标题： 轴子暴胀的引力波各向异性 显示英文标题

标题： Gravitational wave anisotropies from axion inflation

摘要： 暴胀的一个重要预言是产生原初随机引力波背景。由于信号的微弱性以及同时存在由许多未解决的晚期源产生的天体物理背景，观测这一背景具有挑战性。区分两者的可能方法之一是检查它们的各向异性。本文我们计算了由轴子暴胀产生的宇宙背景中引力波各向异性的原初关联函数，在此场景中，暴胀子是一种与规范场耦合的伪Nambu-Goldstone玻色子。在这种情况下，张量模不仅来自任何暴胀模型中存在的真空涨落的标准放大效应，还来自产生的规范场的逆衰变过程。因此，引力波各向异性关联器由两个主要部分组成：来自真空张量模的贡献和来自由规范场激发的张量模的贡献。我们的分析表明，虽然前者（之前文献中研究过）可以忽略不计，但由激发的张量模产生的关联函数，按干涉仪频率处的分数能量密度归一化后，可以达到高达 $\mathcal{O}(10^{-1})$的值。这一结果表明，轴子暴胀能够产生具有潜在被引力波探测器在合理时间框架内观测到的大各向异性。 显示英文摘要

摘要： An important prediction of inflation is the production of a primordial stochastic gravitational wave background. Observing this background is challenging due to the weakness of the signal and the simultaneous presence of an astrophysical background generated by many unresolved late-time sources. One possible way to distinguish between the two is to examine their anisotropies. In this paper we calculate the primordial correlation function of gravitational wave anisotropies in the cosmological background generated by axion inflation, where the inflaton is a pseudo-Nambu-Goldstone boson coupled to gauge fields. In this scenario, tensor modes arise not only from the standard amplification of vacuum fluctuations present in any inflationary model, but also from the inverse decay process of the produced gauge fields. The correlator of gravitational wave anisotropies consists therefore of two main components: the contribution from vacuum tensor modes and the contribution from tensor modes sourced by the gauge fields. Our analysis shows that, while the former, previously studied in the literature, is negligible, the one arising from the sourced tensor modes, normalized by the fractional energy density at interferometer frequencies, can reach values as large as $\mathcal{O}(10^{-1})$. This result shows that axion inflation can generate large anisotropies with the potential to be observed by gravitational wave detectors within a reasonable time frame.