Effects of Mass Varying Neutrinos on Cosmological Parameters as determined from the Cosmic Microwave Background

Abstract: 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.