Phantom crossing or dark interaction?

Abstract

Recent results from DESI BAO measurements, together with Planck CMB and Pantheon+ data, suggest that there may be a 'phantom' phase (wde < -1) in the expansion of the Universe. This inference follows when the w0, wa parametrization for the dark energy equation of state wde 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 wde. Then we use a w0, wa model for the 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 ∼ 0.3. The energy flows from dark matter to dark energy at early times and reverses at later times.