Cosmology of Symmetron Mass-Varying Neutrinos

Abstract

In this thesis we investigate a dynamical cosmological constant called the quintessence. Quintessence is a scalar field varying in both space and time following a chosen potential. To explain the coincidence problem, e.g. why the expansion of the universe is accelerating now, we couple the scalar field to neutrinos. The coupling changes the constant neutrino mass to a mass varying neutrino that depends on the scalar field. However, this coupling causes a fifth force on the neutrinos creating to much clumping on large scales. We suggest to use the screening potential of the symmetron model to prevent this clumping. The symmetron forces the scalar field to zero at high neutrino densities and spontaneously breaks the potential at low neutrino densities making the scalar field active. We modified a standard code for the cosmological evolution (CAMB) to include both the mass varying neutrino and the symmetron. Adding an cosmological constant is still needed to achieve the observed late time accelerated expansion. Simulation where done for three different scenarios, depending on the occurrence of the symmetry breaking. There is a notable effect from the symmetron-neutrino coupling and larger effects as one increases the neutrino mass. However, for all scenarios one observe small changes compared with the standard LCDM.