The cosmic acceleration is one of the most significant cosmological discoveries over the last century. Following the more accurate data a more dramatic result appears: the recent analysis of the observation data (especially from SNe Ia) indicate that the time varying dark energy gives a better fit than a cosmological constant, and in particular, the equation of state parameter $w$ (defined as the ratio of pressure to energy density) crosses -1 at some low redshift region. This crossing behavior is a serious challenge to fundamental physics. In this article, we review a number of approaches which try to explain this remarkable crossing behavior. First we show the key observations which imply the crossing behavior. And then we concentrate on the theoretical progresses on the dark energy models which can realize the crossing -1 phenomenon. We discuss three kinds of dark energy models: 1. two-field models (quintom-like), 2. interacting models (dark energy interacts with dark matter), and 3. the models in frame of modified gravity theory (concentrating on brane world).
The $Λ$CDM model is a remarkably successful model which is consistent with the observations of cosmic microwave background radiation (CMB), baryon acoustic oscillation (BAO), and large scale structure of the Universe. However, the discrepancy in the value of $H_0$ between the local observations and PLANCK observation of CMB was recently pointed out. One of the way to ease the discrepancy is to introduce phantom dark energy instead of the cosmological constant. While, phantom dark energy often suffer from the instabilities. We will investigate the general solution to overcome the difficulty of …
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）
We investigate the possibility of phantom crossing in the dark energy sector and solution for the Hubble tension between early and late universe observations. We use robust combinations of different cosmological observations, namely the CMB, local measurement of Hubble constant ($H_0$), BAO and SnIa for this purpose. For a combination of CMB+BAO data which is related to early Universe physics, phantom crossing in the dark energy sector is confirmed at $95$\% confidence level and we obtain the constraint $H_0=71.0^{+2.9}_{-3.8}$ km/s/Mpc at 68\% confidence level which is in perfect agreement wi…
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）
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）
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））
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）
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）
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）
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）
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）
Beyond $w_0-w_a$ and Phantom Crossing: Testing Models of Coupled Dark Sector
Instituto de Física Teórica da Universidade Estadual Paulista（圣保罗州立大学理论物理研究所）；ICTP South American Institute for Fundamental Research（国际理论物理中心南美基础研究所）；Department of Astronomy/Steward Observatory, University of Arizona（亚利桑那大学天文学系/斯图尔德天文台）
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）
Korea Astronomy and Space Science Institute（韩国天体物理与空间科学研究所）；University of Science and Technology（科学技术大学）；Inter-University Centre for Astronomy and Astrophysics（大学间天文与天体物理中心）；Bogolyubov Institute for Theoretical Physics（博戈留波夫理论物理研究所）
Charging Across the Phantom Divide with Modified Gravity
CEICO, Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Berkeley Center for Cosmological Physics & Berkeley Lab, University of California, Berkeley（加州大学伯克利分校伯克利宇宙学物理中心与伯克利实验室）
