Searches for invisible new particles at Belle II

Abstract: Belle~II has unique sensitivity for a broad class of models postulating the existence of dark matter particles with masses in the MeV--GeV range. We present recent world-leading results from Belle~II searches for several non-SM particles. These include production of $Z'$ bosons, axion-like particles, and dark scalars in association with two muons in $e^+e^-$ collisions; long-lived (pseudo)scalars produced in decays of \textit{B}-mesons; and invisible particles produced in decays of $\tau$ leptons.