Dark matter scattering cross section and dynamics in dark Yang-Mills
  theory
  We calculate for the first time the scattering cross section between lightest
glueballs in $SU(2)$ pure Yang-Mills theory, which are good candidates of dark
matter. In the first step, we evaluate the interglueball potential on lattice
using the HAL QCD method, with several lattice spacings ($\beta = 2.1, 2.2,
2.3, 2.4$, and 2.5). The systematics associated with nonzero angular momentum
effect is removed by subtracting the centrifugal force. The statistical
accuracy is improved by employing the cluster-decomposition error reduction
technique and by using all space-time symmetries. We then determine the low
energy glueball effective Lagrangian and the scattering cross section at low
energy, which is compared with the observational constraint on the dark matter
self-scattering. We derive the lower bound on the scale parameter of the
$SU(2)$ Yang-Mills theory, as $\Lambda > 60$ MeV.
