We study the energy budget of a first-order cosmological phase transition, which is an important factor in the prediction of the resulting gravitational wave spectrum. Formerly, this analysis was based mostly on simplified models as for example the bag equation of state. Here, we present a model-independent approach that is exact up to the temperature dependence of the speed of sound in the broken phase. We find that the only relevant quantities that enter in the hydrodynamic analysis are the speed of sound in the broken phase and a linear combination of the energy and pressure differences between the two phases which we call pseudotrace (normalized to the enthalpy in the broken phase). The pseudotrace quantifies the strength of the phase transition and yields the conventional trace of the energy-momentum tensor for a relativistic plasma (with speed of sound squared of one third). We study this approach in several realistic models of the phase transition and also provide a code snippet that can be used to determine the efficiency coefficient for a given phase transition strength and speed of sound. It turns out that our approach is accurate to the percent level for moderately strong phase transitions, while former approaches give at best the right order of magnitude.

中文翻译：

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宇宙学一阶相变的与模型无关的能量收支——超越袋子模型的合理论证

我们研究一阶宇宙相变的能量收支，这是预测引力波谱的一个重要因素。以前，这种分析主要基于简化模型，例如袋子状态方程。在这里，我们提出了一种与模型无关的方法，该方法完全取决于破碎相中声速的温度依赖性。我们发现进入流体动力学分析的唯一相关量是破碎相中的声速以及两相之间的能量和压力差的线性组合，我们称之为赝迹（归一化为破碎相中的焓） . 伪迹量化了相变的强度，并产生了相对论等离子体（声速为三分之一）的能量-动量张量的常规迹线。我们在相变的几个现实模型中研究了这种方法，并提供了一个代码片段，可用于确定给定相变强度和声速的效率系数。事实证明，对于中等强度的相变，我们的方法准确到百分比水平，而以前的方法最多只能给出正确的数量级。