Growing Neutrino Cosmology

In growing neutrino models, the neutrino mass increases in time and stops the dynamical evolution of a dark energy scalar field, thus explaining the ‘why now’ problem. A new attractive force, mediated by the ‘cosmon’ scalar field, makes non relativistic neutrino form lumps on the scales of superclusters and beyond. Nonlinear neutrino lumps are predicted to form at redshift z ≈ 1 and, if observed, could be an indication for a new attractive force stronger than gravity. It has been recently proposed 1) 3) that a growing mass of the neutrinos may play a key role in stopping the dynamical evolution of the dark energy scalar field, the cosmon 4) 8). In these models, the onset of accelerated expansion is triggered by neutrinos becoming non relativistic. For late cosmology, z . 5, the overall cosmology is very similar to the usual ΛCDM concordance model with a cosmological constant, such that the equation of state of dark energy is close to w = −1 and the expansion of the universe accelerates. In “growing neutrino cosmologies” the present dark energy density ρh(t0) can be expressed in terms of the present average neutrino mass mν(t0)