Dark Sector Searches at e+e− Colliders

The Standard Model (SM) of particle physics is one of the most successful frameworks in modern physics, yet it leaves several fundamental questions unanswered, including the nature of dark matter (DM). Precise knowledge of DM is crucial for testing astrophysical and cosmological observations and for determining the matter density of our Universe. Many hidden dark-sector models beyond the SM open the possibility of coupling between DM and SM particles via various portals. The corresponding new-physics particles include light Higgs boson, dark photon, axion-like particle, and spin-1/2 fermions. Furthermore, the introduction of a dark baryon could simultaneously explain the origin of DM and the observed matter-antimatter asymmetry in the Universe. If these hypothetical particles have masses of a few GeV, they can be explored at high-intensity e+e− colliders, such as the BaBar, Belle/Belle II, and BESIII experiments. This report reviews the current status of DM searches at e+e− colliders, with a focus on portal-based scenarios.