In inhomogeneous cosmology, restricting attention to an irrotational dust matter model, backreaction arises in terms of the deviation of the averaged spatial scalar curvature from a constant-curvature model on some averaging domain $D$, $W_D$, and the kinematical backreaction $Q_D$. These backreaction variables can be modeled as an effective scalar field, called the `morphon field'. The general cosmological equations still need a closure condition to be solved. A simple example is the class of scaling solutions where $W_D$ and $Q_D$ are assumed to follow a power law of the volume scale factor $a_D$. But while they can describe models of quintessence, these and other models still assume the existence of dark matter in addition to the known sources. Going beyond scaling solutions by using a model for structure formation that we argue is reasonably generic, we investigate the correspondence between the morphon field and fundamental scalar field dark matter models, in order to describe dark matter as an effective phenomenon arising from kinematical backreaction and the averaged spatial curvature of the inhomogeneous Universe. While we find significant differences with those fundamental models, our main result is that the energy budget on typical collapsing domains is provided by curvature and matter in equal parts already around the turn-around time, leading to curvature dominance thereafter and increasing to a curvature contribution of $3/4$ of the energy budget at the onset of virialization. Kinematical backreaction is subdominant at early stages, but its importance rises quickly after turn-around and dominates the curvature contribution in the final phase of the collapse. We conclude that backreaction can indeed mimic dark matter (in the energy budget) during the collapse phase of megaparsec-scale structures.
Radiation from collapsing shells, semiclassical backreaction and black hole formation
本文详细分析了坍缩壳层周围的量子场论，并讨论了与辐射通量发射和黑洞形成有关的几个概念性问题。显式计算使用模型的崩溃壳，原来是解析可解的。我们使用在这个模型中获得的见解，得出可靠的结论，更现实的模型。我们首先表明，任何壳质量$M$塌缩到一个半径接近$r=2M$将发出近似热辐射的一段时间。特别是，一个壳层从某个初始半径坍缩到最终半径$2M(1-ε^2)^{-1}$（其中$ε\ll 1$）而不形成黑洞，它将在周期$M\lesssim t \lesssim M\ln (1/ε^2)$期间发射热辐射。稍后（$t\gg M \ln(1/ε^2)$），来自这样一个壳层的通量将按指数衰减到零。接下来，我们研究使用应力张量的真空期望值计算的反作用对坍缩的影响。我们发现，在任何现实的坍缩场景中，逆反应效应的\emph{not}阻止事件视界的形成。事件视界形成的时间，当然，由于辐射通量的原因而延迟--辐射通量减少了壳层的质量--但这种效应不足以阻止视界的形成。我们还澄清了几个概念问题，并在论文的附录中提供了计算的教学细节。
Institute of Cosmology & Gravitation, University of Portsmouth（宇宙学与引力研究所，朴茨茅斯大学）；Department of Physics, University of the Western Cape（物理系，西开普大学）；Hierarchical Intelligence Lab（分层智能实验室）
Post-collapse Lagrangian perturbation theory in three dimensions
Institute for Advanced Research, Nagoya University（名古屋大学高等研究院）；Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University（名古屋大学小林-益川粒子宇宙起源研究所）；Sorbonne Université, CNRS, UMR7095, Institut d’Astrophysique de Paris（索邦大学，法国国家科学研究中心，联合研究实验室7095，巴黎天体物理研究所）；Center for Gravitational Physics and Quantum Information, Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所引力物理与量子信息中心）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai institute for Advanced Study, University of Tokyo（东京大学前沿研究机构，卡弗里宇宙物理学与数学研究所（WPI））；Korea Institute for Advanced Study（韩国高等科学研究院）；Division of Theoretical Physics, Ruđer Bošković Institute（鲁德·博什科维奇研究所理论物理部）；Department of Astrophysics, University of Vienna（维也纳大学天体物理学系）；Faculty of Mathematics, University of Vienna（维也纳大学数学学院）
