Upper limits on neutrino masses from cosmology

The latest results from the WMAP satellite [1] confirm the success of the ΛCDM model, where ∼ 75 % of the mass-energy density is in the form of dark energy, with matter, most of it in the form of cold dark matter (CDM) making up the remaining 25 % . Neutrinos with masses on the eV scale or below will be a hot component of the dark matter and will free-stream out of overdensities and thus wipe out small-scale structures. This fact makes it possible to use observations of the clustering of matter in the universe to put upper bounds on the neutrino masses. An excellent review of the subject can be found in [3]. With the improved quality of cosmological data sets seen in recent years, the upper limits have improved, and some quite impressive claims have been made in the recent literature. I will in the following summarize the latest upper bounds and point out some of the potential systematic uncertainties that need to be clarified in the future.