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arXiv 1203.2601astro-ph.CO
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CMB光谱的建立:黑体光球的精确解析解

Creation of the CMB spectrum: precise analytic solutions for the blackbody photosphere

Rishi Khatri, Rashid A. Sunyaev

摘要:

CMB的黑体光谱是在红移z>2x10^6的黑体光球中产生的。在早期,宇宙的密度和温度足以在重子物质(电子和离子)和光子之间建立完全的热平衡。任何远离黑体光谱的扰动都被指数抑制。新的物理学,例如暗物质的湮灭和衰变,可以在红移z> 10 ^5时向CMB添加能量和光子,并导致具有非零化学势的玻色-爱因斯坦光谱($μ$)。为了计算$μ$型光谱畸变并约束潜在的新物理,需要精确地演化z~ 2 × 10^6临界红移附近的CMB光谱。虽然数值计算所涉及的重要过程(双康普顿过程,康普顿化和韧致辐射)并不困难,解析解更快,更容易计算,并提供有价值的物理见解。我们提供精确的(优于1%)的解析解的衰减$μ$,创建在较早的时代,包括所有三个过程,双康普顿,康普顿散射热电子和韧致辐射的限制小的扭曲。这是对现有解决方案的显著改进,其精度为~10%或更差。我们也给出了一个普查的重要来源的能量注入到CMB在标准宇宙学。特别是,对电子正电子湮没和原始核合成的扭曲的计算以一种戏剧性的方式说明了早期宇宙平衡恢复过程的强度。最后,我们指出了标准宇宙学中的三重简并,即,由重子和电子的绝热冷却、Silk阻尼和热产生的WIMP暗物质的湮灭引起的$μ$和$y$畸变具有相似的数量级(~ 10^{-8}-10 ^{-10})。

英文摘要:

The blackbody spectrum of CMB was created in the blackbody photosphere at redshifts z>2x10^6. At these early times, the Universe was dense and hot enough that complete thermal equilibrium between baryonic matter (electrons and ions) and photons could be established. Any perturbation away from the blackbody spectrum was suppressed exponentially. New physics, for example annihilation and decay of dark matter, can add energy and photons to CMB at redshifts z>10^5 and result in a Bose-Einstein spectrum with a non-zero chemical potential ($μ$). Precise evolution of the CMB spectrum around the critical redshift of z~2x10^6 is required in order to calculate the $μ$-type spectral distortion and constrain the underlying new physics. Although numerical calculation of important processes involved (double Compton process, comptonization and bremsstrahlung) is not difficult, analytic solutions are much faster and easier to calculate and provide valuable physical insights. We provide precise (better than 1%) analytic solutions for the decay of $μ$, created at an earlier epoch, including all three processes, double Compton, Compton scattering on thermal electrons and bremsstrahlung in the limit of small distortions. This is a significant improvement over the existing solutions with accuracy ~10% or worse. We also give a census of important sources of energy injection into CMB in standard cosmology. In particular, calculations of distortions from electron-positron annihilation and primordial nucleosynthesis illustrate in a dramatic way the strength of the equilibrium restoring processes in the early Universe. Finally, we point out the triple degeneracy in standard cosmology, i.e., the $μ$ and $y$ distortions from adiabatic cooling of baryons and electrons, Silk damping and annihilation of thermally produced WIMP dark matter are of similar order of magnitude (~ 10^{-8}-10^{-10}).

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