The origin of the finite dip in the curvature power spectrum of instantaneous Slow-Roll (SR)-Ulta-Slow-Roll (USR)-SR inflation remains controversial at linear order, and its full spectral features still lack a complete asymptotic analytical description. We revisit linear perturbation dynamics in this framework. Using the junction method and asymptotic expansions of Hankel functions, we for the first time derive accurate and simple asymptotic expressions for mode evolution and the resulting power spectrum, based on three systematic rules for dominant-term identification across transitions. We find the finite dip arises from cancellation between two growing modes within linear perturbation theory, rather than between constant and growing terms as previously suggested. We also provide analytical descriptions of the amplitude enhancement and the two oscillatory patterns observed in the spectrum. All asypmtotic analytical results are validated by numerical calculations with the reconstructed SR-USR-SR inflationary potential.
Running into tension: primordial black holes from ultra-slow-roll inflation, spectral running, and the Hubble tension
University of Trento（特伦托大学）；Trento Institute for Fundamental Physics and Applications (TIFPA)-INFN（特伦托基础物理与应用研究所（TIFPA）-意大利国家核物理研究所）；New York University Abu Dhabi（纽约大学阿布扎比分校）
Proving the absence of large one-loop corrections to the power spectrum of curvature perturbations in transient ultra-slow-roll inflation within the path-integral approach
Primordial Black Holes from Inflation with a Spectator Field
University of Manitoba（曼尼托巴大学）；University of Winnipeg（温尼伯大学）；Santa Cruz Institute for Particle Physics（圣克鲁兹粒子物理研究所）；University of California, Santa Cruz（加州大学圣克鲁兹分校）；Yale University（耶鲁大学）；Massachusetts Institute of Technology（麻省理工学院）
Stability analysis and future singularity of the $m^2 R \Box^{-2} R$ model of non-local gravity
我们分析了马焦雷和Mancarella提出的模型的经典稳定性，其中重力被修改的一个术语$\sim m^2 R \Box^{-2} R$产生的宇宙膨胀的后期时间加速。我们的研究考虑了可能导致不稳定性的度量的所有激发。在识别这些模式时有一些微妙之处，因为非局部场论包含的动态场与自由度并不对应。由于其中一些是幽灵般的，我们澄清了这种模式的稳定性的解决方案，是平坦的时空和宇宙学的解决方案的影响。然后我们发现平坦时空在标量扰动下是不稳定的，但这种不稳定性只在宇宙尺度上表现出来，即在这个解的有效区域之外。因此，FLRW解的稳定性与此相关，在这种情况下，通过数值研究可知标量扰动表现良好。通过寻找解析解的比例因子，这导致一个大的裂缝奇异性的后期行为，我们认为，在未来的线性扰动是有界的，因为哈勃摩擦的支配。特别是，这种效应抑制了导致闵可夫斯基时空不稳定的标量鬼扰动。因此，该模型在现象学上仍然可行。
Nonlinear Matter Power Spectrum from relativistic $N$-body Simulations: $Λ_{\rm s}$CDM versus $Λ$CDM
Istanbul Technical University（伊斯坦布尔理工大学）；University of Sheffield（谢菲尔德大学）；Center for Advanced Systems Understanding（高级系统理解中心）；Helmholtz-Zentrum Dresden-Rossendorf（德累斯顿-罗斯多夫亥姆霍兹中心）；Deutsches Zentrum für Astrophysik（德国天体物理中心）；Astronomical Observatory, Odesa I.I. Mechnikov National University（敖德萨伊.I.梅契尼科夫国立大学天文台）
