes, we simulate the CRDM energy spectrum evolution under the dark sector splitting. Our results reveal a significant energy-dependent modification of the CRDM flux. For a 1 keV dark matter (DM) mass and a coupling of gD=3, the CRDM flux can be enhanced by a factor up to 1.12 in the O(10⁻² ~ 1) MeV energy range for 2m_χ mA^ 10⁻² MeV, while it is suppressed by more than $50%$ at energy around 100 MeV for mA^ 10⁻³ MeV. We then translate these effects into the experimental sensitivities for PandaX-4T, Super-Kamiokande, and JUNO. At mA^ = 10⁻³ MeV and gD=3, the bounds on the kinetic mixing parameter ε² are relaxed by factors of 1.02, 1.6 and 1.4, respectively. Finally, we demonstrate that the parameter space considered is consistent with those astrophysical constraints on dark matter self-interactions from observations of the Bullet Cluster.