An Interacting Two-Fluid Scenario for Quintom Dark Energy

The Quintom dark energy is a proposal that explains the recent observations that mildly favor the equation of state of dark energy ω crossing -1 near the past. The Quintom model is often constructed by two scalar fields, where one is the quintessence feld and another is the phantom field. The cosmological implication of the coupling of the two fields of the dark energy is out of question worth investigating. However, the consideration of the coupling in the field scenario is somewhat complex thus we propose an interacting two-fluid Quintom scenario for simplicity. The interaction between the two components is parametrized by a constant 71 in this scenario. The cosmological implications of this parametrization are investigated in detail in this paper. Also, a diagnostic for this model is performed by using the statefinder pairs {s, r} and {q, r}.

Reconstructing Quintom from WMAP 5-year Observations:Generalized Ghost Condensate

In the 5-year WMAP data analysis, a new parametrization form for dark energy equation-of-state was used, and it has been shown that the equation-of-state, w（z）, crosses the cosmological-constant boundary w = -1. Based on this observation, in this paper, we investigate the reconstruction of quintom dark energy model. As a single-real-sealarfield model of dark energy, the generalized ghost condensate model provides us with a successful mechanism for realizing the quintom-like behavior. Therefore, we reconstruct this scalar-field quintom dark energy model from the WMAP 5-year observational results. As a comparison, we also discuss the quintom reconstruction based on other specific dark energy ansatzs, such as the CPL parametrization and the holographic dark energy scenarios.

Quintom cosmology and modified gravity after DESI 2024

We reconstruct the cosmological background evolution under the scenario of dynamical dark energy through the Gaussian process approach,using the latest Dark Energy Spectroscopic Instrument(DESI)baryon acoustic oscillations(BAO)combined with other observations.Our results reveal that the reconstructed dark-energy equation-of-state(EoS)parameter w(z)exhibits the so-called quintom-B behavior,crossing-1 from phantom to quintessence regime as the universe expands.We investigate under what situation this type of evolution could be achieved from the perspectives of field theories and modified gravity.In particular,we reconstruct the corresponding actions for f(R),f(T),and f(Q)gravity,respectively.We explicitly show that,certain modified gravity can exhibit the quintom dynamics and fit the recent DESI data efficiently,and for all cases the quadratic deviation from theΛCDM scenario is mildly favored.

Resolving Hubble tension with quintom dark energy model

Recent low-redshift observations have yielded the present-time Hubble parameter value H0=74 kms^-1 Mpc^-1.This value is approximately 10%higher than the predicted value of Ho=67.4 kms^-1 Mpc^-1,based on Planck's observations of the Cosmic Microwave Background radiatio n(CMB)and the AC DM model.Phenomenologically,we show that,by adding an extra component,X,with negative density to the Friedmann equation,it can address the Hubble tension without changing the Planck's constraint on the matter and dark energy densities.To achieve a sufficiently small extra negative density,its equation-of-state parameter must satisfy 1/3 ≤ wx ≤ 1.We propose a quintom model of two scalar fields that realizes this condition and potentially alleviate the Hubble tension.One scalar field acts as a quintessence,while another "Wphantom" scalar con formally couples to matter such that a viable cosmological scenario is achieved.The model only depends on two parameters,心and 6,which represent the rolling tendency of the self-interacting potential of the quintessenee and the strength of the conformal phantom-matter coupling,respectively.The toy quintom model with H0=73.4 kms^-1 Mpc^-1(Quintom I)yields a good Supernovae-Ia luminosity fit and acceptable rBAO fit but slightly small acoustic multipole lA=285.54.A full parameter scan revealed that the quintom model was superior to the ACDM model in certain regions of the parameter space,0.02<δ<0.10,Ω(0)m<0.31,while significantly alleviating the Hubble tension,although it is not completely resolved.A benchmark quintom model.Quintom II,is presented as an example.

Analysis of Possible Evolution of Dark Energy by Using a Power Series

We simulate the density of dark energy by using a power series to analyse the possible evolution of dark energy. The parameters are constrained from the newly released Cold sample of the supernova dataset. The evolutions of dark energy, as the power series from two free parameters to five free parameters, have the common and the different characters. We may conclude that either the density of dark energy possibly oscillates or increases after it decreases to a minimum value. Accordingly, the state equation of dark energy oscillates or evolves from ωde〉 -1 in the past to ωee〈 -1 around the present epoch.