Related papers: Crossing the Phantom Divide
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…
Phantom dark energy is a proposal that explains the current observations that mildly favor the equation of state of dark energy $\omega^{de}$ crossing -1 at 68% confidence level. However, phantom fields are generally ruled out by…
We consider a Tsallis holographic dark energy model with interaction between dark energy and matter. The density of dark energy is taken as $\rho_d \sim 3C^2/L^{4-2\gamma}$, where $C$, $\gamma$ are constants. The event horizon is chosen as…
Ever since the first observations that we are living in an accelerating universe, it has been asked what dark energy is. There are various explanations all of which with have various draw backs or inconsistencies. Here we show that using a…
Dark energy with the usually used equation of state $p=w\rho$, where $w=const<0$ is hydrodynamically unstable. To overcome this drawback we consider the cosmology of a perfect fluid with a linear equation of state of a more general form…
An interacting dark energy model with interaction term $Q= \lambda_m H\rho_m+\lambda_dH\rho_d$ is considered. By studying the model near the transition time, in which the system crosses the w=-1 phantom-divide-line, the conditions needed to…
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…
We study possible crossing of the phantom divide line in a DGP-inspired $F(R,\phi)$ braneworld scenario where scalar field and curvature quintessence are treated in a unified framework. With some specific form of $F(R,\phi)$ and by adopting…
We review the equation of state for dark energy in modified gravity theories. In particular, we summarize the generic feature of the phantom divide crossing in the past and future in viable $f(R)$ gravity models.
Cosmology where the effective dark energy crosses $w=-1$ can be realized in Horndeski gravity with shift symmetric terms plus a linear potential. We highlight the special role of the nearly conserved scalar charge. The theory is highly…
Recent cosmological data, including DESI DR2, highlight significant tensions within the $\Lambda$CDM paradigm. When analyzed in the context of General Relativity (GR), the latest DESI data favor a dynamical dark energy (DDE) equation of…
We investigate the possibility of crossing a phantom divide line in the extension of symmetric teleparallel gravity or the $f(Q)$ gravity, where $Q$ is the non-metricity. We study the cosmic evolution of the effective equation of state…
The $\Lambda$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…
We study the late-time cosmological dynamics of a two-field dark energy model consisting of a canonical quintessence scalar field and a phantom scalar field in a spatially flat FLRW universe. The fields are minimally coupled to gravity and…
Recent results from DESI BAO measurements, together with Planck CMB and Pantheon+ data, suggest that there may be a `phantom' phase ($w_{\rm de}<-1$) in the expansion of the Universe. This inference follows when the $w_0, w_a$…
The thermodynamic properties of dark energy fluids described by an equation of state parameter $\omega=p/\rho$ are rediscussed in the context of FRW type geometries. Contrarily to previous claims, it is argued here that the phantom regime…
The dark energy transition between quintessence ($w>-1$) and phantom ($w<-1$) regimes (the crossing of the cosmological constant boundary) is studied using the dark energy equation of state. Models characterized by this type of transition…
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…
Choosing various natural forms for the equation-of-state parameter w and the bulk viscosity \zeta, we discuss how it is possible for a dark energy fluid to slide from the quintessence region across the divide w=-1 into the phantom region,…
There is accumulating observational evidence (based on SnIa data) that the dark energy equation of state parameter $w$ may be evolving with time and crossing the phantom divide barrier $w=-1$ at recent times. The confirmation of these…