Effects of Mass Varying Neutrinos on Cosmological Parameters as
  determined from the Cosmic Microwave Background
  In models with a light scalar field (the `acceleron') coupled to neutrinos,
neutrino masses depend on neutrino density. The resulting coupled system of
mass varying neutrinos (MaVaNs) and the acceleron can act as a negative
pressure fluid and is a candidate for dark energy \cite{Fardon:2003eh} . MaVaNs
also allow for higher $\Sigma$m$_\nu$ than terrestrial bounds, giving late
forming warm dark matter. In this paper we study the effect of increasing
neutrino mass on the CMB spectrum, implementing MaVaNs cosmology using CMBEASY.
We find that the CMB spectrum is only affected at very low multipoles. Cosmic
variance allows for significant warm dark matter at late times. This implies
that in MaVaNs cosmology $\sigma_8$ as determined by the CMB may not be a good
determinant of structure evolution at late times, potentially reducing the
tension between $\sigma$$_{8}$ as reported by Planck Collaboration
\cite{PlanckSZ:2013} without increasing the tension in the Planck determined
value of Hubble's constant. In addition, in MaVaNs theories, CMB data do not
necessarily constrain possible neutrino mass results in terrestrial
experiments.
