Constraining Decaying Dark Matter

We revisited the decaying dark matter (DDM) model, in which one collisionless particle decays early into two collisionless particles, that are potentially dark matter particles today. The effect of DDM will be manifested in the cosmic microwave background (CMB) and structure formation. With a systematic modification of CMB calculation tool \texttt{camb}, we can numerically calculated this effect, and compare it to observations. Further Markov Chain Monte Carlo \texttt{cosmomc} runnings update the constraints in that model: the free streaming length $\lambda_{FS}\lesssim0.5$Mpc for nonrelativistic decay, and $((M_{DDM}/keV) Y)^2 (T_d/yr)\lesssim5\times10^{-5}$ for relativistic decay.