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arXiv 1610.04451astro-ph.COgr-qc
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轻子-光子宇宙中的熵产生

Entropy Production in a Lepton-Photon Universe

Lars Husdal, Iver Brevik

备注：
8 pages, 5 figures. Second version. Accepted by Astrophysics and Space Science. Added more discussion and made one figure clearer
发表信息：
Astrophys Space Sci (2017) 362: 39
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摘要：

我们通过使用一个模型来研究早期宇宙中轻子时代的熵产生，在这个模型中，我们排除了除了轻子和光子之外的所有粒子。我们假设一个温度依赖性粘度，正如我们中的一个人最近使用相对论动力学理论计算的那样（Husdal 2016）。我们只考虑体粘滞系数，由于空间各向同性，剪切粘滞系数被忽略。熵产生的速率在中微子退耦之前是最高的。我们的结果表明，在轻子时代的熵增加是相当小的，约0.071%，在一个去耦温度为$T=10^{10}~\mathrm{K}$。这个结果比Caderni和Fabbri（1977）早先得到的结果略小。中微子退耦之后，宇宙进入光子时代，动力学理论不再支持体粘滞的出现。在高温和稳定的颗粒比下，熵产生（d $σ$ /d $T$）为$T^{-8}$，总熵（$Δσ$）为$T^{-7}$增加。在中微子退耦之前，这些速率会稍微下降，此时$Δσ\propto T^{-6.2}$。

英文摘要：

We look at the entropy production during the lepton era in the early Universe by using a model where we exclude all particles except the leptons and photons. We assume a temperature dependent viscosity as calculated recently by one of us (Husdal 2016) with use of relativistic kinetic theory. We consider only the bulk viscosity, the shear viscosity being omitted because of spatial isotropy. The rate of entropy production is highest just before the neutrinos decouple. Our results show that the increase in entropy during the lepton era is quite small, about 0.071 % at a decoupling temperature of $T=10^{10}~\mathrm{K}$. This result is slightly smaller than that obtained earlier by Caderni and Fabbri (1977). After the neutrino decoupling, when the Universe has entered the photon era, kinetic-theory arguments no longer support the appearance of a bulk viscosity. At high temperatures and a stable particle ratio, entropy production (d$σ$/d$T$) goes as $T^{-8}$, with the total entropy ($Δσ$) increasing as $T^{-7}$. These rates go slightly down just before the neutrinos decouple, where $Δσ\propto T^{-6.2}$.

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