Phantom crossing or dark interaction?

TL;DR

This paper explores whether the observed phantom behavior in dark energy could be an effective phenomenon caused by dark matter-dark energy interactions, rather than an intrinsic property of dark energy itself.

Contribution

It introduces a model with a physically motivated intrinsic dark energy equation of state and demonstrates that dark matter-dark energy interaction can mimic phantom crossing effects.

Findings

Data favors a phantom crossing in the effective dark energy at low significance.

Intrinsic dark energy remains non-phantom without priors.

Interaction between dark matter and dark energy is significant at over 3σ around z~0.3.

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 $3\sigma$ at $z\sim0.3$. The energy flows from dark matter to dark energy at early times and reverses at later times.