标题： 膨胀期间是否存在非平凡的 $c_T$ 的影响？ 显示英文标题

标题： Is there an effect of a nontrivial $c_T$ during inflation?

摘要： 近期，我们已经证明原初引力波（GWs）的传播速度 $c_T$ 在暴胀期间可能非平凡地变化，这可能会在原初引力波的功率谱中诱导局部振荡。 本文中，我们数值验证了尽管通过度规的非同位重新定义可以使非平凡的 $c_T$ 被设为 1，但具有 $c_T=1$ 的框架中的功率谱与原始非同位框架中的功率谱完全相同，即功率谱中振荡形状仍然保留下来，因为这里 $c_T$ 的效应实际上被编码在非平凡变化的哈勃参数中。 此外，我们还阐明了如何通过对暴胀期间迅速减小 $c_T$ 来获得蓝倾斜的引力波谱。 显示英文摘要

摘要： Recently, we have shown that the propagation speed $c_T$ of the primordial gravitational waves (GWs) might be nontrivially varying during inflation, which could induce local oscillations in the power spectrum of primordial GWs. In this paper, we numerically confirm that, although with a disformal redefinition of the metric the nontrivial $c_T$ may be set as unity, the power spectrum in the frame with $c_T=1$ is completely the same as that in the original disformal frame, i.e., the oscillating shape in the power spectrum is still reserved, since here the effect of $c_T$ is actually encoded in the nontrivially varying Hubble parameter. In addition, we also clarify how to obtain a blue-tilted GWs spectrum by imposing a rapidly decreasing $c_T$ during inflation.