We argue that primordial gravitational waves have a spectral break and its information is quite useful for exploring the early universe. Indeed, such a spectral break can be a fingerprint of the end of inflation, and the amplitude and the frequency at the break can tell us the energy scale of inflation and the reheating temperature simultaneously. In order to investigate the spectral break, we give an analytic formula for evolution of the Hubble parameter around the end of inflation where the slow roll approximation breaks down. We also evaluate the spectrum of primordial gravitational waves around the break point semi-analytically using the analytic formula for the inflationdynamics.

我们认为，原始引力波具有频谱破裂，其信息对于探索早期宇宙非常有用。的确，这样的频谱断裂可能是膨胀结束的指纹，并且断裂处的幅度和频率可以同时告诉我们膨胀的能量尺度和再加热温度。为了研究频谱破裂，我们给出了在缓慢滚动逼近分解的充气结束时哈勃参数演化的解析公式。我们还使用膨胀动力学的解析公式半解析地评估了断裂点附近的原始引力波的频谱。