In this work we propose a simple general parametrization scheme of the Hubble parameter for the scalar field dark energy models. In our approach it is possible to incorporate both the quintessence and phantom scalar field in a single analytical scheme and write down relevant cosmological parameters which are independent of the nature of the scalar field. A general condition for the phantom barrier crossing has also been obtained. To test this approach, a well behaved parametrization of the normalized Hubble parameter has been considered and a wide variety of observational data like CMB data, Supernovae data, BAO data etc. has been used to constraint the various cosmological parameters. It has been found that data prefer the present value of the equation of state of the dark energy to be in the phantom domain. One interesting outcome of this analysis is that although the current value of the dark energy equation of state is phantom in nature, a phantom crossing of the EOS has taken place in the recent past. We have also carried out the Bayesian model comparison between $ΛCDM$ model and the proposed model which indicates that this model is favored by data as compared to $ΛCDM$ model.
We explore a cyclic universe due to phantom and quintessence fields. We find that, in every cycle of the evolution of the universe, the phantom dominates the cosmic early history and quintessence dominates the cosmic far future. In this model of universe, there are infinite cycles of expansion and contraction. Different from the inflationary universe, the corresponding cosmic space-time is geodesically complete and quantum stable. But similar to the Cyclic Model, the flatness problem, the horizon problem and the large scale structure of the universe can be explained in this cyclic universe.
We analyze the possibility to distinguish between quintessence and phantom scalar field models of dark energy using observations of luminosity distance moduli of SNe Ia, CMB anisotropies and polarization, matter density perturbations and baryon acoustic oscillations. Among the present observations only Planck data on CMB anisotropy and SDSS DR9 data on baryon acoustic oscillations may be able to decide between quintessence or phantom scalar field models, however for each model a set of best-fit parameters exists, which matches all data with similar goodness of fit. We compare the relative diff…
We present a nonparametric form-invariance transformation through which we establish a link between phantom and tachyonic models in flat Friedmann-Robertson-Walker cosmologies.
We constrain the parameters of dynamical dark energy in the form of a classical scalar field with barotropic equation of state jointly with other cosmological parameters using various combined datasets including the CMB power spectra from WMAP7, the baryon acoustic oscillations in the space distribution of galaxies from SDSS DR7 and WiggleZ, the light curves of SN Ia from 3 different compilations: SDSS (SALT2 and MLCS2k2 light curve fittings), SNLS3 and Union2.1. The considered class of models involves both quintessential and phantom subclasses. The analysis has shown that the phantom models a…
In this paper, we investigate the Noether symmetries of $F(T)$ cosmology involving matter and dark energy. In this model, the dark energy is represented by a canonical scalar field with a potential. Two special cases for dark energy are considered including phantom energy and quintessence. We obtain $F(T)\sim T^{3/4},$ and the scalar potential $V(ϕ)\simϕ^2$ for both models of dark energy and discuss quantum picture of this model. Some astrophysical implications are also discussed.
We present a novel dark energy candidate, based upon the existence and dynamics of Ghost D-branes in a warped compactification of type IIB string theory. Gp-branes cancel the combined BPS sectors of the Dp-branes, while they preserve the same supersymmetries. We show that this scenario can naturally lead to either quintessence or phantom-like behaviors, depending on the form of the involved potentials and brane tension.
The self-gravitating gas in the Newtonian limit is studied in the presence of dark energy with a linear and constant equation of state. Entropy extremization associates to the isothermal Boltzmann distribution an effective density that includes `dark energy particles', which either strengthen or weaken mutual gravitational attraction, in case of quintessence or phantom dark energy, respectively, that satisfy a linear equation of state. Stability is studied for microcanonical (fixed energy) and canonical (fixed temperature) ensembles. Compared to the previously studied cosmological constant cas…
We consider ideal fluid and equivalent scalar field dark energy universes where all four known types of finite-time, future singularities occur at some parameter values. It is demonstrated that pressure/energy density of such quintessence/phantom dark energy diverges in spherically-symmetric spacetime at finite radius or at the center. This may cause the instability of the relativistic star or black hole in such universe. The resolution of the problem via the extra modification of the equation of state is briefly discussed.
In the framework of phantom quintessence cosmology, we use the Noether Symmetry Approach to obtain general exact solutions for the cosmological equations. This result is achieved by the quintessential (phantom) potential determined by the existence of the symmetry itself. A comparison between the theoretical model and observations is worked out. In particular, we use type Ia supernovae and large scale structure parameters determined from the 2-degree Field Galaxy Redshift Survey (2dFGRS)and from the Wide part of the VIMOS-VLT Deep Survey (VVDS). It turns out that the model is compatible with t…
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…
In the present work, motivated by the work of Cai and Su [Phys. Rev. D {\bf 81}, 103514 (2010)], we propose a new type of interaction in dark sector, which can change its sign when our universe changes from deceleration to acceleration. We consider the cosmological evolution of quintessence and phantom with this type of interaction, and find that there are some scaling attractors which can help to alleviate the cosmological coincidence problem. Our results also show that this new type of interaction can bring new features to cosmology.
We investigate cosmological scenarios with a non-minimal derivative coupling between the scalar field and the curvature, examining both the quintessence and the phantom cases in zero and constant potentials. In general, we find that the universe transits from one de Sitter solution to another, determined by the coupling parameter. Furthermore, according to the parameter choices and without the need for matter, we can obtain a Big Bang, an expanding universe with no beginning, a cosmological turnaround, an eternally contracting universe, a Big Crunch, a Big Rip avoidance and a cosmological boun…
We investigate quintessence and phantom dark energy scenarios, in which the scalar fields evolve in nearly flat potentials and are non-minimally coupled to gravity. We show that all such models converge to a common behavior and we provide the corresponding approximate analytical expressions for $w(Ω_ϕ)$ and $w(a)$. We find that non-minimal coupling leads to richer cosmological behavior comparing to its minimal counterpart. In addition, comparison with Baryon Acoustic Oscillation and latest Supernovae data reveals that agreement can be established more easily and with less strict constraints on…
Motivated by the mathematic theory of split-complex numbers (or hyperbolic numbers, also perplex numbers) and the split-quaternion numbers (or coquaternion numbers), we define the notion of split-complex scalar field and the split-quaternion scalar field. Then we explore the cosmic evolution of these scalar fields in the background of spatially flat Friedmann-Robertson-Walker Universe. We find that both the quintessence field and the phantom field could naturally emerge in these scalar fields. Introducing the metric of field space, these theories fall into a subclass of the multi-field theorie…
We examine dark energy models in which a quintessence or a phantom field, $ϕ$, rolls near the vicinity of a local minimum or maximum, respectively, of its potential $V(ϕ)$. Under the approximation that $(1/V)(dV/dϕ) \ll 1$, [although $(1/V)(d^2 V/dϕ^2)$ can be large], we derive a general expression for the equation of state parameter $w$ as a function of the scale factor for these models. The dynamics of the field depends on the value of $(1/V)(d^2 V/dϕ^2)$ near the extremum, which describes the potential curvature. For quintessence models, when $(1/V)(d^2 V/dϕ^2)<3/4$ at the potential minimum…
Past analyses of the equation of state (EoS) of the Dark Energy (DE) were not incompatible with a phantom phase near our time. This has been the case in the years of WMAP observations, in combination with the remaining cosmological observables. Such situation did not completely disappear from the data collected from the Planck satellite mission. In it the EoS analysis may still be interpreted as suggesting w<-1, and so a mildly evolving DE cannot be discarded. In our opinion the usual ansatzs made on the structure of the EoS for dynamical DE models (e.g. quintessence and the like) are too simp…
Tachyonic scalar field-driven late universe with dust matter content is considered. The cosmic expansion is modeled with power-law and phantom power-law expansion at late time, i.e. $z \lesssim 0.45$. WMAP7 and its combined data are used to constraint the model. The forms of potential and the field solution are different for quintessence and tachyonic cases. Power-law cosmology model (driven by either quintessence or tachyonic field) predicts unmatched equation of state parameter to the observational value, hence the power-law model is excluded for both quintessence and tachyonic field. In the…
We confront two types of phantom dark energy potential with observational data. The models we consider are the power-law potential, $V\propto ϕ^μ$, and the exponential potential, $V\propto \exp(λϕ/{M_P})$. We fit the models to the latest observations from SN-Ia, CMB and BAO, and obtain tight constraints on parameter spaces. Furthermore, we apply the goodness-of-fit and the information criteria to compare the fitting results from phantom models with that from the cosmological constant and the quintessence models presented in our previous work. The results show that the cosmological constant is …
We derive an analytical expression for the growth rate of matter density perturbations on the phantom brane (which is the normal branch of the Dvali-Gabadadze-Porrati model). This model is characterized by a phantomlike effective equation of state for dark energy at the present epoch. It agrees very well with observations. We demonstrate that the traditional parametrization $f=Ω_m^γ$ with a quasiconstant growth index $γ$ is not successful in this case. Based on a power series expansion at large redshifts, we propose a different parametrization for this model: $f=Ω_m^γ\left(1+\frac{b}{\ell H}\r…
We present a new parameterization of quintessence potentials for dark energy based directly upon the dynamical properties of the equations of motion. Such parameterization arises naturally once the equations of motion are written as a dynamical system in terms of properly defined polar variables. We have identified two different classes of parameters, and we dubbed them as dynamical and passive parameters. The dynamical parameters appear explicitly in the equations of motion, but the passive parameters play just a secondary role in their solutions. The new approach is applied to the so-called …
In this work, we have studied accretion of the dark energies onto Morris-Thorne wormhole. For quintessence like dark energy, the mass of the wormhole decreases and phantom like dark energy, the mass of wormhole increases. We have assumed two types of dark energy like variable modified Chaplygin gas (VMCG) and generalized cosmic Chaplygin gas (GCCG). We have found the expression of wormhole mass in both cases. We have found the mass of the wormhole at late universe and this is finite. For our choices the parameters and the function $B(a)$, these models generate only quintessence dark energy (no…
The cosmic coincidence problem is a serious challenge to dark energy model. We suggest a quantitative criteria for judging the severity of the coincidence problem. Applying this criteria to three different interacting models, including the interacting quintessence, interacting phantom, and interacting Chaplygin gas models, we find that the interacting Chaplygin gas model has a better chance to solve the coincidence problem. Quantitatively, we find that the coincidence index C for the interacting Chaplygin gas model is smaller than that for the interacting quintessence and phantom models by six…
In this work we investigate the spherical collapse model in flat FRW universe containing dark energy component. We consider the Holographic Dark Energy (HDE) model as a dynamical dark energy scenario with slowly time varying EoS parameter $w_Λ$ in order to calculate the effect of dark energy on the scenario of structure formation in the universe. We first calculate the evolution of density perturbation in linear regime for both phantom and quintessence behavior of HDE model and compare the results with standard CDM and $Λ$ CDM models. Then we calculate the evolution of two parameters character…
Phantom dark energy is a proposal that explains the current observations that mildly favor the equation of state of dark energy $ω^{de}$ crossing -1 at 68% confidence level. However, phantom fields are generally ruled out by ultraviolet quantum instabilities. To overcome this discrepancy, in this paper we propose a mechanism to show that how the presence of bulk viscosity in the cosmic fluid can temporarily drive the fluid into the phantom region ($ω<-1$). As time is going on, phantom decays and ultimately $ω^{de}$ approaches to -1. Then we show these quintessence and phantom descriptions of n…
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）
We study the dynamical properties of tracker quintessence models using a general parametrization of their corresponding potentials, and show that there is a general condition for the appearance of a tracker behavior at early times. Likewise, we determine the conditions under which the quintessence tracker models can also provide an accelerating expansion of the universe with an equation of state closer to $-1$. Apart from the analysis of the background dynamics, we also include linear density perturbations of the quintessence field in a consistent manner and using the same parametrization of t…
With a parametric form of the equation of state parameter of dark energy, a quintessence potential has been reconstructed. The potential is found to be a generalization of a double exponential potential. The constraints on the parameters are obtained by maximum likelihood analysis using observational Hubble data, type Ia supernova data, baryon acoustic oscillation data and the CMB shift parameter data. Th emodel shows preference towards the phantom behaviour of dark energy.
Extended quintessence is obtained by coupling a normal scalar field to the Ricci scalar defined in the metric formalism. In this paper, we propose a new extended quintessence dark energy by introducing a non-minimal coupling between the quintessence and gravity, but with the Ricci scalar given from the Palatini formalism rather than the metric one. We find that the equation of state of the new extended quintessence can cross the phantom divide line, and moreover, it oscillates around the -1 line. We also show that the universe driven by the new extended quintessence will enter a dark energy do…
Recently we proposed a new approach to the testing of dark energy models based on the observational data. In that work we focused particularly on quintessence models for demonstration and invoked a widely used parametrization of the dark energy equation of state. In this paper we take the more recent SN Ia, CMB and BAO data, invoke the same parametrization, and apply this method of consistency test to five categories of dark energy models, including the LCDM model, the generalized Chaplygin gas, and three quintessence models: exponential, power-law and inverse-exponential potentials. We find t…
Phase-Space Analysis of Quadratic Dark Energy: Stable Attractors and Their Observational Signatures
Plasma Physics Research Center, Science and Research Branch, Islamic Azad University（伊斯兰阿扎德大学科学研究中心等离子体物理研究中心）；School of Astronomy, Institute for Research in Fundamental Sciences (IPM)（基础科学研究院天文学院）
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）
The reconstruction of a (non)canonical scalar field Lagrangian from the dark energy Equation of State (EoS) parameter is studied, where it is shown that any EoS parametrization can be well reconstructed in terms of scalar fields. Several examples of EoS parameters are studied and the particular scalar field Lagrangian is reconstructed. Then, we propose some new parametrizations that may present a (fast) transition to a phantom dark energy EoS (where $w_{DE}<-1$) and the scalar field Lagrangian is also reconstructed numerically. Furthermore, the properties of these parametrizations of the dark …
Classification of dark energy models in the plane of w and w', where w is the dark energy equation of state and w' its time-derivative in units of the Hubble time, has been studied in the literature. We take the current SN Ia, CMB and BAO data, invoke a widely used parametrization of the dark energy equation of state, and obtain the constraints on the w -w' plane. We find that dark energy models including the cosmological constant, phantom, non-phantom barotropic fluids, and monotonic up-rolling quintessence are ruled out at the 68.3% confidence level based on the current observational data. D…
We give the three-dimensional dynamical autonomous systems for most of the popular scalar field dark energy models including (phantom) quintessence, (phantom) tachyon, k-essence and general non-canonical scalar field models, change the dynamical variables from variables $(x, y, λ)$ to observable related variables $(w_ϕ, Ω_ϕ, λ)$, and show the intimate relationships between those scalar fields that the three-dimensional system of k-essence can reduce to (phantom) tachyon, general non-canonical scalar field can reduce to (phantom) quintessence and k-essence can also reduce to (phantom) quintesse…
In this paper we have investigated the general form of viscous and non-viscous dark energy equation of state (EoS) parameter in the scope of anisotropic Bianchi type I space-time. We show that the presence of bulk viscosity causes transition of $ω^{de}$ from quintessence to phantom but the phantom state is an unstable state (as expected) and EoS of DE tends to $-1$ at late time. Then we show this phantomic description of the viscous dark energy and reconstruct the potential of the phantom scalar field. It is found that bulk viscosity pushes the universe to a darker region. We have also shown t…
In this Letter, we find suitable potentials in the multiple scalar fields scenario by using the Noether symmetry approach. We discussed three models with multiple scalar fields: N-quintessence with positive kinetic terms, N-phantom with negative kinetic terms and N-quintom with both positive and negative kinetic terms. In the N-quintessence case, the exponential potential which could be derived from several theoretic models is obtained from the Noether conditions. In the N-phantom case, the potential $\frac{V_{0}}{2}(1-\cos(\sqrt{\frac{3N}{2}}\fracϕ{m_{pl}}))$, which could be derived from the …
A model consisting of quintessence scalar field interacting with cold dark matter is considered. Conditions required to reach $w_d=-1$ are discussed. It is shown that depending on the potential considered for the quintessence, reaching the phantom divide line puts some constraints on the interaction between dark energy and dark matter. This also may determine the ratio of dark matter to dark energy density at $w_d=-1$.
In this paper we consider quintessence reconstruction of interacting holographic dark energy in a non-flat background. As system's IR cutoff we choose the radius of the event horizon measured on the sphere of the horizon, defined as $L=ar(t)$. To this end we construct a quintessence model by a real, single scalar field. Evolution of the potential, $V(ϕ)$, as well as the dynamics of the scalar field, $ϕ$, are obtained according to the respective holographic dark energy. The reconstructed potentials show a cosmological constant behavior for the present time. We constrain the model parameters in …
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）
The Pseudo-Nambu-Goldstone Boson (PNGB) potential, defined through the amplitude $M^4$ and width $f$ of its characteristic potential $V(ϕ) = M^4[1 + \cos(ϕ/f)]$, is one of the best-suited models for the study of thawing quintessence. We analyze its present observational constraints by direct numerical solution of the scalar field equation of motion. Observational bounds are obtained using Supernovae data, cosmic microwave background temperature, polarization and lensing data from {\it Planck}, direct Hubble constant constraints, and baryon acoustic oscillations data. We find the parameter rang…
We study generic solutions in a non-minimally coupled to gravity scalar field cosmology. It is shown that dynamics for both canonical and phantoms scalar fields with the potential can be reduced to the dynamical system from which the exact forms for an equation of the state parameter can be derived. We have found the stationary solutions of the system and discussed their stability. Within the large class of admissible solutions we have found a non-degenerate critical points and we pointed out multiple attractor type of trajectory travelling in neighborhood of three critical points at which we …
In this work, we have studied the accretion of $(n+2)$-dimensional charged BTZ black hole (BH). The critical point and square speed of sound have been obtained. The mass of the BTZ BH has been calculated and we have observed that the mass of the BTZ BH is related with square root of the energy density of dark energy which accretes onto BH in our accelerating FRW universe. We have assumed modified Chaplygin gas (MCG) as a candidate of dark energy which accretes onto BH and we have found the expression of BTZ BH mass. Since in our solution of MCG, this model generates only quintessence dark ener…
We examine the Chevallier-Polarski-Linder (CPL) parametrization, in the context of quintessence and barotropic dark energy models, to determine the subset of such models to which it can provide a good fit. The CPL parametrization gives the equation of state parameter $w$ for the dark energy as a linear function of the scale factor $a$, namely $w = w_0 + w_a(1-a)$. In the case of quintessence models, we find that over most of the $w_0$, $w_a$ parameter space the CPL parametrization maps onto a fairly narrow form of behavior for the potential $V(ϕ)$, while a one-dimensional subset of parameter s…
Using the "teleparallel" equivalent of General Relativity as the gravitational sector, which is based on torsion instead of curvature, we add a canonical scalar field, allowing for a nonminimal coupling with gravity. Although the minimal case is completely equivalent to standard quintessence, the nonminimal scenario has a richer structure, exhibiting quintessence-like or phantom-like behavior, or experiencing the phantom-divide crossing. The richer structure is manifested in the absence of a conformal transformation to an equivalent minimally-coupled model.
