Model independent constraints on mass-varying neutrino scenarios
  Models of dark energy in which neutrinos interact with the scalar field
supposed to be responsible for the acceleration of the universe usually imply a
variation of the neutrino masses on cosmological time scales. In this work we
propose a parameterization for the neutrino mass variation that captures the
essentials of those scenarios and allows to constrain them in a model
independent way, that is, without resorting to any particular scalar field
model. Using WMAP 5yr data combined with the matter power spectrum of SDSS and
2dFGRS, the limit on the present value of the neutrino mass is $m_0 \equiv
m_{\nu}(z=0) < 0.43 (0.28)$ eV at 95% C.L. for the case in which the neutrino
mass was lighter (heavier) in the past, a result competitive with the ones
imposed for standard (i.e., constant mass) neutrinos. Moreover, for the ratio
of the mass variation of the neutrino mass $\Delta m_{\nu}$ over the current
mass $m_0$ we found that $\log[|\Delta m_{\nu}|/m_0] < -1.3 (-2.7)$ at 95% C.L.
for $\Delta m_{\nu} < 0 (\Delta m_{\nu} > 0)$, totally consistent with no mass
variation. These stringent bounds on the mass variation are not related to the
neutrino free-streaming history which may affect the matter power spectrum on
small scales. On the contrary, they are imposed by the fact that any
significant transfer of energy between the neutrino and dark energy components
would lead to an instability contradicting CMB and large scale structure data
on the largest observable scales.
