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GW background is much larger than that of kinks if they coexist in some frequency band. However, a loop cannot emit GWs with frequencies smaller than the inverse of its size. Thus there is a cut on the low frequency side of the spectrum of GWs from loops corresponding to the inverse of the loop size ∼ ( αt ) − $^{1}$. If α ∼ Gµ , the spectrum of GWs from loops begins to appear at ω ≳ 10 − 12 Hz, and this covers the frequency band where both pulsar timing arrays and GW detectors have good sensitivity. However, α is one of the most unknown parameters in the cosmic string model. According to some recent simulations [12], α may be much greater and the broader region may be covered by loops’ GW. On the other hand, some recent studies [10, 11] show the possibility that α is extremely small, say, α ∼ ( Gµ ) n with n ≳ 1. In such a case, GWs from loops dominate only very high-frequency region and GWs from kinks may be observable at low-frequency region. For example, if α ≲ 10 − $^{9}$, the band of SKA [23] can be used for detection of GWs from kinks, and for Gµ ∼ 10 − $^{7}$, Ω$_{gw}$ 

