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arXiv 2006.00438astro-ph.CO
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LISA能探测到银河系宇宙弦环中的谐波引力波吗?

Will LISA Detect Harmonic Gravitational Waves from Galactic Cosmic String Loops?

Zimu Khakhaleva-Li, Craig J. Hogan

摘要:

近年来,随着脉冲星定时阵列(PTA)的$Gμ\lesssim 10^{-11}$的出现,宇宙弦的观测取得了迅速的进展,对它们的性质提出了越来越严格的限制。低张力的宇宙弦环在银河系中由于慢的弦环衰变和低的引力反冲而聚集,导致银河系中弦环丰度的极大增强。由于平均间隔低至仅千秒差距的一小部分,并且引力波(GW)发射的总功率由跨越宽角度尺度的谐波模式主导,位于附近的解析环是强大的、持久的和高度单色的GW源,其谐波签名不被任何其他源复制,这使得它们成为即将推出的激光干涉仪空间天线(LISA)直接探测的主要目标,其频率范围非常匹配。不像检测率与环路丰度成比例的突发检测,谐波信号的检测率是GW发射强度、环路丰度和其他噪声源之间复杂相互作用的结果,并且最适合通过数值模拟来研究。我们开发了一个强大而灵活的框架来模拟银河系中的环路,以预测LISA从解析环路中直接检测谐波信号。我们的模拟表明,在参数空间中最容易进入的区域由大回路$α=0.1$与低张力$10^{-21}\lesssim Gμ\lesssim 10^{-19}$。直接探测场论宇宙弦是不可能的,探测概率为1年任务的$p_{\mathrm{det}}\lesssim 2\%$。一个扩展表明,直接检测宇宙超弦的相互交换概率低是非常有前途的。通过LISA观测从分辨的环中寻找谐波GW信号将潜在地对弦论施加物理约束。

英文摘要:

Rapid advancement in the observation of cosmic strings has been made in recent years placing increasingly stringent constraints on their properties, with $Gμ\lesssim 10^{-11}$ from Pulsar Timing Array (PTA). Cosmic string loops with low string tension clump in the Galaxy due to slow loop decay and low gravitational recoil, resulting in great enhancement to loop abundance in the Galaxy. With an average separation of down to just a fraction of a kpc, and the total power of gravitational wave (GW) emission dominated by harmonic modes spanning a wide angular scale, resolved loops located in proximity are powerful, persistent, and highly monochromatic sources of GW with a harmonic signature not replicated by any other sources, making them prime targets for direct detection by the upcoming Laser Interferometer Space Antenna (LISA), whose frequency range is well-matched. Unlike detection of bursts where the detection rate scales with loop abundance, the detection rate for harmonic signal is the result of a complex interplay between the strength of GW emission, loop abundance, and other sources of noise, and is most suitably studied through numerical simulations. We develop a robust and flexible framework for simulating loops in the Galaxy for predicting direct detection of harmonic signal from resolved loops by LISA. Our simulation reveals that the most accessible region in the parameter space consists of large loops $α=0.1$ with low tension $10^{-21}\lesssim Gμ\lesssim 10^{-19}$. Direct detection of field theory cosmic strings is unlikely, with the detection probability $p_{\mathrm{det}}\lesssim 2\%$ for a 1-year mission. An extension suggests that direct detection of cosmic superstrings with a low intercommutation probability is very promising. Searching for harmonic GW signal from resolved loops through LISA observations will potentially place physical constraints on string theory.

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