Applying the parametrization of dark energy density, we can construct directly independent-model potentials. In Born-Infeld type phantom dark energy model, we consider four special parametrization equation of state parameter. The evolutive behavior of dark energy density with respect to red-shift $z$, potentials with respect to $ϕ$ and $z$ are shown mathematically. Moreover, we investigate the effect of parameter $η$ upon the evolution of the constructed potential with respect to $z$. These results show that the evolutive behavior of constructed Born-Infeld type dark energy model is quite different from those of the other models.
We study the quantum avoidance of the big rip singularity in the Eddington-inspired-Born-Infeld (EiBI) phantom model. Instead of considering a simple phantom dark energy component, which is described by a perfect fluid, we consider a more fundamental degree of freedom corresponding to a phantom scalar field with its corresponding potential, which would lead the classical universe to a big rip singularity. We apply a quantum geometrodynamical approach by performing an appropriate Hamiltonian study including an analysis of the constraints of the system. We then derive the Wheeler-DeWitt (WDW) eq…
Quantum Cosmology and Dark Energy Model of Born-Infeld Type Scalar Field
本文考虑了引力与Born-Infeld（B-I）型标量场$ϕ$相互作用的量子模型.相应的Wheeler-Dewitt方程可以解析求解非常大和非常小的宇宙尺度因子。在小宇宙标度因子趋于极限的情况下，可以应用Vilenkin、Hartle和Hawking的方法得到宇宙的波函数。Vilenkin和Hartle-Hawking的波函数都预言了非零的宇宙学常数。Vilenkin波函数预言宇宙具有尽可能大的宇宙学常数，而Hartle-Hawking波函数预言宇宙具有正的宇宙学常数，等于$\frac{1}λ$。这与Coleman关于宇宙学常数为零的结果不同，也与Hawking关于线性标量场量子宇宙学中宇宙学常数为零的预言不同。我们认为宇宙中的暗能量可能是由具有势的B-I型标量场产生的，宇宙可能经历一个加速膨胀阶段。状态方程参数在$-1<$ w $<-{1/3}$范围内。当势为$V(ϕ)=\frac{1}λ$时，我们的拉格朗日量描述了查氏气体.为了解释态参量w $<-1$的观测结果，我们还研究了负动能的幻影模型。我们发现，对于幻影B-I型标量场，弱能量条件和强能量条件都不成立。最后，我们详细研究了幻象B-I标量场的一个特殊势，其形式为$V_0(1+\fracϕ{ϕ_0})e^{-(\fracϕ{ϕ_0})}$。数值分析表明了系统的吸引子性质。
Data-Driven Discovery of a Simple Phantom-Crossing Dark Energy Parametrization
Swansea University（斯旺西大学）；Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所）；Research Center for the Early Universe (RESCEU), Graduate School of Science, The University of Tokyo（东京大学理学研究系早期宇宙研究中心）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study (UTIAS), The University of Tokyo（东京大学宇宙物质理论研究机构（WPI）卡弗里宇宙物理数学研究所）；Università di Bologna（博洛尼亚大学）
We re-examine the quantum geometrodynamical approach within the Eddington-inspired-Born-Infeld theory of gravity, which was first proposed in our previous work [1]. A thorough analysis of the classical Hamiltonian with constraints is carried and the correctness and self-consistency of the modified Wheeler-DeWitt equation (WDW) is studied. We find that based on the newly obtained WDW equation derived with the use of the Dirac brackets, the conclusion reached in Ref.[1] can be corroborated. The big rip singularity present in the classical theory, and induced by a phantom perfect fluid, is expect…
We consider different scenarios of the evolution of the universe, where the singularities or some non-analyticities in the geometry of the spacetime are present, trying to answer the following question: is it possible to conserve some kind of notion of particle corresponding to a chosen quantum field present in the universe when the latter approaches the singularity? We study scalar fields with different types of Lagrangians, writing down the second-order differential equations for the linear perturbations of these fields in the vicinity of a singularity. If both independent solutions are regu…
In this paper, we study the holographic dark energy density and interacting extended Chaplygin gas energy density in the Einstein gravity. We reconstruct the scalar field and the scalar potential describing the extended Chaplygin gas. In the special case, we obtain energy density and investigate some cosmological parameters. Assuming interaction between components we find energy density for some different parametrization of total EoS. We analyze tensor to scalar ratio and use recent observational data of BICEP2 to fix the model parameters.
The quantum effects close to the classical big rip singularity within the Eddington-inspired-Born-Infeld theory (EiBI) are investigated through quantum geometrodynamics. It is the first time that this approach is applied to a modified theory constructed upon Palatini formalism. The Wheeler-DeWitt (WDW) equation is obtained and solved based on an alternative action proposed in Ref.[1], under two different factor ordering choices. This action is dynamically equivalent to the original EiBI action while it is free of square root of the spacetime curvature. We consider a homogeneous, isotropic and …
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）
Dark energy equation of state $w(z)$ parametrizations with two parameters and given monotonicity are generically either convex or concave functions. This makes them suitable for fitting either freezing or thawing quintessence models but not both simultaneously. Fitting a dataset based on a freezing model with an unsuitable (concave when increasing) $w(z)$ parametrization (like CPL) can lead to significant misleading features like crossing of the phantom divide line, incorrect $w(z=0)$, incorrect slope \etc that are not present in the underlying cosmological model. To demonstrate this fact we g…
To CPL, or not to CPL? What we have not learned about the dark energy equation of state
Instituto de Física Teórica (IFT) UAM-CSIC（理论物理研究所（IFT）UAM-CSIC）；CERCA/ISO, Department of Physics, Case Western Reserve University（凯斯西储大学物理系 CERCA/ISO）；Astrophysics Group & Imperial Centre for Inference and Cosmology, Department of Physics, Imperial College London（帝国理工学院物理系天体物理学小组与推断与宇宙学帝国中心）
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）
Phantom dark energy can produce amplified cosmic acceleration at late times, thus increasing the value of $H_0$ favored by CMB data and releasing the tension with local measurements of $H_0$. We show that the best fit value of $H_0$ in the context of the CMB power spectrum is degenerate with a constant equation of state parameter $w$, in accordance with the approximate effective linear equation $H_0 + 30.93\; w - 36.47 = 0$ ($H_0$ in $km \; sec^{-1} \; Mpc^{-1}$). This equation is derived by assuming that both $Ω_{0 \rm m}h^2$ and $d_A=\int_0^{z_{rec}}\frac{dz}{H(z)}$ remain constant (for inva…
In this work we explore under a holographic approach the dark energy - dark matter interaction in a non-flat Friedmann-Lemaitre-Robertson-Walker spacetime, with a cut-off for the dark energy component given in terms of the Hubble scale. Based on results coming from the use of observational data, we consider a positive interaction $Q$-term together with a Chevallier-Polarsky-Linder type parametrization for the coincidence parameter, we realize that the model admits a Type III future singularity, in this singular universe we have that for a null value of the curvature parameter its scale factor …
Constraints on a dark energy dominated Universe are obtained from an interplay between Bayesian Machine Learning and string Swampland criteria. The approach here differs from previous studies, since in the generative process Swampland criteria are used and, only later, the results of the fit are validated, by using observational data-sets. A generative process based Bayesian Learning approach is applied to two models and the results are validated by means of available $H(z)$ data. For the first model, a parametrization of the Hubble constant is considered and, for the second, a parametrization…
Falsifiable anthropic model from the string landscape
School of Physics and Astronomy, Sun Yat-sen University（中山大学物理与天文学院）；CSST Science Center for the Guangdong-Hong Kong-Macau Greater Bay Area（粤港澳大湾区子午线工程科学中心）
We investigate the generalized Chevallier-Polarski-Linder (CPL) parametrization, which contains the pivoting redshift $z_p$ as an extra free parameter. We use various data combinations from cosmic microwave background (CMB), baryon acoustic oscillations (BAO), redshift space distortion (RSD), weak lensing (WL), joint light curve analysis (JLA), cosmic chronometers (CC), and we include a Gaussian prior on the Hubble constant value, in order to extract the observational constraints on various quantities. For the case of free $z_p$ we find that for all data combinations it always remains unconstr…
Comparison of Standard Ruler and Standard Candle constraints on Dark Energy Models
我们比较了用最近的标准标尺数据（z=0.2和z=0.35处的重子声学振荡（BAO）和宇宙微波背景（CMB）位移参数R和l_a）得到的暗能量模型约束与用最近的Ia型超新星（SnIa）标准烛光数据（ESSENCE+SNLS+HST from Davis et.等）。我们发现，即使两类数据在2σ水平上与LCDM一致，两类数据之间也存在系统差异。特别地，我们发现，对于3年WMAP数据（WMAP 3）最佳拟合的2σ范围内的所有参数（Ω_0m，Ω_b），LCDM与SnIa数据的一致性显著高于与CMB+BAO数据的一致性。例如，对于对应于WMAP 3最佳拟合值的（Ω_0m，Ω_b）=（0.24，0.042），暗能量状态参数化方程w（z）=w_0 + w_1（z/（1+z））的最佳拟合值与使用SnIa数据的LCDM（w_0=-1，w_1 = 0）相距0.5σ，与使用CMB+BAO数据的LCDM相距1.7σ。在早期数据中存在类似的趋势（SNLS vs CMB+BAO，z=0.35）。这种趋势是这样的，标准标尺CMB+BAO数据显示出轻微倾向于穿过体模分界线w=-1，而最近的SnIa数据有利于LCDM。尽管在趋势上有这种轻微的差异，但我们没有发现违反宇宙距离对偶关系η \equiv d_L（z）/（d_A（z）（1+z）^2）=1的统计上显著的证据。例如，使用Ω_0 m =0.24的先验，我们发现在0…
Conformal Killing Gravity: New Constraints from DESI DR2 BAO datasets
Babeș-Bolyai University（博拜什-鲍约蒂大学）；Khazar University（哈扎尔大学）；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）；Università degli Studi di Milano（米兰大学）；INFN, Sez, di Milano（意大利国家核物理研究所（INFN）米兰分部）；Madhabdev University（马德哈布德夫大学）；Zhejiang Normal University（浙江师范大学）
Dark Energy in the DESI Era: A Brief Review of Evidence, Beyond-$Λ$CDM Interpretations, and Tensions
College of Sciences, Northeastern University（东北大学理学院）；School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, UCAS（杭州高等研究院基础物理与数学科学学院，UCAS）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；MOE Key Laboratory of Data Analytics and Optimization for Smart Industry, Northeastern University（东北大学智能工业数据优化与分析教育部重点实验室）；National Frontiers Science Center for Industrial Intelligence and Systems Optimization, Northeastern University（东北大学工业智能与系统优化前沿科学中心）
