Nonequilibrium neutrino statistical mechanics in the expanding Universe

Journal Article · Thu Oct 15 00:00:00 EDT 1992 · Physical Review, D (Particles Fields); (United States)

DOI:https://doi.org/10.1103/PhysRevD.46.3372· OSTI ID:6950143

Dodelson, S ^[1]; S Turner, M ^[2]

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1. NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States)
2. NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States) Departments of Physics and Astronomy ( ) Astrophysics, Enrico Fermi Institute, The University of Chicago, Chicago, Illinois 60637-1433 (United States)

We study neutrino decoupling in the early Universe ({ital t}{similar to}sec,{ital T}{similar to}MeV) by integrating the Boltzmann equations that govern the neutrino phase-space distribution functions. In particular, we compute the distortions in the {nu}{sub {ital e}} and {nu}{sub {mu}}/{nu}{sub {tau}} phase-space distributions that arise in the standard cosmology due to {ital e}{sup {plus minus}} 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 {mu} and {tau} neutrinos at the highest neutrino momenta, and correspond to an increase in the energy density of {nu}{sub {ital e}}'s of about 1.2% and in the energy density of {nu}{sub {mu}}/{nu}{sub {tau}}'s of about 0.5% (roughly one additional relic neutrino per cm{sup {minus}3} per species). The distortion for electron neutrinos is larger than that for {mu} and {tau} neutrinos because electron neutrinos couple to {ital e}{sup {plus minus}}'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 {sup 4}He abundance, {Delta}{ital Y}{congruent}1--2{times}10{sup {minus}4}.

• OSTI ID: 6950143
• Journal Information: Physical Review, D (Particles Fields); (United States), Vol. 46:8; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
UNIVERSE
NEUTRINOS
ANNIHILATION
BOLTZMANN EQUATION
BOLTZMANN STATISTICS
CHARGED-CURRENT INTERACTIONS
COSMOLOGY
CP INVARIANCE
DECOUPLING
DISTRIBUTION FUNCTIONS
ELECTRON NEUTRINOS
ELECTRON-POSITRON INTERACTIONS
ENERGY DENSITY
MUON NEUTRINOS
NEUTRAL-CURRENT INTERACTIONS
NUCLEOSYNTHESIS
PHASE SPACE
STATISTICAL MECHANICS
TAU NEUTRINOS
THERMAL EQUILIBRIUM
BASIC INTERACTIONS
DIFFERENTIAL EQUATIONS
ELECTROMAGNETIC INTERACTIONS
ELEMENTARY PARTICLES
EQUATIONS
EQUILIBRIUM
FERMIONS
FUNCTIONS
HEAVY LEPTONS
INTERACTIONS
INVARIANCE PRINCIPLES
LEPTON-LEPTON INTERACTIONS
LEPTONS
MASSLESS PARTICLES
MATHEMATICAL SPACE
MECHANICS
PARTIAL DIFFERENTIAL EQUATIONS
PARTICLE INTERACTIONS
POSTULATED PARTICLES
SPACE
SYNTHESIS
662110* - General Theory of Particles & Fields- Theory of Fields & Strings- (1992-)
661100 - Classical & Quantum Mechanics- (1992-)