宇宙膨胀物理学的丰富与美丽--氦的贡献
The Richness and Beauty of the Physics of Cosmological Recombination: The Contributions from Helium
摘要：
描述宇宙重组时代的物理成分非常简单，也非常容易理解。这一事实使我们能够考虑各种各样的过程，仍然发现潜在的可衡量的后果。在这篇文章中，我们强调了最近研究的一些与宇宙学氢和氦复合有关的详细物理学。这些考虑的影响是双重的：（i）在这一时期相关的光子释放导致宇宙微波背景（CMB）能谱与完美黑体的有趣和独特的偏差，特别是在分米波长处，可能在不久的将来变得可观察到。尽管氦的丰度相当小，但它也为完整的复合光谱贡献了相当数量的光子，由于氦复合动力学的差异和所有成分的非平凡叠加，导致额外的独特光谱特征。观测氢和氦复合时期的光谱畸变，原则上将提供一种额外的方法来确定宇宙的一些关键参数（例如比熵，CMB温度和氦的星前丰度），而不受宇宙方差的限制。它还使我们能够用直接的观测证据来对抗我们对复合过程的详细理解。(ii)随着高精度宇宙微波背景数据的出现，例如使用普朗克探测器或CMBpol可以获得的数据，对宇宙电离历史的非常精确的理论理解对于解释宇宙微波背景温度和偏振各向异性是必要的。（节略）
英文摘要：
The physical ingredients to describe the epoch of cosmological recombination are amazingly simple and well-understood. This fact allows us to take into account a very large variety of processes, still finding potentially measurable consequences. In this contribution we highlight some of the detailed physics that were recently studied in connection with cosmological hydrogen and helium recombination. The impact of these considerations is two-fold: (i) the associated release of photons during this epoch leads to interesting and unique deviations of the Cosmic Microwave Background (CMB) energy spectrum from a perfect blackbody, which, in particular at decimeter wavelength, may become observable in the near future. Despite the fact that the abundance of helium is rather small, it also contributes a sizeable amount of photons to the full recombination spectrum, which, because of differences in the dynamics of the helium recombinations and the non-trivial superposition of all components, lead to additional distinct spectral features. Observing the spectral distortions from the epochs of hydrogen and helium recombination, in principle would provide an additional way to determine some of the key parameters of the Universe (e.g. the specific entropy, the CMB monopole temperature and the pre-stellar abundance of helium), not suffering from limitations set by cosmic variance. Also it permits us to confront our detailed understanding of the recombination process with direct observational evidence. (ii) with the advent of high precision CMB data, e.g. as will be available using the Planck Surveyor or CMBpol, a very accurate theoretical understanding of the ionization history of the Universe becomes necessary for the interpretation of the CMB temperature and polarization anisotropies. (abridged)
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