Interacting Dark Sector field theory with phantom crossing

TL;DR

This paper proposes a field-theoretic interacting dark-energy model that naturally explains recent observational evidence of the dark energy equation of state crossing the phantom divide, consistent with multiple cosmological data sets.

Contribution

It introduces a novel fermion-scalar field interaction model that accounts for the phantom crossing while remaining theoretically well-behaved.

Findings

Model fits DESI, Planck, and supernova data well.

Reconstructs a recent double crossing of the phantom divide.

Predicts ultralight fermionic dark matter of about 1.9×10^{-3} eV.

Abstract

Recent results from the Dark Energy Spectroscopic Instrument (DESI) provide evidence for a dynamical dark-energy component, whose equation of state appears to have recently crossed the phantom divide. In this Letter, we present an interacting dark-energy model, grounded in field theory, that naturally accommodates such a double crossing. In our framework, fermionic dark matter is coupled via a Yukawa interaction to a tachyonic scalar field governed by Born-Infeld dynamics. The phantom crossing arises at the level of the effective dark-energy equation of state, while the underlying scalar-field dynamics remains nonphantom and well bounded. We confront our model with data including BAO from the DESI (DR2) survey, CMB distance priors from Planck 2018, and the latest Type Ia supernovae compilations, obtaining robust constraints across the different data combinations and reconstructing a recent double crossing of the phantom divide. Furthermore, under naturalness assumptions, the model expects an ultralight fermionic dark matter mass of order $1.9\times10^{-3}\,\mathrm{eV}$, suggesting a possible connection with new light particles in the dark sector and motivating future tests with cosmological perturbations.