Nonlinear growing neutrino cosmology
  The energy scale of Dark Energy, $\sim 2 \times 10^{-3}$ eV, is a long way
off compared to all known fundamental scales - except for the neutrino masses.
If Dark Energy is dynamical and couples to neutrinos, this is no longer a
coincidence. The time at which Dark Energy starts to behave as an effective
cosmological constant can be linked to the time at which the cosmic neutrinos
become nonrelativistic. This naturally places the onset of the Universe's
accelerated expansion in recent cosmic history, addressing the why-now problem
of Dark Energy. We show that these mechanisms indeed work in the Growing
Neutrino Quintessence model - even if the fully nonlinear structure formation
and backreaction are taken into account, which were previously suspected of
spoiling the cosmological evolution. The attractive force between neutrinos
arising from their coupling to Dark Energy grows as large as $10^6$ times the
gravitational strength. This induces very rapid dynamics of neutrino
fluctuations which are nonlinear at redshift $z \approx 2$. Nevertheless, a
nonlinear stabilization phenomenon ensures only mildly nonlinear oscillating
neutrino overdensities with a large-scale gravitational potential substantially
smaller than that of cold dark matter perturbations. Depending on model
parameters, the signals of large-scale neutrino lumps may render the cosmic
neutrino background observable.
