Nuclear, Particle, Astroparticle and Cosmology (NUPAC) Seminars
Nucleosynthesis, Neff , and Neutrino Mass implications from Dark Radiation
Presented by Evan Grohs (UC San Diego)
With the advent of powerful Cosmic Microwave Background (CMB) telescopes, we are entering the era of precision cosmology. The standard cosmological model has come under increased scrutiny with precise CMB and astronomical measurements. The fi ve measurements of interest are: the primordial deuterium abundance; the primordial 4He abundance; Neff ; the sum of the light neutrino masses; and the baryon-to-photon ratio. We look at the eff ect of extra relativistic degrees of freedom (the so-called Dark Radiation) in the early universe and the repercussions on the five cosmological measurements. Heavy-particle decay produces non-thermal neutrinos which can change the neutron to proton ratio and subsequently the primordial light-nuclide abundances of deuterium and 4He. Although the decays raise the energy density in the neutrino seas, it also causes the phenomenon dilution which lowers the energy of the neutrino seas with respect to the plasma. The competition between dilution and added non-thermal neutrino energy aff ects both Neff and the sum of the light neutrino masses. In addition, dilution can change the effective temperature of other decoupled particle species. In the theory of sterile neutrino dark matter, dilution scenarios produce an Omegam ~ 25% using a sterile neutrino with mass of a few keV and effective temperature lower than the photon temperature. We also investigate the e ffect of active-sterile oscillations prior to Big Bang Nucleosynthesis for sterile neutrino masses of a few eV.
2:00 pm, Tuesday, September 10, 2013
PAIS-2540, PAIS
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