A New Spin on Primordial Hydrogen Recombination and a Refined Model for Spinning Dust Radiation
A New Spin on Primordial Hydrogen Recombination and a Refined Model for Spinning Dust Radiation
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原始氢复合的新旋转和旋转尘埃辐射的改进模型
DOI：
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发表时间：
2011
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通讯作者：
Y. Ali
中科院分区：
文献类型：
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作者：
Y. Ali
这篇论文描述了两个主题的理论计算：大爆炸后大约40万年的电子-质子等离子体的原始复合和今天星际介质中旋转的尘埃颗粒的电偶极辐射。由于原生氢复合理论上的不确定性对预测的宇宙微波背景各向异性功率谱的影响，它最近重新引起了人们的关注。原始重组问题的物理学可以分为两个性质不同的方面。一方面，为了得到能见度函数峰值附近的精确复合历史，需要对光学厚度莱曼线中的非热辐射场进行详细的处理。另一方面，受激复合和非平衡效应在后期是重要的，为了正确计算电离历史的低红移端，需要进行多能级计算。问题的另一个方面是对计算效率的要求，因为在分析CMB数据时，必须在马尔可夫链中评估大量的重组历史。本文提出了一种有效的多能级原子计算方法，将多能级原子计算速度提高了5个数量级以上。以前被忽略的辐射传递效应的影响被量化，并且明确地被证明是可以忽略的。最后，描述了作者编写的部分快速高精度原始重组代码的数值实现。本论文的第二部分致力于CMB实验的一个潜在的银河系前景：微小尘埃颗粒的旋转发射。首先经典地描述了尘埃颗粒的旋转状态，并假设颗粒绕其最大惯性轴旋转。然后取消了这一假设，并对具有随机化章动状态的盘状颗粒进行了量子力学计算。在这两种情况下，总颗粒角动量的概率分布都是用Fokker-Planck方程计算的，由此得到的发射率是作为环境参数的函数。这些计算是在作者编写的公共代码中实现的。
This thesis describes theoretical calculations in two subjects: the primordial recombination of the electron-proton plasma about 400,000 years after the Big Bang and electric dipole radiation from spinning dust grains in the present-day interstellar medium. Primordial hydrogen recombination has recently been the subject of a renewed attention because of the impact of its theoretical uncertainties on predicted cosmic microwave background (CMB) anisotropy power spectra. The physics of the primordial recombination problem can be divided into two qualitatively different aspects. On the one hand, a detailed treatment of the non-thermal radiation field in the optically thick Lyman lines is required for an accurate recombination history near the peak of the visibility function. On the other hand, stimulated recombinations and out-of equilibrium effects are important at late times and a multilevel calculation is required to correctly compute the low-redshift end of the ionization history. Another facet of the problem is the requirement of computational efficiency, as a large number of recombination histories must be evaluated in Markov chains when analyzing CMB data. In this thesis, an effective multilevel atom method is presented, that speeds up multilevel atom computations by more than 5 orders of magnitude. The impact of previously ignored radiative transfer effects is quantified, and explicitly shown to be negligible. Finally, the numerical implementation of a fast and highly accurate primordial recombination code partly written by the author is described. The second part of this thesis is devoted to one of the potential galactic foregrounds for CMB experiments: the rotational emission from small dust grains. The rotational state of dust grains is described, first classically, and assuming that grains are rotating about their axis of greatest inertia. This assumption is then lifted, and a quantum-mechanical calculation is presented for disk-like grains with a randomized nutation state. In both cases, the probability distribution for the total grain angular momentum is computed with a Fokker-Planck equation, and the resulting emissivity is evaluated, as a function of environmental parameters. These computations are implemented in a public code written by the author.