标题： 从广义源中产生的原初引力波的阻尼 显示英文标题

标题： Damping of Primordial Gravitational Waves from Generalized Sources

摘要： 已经证明，具有各向异性应力张量的宇宙学背景，适用于自由传播的热中微子背景，可以在原初引力波进入视界后对其进行阻尼，从而影响由于这些张量模式引起的CMB B模式极化特征。 在这里，我们推广了这一结果，并研究了这种效应对于非零中微子质量、额外中微子种类以及可能的来自轴子弦的相对论性轴子背景的敏感性。 特别是，具有在O(1) eV量级的宇宙学上有意义的中微子质量的额外中微子，将明显减少相对于无质量中微子的阻尼，对于引力波模式具有$k\tau_0 \approx 100-200$，其中$\tau_0 \approx 2/H_0$和$H_0$是当前的哈勃参数，而轴子背景将产生与中微子产生的阻尼不同的相位依赖性阻尼。 显示英文摘要

摘要： It has been shown that a cosmological background with an anisotropic stress tensor, appropriate for a free streaming thermal neutrino background, can damp primordial gravitational waves after they enter the horizon, and can thus affect the CMB B-mode polarization signature due to such tensor modes. Here we generalize this result, and examine the sensitivity of this effect to non-zero neutrino masses, extra neutrino species, and also a possible relativistic background of axions from axion strings. In particular, additional neutrinos with cosmologically interesting neutrino masses at the O(1) eV level will noticeably reduce damping compared to massless neutrinos for gravitational wave modes with $k\tau_0 \approx 100-200$, where $\tau_0 \approx 2/H_0$ and $H_0$ is the present Hubble parameter, while an axion background would produce a phase-dependent damping distinct from that produced by neutrinos.