  We present a model of self-interacting dark matter based on QCD-like theories
and inspired by the proximity of $a_0(980\pm 20)$ to the $K\bar{K}(990)$
threshold. Dark matter is comprised of dark pions which self-scatter via the
$\sigma$ resonance close to the $\pi\pi$ threshold. While the linear sigma
model serves as a qualitative guide, a fully unitary description of the
scattering in the strongly coupled regime is given by effective range theory.
The introduction of a kinetically mixed dark photon allows the dark pion to
either freeze-out or -in. We study the viable parameter space which explains
the observed relic abundance while evading all current constraints. Searches
for dark matter self interactions at different scales, (in)direct detection
signals, and (in)visibly-decaying dark photons will test this model in the near
future.
