Probing Dark Energy with Neutrino Number
  From measurements of the cosmic microwave background (CMB), the effective
number of neutrino is found to be close to the standard model value Neff =
3.046 for the \LambdaCDM cosmology. One can obtain the same CMB angular power
spectrum as that of \LambdaCDM for the different value of Neff by using the
different dark energy model (i.e. for the different value of w). This
degeneracy between Neff and w in CMB can be broken from future galaxy survey
using the matter power spectrum.
