AI 中文总结
该研究通过格点模拟发现畴壁网络演化近似具有宇宙学普适性，粒子视界起关键作用，闭合畴壁及引力波频谱存在普适性破坏，还给出了近峰引力波频谱的拟合公式。
AI 中文摘要
我们研究了双势阱模型中产生的畴壁（DWs）在不同早期宇宙学中的性质，涵盖从尘埃、刚硬物质主导到有效闵可夫斯基空间的极限情形。通过格点模拟，我们证明了畴壁网络的演化相对于宇宙学状态方程（EoS）呈现近似普适性：给定大体积内的畴壁面积主要由粒子视界决定，而宇宙膨胀的细节仅起次要作用。由此可知，粒子视界而非哈勃速率的倒数对畴壁演化至关重要，它决定了网络的关联长度及其现象学，例如发射引力波（GWs）的特征波长。闭合畴壁的形成对宇宙学EoS非常敏感，因此会破坏普适性，但它们在总网络中的占比过小，无法改变整体图景。在湮灭（有偏）畴壁产生的引力波频谱特性中也观察到普适性的破坏：i）频谱的红外斜率取决于EoS参数；ii）频谱的紫外部分存在一个平台，且随着EoS变硬而愈发明显。不过，在与脉冲星计时阵列及其他随机引力波背景探测最相关的近峰区域，EoS的依赖关系相当微弱。针对一系列原初宇宙学，我们给出了近峰处频谱的拟合公式。
英文摘要
We study properties of domain walls (DWs) arising in the model with a double well potential assuming different early universe cosmologies: from dust through stiff matter domination to the limit of effective Minkowski space. Using lattice simulations we demonstrate that evolution of DW networks exhibits an approximate universality with respect to the cosmological equation of state (EoS). Namely, the wall area inside a given large volume is mainly determined by the particle horizon, while details of cosmic expansion play a subdominant role. As it follows, particle horizon rather than the inverse Hubble rate is pivotal in DW evolution defining the network correlation length and hence its phenomenology, e.g., the characteristic wavelength of emitted gravitational waves (GWs). Formation of closed DWs is shown to be very sensitive to the cosmological EoS and hence violate the universality, but their contribution to the total network is too small to change the overall picture. The universality breaking is also observed in the spectral properties of GWs from annihilating (biased) DWs: i) the IR slope of the spectrum depends on the EoS parameter; ii) there is a plateau in the UV part of the spectrum, which gets more pronounced as one stiffens the EoS. However, the dependence on the EoS is rather weak in the near peak region, which is most relevant from the viewpoint of pulsar timing arrays and other searches for the stochastic GW background. For a selection of primordial cosmologies, we provide fitting formulae for the spectra near the peak.
Comments30 pages, 8 figures
