In a recent paper, the NANOGrav collaboration studied new physics explanations of the observed pulsar timing residuals consistent with a stochastic gravitational wave background (SGWB) [1], including cosmic strings in the Nambu-Goto (NG) approximation. Analysing one of current models for the loop distribution, it was found that the cosmic string model is disfavored compared to other sources, for example, super massive black hole binaries (SMBHBs). When both SMBHB and cosmic string models are included in the analysis, an upper bound on a string tension Gμ≲ 10-10 was derived. However, the analysis did not accommodate results from cosmic string simulations in an underlying field theory, which indicate that at most a small fraction of string loops survive long enough to emit GW. Following and extending our previous study [2], we suppose that a fraction fNG of string loops follow NG dynamics and emit only GWs, and study the three different models of the loop distribution discussed in the LIGO-Virgo-KAGRA (LVK) collaboration analyses. We re-analyse the NANOGrav 15yrs data with our signal models by using the NANOGrav ENTERPRISE analysis code via the wrapper PTArcade. We find that loop distributions similar to LVK Model B and C yield higher Bayes factor than Model A analysed in the NANOGrav paper, as they can more easily accommodate a blue-tilted spectrum of the observed amplitude. Furthermore, because of the degeneracy of Gμ and fNG in determining the signal amplitude, our posterior distribution extends to higher values of Gμ, and in some cases the uppermost value of credible intervals is close to the Cosmic Microwave Background limit Gμ≲ 10-7. Hence, in addition to the pulsar timing array data, further information about the fraction of long-lived loops in a cosmic string network is required to constrain the string tension.

中文翻译：

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修改了 NANOGrav 观测中局部宇宙弦的边界


在最近的一篇论文中，NANOGrav 合作研究了对与随机引力波背景 （SGWB） [1] 一致的观测脉冲星时序残差的新物理解释，包括 Nambu-Goto （NG） 近似中的宇宙弦。分析当前循环分布的一个模型，发现与其他来源相比，例如超大质量黑洞双星 （SMBHB），宇宙弦模型不受欢迎。当分析中同时包括 SMBHB 和宇宙弦模型时，可以得出弦张力 Gμ≲ 10-10 的上限。然而，该分析并未纳入基础场论中的宇宙弦模拟结果，该结果表明最多只有一小部分弦环存活了足够长的时间以发射 GW。遵循并扩展我们之前的研究 [2]，我们假设弦环的一小部分 fNG 遵循 NG 动力学并且只发射 GW，并研究了 LIGO-Virgo-KAGRA （LVK） 合作分析中讨论的三种不同的环分布模型。我们通过包装器 PTArcade 使用 NANOGrav ENTERPRISE 分析代码，使用我们的信号模型重新分析 NANOGrav 15 年数据。我们发现，类似于 LVK 模型 B 和 C 的环分布比 NANOGrav 论文中分析的模型 A 产生更高的贝叶斯因子，因为它们可以更容易地容纳观察到的振幅的蓝色倾斜光谱。此外，由于 Gμ 和 fNG 在确定信号振幅时的简并性，我们的后验分布延伸到更高的 Gμ 值，在某些情况下，可信区间的最高值接近宇宙微波背景极限 Gμ≲ 10-7。 因此，除了脉冲星时序数组数据之外，还需要有关宇宙弦网络中长寿命环分数的更多信息来约束弦张力。