标题： 在膨胀期间是否存在非平凡的$c_T$效应？ 显示英文标题

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

摘要： 最近，我们表明，在暴胀期间原初引力波（GWs）的传播速度$c_T$可能会非平凡地变化，这可能在原初GWs的功率谱中引起局部振荡。 在本文中，我们数值确认，尽管通过度规的非共形重定义可以将非平凡的$c_T$设为单位，但在具有$c_T=1$的框架中的功率谱与原始非共形框架中的功率谱完全相同，即功率谱中的振荡形状仍然保留，因为此处$c_T$的影响实际上被编码在非平凡变化的哈勃参数中。 此外，我们还澄清了如何通过在暴胀期间施加快速下降的$c_T$来获得蓝倾斜的GWs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 same with 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 obtaining a blue-tilt GWs spectrum by imposing a rapidly decreasing $c_T$ during inflation.