Nonequilibrium neutrino statistical mechanics in the expanding Universe.
Nonequilibrium neutrino statistical mechanics in the expanding Universe.
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膨胀宇宙中的非平衡中微子统计力学。
DOI：
10.1103/physrevd.46.3372
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
M. Turner
中科院分区：
文献类型：
--
作者：
S. Dodelson;M. Turner
我们通过积分控制中微子相空间分布函数的玻尔兹曼方程来研究早期宇宙（{ital t}{类似于}sec，{ital t}{类似于}MeV）中的中微子解耦。特别地，我们计算了在标准宇宙学中由于{e}{sup{正负}}湮灭而产生的{nu}{下标e}}和{nu}{下标mu}}/{nu}{下标tau}}相空间分布中的畸变。这些畸变是非热的，有效中微子温度随着中微子动量的增加而增加，在最高的中微子动量下，电子中微子增加了0.7%，{mu}和{tau}中微子增加了0.3%，对应于{nu}{sub {mu}}/{nu}{sub {tau}} s的能量密度增加了约1.2%，{nu}{sub {mu}}/{nu}{sub {mu}} s的能量密度增加了约0.5%（大约每厘米{sup{-}3}种增加一个遗迹中微子）。电子中微子的畸变比{mu}和{tau}中微子的畸变更大，因为电子中微子通过带电电流和中性电流相互作用与{ital e}{sup{正负}}s耦合。我们的结果图解地说明了中微子解耦是一个与动量相关的连续过程。由于微妙的抵消，这些扭曲导致预测的原始{sup 4}He丰度只有微小的变化，{Delta}{ital Y}{全等}1—2{乘以}10{sup{-}4}。
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}.