Evolution of a background space-time metric and sub-horizon matter density perturbations in the Universe is numerically analyzed in viable $f(R)$ models of present dark energy and cosmic acceleration. It is found that viable models generically exhibit recent crossing of the phantom boundary $w_{\rm DE}=-1$. Furthermore, it is shown that, as a consequence of the anomalous growth of density perturbations during the end of the matter-dominated stage, their growth index evolves non-monotonically with time and may even become negative temporarily.
High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；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）；ICREA（加泰罗尼亚高级研究中心）；Institute of Space Sciences (IEEC-CSIC)（空间科学研究所）；Department of Physics, Aristotle University of Thessaloniki（塞萨洛尼基亚里士多德大学物理系）；Center for Theoretical Physics, Khazar University（阿塞拜疆汗沙尔大学理论物理中心）
Phantom-Crossing Dark Energy and the $Ω_m$ Tug-of-War
Princeton University（普林斯顿大学）；Laboratoire univers et particules de Montpellier (LUPM), Centre national de la recherche scientifique (CNRS) et Université de Montpellier（蒙彼利埃大学与法国国家科学研究中心联合宇宙与粒子物理实验室）
Chiellini-Integrable Cosmologies with Phantom Divide Crossing
School of Advanced Sciences, Vellore Institute of Technology（维洛尔理工学院高级科学学院）；Centre for Theoretical Physics and Natural Philosophy, Nakhonsawan Studiorum for Advanced Studies, Mahidol University（马希隆大学那空沙旺高级研究学院理论与自然哲学中心）
Phantom crossing from the Standard Model and General Relativity
Tsung-Dao Lee Institute（致伦研究所）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences (HIAS-UCAS)（中国科学院大学杭州高等研究院基础物理与数学科学学院）；Department of Astronomy, School of Physical Sciences, University of Science and Technology of China（中国科学技术大学物理科学学院天文学系）；CAS Key Laboratory for Research in Galaxies and Cosmology, School of Astronomy and Space Science, University of Science and Technology of China（中国科学院大学天文与空间科学学院星系与宇宙学重点实验室）；Department of Physics & Center for Astronomy and Astrophysics, Fudan University（复旦大学物理系暨天文与天文物理中心）；Laboratori Nazionali di Frascati INFN（INFN弗拉斯卡蒂国家实验室）
National Institute for Theoretical & Computational Science（国家理论与计算科学研究所）；Department of Physics & Astronomy, University of the Western Cape（西开普大学物理与天文学系）
Is Phantom Divide Crossing in General Relativity Completely Impossible? Shortcomings in canonical and minimally coupled scalar field and Possible Solutions in $k$-essence Models
High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；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）；ICREA（加泰罗尼亚高级研究中心）；Institute of Space Sciences (IEEC-CSIC)（空间科学研究所）；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究学院）；Aristotle University of Thessaloniki（塞萨洛尼基亚里士多德大学）；Khazar University（哈扎尔大学）
No evidence for phantom crossing: local goodness-of-fit improvements do not persist under global Bayesian model comparison
University of the Western Cape（西开普大学）；National Institute for Theoretical & Computational Science（理论与计算科学国家研究所）；Missouri University of Science & Technology（密苏里科技大学）；University of Tokyo（东京大学）
Cosmological Evidence for Dark Axion-Dark Baryon Interactions from Apparent Phantom Crossing
University of Pennsylvania（宾夕法尼亚大学）；Simon Fraser University（西蒙菲莎大学）；Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto（多伦多大学加拿大理论天体物理研究所）
Quintom Dark Energy: Future Attractor and Phantom Crossing in Light of DESI DR2 Observation
Mahidol University（玛希隆大学）；Midnapore College (Autonomous)（米德纳波尔学院（自治））；Universidade Federal do Espírito Santo（圣埃斯皮里图联邦大学）；Universidade do Estado do Rio de Janeiro (UERJ)（里约热内卢州立大学）；University of Oslo（奥斯陆大学）
Observational constraints on scalar-vector-tensor dark energy with phantom-divide crossing
Mahidol University（玛希隆大学）；Waseda University（早稻田大学）；Tongji University（同济大学）；Asia Pacific Center for Theoretical Physics（亚太理论物理中心）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo（东京大学宇宙物质起源世界顶尖研究中心（WPI））
Interacting Dark Sector field theory with phantom crossing
Federal University of Paraíba（帕拉伊巴联邦大学）；Government of Paraíba（帕拉伊巴州政府）；University of Science and Technology of China（中国科学技术大学）；University of São Paulo（圣保罗大学）；Yangzhou University（扬州大学）；Shanghai Jiao Tong University（上海交通大学）
