Jingfei Zhang, Xin Zhang, Hongya Liu
Recently, a dark energy model characterized by the age of the universe, dubbed ``agegraphic dark energy'', was proposed by Cai. In this paper, a connection between the quintessence scalar-field and the agegraphic dark energy is established, and accordingly, the potential of the agegraphic quintessence field is constructed.
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In this paper we implement the new agegraphic dark energy model with quintessence field. We demonstrate that the new agegraphic evolution of the universe can be described completely by a single quintessence field. Its potential as a function of the quintessence field is reconstructed numerically. In particular, the analytical solution of the new agegraphic quintessence dark energy model (NAQDE) is approximately obtained in the matter-dominated epoch. Furthermore, we investigate the evolution of the NAQDE model in the $ω-ω'$ phase plane. It turns out that by quantum corrections, the trajectory …
A new dark energy model, named "agegraphic dark energy", has been proposed recently, based on the so-called Károlyházy uncertainty relation, which arises from quantum mechanics together with general relativity. In this note, we extend the original agegraphic dark energy model by including the interaction between agegraphic dark energy and pressureless (dark) matter. In the interacting agegraphic dark energy model, there are many interesting features different from the original agegraphic dark energy model and holographic dark energy model. The similarity and difference between agegraphic dark …
A new dark energy model, named as ``agegraphic dark energy'', has been proposed by one of us (R. G. Cai) in arXiv:0707.4049, based on the Károlyházy uncertainty relation, which arises from the quantum mechanics together with general relativity. Then, in arXiv:0707.4052, it has been extended by including the interaction between the agegraphic dark energy and the pressureless (dark) matter. In this note, we investigate the agegraphic dark energy models without and with interaction by means of statefinder diagnostic and w-w' analysis.
In this note, we propose a new model of agegraphic dark energy based on the Károlyházy relation, where the time scale is chosen to be the conformal time $η$ of the Friedmann-Robertson-Walker (FRW) universe. We find that in the radiation-dominated epoch, the equation-of-state parameter of the new agegraphic dark energy $w_q=-1/3$ whereas $Ω_q=n^2a^2$; in the matter-dominated epoch, $w_q=-2/3$ whereas $Ω_q=n^2a^2/4$; eventually, the new agegraphic dark energy dominates; in the late time $w_q\to -1$ when $a\to\infty$, and the new agegraphic dark energy mimics a cosmological constant. In every sta…
We investigate the age constraint on the agegraphic dark energy model by using two old galaxies (LBDS 53W091 and LBDS 53W069) and the old high redshift quasar APM 08279+5255. We find that the agegraphic dark energy model can easily accommodate LBDS 53W091 and LBDS 53W069. To accommodate APM 08279+5255, one can take the reduced Hubble parameter as large as h=0.64, when the fraction matter energy density $Ω_{m0}\approx 0.22$.
Recently a new model of dynamical dark energy, or time-varying $Λ$, was proposed by Cai [arXiv:0707.4049] by relating the energy density of quantum fluctuations in a Minkowski space-time, namely $ρ_q \equiv 3 n^2 m_P^2/t^2$, where $n\sim {\cal O}(1)$ and t is the cosmic time, to the present day dark energy density. In this note, we show that the model can be adjusted to the present values of dark energy density parameter $Ω_q$ ($\simeq 0.73$) and the equation of state ${\rm w}\Z{q}$ ($\simeq -1$) only if the numerical coefficient $n$ takes a reasonably large value ($n\gtrsim 3$) or the present…
In this work, we consider the cosmological constraints on the new agegraphic dark energy (NADE) proposed in arXiv:0708.0884, by using the observational data of type Ia supernovae (SNIa), the shift parameter from cosmic microwave background (CMB) and the baryon acoustic oscillation (BAO) peak from large scale structures (LSS). Thanks to its special analytic features in the radiation-dominated and matter-dominated epochs, NADE is a single-parameter model in practice because once the single model parameter $n$ is given, all other physical quantities of NADE can be determined correspondingly. The …
In this paper, we use the Type Ia supernova data as well as the CMB and LSS data to constrain the agegraphic dark energy model recently proposed by Cai. Due to its peculiar nature, the parameter $n$ of this model cannot be well constrained by the SNIa data, while the other parameter $Ω_{m0}$ can be constrained to be $0.34\pm0.04$. When combined with CMB and LSS data, the range of $1σ$ confidence level for $n$ is greatly narrowed, albeit still very large. The best fit result is $Ω_{m0}=0.28\pm0.02$, which is consistent with most observations like WMAP and SDSS, and $n=3.4$, of which a meaningfu…
The holographic dark energy model is an attempt for probing the nature of dark energy within the framework of quantum gravity. The dimensionless parameter $c$ determines the main property of the holographic dark energy. With the choice of $c\geq 1$, the holographic dark energy can be described completely by a quintessence scalar field. In this paper, we show this quintessential description of the holographic dark energy with $c\geq 1$ and reconstruct the potential of the quintessence as well as the dynamics of the scalar field.
We present a unified model of dark matter and dark energy. The dark matter field is a modulus corresponding to a flat direction of supersymmetry, which couples, in a hybrid type potential, with the dark energy field. The latter is a light scalar, whose direction is stabilized by non-renormalizable terms. This quintessence field is kept `locked' on top of a false vacuum due to the coupling with the oscillating dark matter field. It is shown that the model can satisfy the observations when we consider low-scale gauge-mediated supersymmetry breaking. The necessary initial conditions are naturally…
Results of a recent study on how the Quintessence scalar could affect the relic abundance of dark matter particles are presented.
Quintessence is a possible candidate for dark energy. In this paper we study the phenomenologies of the fermionic partner of Quintessence, the Quintessino. Our results show that, for suitable choices of the model parameters, the Quintessino is a good candidate for cold or warm dark matter. In our scenario, dark energy and dark matter of the Universe are connected in one chiral superfield.
If the cold dark matter consists of weakly interacting massive particles (WIMPs), anticipated measurements of the WIMP properties at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) will provide an unprecedented experimental probe of cosmology at temperatures of order 1 GeV. It is worth emphasizing that the expected outcome of these tests may or may not be consistent with the picture of standard cosmology. For example, in kination-dominated quintessence models of dark energy, the dark matter relic abundance can be significantly enhanced compared to that obtained from…
We propose a new class of quintessence models in which late times oscillations of a scalar field give rise to an effective equation of state which can be negative and hence drive the observed acceleration of the universe. Our ansatz provides a unified picture of quintessence and a new form of dark matter we call "Frustrated Cold Dark Matter" (FCDM). FCDM inhibits gravitational clustering on small scales and could provide a natural resolution to the core density problem for disc galaxy halos. Since the quintessence field rolls towards a small value, constraints on slow-roll quintessence models …
We propose a simple phenomenological parameterization of quintessence with a time-varying equation of state. In particular, it accounts for the possibility of early dark energy. The quintessence potential can be reconstructed in terms of the present fraction in dark energy, the present equation of state and the amount of early dark energy.
Various astronomical observations point towards the evidence for dark energy. One of the most mysterious problem is the coincidence problem: why dark energy becomes dominant only recently. We present a scenario based on extended quintessence models to explain the late-time domination of dark energy without severe fine-tuning of initial conditions and model parameters.
We consider a model of interacting cosmological constant/quintessence, where dark matter and dark energy behave as, respectively, two coexisting phases of a fluid, a thermally excited Bose component and a condensate, respectively. In a simple phenomenological model for the dark components interaction we find that their energy density evolution is strongly coupled during the universe evolution. This feature provides a possible way out for the coincidence problem affecting many quintessence models.
We investigate the enhancement of neutralino relic density in the context of a realistic cosmological scenario with Quintessence. The accurate relic density computation we perform allows us to be sensitive to both cases with shifts in the abundance at the percent level, and to enhancements as large as 10^6. We thoroughly analyze the dependence on the supersymmetric spectrum and on the mass and composition of the lightest neutralino. We point out that supersymmetric models yielding a wino or higgsino-like lightest neutralino become cosmologically appealing in the presence of Quintessence.
Quintessence - the energy density of a slowly evolving scalar field - may constitute a dynamical form of the homogeneous dark energy in the universe. We review the basic idea and indicate observational tests which may distinguish quintessence from a cosmological constant.
The dark energy crossing of the cosmological constant boundary (the transition between the quintessence and phantom regimes) is described in terms of the implicitly defined dark energy equation of state. The generalizations of the models explicitly constructed to exhibit the crossing provide the insight into the cancellation mechanism which makes the transition possible.
If CDM particles decay and their lifetime is comparable to the age of the Universe, they can modify its equation of state. By comparing the results of numerical simulations with high redshift SN-Ia observations we show that this hypothesis is consistent with present data. Fitting the simplest quintessence models with constant $w_q$ to data leads to $w_q \lesssim -1$. We show that a universe with a cosmological constant or quintessence matter with $w_q \sim -1$ and a decaying Dark Matter has an effective $w_q < -1$ and fits SN data better than stable CDM or quintessence models with $w_q > -1$.
Through the geodesic analysis of a static and axially symmetric space time, we present conditions on the state equation of an isotropic perfect fluid $p=ωd$, when it is considered as dark matter in spiral galaxies. The main conclusion is that it can be an exotic fluid ($-1<ω<-1/3$) as it is found for Quintessence at cosmological scale.
We explore quintessence models of dark energy which exhibit non-minimal coupling between the dark matter and the dark energy components of the cosmic fluid. The kind of coupling chosen is inspired in scalar-tensor theories of gravity. We impose a suitable dynamics of the expansion allowing to derive exact Friedmann-Robertson-Walker solutions once the coupling function is given as input. Coupling functions that lead to self-interaction potentials of the single and double exponential types are the target of the present investigation. The stability and existence of the solutions is discussed in s…
In this talk we present a model of the universe in which dark energy is modelled explicitely with both a dynamical quintessence field and a cosmological constant. Our results confirm the possibility of a collapsing universe (for a given region of the parameter space), which is advantageous for an adequate formulation of both perturbative quantum field and string theories. We have also reproduced the measurements of modulus distance from supernovae with good accuracy.
We discuss the influence of dark energy on structure formation, especially the effects on σ_8. Our interest is particularly focused on quintessence models with time-dependent equation of state and non-negligible quintessence component in the early universe. We obtain an analytic expression for σ_8 valid for a large class of dark energy models. We conclude that structure formation is a good indicator for the history of dark energy and use our results to set constraints on quintessence models.
We explore quintessence models of dark energy which exhibit non-minimal coupling between the dark matter and the dark energy components of the cosmic fluid. The kind of coupling chosen is inspired in scalar-tensor theories of gravity. We impose a suitable dynamics of the expansion allowing to derive exact Friedmann-Robertson-Walker solutions once the coupling function is given as input. Self-interaction potentials of single and double exponential types emerge as result of our choice of the coupling function. The stability and existence of the solutions is discussed in some detail. Although, in…
The holographic dark energy model is one of the important ways for dealing with the dark energy problems in the quantum gravity framework. In this model, the dimensionless parameter $c$ plays an essential role in determining the evolution of the holographic dark energy. In particular, the holographic dark energy with $c\geq 1$ can be effectively described by a quintessence scalar-field. However, according to the requirement of the weak gravity conjecture the variation of the quintessence scalar-field should be less than the Planck mass, which would give theoretic constraints on the parameters …
It is a known fact that a quintessence model with $w_q < -1$ fits the publicly available Super Nova (SN) type Ia data better than a model with cosmological constant or $w_q > -1$. Two types of models have this property: Scalar fields with unconventional kinetic term and models with cosmological constant and a slowly decaying Cold Dark Matter (CDM). In this work we investigate the possibility of replacing the cosmological constant in the latter models with gradual condensation of a scalar field produced during the decay of the CDM and present some preliminary results. The advantage of this clas…
Observations seem to indicate that our universe is presently accelerating due to the presence of dark energy. Quintessence represents a possible way to model the dark energy. In these proceedings, we briefly review its main properties.
We examine the cosmic microwave background (CMB) anisotropy for signatures of early quintessence dark energy -- a non-negligible quintessence energy density during the recombination and structure formation eras. Only very recently does the quintessence overtake the dark matter and push the expansion into overdrive. Because the presence of early quintessence exerts an influence on the clustering of dark matter and the baryon-photon fluid, we may expect to find trace signals in the CMB and the mass fluctuation power spectrum. In detail, we demonstrate that suppressed clustering power on small le…
In this work we present a model of the universe in which dark energy is modelled explicitely with both a dynamical quintessence field and a cosmological constant. Our results confirm the possibility of a future collapsing universe (for a given region of the parameter space), which is necessary for a consistent formulation of string theory and quantum field theory. We have also reproduced the measurements of modulus distance from supernovae with good accuracy.
We investigate the possibility of replacing the cosmological constant with gradual condensation of a scalar field produced during the decay of a superheavy dark matter. The advantage of this class of models to the ordinary quintessence is that the evolution of the dark energy and the dark energy are correlated and cosmological coincidence problem is solved. This model does not need a special form for the quitessence potential and even a simple $ϕ^4$ theory or an axion like scalar is enough to explain the existence of the Dark Energy. We show that the model has an intrinsic feedback between ene…
It has been recently shown that, under some general conditions, it is always possible to find a fourth order gravity theory capable of reproducing the same dynamics of a given dark energy model. Here, we discuss this approach for a dark energy model with a scalar field evolving under the action of an exponential potential. In absence of matter, such a potential can be recovered from a fourth order theory via a conformal transformation. Including the matter term, the function f(R) entering the generalized gravity Lagrangian can be reconstructed according to the dark energy model.
The problem of the cosmic coincidence is a longstanding puzzle. This conundrum may be solved by introducing a coupling between the two dark sectors. In this Letter, we study two cases of the coupled quintessence scenario. $(a)$ Assume that the mass of dark matter particles depends exponentially on the scalar field associated to dark energy and meanwhile the scalar field evolves in an exponential potential; $(b)$ Assume that the mass of dark matter particles depends on a power law function of the scalar field and meanwhile the scalar field evolves in a power law potential. Since the dynamics of…
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