Kazuharu Bamba
We study a model of $F(R)$ gravity in which a crossing of the phantom divide can be realized. In particular, we demonstrate the behavior of $F(R)$ gravity around a crossing of the phantom divide by taking into account the presence of cold dark matter.
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We propose a phantom crossing Dvali--Gabadadze--Porrati (DGP) model. In our model, the effective equation of state of the DGP gravity crosses the phantom divide line. We demonstrate crossing of the phantom divide does not occur within the framework of the original DGP model or the DGP model developed by Dvali and Turner. By extending their model, we construct a model that realizes crossing of the phantom divide. We find that the smaller the value of the new introduced parameter $β$ is, the older epoch crossing of the phantom divide occurs in. Our model can account for late-time acceleration of…
We study thermodynamics of the apparent horizon in $F(R)$ gravity. In particular, we demonstrate that a $F(R)$ gravity model with realizing a crossing of the phantom divide can satisfy the second law of thermodynamics in the effective phantom phase as well as non-phantom one.
We propose a phantom crossing Dvali--Gabadadze--Porrati (DGP) model. In our model, the effective equation of state of the DGP gravity crosses the phantom divide line. We demonstrate crossing of the phantom divide does not occur within the framework of the original DGP model or the DGP model developed by Dvali and Turner. By extending their model, we construct a model that realizes crossing of the phantom divide. DGP models can account for late-time acceleration of the universe without dark energy. Phantom Crossing DGP model is more compatible with recent observational data from Type Ia Superno…
We study the observational constraints on the Phantom Crossing DGP model. We demonstrate that the crossing of the phantom divide does not occur within the framework of the original Dvali-Gabadadze-Porrati (DGP) model or the DGP model developed by Dvali and Turner. By extending their model in the framework of an extra dimension scenario, we study a model that realizes crossing of the phantom divide. We investigate the cosmological constraints obtained from the recent observational data of Type Ia Supernovae, Cosmic Microwave Background anisotropies, and Baryon Acoustic Oscillations. The best fi…
In this paper, we propose two new models in $f(T)$ gravity to realize the crossing of the phantom divide line for the effective equation of state, and we then study the observational constraints on the model parameters. The best fit results suggest that the observations favor a crossing of the phantom divide line.
Dissipative Dark Energy can explain the DESI phantom crossing
本文提出一个简单的耗散暗能量模型，通过引入弱耗散，无需幻影场动力学即可解释DESI观测到的暗能量演化和幻影分界线穿越。
An exact solution describing the evolution of the type Bang-to-Rip with the phantom divide line crossing is constructed in the Chameleon cosmology model, based on two independent functions of the scalar field.
Phantom Crossing and Oscillating Dark Energy with $F(R)$ Gravity
本文在$F(R)$引力框架下，通过数值求解场方程，研究了同时具备幻影穿越与振荡行为的暗能量模型，实现了无需幻影标量场的自然过渡，并得到观测数据支持。
An explicit model of $F(R)$ gravity with realizing a crossing of the phantom divide is reconstructed. In particular, it is shown that the Big Rip singularity may appear in the reconstructed model of $F(R)$ gravity. Such a Big Rip singularity could be avoided by adding $R^2$ term or non-singular viable $F(R)$ theory to the model because phantom behavior becomes transient.
The role of the interaction in reaching and crossing the phantom divide line in the Chaplygin gas model is discussed. We obtain some necessary properties of the interaction that allow the model to arrive at or cross the phantom divide line. We show that these properties put some conditions on the ratio of dark matter to dark energy density in the present epoch.
Crossing the phantom divide in scalar-tensor and vector-tensor theories
该研究通过打破Horndeski理论的位移对称性，构建了一个实现暗能量方程状态跨越虚影界限的模型，避免了理论病态和不稳定性。
We investigate the oscillating effective equation of state (EoS) of the universe around the phantom divide in the framework of $F(R)$ gravity. We illustrate the behavior of $F(R)$ with realizing multiple crossings of the phantom divide.
Recently, type Ia supernovae data appear to support a dark energy whose equation of state $w$ crosses -1, which is a much more amazing problem than the acceleration of the universe. We show that it is possible for the equation of state to cross the phantom divide by a scalar field in the gravity with an additional inverse power-law term of Ricci scalar in the Lagrangian. The necessary and sufficient condition for a universe in which the dark energy can cross the phantom divide is obtained. Some analytical solutions with $w<-1$ or $w>-1$ are obtained. A minimal coupled scalar with different pot…
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 …
In this paper we consider FRW cosmology in modified gravity which contain arbitrary functions $f(ϕ)$. It is shown that the bouncing solution appears in the model whereas the equation of state (EoS) parameter crosses the phantom divider. The reconstruction of the model is also investigated with the aim to reconstruct the arbitrary functions and variables of the model.
We investigate de Sitter solutions in non-local gravity as well as in non-local gravity with Lagrange constraint multiplier. We examine a condition to avoid a ghost and discuss a screening scenario for a cosmological constant in de Sitter solutions. Furthermore, we explicitly demonstrate that three types of the finite-time future singularities can occur in non-local gravity and explore their properties. In addition, we evaluate the effective equation of state for the universe and show that the late-time accelerating universe may be effectively the quintessence, cosmological constant or phantom…
Apparent Phantom Crossing in Gauss-Bonnet Gravity
本文研究了广义相对论中phantom crossing现象，提出了一种新的暗物质模型，解释了DESI观测中暗能量方程状态参数变化的可能性。
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.
We study the equation of state for dark energy and explicitly demonstrate that the future crossings of the phantom divide line $w_{\mathrm{DE}}=-1$ are the generic feature in the existing viable $f(R)$ gravity models. We also explore the future evolution of the cosmological horizon entropy and illustrate that the cosmological horizon entropy oscillates with time due to the oscillatory behavior of the Hubble parameter. The important cosmological consequence is that in the future, the sign of the time derivative of the Hubble parameter changes from negative to positive in these viable $f(R)$ gra…
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 whi…
We construct cosmological models with two scalar fields, which has the structure as in the ghost condensation model or k-essence model. The models can describe the stable phantom crossing, which should be contrasted with one scalar tensor models, where the infinite instability occurs at the crossing the phantom divide. We give a general formulation of the reconstruction in terms of the e-foldings N by including the matter although in the previous two scalar models, which are extensions of the scalar tensor model, it was difficult to give a formulation of the reconstruction when we include matt…
Weinberg's theorem, phantom crossing and screening
本文研究胀子作为暗能量的模型，证明引力子量子修正导致局部屏蔽，并发现幽灵穿越是自然特征；指出状态方程变化受屏蔽限制，只有赋予胀子哈勃率量级质量才能突破单场屏蔽模型的局限。
Cosmology after Phantom Crossing by Horndeski Gravity
该研究探讨了Horndeski引力中宇宙膨胀横越幽灵态后的引力影响，分析了不同路径对暗能量方程状态行为的 implications。
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…
It is known that scalar-tensor theory of gravity admits regular crossing of the phantom divide line $w_{\DE}=-1$ for dark energy, and existing viable models of present dark energy for its particular case -- $f(R)$ gravity -- possess one such crossing in the recent past, after the end of the matter dominated stage. It was recently noted that during the future evolution of these models the dark energy equation of state $w_{\DE}$ may oscillate with an arbitrary number of phantom divide crossings. In this paper we prove that the number of crossings can be infinite, present an analytical condition …
We study a flat 3-brane in presence of a linear $k$ field with nonzero cosmological constant $Λ_{4}$. In this model the crossing of the phantom divide (PD) occurs when the $k$-essence energy density becomes negative. We show that in the high energy regime the effective equation of state has a resemblance of a modified Chaplygin gas while in the low energy regime it becomes linear. We find a scale factor that begins from a singularity and evolves to a de Sitter stable stage while other solutions have a super-accelerated regime and end with a big rip. We use the energy conditions to show when th…
Dark Energy Crosses the Line: Quantifying and Testing the Evidence for Phantom Crossing
本研究量化了暗能量幻影跨越的证据，通过修改CPL参数化排除伪影，发现标准CPL模型始终最优，表明数据确实偏好幻影分界线跨越。
We study a holographic model for the dark energy considered recently in the literature which postulates an energy density $ρ\sim R$, where $R$ is the Ricci scalar curvature. We obtain a cosmological scenario that comes from considering two non-interacting fluids along a reasonable Ansatz for the cosmic coincidence parameter. We adjust the involved parameters in the model according to the observational data and we show that the equation of state for the dark energy experience a cross through the -1 barrier. In addition, we find a disagreement in these parameters with respect to an approach from…
In this paper, we propose two new models in $f(T)$ gravity to realize universe acceleration and phantom crossing due to dark torsion in the formalism. The model parameters are constrained and the observational test are discussed. The best fit results favors an accelerating universe with possible phantom crossing in the near past or future followed respectively by matter and radiation dominated era.
Phantom-Crossing Dark Energy and the $Ω_m$ Tug-of-War
研究通过分析CMB、BAO和SN数据揭示了暗能量方程状态w中幻影穿越的观测偏好，指出Ω_m张力导致幻影穿越模型能统一各数据集的Ω_m值，而五维理论只能缓解SN数据张力但加剧BAO-CMB矛盾。
In this paper we consider a spatially flat Friedmann-Robertson-Walker (FRW) cosmological model with cosmological constant, containing a stiff fluid and a classical Dirac field. The proposed cosmological scenario describes the evolution of effective dark matter and dark energy components reproducing, with the help of that effective multifluid configuration, the quintessential behavior. We find the value of the scale factor where the effective dark energy component crosses the phantom divide. The model we introduce, which can be considered as a modified $Λ$CDM one, is characterized by a set of p…
The Oscillatory Universe, phantom crossing and the Hubble tension
本文研究振荡尺度因子的宇宙学模型，发现其满足晚期观测约束，并能通过哈勃参数在当前时期附近的幽灵性增大来缓解哈勃张力。
Cosmological Evidence for Dark Axion-Dark Baryon Interactions from Apparent Phantom Crossing
研究暗轴子与暗重子相互作用，通过在玻尔兹曼代码中实现相关模型并与CMB、DESI DR₂ BAO和SNe Ia数据对比，发现最佳拟合模型改善了拟合，其暗物质质量演化呈现非单调变化，产生类似早期暗能量的能量注入但对降低当前张力作用有限。
Dynamical Dark Energy Meets Varying Electron Mass: Implications for Phantom Crossing and the Hubble Constant
本文研究了变化电子质量与动态暗能量的相互作用，探讨了幻影交叉对哈勃常数张力的缓解作用。
Observational constraints on scalar-vector-tensor dark energy with phantom-divide crossing
本研究通过DES、DESI及RSD数据约束SVT暗能量模型，发现其能稳定穿越幻影分界，且优于ΛCDM模型，贝叶斯因子大于1。
Chiellini-Integrable Cosmologies with Phantom Divide Crossing
本文提出了一种基于 Chiellini 可积条件的标量场宇宙学模型，能够解析地描述晚期宇宙加速和 phantom 分界线穿越，且无需引入病态不稳定性。
Realizing the phantom-divide crossing with vector and scalar fields
在广义Proca理论中引入规范标量场，提出一个最小模型，使得暗能量状态方程在低红移处从w_DE<-1穿越到w_DE>-1，并确保标量、矢量和张量扇区无鬼魅和拉普拉斯不稳定性，同时准静态近似下μ和Σ接近1，与红移空间畸变和ISW-星系互相关观测一致。
Bimodular Gravity: Vacuum Evolution with a Frame-Dependent Phantom Crossing
通过双度量体积约束，将宇宙常数替换为非常数真空贡献，并发现纯框架依赖的幻影穿越机制。
Phantom crossing or dark interaction?
研究通过分析暗能量方程状态，探讨宇宙膨胀中幻影行为是否由暗物质与非幻影暗能量的相互作用导致，发现有效暗能量存在幻影穿越，但非幻影暗能量方程状态无显著性支持。
Phantom crossing from the Standard Model and General Relativity
基于DESI等观测对非标准暗能量模型的兴趣，提出利用费米子凝聚和广义相对论要素实现低红移幻态穿越，依赖暗能量与反作用相互作用，理论模型与多数据集数据分析一致，给出相关参数值。
No evidence for phantom crossing: local goodness-of-fit improvements do not persist under global Bayesian model comparison
该研究通过比较ΛCDM、w0wa和 thawing quintessence模型，发现w0wa模型在局部拟合上略有改进，但这种改进仅限于参数空间的有限区域，全局贝叶斯证据不支持这种改进，表明没有统计上显著的证据表明动态暗能量或暗能量相交。
We investigate the cosmological evolution in a universe governed by the extended, varying-mass, nonlinear massive gravity, in which the graviton mass is promoted to a scalar-field. We find that the dynamics, both in flat and open universe, can lead the varying graviton mass to zero at late times, offering a natural explanation for its hugely-constrained observed value. Despite the limit of the scenario towards standard quintessence, at early and intermediate times it gives rise to an effective dark energy sector of a dynamical nature, which can also lie in the phantom regime, from which it alw…
Phantom-Divide Crossing in Barrow-Tsallis Holographic Dark Energy with a Scale-Dependent Barrow Exponent
该研究构建含正压流体与全息暗能量的宇宙学模型，解析描述幻影边界穿越，确定熵标度维数表达式，验证结果与标准宇宙学早期阶段一致，还需幻影区域额外暗能量熵以满足热力学定律。
Testing signatures of phantom crossing through full-shape galaxy clustering analysis
通过全形状星系聚类分析，研究暗能量方程状态参数w(z)在红移0.4-0.5范围内穿越鬼分界线的证据。
Phantom-divide crossing and suppressed structure growth in kinetically braided dark energy with momentum exchange
该研究构建线性稳定标量场模型，实现暗能量状态方程穿越与 CDM 结构增长抑制，通过改进 CLASS 计算揭示辐射-物质相等附近的瞬态编织特征，为模型似然分析提供依据。
$Λ$XCDM: a running vacuum strategy for crossing the phantom divide
研究通过ΛXCDM模型拟合多组宇宙学数据，发现其能自然穿越幽灵分界线，宇宙子X表现特殊，该模型比w0waCDM拟合更好且缓解宇宙巧合问题，有望从第一原理解释幽灵分界线穿越，为暗能量相关观测提供理论支持。
Quintessential dark energy crossing the phantom divide
本文受DESI结果启发，研究两类可穿越幻影分界线的精髓暗能量模型，虽需参数调节且高红移演化受限，但拟合数据优于ΛCDM，并指出耦合模型受长程力约束。
Is Phantom Divide Crossing in General Relativity Completely Impossible? Shortcomings in canonical and minimally coupled scalar field and Possible Solutions in $k$-essence Models
本文探讨了广义相对论中幻影到第五要素过渡的可行性，指出单一标量场理论无法实现，但k-本质理论可能提供解决方案，且在修正引力中无需额外微调即可实现。
Phantom Crossing with Quintom Models
本文提出了一种双标量场五幕模型，通过特定势能形式实现幻影到quintessence的平滑过渡，并通过观测数据验证了模型的可行性。
Physical vs phantom dark energy after DESI: thawing quintessence in a curved background
本研究发现，具有非零宇宙曲率的融化型 quintessence 模型能像平坦背景下的 $w_0, w_a$ 参数化一样拟合 DESI 等近期数据，揭示了数据并未强制要求幽灵穿越，该现象仅是参数化导致的人为产物。
Exploring cosmological imprints of phantom crossing with dynamical dark energy in Horndeski gravity
本文在 Horndeski 引力中构建含非最小耦合的动力学暗能量模型，实现无不稳定的幻影跨越与高红移负密度，并利用多类观测数据进行 MCMC 检验。
Addressing the DESI DR2 Phantom-Crossing Anomaly and Enhanced $H_0$ Tension with Reconstructed Scalar-Tensor Gravity
本文在标量-张量引力框架下，通过分析DESI DR2等多源数据，有效解决了幻影交叉异常并缓解了H0张力，得到H0=70.6±1.4 km/s/Mpc，并重构了底层拉格朗日量的解析形式。
Is Phantom Barrier Crossing Inevitable? A Cosmographic Analysis
本研究通过模型无关的宇宙学图景方法分析DESI等数据，发现暗能量状态方程无幻影屏障穿越，并证明$w_{DE}=-1$为阻止穿越的分岔点。
Beyond $w_0-w_a$ and Phantom Crossing: Testing Models of Coupled Dark Sector
本文提出暗物质质量依赖暗能量场的耦合模型，在玻尔兹曼求解器中实现并利用CMB、BAO和SNIa数据约束，实现幻影穿越，拟合优度媲美$w_0-w_a$参数化。
Phantom-Divide Crossing in Exponentially Coupled Quintessence and the Role of Neutrino-Mass Freedom
基于Planck CMB、DESI BAO和DES-Dovekie超新星数据，研究指数耦合精质暗能量模型，发现固定中微子质量时耦合参数β以>3σ偏离零，支持幻影分割穿越；释放中微子质量自由度后，耦合偏好减弱，模型与w0waCDM统计不可区分。
Interacting Dark Sector field theory with phantom crossing
本文提出一个基于场论的相互作用暗能量模型，能够自然地容纳暗能量方程状态近期跨越幻影分界线的双重跨越。模型中，费米子暗物质通过杨-米尔斯相互作用与由Born-Infeld动力学支配的超光速标量场耦合，幻影跨越出现在有效暗能量方程状态的层面，而底层标量场动力学仍为非幻影且有界。该模型与包括DESI（DR2）巡天的BAO数据、Planck 2018的宇宙微波背景距离先验数据以及最新Ia型超新星编目数据相结合，获得了不同数据组合下的稳健约束，并重构了最近的幻影分界线双重跨越。此外，在自然性假设下，该模型预计超轻费米子暗物质质量约为1.9×10⁻³ eV，暗示了暗物质领域新轻粒子的可能联系，并推动了未来利用宇宙扰动进行的测试。
Mimetic-Metric-Torsion with induced Axial mode and Phantom barrier crossing
扩展mimetic-metric-torsion引力理论，使mimetic标量场同时作为挠率迹和轴向模式的源，实现暗区几何统一，并证明宇宙演化中的超加速和低红移幻影屏障平滑跨越的可行性。
Metastable Dark Energy on the Phantom Brane
本研究在最小幻影膜上提出亚稳态暗能量模型，通过衰变与膜屏蔽的相互作用实现幻影分界线穿越，与DESI观测一致，优于ΛCDM。
Charging Across the Phantom Divide with Modified Gravity
本文研究在Horndeski引力中通过平移对称项加线性势实现有效暗能量状态方程穿越w=-1的宇宙学，指出近守恒标量电荷的特殊作用，并识别三种穿越方式，但发现它们均难以拟合当前数据。
Coupled Dark Energy and Dark Matter for DESI: An Effective Guide to the Phantom Divide
本文研究了暗能量与暗物质耦合模型，通过场依赖质量m(ϕ)实现相互作用，探讨了有效方程状态w_eff(z)可能穿越幻影分界线而不引入幻影标量场的机制。
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