Dark energy from mass varying neutrinos

Abstract

We show that mass varying neutrinos (MaVaNs) can behave as a negative pressure fluidwhich could be the origin of the cosmic acceleration. We derive a model independentrelation between the neutrino mass and the equation of state parameter of the neutrinodark energy, which is applicable for general theories of mass varying particles. The neutrinomass depends on the local neutrino density and the observed neutrino mass can exceed thecosmological bound on a constant neutrino mass. We discuss microscopic realizations of theMaVaN acceleration scenario, which involve a sterile neutrino. We consider naturalnessconstraints for mass varying particles, and find that both eV cut-offs and eVmass particles are needed to avoid fine-tuning. In microscopic realizations of thisscenario with a sterile neutrino, these considerations give the sterile neutrino amaximum mass today of order an eV, which could be detectable at MiniBooNE.Because the sterile neutrino was much heavier at earlier times, constraints frombig bang nucleosynthesis on additional states are not problematic. We considerregions of high neutrino density and find that the most likely place today to findneutrino masses which are significantly different from the neutrino masses inour solar system is in a supernova. The possibility of different neutrino massin different regions of the galaxy and the local group could be significant forZ-burst models of ultra-high energy cosmic rays. We also consider the cosmology of and theconstraints on the ‘acceleron’, the scalar field which is responsible for the varying neutrinomass, and briefly discuss neutrino density dependent variations in other constants, such asthe fine structure constant.