TY - JOUR

T1 - Quantum kinetic equation and cosmic pair annihilation

AU - Matsumoto, Sh

AU - Yoshimura, M.

PY - 1999/6/15

Y1 - 1999/6/15

N2 - Pair annihilation of heavy stable particles that occurs in the early universe is investigated, and a quantum kinetic equation for the momentum distribution of the annihilating particle is derived, using the influence functional method. A bosonic field theory model is used to describe the pair annihilation in the presence of decay product particles making up a thermal environment. A crossing symmetric Hartree approximation that determines self-consistently the equilibrium distribution is developed for an otherwise intractable theory. The time evolution equation and its Markovian approximation are derived to give a generalized Boltzmann equation including off-shell effects. The narrow width approximation to an energy integral in this equation gives the usual Boltzmann equation in a thermal bath of light particles. The off-shell effect is a correction to the Boltzmann equation at high temperatures, but is dominant at low temperatures. The effect changes the equilibrium distribution from the familiar 1/(eωk/T-1) to a modified one given by a Gibbs formula. Integrated over momenta, the particle number density becomes roughly of order (coupling) X √T/MT3 at low temperatures for S-wave annihilation. The relic mass density in the present universe is insensitive to the coupling strength in a large range of the mass and the coupling parameters, and scales with the WIMP mass as ≈6×104 eV cm-3 (M/GeV)4/3. The bound from the closure density gives an upper WIMP mass bound roughly of order 1 GeV in the present model.

AB - Pair annihilation of heavy stable particles that occurs in the early universe is investigated, and a quantum kinetic equation for the momentum distribution of the annihilating particle is derived, using the influence functional method. A bosonic field theory model is used to describe the pair annihilation in the presence of decay product particles making up a thermal environment. A crossing symmetric Hartree approximation that determines self-consistently the equilibrium distribution is developed for an otherwise intractable theory. The time evolution equation and its Markovian approximation are derived to give a generalized Boltzmann equation including off-shell effects. The narrow width approximation to an energy integral in this equation gives the usual Boltzmann equation in a thermal bath of light particles. The off-shell effect is a correction to the Boltzmann equation at high temperatures, but is dominant at low temperatures. The effect changes the equilibrium distribution from the familiar 1/(eωk/T-1) to a modified one given by a Gibbs formula. Integrated over momenta, the particle number density becomes roughly of order (coupling) X √T/MT3 at low temperatures for S-wave annihilation. The relic mass density in the present universe is insensitive to the coupling strength in a large range of the mass and the coupling parameters, and scales with the WIMP mass as ≈6×104 eV cm-3 (M/GeV)4/3. The bound from the closure density gives an upper WIMP mass bound roughly of order 1 GeV in the present model.

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U2 - 10.1103/PhysRevD.59.123511

DO - 10.1103/PhysRevD.59.123511

M3 - Article

AN - SCOPUS:17144391153

SN - 0556-2821

VL - 59

SP - 1

EP - 30

JO - Physical review D: Particles and fields

JF - Physical review D: Particles and fields

IS - 12

M1 - 123511

ER -