  The effects of mass-varying neutrinos on cosmic microwave background (CMB)
anisotropies and large scale structures (LSS) are studied. In these models,
dark energy and neutrinos are coupled such that the neutrino masses are
functions of the scalar field playing the role of dark energy. We begin by
describing the cosmological background evolution of such a system. It is
pointed out that, similar to models with a dark matter/dark energy interaction,
the apparent equation of state measured with SNIa can be smaller than -1. We
then discuss the effect of mass-varying neutrinos on the CMB anisotropies and
the matter power spectrum. A suppression of power in the CMB power spectrum at
large angular scales is usually observed. We give an explanation for this
behaviour and discuss different couplings and quintessence potentials to show
the generality of the results obtained. We perform a likelihood analysis using
wide-ranging SNIa, CMB and LSS observations to assess whether such theories are
viable. Treating the neutrino mass as a free parameter we find that the
constraints on the coupling are weak, since CMB and LSS surveys give only upper
bounds on the neutrino mass. However, fixing a priori the neutrino masses, we
find that there is some evidence that the existence of such a coupling is
actually preferred by current cosmological data over the standard LambdaCDM
cosmology.
