Fredagskollokvium (NB note time and place!): Christof Wetterich: Have neutrinos to do with Dark Energy ?

In contrast to other particles, not much is known about the time-dependence of the tiny neutrino masses. We discuss a scenario where the neutrino mass grows on cosmological time scales due to the time evolution of a cosmological scalar field - the cosmon. As soon as the neutrinos become non-relativistic at redshift around five they stop the further evolution of the cosmon. From that time on the potential energy of the cosmon acts similar to a cosmological constant and the accelerated expansion of the Universe sets in soon afterwards. The present dark energy density is computable in terms of the neutrino masses and comes out in the right order of magnitude, explaining why dark energy becomes important only in the present cosmological epoch. Realistic models of dynamical dark energy can be built for this scenario, and observational tests are possible. In particular , neutrinos form lumps much larger than clusters of galaxies. Their gravitational potential will show up in a number of present or future cosmological observations.