论文标题
早期宇宙中NEC侵犯的纳米霍茨引力波
Nanohertz gravitational waves from NEC violation in the early universe
论文作者
论文摘要
我们研究了与脉冲星时阵列阵列实验相关的纳米赫兹引力波，该实验来自早期宇宙中无效的能量条件（NEC）违规的量子波动。 NEC违规允许使用比例因子$ a \ propto（-t）^{ - p} $（$ p> 0 $）加速扩展，这给出了张量光谱索引$ n_t = 2/（p+1）> 0 $。为了逃避大爆炸核合成（BBN）的约束，我们将NEC侵入阶段连接到随后的短慢倾通货膨胀阶段，以标准的重新加热结束，从而降低了频谱的高频部分。在立方Horndeski理论中构建了一个明确的模型，该理论允许稳定侵犯NEC。我们介绍了具有不同最大哈勃参数（确定重力波的峰值幅度），不同通货膨胀的哈勃参数（确定高频重力波的振幅）以及通货膨胀相（基本确定光谱频率的峰值）的数值示例。我们以$ n_t = 0.8 $，$ 0.9 $和$ 0.95 $的$ f \ f \ lyssim 1/{\ rm yr} $显示光谱，这与最近的nanograv结果一致。我们还检查它们是否与BBN约束不矛盾。我们讨论如何在NEC侵入阶段产生曲率扰动的几乎规模不变光谱。
We study nanohertz gravitational waves relevant to pulsar timing array experiments from quantum fluctuations in the early universe with null energy condition (NEC) violation. The NEC violation admits accelerated expansion with the scale factor $a\propto (-t)^{-p}$ ($p>0$), which gives the tensor spectral index $n_t=2/(p+1)>0$. To evade the constraint from Big Bang nucleosynthesis (BBN), we connect the NEC-violating phase to a subsequent short slow-roll inflationary phase which ends with standard reheating, and thereby reduce the high frequency part of the spectrum. An explicit model is constructed within the cubic Horndeski theory which allows for stable violation of the NEC. We present numerical examples of the background evolution having the different maximal Hubble parameters (which determine the peak amplitude of gravitational waves), the different inflationary Hubble parameters (which determine the amplitudes of high frequency gravitational waves), and different durations of the inflationary phase (which essentially determine the peak frequency of the spectrum). We display the spectra with $n_t=0.8$, $0.9$, and $0.95$ for $f\lesssim 1/{\rm yr}$, which are consistent with the recent NANOGrav result. We also check that they do not contradict the BBN constraint. We discuss how the nearly scale-invariant spectrum of curvature perturbations is produced in the NEC-violating phase.
