Hidden sectors in plain sight

The ubiquity of dark matter, the origin of the matter-antimatter asymmetry, and neutrino oscillations point to the existence of as-yet unidentified new particles and/or forces. These feebly interacting particles, part of their own hidden sector of particle physics, could be produced copiously in colliders but lie undiscovered in existing data. Motivated by examples of hidden sectors that solve outstanding problems in the SM, I will show how new searches using data from lower energy electron-positron colliders such as BaBar and Belle II can discover hidden particles that might have otherwise been missed. I will also briefly discuss synergies with high-energy colliders, with the LHC offering both challenges and opportunities for hidden sectors.