Constraints on Chiral-Quintom dark energy after DESI DR2 and impact on unifying dark energy with inflation

TL;DR

This paper introduces the Chiral-Quintom two-field dark energy model with kinetic mixing governed by κ and an exponential potential, aiming to unify inflation and late-time acceleration while allowing phantom-divide crossing without instabilities. By recasting the background dynamics into Hubble-normalized variables and performing MCMC analyses against Pantheon+, Union3.0, CC, and DESI DR2 BAO data, the authors compare against ΛCDM and w0w_aCDM using AIC. They find that the model can fit current low-redshift data with weak to strong evidence depending on the dataset, and that the dark-energy equation of state w_CQ(z) remains dynamical with a phantom-crossing capability, while λ is constrained to negative values and a κ/λ hierarchy is favored. The work suggests that multi-field dark energy offers a flexible and potentially superior description of the Universe’s expansion history and motivates further tests with CMB data and upcoming surveys.

Abstract

The recent data release DR2 from the Dark Energy Spectroscopic Instrument (DESI) has reinforced compelling evidence supporting the dynamical nature of dark energy. In this respect, we here explore a two-scalar field cosmological model, dubbed Chiral-Quintom paradigm, that allows for a unified description of early- and late-time cosmic accelerations, namely inflation and dark energy, respectively. Moreover, we show that it provides a mechanism to cross the phantom divide without instabilities. To do so, we first focus on scenarios where the scalar fields evolve under an exponential potential, leading to distinct cosmological behaviors, including tracking solutions and slow-roll or hyperbolic inflation. Afterwards, by considering a nonlinear potential and a mixing in the kinetic sector, we show that the model can also describe the matter-dominated era, offering a potential unification of the dark sector. Accordingly, we place bounds on this double-field paradigm by employing recent low-redshift observational data, including supernovae from the Pantheon+ and Union3.0 compilations, observational Hubble parameter measurements, and baryon acoustic oscillation data from the latest DESI release. By means of the Akaike information criterion, the standard $Λ$CDM scenario and the $w_0w_a$CDM model are thus compared with the Chiral-Quintom approach, showing that, in principle, multiple-field dynamics does not seem to be ruled out, ultimately providing a flexible framework for describing late-time dynamics.

Figures (2)

• Figure 1: Evolution of the dark energy equation of state parameter $w_{CQ}\left( z\right)$ for the posterior variables of Table \ref{['best1']} within $1\sigma$. Solid lines are for the mean values. We observe that the present acceleration phase is described by the asymptotic solution where the two scalar fields contribute to the cosmic fluid.
• Figure 2: Contour plots based on $1\sigma$ and $2\sigma$ confidence levels for the Chiral-Quintom model.