Phantom crossing or dark interaction?

TL;DR

This paper investigates whether a phantom-like expansion ($w_{ m de}<-1$) inferred from recent cosmological data can be explained by a non-gravitational interaction between dark matter and dark energy rather than intrinsic phantom behavior. By modeling the intrinsic dark energy with a thawing quintessence-like equation of state and describing the observed evolution with an effective CPL form $w^{\rm eff}_{\rm de}$, the authors reconstruct the interaction function $Q(z)$ and compute the background evolution $H(z)$ under DESI DR2 BAO, Planck CMB, and Pantheon+ data. The analysis finds that the intrinsic $w_{ m de}(z)$ remains non-phantom, while the effective $w^{\rm eff}_{\rm de}(z)$ shows phantom behavior only at high redshift with low significance; the inferred $Q(z)$ changes sign around $z\sim0.5$, indicating DM→DE energy transfer early and DE→DM transfer late. Model comparisons with a flat CPL parametrization show no decisive evidence to prefer one model over the other, though some criteria mildly favor CPL; overall, an interacting dark energy scenario provides a viable alternative to LCDM and phantom DE, consistent with current observations.

Abstract

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 $w_0, w_a$ parametrization for the dark energy equation of state $w_{\rm de}$ is used to fit the data. Since phantom dark energy in general relativity is unphysical, we investigate the possibility that the phantom behaviour is not intrinsic, but effective -- due to a non-gravitational interaction between dark matter and non-phantom dark energy. To this end, we assume a physically motivated thawing quintessence-like form of the intrinsic dark energy equation of state $w_{\rm de}$. Then we use a $w_0, w_a$ model for the \emph{effective} equation of state of dark energy. We find that the data favours a phantom crossing for the effective dark energy, but only at low significance. The intrinsic equation of state of dark energy is non-phantom, without imposing any non-phantom priors. A nonzero interaction is favoured at more than $3σ$ at $z\sim0.3$. The energy flows from dark matter to dark energy at early times and reverses at later times.

Figures (5)

• Figure 1: Triangle plot for DESI DR2 BAO + CMB + Pantheon+ constraints.
• Figure 2: Intrinsic ( left) and effective ( right) equations of state for dark energy, with uncertainties. The $\Lambda$ model is the straight red line.
• Figure 3: Evolution of the interaction, relative to the contribution of intrinsic dark energy.
• Figure 4: Evolution of the effective dark matter equation of state ( left) and the dark sector energy densities ( right).
• Figure 5: Comparison of the effective equations of state in the interacting model and flat CPL.