Quintessential dark energy crossing the phantom divide

TL;DR

This paper investigates two classes of quintessence models capable of crossing the phantom divide in dark energy's equation of state, showing they fit observational data better than CDM but face constraints from dark matter interactions.

Contribution

It introduces and analyzes two novel quintessence models with higher kinetic terms or variable dark matter mass that can cross the phantom divide and improve data fitting.

Findings

Models require moderate parameter tuning.

Achieve crossing of the phantom divide in dark energy.

Models fit data better than CDM but face constraints from dark matter interactions.

Abstract

Motivated by recent results from the DESI collaboration, we explore two classes of quintessence models that can give rise to crossing of the dark energy equation of state through the ``phantom divide'' $w=-1$. These are models with Lagrangians that involve higher powers of the kinetic energy $\dot\phi^2$, or where the dark matter (DM) mass is a function of $\phi$. Both have similar features with respect to the reconstructed redshift-dependent $w(z)$: moderate tuning of parameters is required to achieve the desired shape, and it is difficult or impossible for $w(z)$ to continue evolving smoothly as $z$ becomes large. Nevertheless, they give a strong improvement over $\Lambda$CDM in fitting the data. We point out that models of coupled dark matter and dark energy that cross the phantom divide are under pressure from constraints on long-range DM forces. They rule out the simplest renormalizable coupling of scalar DM to quintessence, but leave the fermionic case marginally allowed, while exponentially coupled models are safe from current constraints.