Mathematics – Logic
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........21j&link_type=abstract
PhD Dissertation, Massachusetts Inst. of Tech. Cambridge, MA United States
Mathematics
Logic
1
Background Radiation, Dark Matter, Intergalactic Media, Ionization, Neutrinos, Particle Decay, Astronomical Models, Cosmic Background Explorer Satellite, Helium, Hydrogen, Microwaves, Photons, Photoionization
Scientific paper
This thesis describes a possible solution to two unresolved problems in the standard cosmological model: the identity of the dark matter and the apparent reionization of neutral hydrogen in the intergalactic medium (IGM). In particular, we consider the possibility that radiatively decaying neutrinos with mass, mnu approximately 30-60 eV, and lifetime, taunu approximately 1022-1024 sec, constitute the dark matter and are the source of ionizing photons which reionized the IGM. We describe in detail the thermal and ionization history of the universe in the decaying dark matter (DDM) scenario and compare several theoretical predictions of the DDM scenario with observations. Specifically, we compute the intensity of the diffuse photon background today as a result of all past neutrino decays, the photoionizing background at intermediate redshifts, z less than 4, and the relic densities of hydrogen and helium. For each observable, we show the constraints on the mass and lifetime of the decaying neutrino. We also analyze the recent sub-horizon scale South Pole microwave background anisotropy experiment in light of the detection of superhorizon scale microwave background fluctuations by COBE. In this analysis, we show that if the standard recombination history is assumed, the null result of the South Pole experiment is inconsistent (at greater than 95% confidence level) with COBE-normalized, adiabatic structure formation models, for a large range of cosmological parameters. In the DDM scenario, the inconsistency is ameliorated.
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