Field Models Of Dark Energy Research Articles

Comparison of perturbations in fluid and scalar field models of dark energy

We compare perturbations in a fluid model of dark energy with those in a scalar field. As compared to the $\ensuremath{\Lambda}\mathrm{CDM}$ model, large scale matter power spectrum is suppressed in fluid model as well as in a generic quintessence dark energy model. To check the efficacy of fluid description of dark energy in emulating a scalar field, we consider a potential which gives the same background evolution as a fluid with a constant equation of state. We show that for sub-Hubble scales, a fluid model effectively emulates a scalar field model. At larger scales, where dark energy perturbations may play a significant role, the fluid analogy breaks down and the evolution of matter density contrast depends on individual scalar field models.

Reconstructing quintom from Ricci dark energy

Holographic dark energy with Ricci scalar as IR cutoff called Ricci dark energy (RDE) probes the nature of dark energy with respect to the holographic principle of quantum gravity theory. Scalar field dark energy models like quintom are often regarded as an effective description of some underlying theory of dark energy. In this Letter, we find how the generalized ghost condensate model (GGC) that can easily realize quintom behavior can be used to effectively describe the RDE and reconstruct the function h(ϕ) of GGC.

Quantum induced ω = −1 crossing of the quintessence and phantom models

Considering the single scalar field models of dark energy, i.e. the quintessence and phantom models, it is shown that the quantumeffects can cause the system crosses the ω = −1 line. Thisphenomenon does not occur in classical level. The quantum effectsare described via the account of conformal anomaly.

New infrared cut-off for the holographic scalar fields models of dark energy

Introducing a new infrared cut-off for the holographic dark-energy, we study the correspondence between the quintessence, tachyon, K-essence and dilaton energy density with this holographic dark energy density in the flat FRW universe. This correspondence allows to reconstruct the potentials and the dynamics for the scalar fields models, which describe accelerated expansion.

Can cosmological observations uniquely determine the nature of dark energy?

The observational effect of all minimally coupled scalar field models of dark energy can be determined by the behavior of the following two parameters: (1) equation of state parameter $w$, which relates dark energy pressure to its energy density, and (2) effective speed of sound ${c}_{e}^{2}$, which relates dark energy pressure fluctuation to its density fluctuation. In this paper we show that these two parameters do not uniquely determine the form of a scalar field dark energy Lagrangian even after taking into account the perturbation in the scalar field. We present this result by showing that two different forms of scalar field Lagrangian can lead to the same values for these paired parameters. It is well known that from the background evolution the Lagrangian of the scalar field dark energy cannot be uniquely determined. The two models of dark energy presented in this paper are indistinguishable from the evolution of background as well as from the evolution of perturbations from a Friedmann-Robertson-Walker metric.

Exploring parameter constraints on quintessential dark energy: The exponential model

We present an analysis of a scalar field model of dark energy with an exponential potential using the Dark Energy Task Force (DETF) simulated data models. Using Markov Chain Monte Carlo sampling techniques we examine the ability of each simulated data set to constrain the parameter space of the exponential potential for data sets based on a cosmological constant and a specific exponential scalar field model. We compare our results with the constraining power calculated by the DETF using their ``$w_0-w_a$'' parametrization of the dark energy. We find that respective increases in constraining power from one stage to the next produced by our analysis give results consistent with DETF results. To further investigate the potential impact of future experiments, we also generate simulated data for an exponential model background cosmology which can not be distinguished from a cosmological constant at DETF ``Stage 2'', and show that for this cosmology good DETF Stage 4 data would exclude a cosmological constant by better than 3$\sigma$.

Coincidence problem in YM field dark energy model

The coincidence problem is studied in the effective Yang-Mills condensate dark energy model. As the effective YM Lagrangian is completely determined by quantum field theory, there is no adjustable parameter in this model except the energy scale, and the cosmic evolution only depends on the initial conditions. For generic initial conditions with the YM condensate subdominant to the radiation and matter, the model always has a tracking solution, the Universe transits from matter-dominated into the dark energy dominated stage only recently $z\sim 0. 3$, and evolve to the present state with $\Omega_{y}\sim 0.73$ and $\Omega_m\sim 0.27$.

Interacting quintessence, the coincidence problem, and cosmic acceleration

Faced by recent evidence for a flat universe dominated by dark energy, cosmologists grapple with deep cosmic enigmas such as the cosmological constant problem, extreme fine-tuning and the cosmic coincidence problem. The extent to which we observe the dimming of distant supernovae suggests that the cosmic acceleration is as least as severe as in cosmological constant models. Extrapolating this to our cosmic future implies terrifying visions of either a cold and empty universe or an explosive demise in a ``Big Rip.'' We construct a class of dynamical scalar field models of dark energy and dark matter. Within this class we can explain why supernovae imply a cosmic equation of state $w\ensuremath{\lesssim}\ensuremath{-}1$, address fine-tuning issues, protect the universe from premature acceleration and predict a constant fraction of dark energy to dark matter in the future (thus solving the coincidence problem), satisfy the dominant energy condition, and ensure that gravitationally bound objects remain so forever (avoid a Big Rip). This is achieved with a string theory inspired Lagrangian containing standard kinetic terms, exponential potentials and couplings, and parameters of order unity.

Dark Energy Model with Canonical Scalar Field and Non-Linear Born–Infeld Type Scalar Field

In this paper, we propose the non-linear Born–Infeld scalar field and canonical scalar field dark energy models with the potential \(\frac{\lambda }{4}( {\phi ^2 - \sigma ^2 })^2 + V_0\), which admits late time de Sitter attractor solution. The attractor solution corresponds to an equation of state ω_φ → − 1 and a cosmic density parameter Ω_φ → 1, which are important features for a dark energy model that can meet the current observations. dark energy; canonical scalar field, non-linear Born–Infeld type scalar field, attractor solution.

The state equation of Yang–Mills field dark energy models

In this paper, we study the possibility of building Yang–Mills (YM) field dark energy models with equation of state (EoS) crossing −1, and find that it cannot be realized by the single YM field models, no matter what kind of Lagrangian or initial condition. But the states of −1 < ω < 0 and ω < −1 all can be naturally got in this kind of model. The former is like a quintessence field, and the latter is like a phantom field. This states that one can build a model with two YM fields, one with the initial state of −1 < ω < 0, and the other with ω < −1. We give an example model of this kind, and find that its EoS is larger than −1 in the past and less than −1 at the present time. We also find that this change must be from ω > −1 to <−1, and it will go to the critical state of ω = −1 with the expansion of the universe, which character is the same as the single YM field models, and the big rip is naturally avoided.

Wandw′of scalar field models of dark energy

Important observables to reveal the nature of dark energy are the equation of state $w$ and its time derivative in units of the Hubble time ${w}^{\ensuremath{'}}$. Recently, it was shown that the simplest scalar field models of dark energy (quintessence) occupy rather narrow regions in the $w\ensuremath{-}{w}^{\ensuremath{'}}$ plane. We extend the $w\ensuremath{-}{w}^{\ensuremath{'}}$ plane to $w&lt;\ensuremath{-}1$ and derive bounds on ${w}^{\ensuremath{'}}$ as a function of $w$ for tracker phantom dark energy. We also derive bounds on tracker k-essence. The observational window for ${w}^{\ensuremath{'}}$ for $w&lt;\ensuremath{-}1$ is not narrow, $\ensuremath{\sigma}({w}^{\ensuremath{'}})\ensuremath{\lesssim}6|1+w|$.

Scalar Field Model of Dark Energy In the Double ComplexSymmetric Gravitational Theory

The scalar field model of dark energy is established in the doublecomplex symmetric gravitational theory. The universe we live in is takenas the real part of double complex space ℳC4(J). The twocases of scalar field (ordinary and phantom scalar field) are discussedin a unified way. Not only can the double Friedmann equations beobtained, but also the equation of state for dark energy, potentialV(ϕ) and scalar field ϕ can be expressed. Hence, a new methodis proposed to study dark energy and the evolution of the universe.

A single scalar field model of dark energy with equation of state crossing−1

In this paper we study the possibility of building models of dark energy with equation of state across−1 andpropose explicitly a model with a single scalar field which gives rise to an equation of state larger than−1 in the pastand less than −1 at the present time, consistent with the current observations.

Dark energy condensation

The two most popular candidates for dark energy, i.e. a cosmological constant and quintessence, are very difficult to distinguish observationally, mostly because the quintessence field does not have sizable fluctuations. We study a scalar field model for dark energy in which the scalar field is invariant under reflection symmetry $\ensuremath{\phi}\ensuremath{\rightarrow}\ensuremath{-}\ensuremath{\phi}$. Under general assumptions, there is a phase transition at late times ($z\ensuremath{\lesssim}0.5$). Before the phase transition, the field behaves as a cosmological constant. After the phase transition, a time-dependent $\ensuremath{\phi}$-condensate forms, the field couples with dark matter and develops sizable perturbations tracking those of dark matter. The background cosmological evolution is in agreement with existing observations, but might be clearly distinguished from that of a cosmological constant by future Supernovae surveys. The growth of cosmological perturbations carries the imprint of the phase transition, however a nonlinear approach has to be developed in order to study it quantitatively.

Constraints on perfect fluid and scalar field dark energy models from future redshift surveys

We discuss the constraints that future photometric and spectroscopic redshift surveys can put on dark energy through the baryon oscillations of the power spectrum. We model the dark energy either with a perfect fluid or a scalar field and take into account the information contained in the linear growth function. We show that the growth function helps to break the degeneracy in the dark energy parameters and reduce the errors on w 0 , w 1 roughly by 30 per cent, making more appealing multicolour surveys based on photometric redshifts. We find that a 200-deg 2 spectroscopic survey reaching z 3 can constrain w 0 , w 1 to within Δw 0 = 0.21, Δw 1 = 0.26, to Δw 0 = 0.39, Δw 1 = 0.54 using photometric redshifts with an absolute uncertainty of 0.02, and to Δw 0 = 0.43, Δw 1 = 0.66 with an uncertainty of 0.04. In the scalar field case, we show that the slope n of the inverse power-law potential for dark energy can be constrained to An = 0.26 (spectroscopic redshifts) or Δn = 0.40 (photometric redshifts), i.e. better than with future ground-based supernovae surveys or cosmic microwave background data.

SO(1, 1) dark energy model and the universe transition

We suggest the SO(1, 1) scalar field model of dark energy. In this model, the Lagrangian may be decomposed as that of the real quintessence model and the negative coupling energy term of Φ to a. The existence of the coupling term Lc leads to a wider range of wΦ and overcomes the problem of negative kinetic energy in the phantom universe model. We propose a power-law expansion kinetics model of the universe with time-dependent power, which can describe the universe transition from ordinary acceleration to super acceleration. We also give a simple discussion of the Big Rip singularity, and point out the possibility that the universe driven by a phantom avoids it.

Nonextensive scalar field theories and dark energy models

Current astronomical measurements indicate that approximately 73% of the universe is made up of dark energy. Stochastically quantized self-interacting scalar fields can serve as suitable models to generate dark energy. We study a particular model where the scalar field theory underlying dark energy exhibits strongest possible chaotic behaviour. It is shown that the fluctuating chaotic field momenta obey a generalized (nonextensive) statistical mechanics, with an entropic index q given by q=3, respectively, q=−1 if the escort formalism is used.

COBEDMR–normalized Dark Energy Cosmogony

Likelihood analyses of the COBE-DMR sky maps are used to determine the normalization of the inverse-power-law-potential scalar field dark energy model. Predictions of the DMR-normalized model are compared to various observations to constrain the allowed range of model parameters. Although the derived constraints are restrictive, evolving dark energy density scalar field models remain an observationally-viable alternative to the constant cosmological constant model.

Distinguishing among scalar field models of dark energy

We show that various scalar field models of dark energy predict degenerate luminosity distance history of the Universe and thus cannot be distinguished by supernovae measurements alone. In particular, models with a vanishing cosmological constant (the value of the potential at its minimum) are degenerate with models with a positive or negative cosmological constant whose magnitude can be as large as the critical density. Adding information from CMB anisotropy measurements does reduce the degeneracy somewhat but not significantly. Our results indicate that a theoretical prior on the preferred form of the potential and the field's initial conditions may allow to quantitatively estimate model parameters from data. Without such a theoretical prior only limited qualitative information on the form and parameters of the potential can be extracted even from very accurate data.