Glueball scattering cross section in lattice SU(2) Yang-Mills theory

We calculate the scattering cross section between $0^{++}$ glueballs of the SU(2) Yang-Mills theory on lattice using the indirect (HAL QCD) method. We employ the cluster-decomposition error reduction technique and use all space-time symmetries to improve the signal. The relation between the interglueball cross section and the scale parameter $\Lambda$ is determined as $\sigma_{\phi \phi}$ = (3.5 - 8.0) $\Lambda^{-2}$ (stat.+sys.). From the observational constraints of galactic collisions, we obtain the lower bound $\Lambda$ > 60 MeV. We also discuss the naturalness of the Yang-Mills theory as the theory explaining dark matter.