标题： 气泡动力学：尘埃内部的（成核）辐射 显示英文标题

标题： Bubble dynamics: (nucleating) radiation inside dust

摘要： 我们考虑两个由时间类薄壳分隔的空间平坦弗里德曼-罗伯逊-沃尔克时空，在非平凡情况下，内部有限区域包含辐射，外部区域充满尘埃。 然后我们将证明，虽然演化由一大组约束决定，但可以通过在壳达到最小尺寸后的短时间形式展开来获得气泡半径演化的解析描述。 特别是，我们将发现一个初始膨胀速度为零的辐射气泡可以与膨胀的尘埃外部匹配，但不能与坍缩的尘埃外部匹配，无论尘埃的能量密度如何。 前者可以用来描述在膨胀尘埃云中形成辐射气泡的核化过程，尽管最终配置包含的能量比初始尘埃更多，因此坍缩辐射转化为坍缩尘埃的过程在能量上更有利。 然而，我们推测尘埃内部可能存在（小的）衰减真空能量或宇宙常数仍可能触发核化。 最后，我们的微扰（但解析）方法可以很容易地适应壳内和壳外不同物质的组合，以及更一般的表面密度，这对于宇宙学和相变期间缺陷形成的研究所具有相关性。 显示英文摘要

摘要： We consider two spatially flat Friedmann-Robertson-Walker spacetimes divided by a time-like thin shell in the nontrivial case in which the inner region of finite extension contains radiation and the outer region is filled with dust. We will then show that, while the evolution is determined by a large set of constraints, an analytical description for the evolution of the bubble radius can be obtained by formally expanding for short times after the shell attains its minimum size. In particular, we will find that a bubble of radiation, starting out with vanishing expansion speed, can be matched with an expanding dust exterior, but not with a collapsing dust exterior, regardless of the dust energy density. The former case can then be used to describe the nucleation of a bubble of radiation inside an expanding dust cloud, although the final configuration contains more energy than the initial dust, and the reverse process, with collapsing radiation transforming into collapsing dust, is therefore energetically favored. We however speculate a (small) decaying vacuum energy or cosmological constant inside dust could still trigger nucleation. Finally, our perturbative (yet analytical) approach can be easily adapted to different combinations of matter inside and outside the shell, as well as to more general surface density, of relevance for cosmology and studies of defect formation during phase transitions.