一阶相变诱导的大爆炸中的引力波回声
Gravitational Wave Echoes of the First Order Phase Transition in a Kination-Induced Big Bang
AI总结：
研究了一阶相变诱导的大爆炸中Kination主导时期产生的引力波信号，通过相变和泡渗透条件分析其振幅和频率范围，解释了脉冲星定时实验信号并可被LISA等干涉仪探测。
摘要：
引力波（GWs）在早期宇宙中一阶相变（FOPTs）期间产生的现象为非标准宇宙学历史提供了强有力的探测手段。我们研究了在Kination诱导的大爆炸情景中，一阶相变结束Kination主导时期所产生的引力波生成。在此情景中，一个Kination主导时期通过相变结束，该相变将宇宙重新加热到辐射主导时期。一个滚动标量场驱动Kination时期。在我们考虑的具体模型中，其导数耦合到第二个标量（隧道场）动态地将后者困在虚假真空之中，相变的触发是由于Kination场因哈勃摩擦而减缓。我们计算了由此产生的随机引力波背景，给出了泡核化和碰撞的峰值振幅和频率的解析估计和数值结果。在所有情况下，我们发现从泡渗透条件得出的上界Ω_GW h² ≲ 2×10⁻⁷。在假真空能量在相变中占主导地位（但Kination场驱动一阶相变）的情况下，我们发现Ω_GW h² ≳ 10⁻¹²。我们进一步发现，相变期间的哈勃尺度在广泛的模型参数范围内被限制为O(10⁻¹³)M²/M_Pℓ ≲ H* ≲ O(0.1)M²/M_Pℓ，其中M是控制Kination和隧道场之间相互作用强度的尺度。预测的信号覆盖从nHz到MHz的频率范围，使该模型能够解释脉冲星定时实验报告的信号，并被LISA、先进LIGO、宇宙探索者和BBO等干涉仪所约束或探测。有趣的是，即使裸露的隧道势能有一个单一的最小值，一阶相变也可能发生，因为动态耦合隧道场和Kination场产生了元稳定性。
英文摘要：
Gravitational waves (GWs) produced during first-order phase transitions (FOPTs) in the early universe provide a powerful probe of nonstandard cosmological histories. We study GW production from a FOPT ending a kination-dominated epoch in the Kination-Induced Big Bang scenario, in which a period of kination domination terminates through a phase transition that reheats the universe into radiation domination. A rolling scalar field drives the kination epoch. In the specific model we consider, its derivative coupling to a second scalar (tunneling field) dynamically traps the latter in a false vacuum, with the phase transition triggered as the kination field slows due to Hubble friction. We compute the resulting stochastic GW background from bubble nucleation and collisions, presenting analytic estimates and numerical results for the peak amplitude and frequency. In all cases we find an upper bound $Ω_{\rm GW} h^2\lesssim 2\times10^{-7}$ from the bubble percolation condition. In the case where the false vacuum energy dominates at the transition (yet the kination field drives the FOPT), we find $Ω_{\rm GW}h^2\gtrsim 10^{-12}$. We further find that the Hubble scale during the phase transition across a broad set of model parameters is bounded by $\mathscr{O}(10^{-13})M^2/M_{\rm Pl}\lesssim H_* \lesssim \mathscr{O}(0.1)M^2/M_{\rm Pl}$, where $M$ is the mass-scale controlling the strength of the interaction between the kination and tunneling fields. The predicted signal spans frequencies from nHz to MHz, allowing the model to explain the signal reported by Pulsar Timing Array experiments and to be constrained or probed by interferometers such as LISA, Advanced LIGO, Cosmic Explorer, and BBO. Interestingly, a FOPT can occur even if the bare tunneling potential has a single minimum, as metastability is generated dynamically by the coupling between the tunneling and the kination field.
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