Cold dark matter may be in a metastable state and decays to other particles with a very long lifetime. If the decaying products of the dark matter are weakly interacting, e.g., neutrinos, then it would have little impact on astrophysical processes and is therefore difficult to observe. However, such a decay would affect the expansion history of the Universe because of the change of the equation of state. We utilize a high-quality type Ia supernovae data set selected from several recent observations and the position of the first peak of the cosmic microwave background angular spectrum given by the Wilkinson Microwave Anisotropy Probe three-year data to constrain the dark matter decay-to-neutrino rate $\Gamma =\alpha {\Gamma }_{\chi }$, where $\alpha$ is the fraction of the rest mass which gets converted to neutrinos, and ${\Gamma }_{\chi }$ is the decay width. We find that ${\Gamma }^{-1}>0.7\times {10}^3\mathrm{Gyr}$ at 95.5% confidence level.

• Received 20 February 2008

DOI:https://doi.org/10.1103/PhysRevD.77.103511