Search for a Dark Leptophilic Scalar $\phi_L$ in $e^+e^-\to tau+tau-\phi_L$ with the BABAR detector
Many models of dark matter and hidden sectors predict new particles with masses below the electroweak scale. Low-energy electron-positron colliders such as BABAR are ideally suited to discover these hidden-sector particles. We present a recent search for prompt and long-lived hidden scalars produced in association with tau leptons and decaying into a lepton pair. This search is sensitive to viable models that could account for the muon $g-2$ excess. We also present results a search for dark muonic forces, and for invisible particles produced in six-quark final states. These examples show the importance of B-factories in constraining and discovering new hidden-sector physics beyond the Standard Model.