标题： 来自一阶相变的新高频引力波 显示英文标题

标题： New high-frequency gravitational waves from first-order phase transitions

摘要： 一阶相变在早期宇宙中是引力波（GWs）的一个有说服力的来源。 在本信中，我们确定了一种之前被忽视的引力波产生机制：引力过渡辐射，这是由粒子穿过膨胀气泡壁时质量变化而发射的引力子产生的。 与气泡碰撞或声波等传统源不同，这种机制在由洛伦兹收缩的壁厚设定的微观尺度上运行，导致在显著更高的频率下发射引力波。 所产生的频谱具有独特的形状，其峰值频率红移到$f_{\rm peak}\sim \gamma_w T_0\sim \gamma_w\times 10^{10}\,{\rm Hz}$，其中$\gamma_w$是壁速度的洛伦兹提升因子，$T_0$是宇宙当前的温度。 这种机制是普遍的，并预计对于域壁和其他相对论性界面也会以类似的方式运行。 显示英文摘要

摘要： First-order phase transitions in the early Universe are a well-motivated source of gravitational waves (GWs). In this Letter, we identify a previously overlooked GW production mechanism: gravitational transition radiation, arising from graviton emission by particles whose mass changes as they pass through expanding bubble walls. Unlike conventional sources such as bubble collisions or sound waves, this mechanism operates at the microscopic scale set by the Lorentz-contracted wall thickness, leading to GW emission at significantly higher frequencies. The resulting spectrum features a distinctive shape with a peak frequency redshifting to $f_{\rm peak}\sim \gamma_w T_0\sim \gamma_w\times 10^{10}\,{\rm Hz}$ where $\gamma_w$ is the Lorentz boost factor of the wall velocity and $T_0$ is the current temperature of the Universe. This mechanism is generic and is expected to operate similarly for domain walls and other relativistic interfaces.