近日，美国纽约大学Isabel Garcia Garcia及其研究小组取得一项新进展。经过不懈努力，他们对气泡壁上的反射过程进行了研究。相关成果已于2023年9月4日在国际知名学术期刊《高能物理杂志》上发表。
该研究团队探讨了在大质量暗光子存在的情况下气泡壁膨胀的动力学。这些暗光子的质量会随着它们穿过气泡壁而变化。研究人员发现，对于足够薄的壁，存在一种瞬态运动机制，其特征是纵向模式具有恒定的反射概率，而不是横向模式。这种效应对早期宇宙中膨胀真空气泡的动力学具有重要意义。
最值得注意的是，这种效应在膨胀界面上形成了一个新的压力源。这个压力源的特征是非单调依赖于气泡壁的γ-因子，并在中等γ-因子处达到峰值，研究人员称之为最大动压。当这种压力大到足以阻止气泡壁的加速时，真空能量密度的差异就会使一小部分暗光子具有相对论性，将它们变成暗辐射。如果暗辐射直到晚些时候仍保持相对论性，那么强度α约为10-2至10-1的相变可能对Neff有可观测的贡献。
附：英文原文
Title: Reflections on bubble walls
Author: Garcia, Isabel Garcia, Koszegi, Giacomo, Petrossian-Byrne, Rudin
Issue&Volume: 2023-09-04
Abstract: We discuss the dynamics of expanding bubble walls in the presence of massive dark photons whose mass changes as they cross the wall. For sufficiently thin walls, we show that there exists a transient kinematic regime characterized by a constant reflection probability of longitudinal — but not transverse — modes. This effect can have important implications for the dynamics of expanding vacuum bubbles in the early Universe. Most notably, it leads to a new source of pressure on the expanding interface, featuring a non-monotonic dependence on the γ-factor of the bubble walls and reaching a peak at intermediate γ-factors that we dub Maximum Dynamic Pressure. When this pressure is large enough to halt the acceleration of the bubble walls, the difference in vacuum energy densities goes into making a fraction of the dark photons relativistic, turning them into dark radiation. If the dark radiation remains relativistic until late times, an observable contribution to Neff is possible for phase transitions with strength α ～ 10-2 -10-1.
DOI: 10.1007/JHEP09(2023)013
Source: https://link.springer.com/article/10.1007/JHEP09(2023)013