2014/03/31 by Hiroyuki Ishida, Motohiko Kusakabe, Hiroshi Okada
Physics and Astronomy · #Baryon #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #Electron #Fermion #Inverse #Lithium (medication) #Neutrino #Neutrino Physics Research #Neutrino oscillation #Nuclear physics #Particle physics #Physics #Production (economics) #Sterile neutrino #astro-ph.CO #hep-ph
paper · pdf · doi:10.1103/physrevd.90.083519
published as Phys. Rev. D 90, 083519 (2014) · 34 pages, 16 figures, major corrections made, contents extended, Figures corrected and added, conclusion unchanged
arxiv created 2014/08/11 · openalex publication_date 2014/10/20 · arxiv updated 2014/10/29 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The primordial lithium abundance inferred from spectroscopic observations of metal-poor stars is \ensuremath∼3 times smaller than the theoretical prediction in the standard big bang nucleosynthesis (BBN) model. We assume a simple model composed of standard model particles and a sterile neutrino \ensuremathνH with mass of O(10) MeV which decays long after BBN. We then investigate cosmological effects of a sterile neutrino decay, and check if a sterile neutrino can reduce the primordial lithium abundance. We formulate the injection spectrum of nonthermal photon induced by the \ensuremathνH decay. We take into account the generation of electrons and positrons, e^\ifmmode±\else\textpm\fi's, and active neutrinos at the \ensuremathνH decay, the primary photon production via the inverse Compton scattering of cosmic background radiation (CBR) by energetic e^\ifmmode±\else\textpm\fi, and electromagnetic cascade showers induced by the primary photons. The steady state injection spectrum is then derived as a function of the \ensuremathνH mass and the photon temperature. The \ensuremathνH decay produces energetic active neutrinos which are not thermalized, and e^\ifmmode±\else\textpm\fi's which are thermalized. We then derive formulas relevant to the \ensuremathνH decay rates and formulas for the baryon-to-photon ratio \ensuremathη and effective neutrino number Neff. The initial abundance, mass, and lifetime of \ensuremathνH are taken as free parameters. We then consistently solve (1) the cosmic thermal history, (2) nonthermal nucleosynthesis induced by the nonthermal photons, (3) the \ensuremathη value, and (4) the Neff value. We find that an effective 7Be destruction can occur only if the sterile neutrino decays at photon temperature T=O(1) keV. Amounts of energy injection at the \ensuremathνH decay are constrained from limits on primordial D and 7Li abundances, the Neff value, and the CBR energy spectrum. We find that 7Be is photodisintegrated and the Li problem is partially solved for the lifetime 104--105 s and the mass \ensuremath\gtrsim14 MeV. 7Be destruction by more than a factor of 3 is not possible because of an associated D overdestruction. In the parameter region, the \ensuremathη value is decreased slightly, while the Neff value is increased by a factor of \mathrm\ensuremathΔNeff\ensuremath\lesssim1. In this study, errors in photodisintegration cross sections of 7Be(\ensuremathγ,\ensuremathα)3He and 7Li(\ensuremathγ,\ensuremathα)3H that have propagated through the literature are corrected, and new functions are derived based on recent nuclear experiments. It is found that the new photodisintegration rates are 2.3 to 2.5 times smaller than the old rates. The correct cross sections thus indicate significantly smaller efficiencies of 7Be and 7Li photodisintegration. Abundances of sterile neutrino necessary for the 7Li reduction are much smaller than thermal freeze-out abundances. The relic sterile neutrino, therefore, must be diluted between the freeze-out and BBN epochs by some mechanism.