DESI constraints on two-field quintessence with exponential potentials

TL;DR

This paper examines a two-field quintessence model with exponential potentials, demonstrating it can emulate single-field dynamics and is moderately favored over the standard cosmological model based on current observational data.

Contribution

It introduces a two-field quintessence framework with exponential potentials that can reproduce cosmic acceleration and is supported by Bayesian analysis against observational data.

Findings

Moderate Bayesian evidence against flat ΛCDM with Δ ln B ~ 4.

Slopes of exponential potentials are close to 1, with the effective single-field slope constrained below unity.

Model aligns with higher-dimensional theories and current observational constraints.

Abstract

We investigate a quintessence model involving two scalar fields with double-exponential potentials. This configuration allows the system as a whole to emulate the dynamics of a single field with a shallower potential, enabling scalar fields that individually cannot drive cosmic acceleration to collectively achieve and sustain it. We assess the viability of this model by performing a fully Bayesian analysis and confronting its predictions with observational data, including the Planck 2018 Cosmic Microwave Background (CMB) shift parameters, the newly released Dark Energy Spectroscopic Instrument (DESI) DR2 Baryon Acoustic Oscillation (BAO) measurements, and the Dark Energy Survey Year 5 (DESY5) Type Ia supernova (SnIa) sample. Our analysis shows that the two-field quintessence model yields a log Bayes factor relative to the flat $\Lambda$CDM model of $\Delta \ln B \sim 4$, indicating moderate evidence against the latter. We also find that the central values of the two slopes of the exponential potentials are both close to 1, whereas the slope of an effective single-field system is constrained to be less than order unity. This property is theoretically desirable from the perspective of higher-dimensional theories. Thus, the two-field quintessence model with exponential potentials provides a physically motivated and compelling mechanism that is consistent with both observational and theoretical requirements.