Nonequilibrium neutrino statistical mechanics in the expanding universe
Apr, 1992
43 pages
Published in:
- Phys.Rev.D 46 (1992) 3372-3387
Report number:
- FERMILAB-PUB-92-084-A
Citations per year
Abstract: (APS)
We study neutrino decoupling in the early Universe (t∼sec,T∼MeV) by integrating the Boltzmann equations that govern the neutrino phase-space distribution functions. In particular, we compute the distortions in the νe and νμντ phase-space distributions that arise in the standard cosmology due to e± annihilations. These distortions are nonthermal, with the effective neutrino temperature increasing with neutrino momentum, approaching a 0.7% increase for electron neutrinos and a 0.3% increase for μ and τ neutrinos at the highest neutrino momenta, and correspond to an increase in the energy density of νe's of about 1.2% and in the energy density of νμντ's of about 0.5% (roughly one additional relic neutrino per cm−3 per species). The distortion for electron neutrinos is larger than that for μ and τ neutrinos because electron neutrinos couple to e±'s through both charged- and neutral-current interactions. Our results graphically illustrate that neutrino decoupling is a continuous process which is momentum dependent. Because of subtle cancellations, these distortions lead to only a tiny change in the predicted primordial He4 abundance, ΔY≃1−2×10−4.- astrophysics
- statistical mechanics
- neutrino: decoupling
- decoupling: neutrino
- phase space
- energy: density
- Boltzmann equation
- nucleus: production
- production: nucleus
- numerical calculations
References(9)
Figures(0)