We investigate quintom cosmology in FRW universes using isomorphic models consisting of three coupled oscillators, one of which carries negative kinetic energy. In particular, we examine the cosmological paradigms of minimally-coupled massless quintom, of two conformally-coupled massive scalars and of conformally-coupled massive quintom, and we obtain their qualitative characteristics as well as their quantitative asymptotic behavior. For open or flat geometries, we find that, independently of the specific initial conditions, the universe is always led to an eternal expansion.
Lanzhou University（兰州大学）；University of Science and Technology of China（中国科学技术大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）
Recent low-redshift observations give value of the present-time Hubble parameter $H_{0}\simeq 74~\rm{km s}^{-1}\rm{Mpc}^{-1}$, roughly 10\% higher than the predicted value $H_{0}=67.4~\rm{km s}^{-1}\rm{Mpc}^{-1}$ from Planck's observations of the Cosmic Microwave Background radiation~(CMB) and the $Λ$CDM model. Phenomenologically, we show that by adding an extra component X with negative density in the Friedmann equation, it can relieve the Hubble tension without changing the Planck's constraint on the matter and dark energy densities. For the extra negative density to be sufficiently small, i…
UV-complete and stable Quintom Dark Energy models in the light of DESI DR2
Theoretical Physics Division, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所理论物理室）；China Center of Advanced Science and Technology, Beijing（中国高等科学技术中心）
University of Science and Technology of China（中国科学技术大学）；CAS Key Laboratory for Research in Galaxies and Cosmology, School of Astronomy and Space Science, University of Science and Technology of China（中国科学院星系与宇宙学重点实验室，中国科学技术大学天文与空间科学学院）；Huazhong University of Science and Technology（华中科技大学）；Interdisciplinary Center for Theoretical Study & Peng Huanwu Center for Fundamental Theory, University of Science and Technology of China（中国科学技术大学理论物理交叉中心及彭桓武基础理论中心）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）
Holographic Ricci dark energy: Current observational constraints, quintom feature, and the reconstruction of scalar-field dark energy
在这项工作中，我们考虑的宇宙学约束的全息里奇暗能量提出的高等。[Phys. Rev. D 79，043511（2009）]，利用现有的观测数据。全息Ricci暗能量的主要特征由模型中的正数值参数$α$决定。当$α<1/2$时，全息里奇暗能量将表现出类似五等分的行为;即，它的状态方程将跨越宇宙常数边界$w=-1$。参数$α$只能通过观察确定。因此，利用观测数据约束参数$α$，对于刻画暗能量的演化特征和预测宇宙的命运具有非常重要的意义。本文利用307颗Ia型超新星的Union样本、Wilkinson微波各向异性探测器5年观测给出的宇宙微波背景位移参数和Sloan数字巡天的重子声学振荡测量结果，导出了全息Ricci暗能量模型的约束条件。联合分析给出了最佳拟合结果（$σ$不确定度为1）：$α=0.359^{+0.024}_{-0.025}$和$Ω_{\rm m0}=0.318^{+0.026}_{-0.024}$。也就是说，根据观测，全息利玛窦暗能量呈现出五分之一的特征。最后，根据宇宙学约束的结果，我们讨论了基于全息Ricci真空能量的标量场暗能量重构问题。
Realization of quintom dark energy after DESI DR2 in Nieh-Yan modified teleparallel gravity
University of Science and Technology of China（中国科学技术大学）；Interdisciplinary Center for Theoretical Study, University of Science and Technology of China（中国科学技术大学交叉理论研究中心）；Peng Huanwu Center for Fundamental Theory（彭桓武基础理论中心）
Probing the dynamics of dark energy with divergence-free parametrizations: A global fit study
CPL参数化对于利用观测数据研究暗能量的性质是非常重要的。然而，CPL参数化只考虑了暗能量过去的演化，而不关心暗能量未来的演化，因为$w(z)$在遥远的未来会发散。在最近的一篇论文[J. Z. Ma和X. Zhang，Phys. Lett. B { \bf 699}，233（2011）]，已经提出了用于暗能量的鲁棒的新颖的参数化，$w(z)=w_0+w_1({\ln (2+z)\over 1+z}-\ln2)$，成功地避免了CPL参数化中的未来发散问题。另一方面，振荡参数化（由振荡五分模型激发）也可以避免未来的发散问题。在这封信中，我们使用这两种无发散参数化来探索暗能量在整个演化历史中的动力学。利用7年WMAP温度和偏振功率谱、SDSS DR 7和SN Ia Union 2样品的物质功率谱数据，对这两个动力学暗能量模型进行了全马尔可夫链蒙特卡罗（Markov Chain Monte Carlo）研究.我们发现，最适合的暗能量模型是一个五分模型，在演化过程中，EOS跨越-1。然而，虽然五分模型更受青睐，我们发现，宇宙学常数仍然不能排除。
The paper proposes a novel cosmological model based on a two-field scenario, where the two fields are independently coupled with a specific invariant, based on cubic contractions of the Riemann tensor. After obtaining the modified Friedmann equations and the specific Klein-Gordon relations, the investigation studies the corresponding physical features by adopting the linear stability theory in a quintom scenario case where the coupling functions and potential energies have an exponential behavior. The corresponding investigation revealed a high complexity of the phase space structure, with var…
The cosmological models exhibiting tracker properties have great significance in the context of dark energy as they can reach the present value of dark energy density from a wide range of initial conditions, thereby alleviating both the fine-tuning and the cosmic coincidence problem. The $α$-attractors, which are originally discussed in the context of inflation, can exhibit the properties of dark energy as they can behave like cosmological trackers at early times and show the late time behaviour of a cosmological constant. In the present paper, we study the Oscillatory Tracker Model (OTM), whi…
Evidence for evolving dark energy from DESI DR2 BAO and Pantheon$^+$, DES-Dovekie, and Union3
Babeș-Bolyai University（巴布什-波雅伊大学）；Khazar University（哈萨尔大学）；Università di Napoli “Federico II”（那不勒斯费德里科二世大学）；Istituto Nazionale di Fisica Nucleare (INFN), sez. di Napoli（意大利国家核物理研究所（INFN），那不勒斯分部）；Scuola Superiore Meridionale（南方高等学院）；Lovely Professional University（洛维专业大学）；University of Geneva（日内瓦大学）；Zhejiang Normal University（浙江师范大学）
