Mixed dark matter was a theory of dark matter which was promising up to the late 1990s.
"Mixed" dark matter is also called hot + cold dark matter. Hot dark matter has only one known form – neutrinos, although other forms are speculated to exist.Cosmologically important dark matter is now believed to be pure cold dark matter. However, in the early 1990s, the power spectrum of fluctuations in the galaxy clustering did not agree entirely with the predictions for a standard cosmology built around pure cold dark matter. Mixed dark matter with a composition of about 80% cold and 20% hot (neutrinos) was investigated and found to agree better with observations. This model was made obsolete by the discovery in 1998 of the acceleration of universal expansion, which eventually led to the dark energy + dark matter paradigm of this decade.