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arXiv 0804.3249astro-phgr-qchep-ph
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暴胀引起的引力波背景谱的精确计算

Precision calculations of the gravitational wave background spectrum from inflation

Sachiko Kuroyanagi, Takeshi Chiba, Naoshi Sugiyama

备注：
15 pages, 7 figures, accepted for publication in PRD, This version contains major revisions over the previous version, with added calculations of neutrino anisotropic stress; typos corrected
发表信息：
Phys.Rev.D79:103501,2009
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摘要：

对各种暴胀模型在宽频率范围内的暴胀过程中量子涨落所产生的引力波背景谱进行了数值计算。我们考虑了四个因素：未采用慢滚近似时暴胀过程中标量场的动力学，再加热过程中小耦合常数标量场的费米子衰变，辐射占优时期有效自由度g * 的变化，以及自由流中微子的各向异性应力.通过数值求解膨胀期间和之后直到现在的引力波的演化，可以在宽频谱上全面而准确地检查所有这些效应，即使在非常高的频率下。我们发现：（i）该谱与用慢滚近似在CMB标度附近进行泰勒展开得到的谱有很大的偏差;（ii）由于再加热效应，该谱具有特征频率依赖性;（iii）由于g_* 变化和中微子各向异性应力，该谱具有阻尼。我们建议，未来的引力波背景的分析应该考虑到这样一个事实，即分析估计使用泰勒展开高估了频谱的振幅。

英文摘要：

The spectrum of the gravitational wave background originating from quantum fluctuations during inflation is calculated numerically for various inflation models over a wide range of frequencies. We take into account four ingredients : the scalar field dynamics during inflation making no use of the slow-roll approximation, the fermionic decay of the scalar field with a small coupling constant during the reheating process, the change of the effective number of degrees of freedom g_* in the radiation-dominated era, and the anisotropic stress of free-streaming neutrinos. By numerically solving the evolution of gravitational waves during and after inflation up to the present, all of these effects can be examined comprehensively and accurately over a broad spectrum, even at very high frequencies. We find that the spectrum shows (i) a large deviation from the spectrum less accurate obtained by Taylor expanding around the CMB scale using the slow-roll approximation (ii) a characteristic frequency dependence due to the reheating effect, and (iii) damping due to the g_* changes and the neutrino anisotropic stress. We suggest that future analysis of the gravitational wave background should take into consideration the fact that analytical estimates using the Taylor expansion overestimate the amplitude of the spectrum.

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