Sigma_8 tension and dark matter-dark radiation interaction

Stimulated by the sigma_8 tension that  the sigma_8 value derived from LSS measurements is ~ 3\sigma lower than that derived from CMB assuming LCDM, there have been many discussions about the signatures of new physics, e.g. interacting dark sector. In several previous works, the dark matter-dark radiation (DM-DR)interaction was claimed to be favored by more than 3\sigma significance level by the LSS measurements. In this talk, I will show the prior claims are too optimistic since they somehow ignored the uncertainty in the mass-observable relation of the LSS measurements. Including this uncertainty in the analysis, we will find no preference for the DM-DR interaction. To resolve the DM-DR interaction, we could either rely on future LSS measurements with reduced uncertainties, or go deeper into measurements of smaller scales, e.g., Lyman-alpha forest.