论文标题

引起统计上各向异性标量扰动引起的引力波

Induced gravitational waves from statistically anisotropic scalar perturbations

论文作者

Chen, Chao, Ota, Atsuhisa

论文摘要

标量引起的重力波(SIGWS)正在通过重力波测量值探测极度短尺度的标量扰动,引起了人们的注意。在本文中,我们研究了来自统计上各向异性标量扰动的SIGW,这些sigw在存在矢量场的存在下是在通货膨胀场景中的动机。尽管SIGW能量光谱的整体平均值对于标准统计上的各向同性标量扰动是各向同性的,但源中的统计各向异性引入了差分SIGW能量谱的多极矩。我们考虑标量功率谱中的四极性各向异性,并表明SIGW频谱的各向异性最高为$ \ ell = 4 $。我们介绍多极矩的通用公式,然后将其应用于三角洲功能和对数正常源光谱。我们发现了对前一种情况的分析表达式,并表明多极矩的红外尺度与各向同性SIGW相同。有趣的是,单极在高$ K $尾部中具有额外的局部最小值,这是与各向同性SIGWS区分开的关键功能。后一个对数正常情况是对窄峰源的分析,我们对宽峰进行数值计算。正如人们所期望的那样,随着源宽度的增加,多极力矩变得更宽。我们的结果有助于测试通过SIGWS极小尺度上原始密度扰动的各向同性。

Scalar-induced gravitational waves (SIGWs) are attracting growing attention for probing extremely short-scale scalar perturbations via gravitational wave measurements. In this paper, we investigate the SIGWs from statistically anisotropic scalar perturbations, which are motivated in inflationary scenarios in the presence of, e.g., a vector field. While the ensemble average of the SIGW energy spectrum is isotropic for the standard statistically isotropic scalar perturbations, the statistical anisotropy in the source introduces the multipole moments of the differential SIGW energy spectrum. We consider quadrupole anisotropy in the scalar power spectrum and show that the SIGW spectrum has anisotropies up to $\ell=4$. We present generic formulas of the multipole moments and then apply them to the delta-function-like and log-normal source spectra. We find analytic expressions for the former case and show that the infrared scalings of the multipole moments are the same as the isotropic SIGWs. Interestingly, the monopole has an additional local minimum in the high-$k$ tail, a key feature to distinguish from the isotropic SIGWs. The latter log-normal case is analytic for the narrow-peak source, and we perform the numerical calculation for the broad peak. As one expects, the multipole moments become broader with increasing source width. Our results are helpful to test the isotropy of primordial density perturbations at extremely small scales through SIGWs.

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