We discuss the interpretation of the detected signal by pulsar timing array (PTA) observations as a gravitational wave background of cosmological origin. We combine NANOGrav 15-years and EPTA-DR2new datasets and confront them against backgrounds from supermassive black hole binaries (SMBHBs), and cosmological signals from inflation, cosmic (super)strings, first-order phase transitions, Gaussian and non-Gaussian large scalar fluctuations, and audible axions. We find that scalar-induced, and to a lesser extent audible axion and cosmic superstring signals, provide a better fit than SMBHBs. These results depend, however, on modeling assumptions, so further data and analysis are needed to reach robust conclusions. Independently of the signal origin, the data strongly constrain the parameter space of cosmological signals, for example, setting an upper bound on primordial non-Gaussianity at PTA scales as $|f_{\mathtt{nl}}|\lesssim 2.34$ at 95% C.L.

中文翻译：

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脉冲星计时阵列数据的宇宙学背景解释

我们讨论了脉冲星计时阵列（PTA）观测检测到的信号作为宇宙学起源的引力波背景的解释。我们结合了NANOGrav 15 年数据集和EPTA-DR2new数据集，并将它们与超大质量黑洞双星 (SMBHB) 的背景以及来自暴胀、宇宙（超）弦、一阶相变、高斯和非高斯大标量的宇宙学信号进行对比波动和可听见的轴子。我们发现标量引起的以及在较小程度上可听见的轴子和宇宙超弦信号比 SMBHB 提供了更好的拟合。然而，这些结果取决于建模假设，因此需要进一步的数据和分析才能得出可靠的结论。与信号来源无关，数据强烈约束宇宙学信号的参数空间，例如，将 PTA 尺度的原始非高斯性上限设置为$|F_{\mathtt{NL}}|\lesssim 2.34$95% CL 时