Quintessential interpretation of the evolving dark energy in light of DESI

TL;DR

The paper tackles whether DESI's evidence for evolving dark energy, encapsulated in $w(a)=w_0+w_a(1-a)$, can be explained by quintessence. It maps the linear $w(a)$ to a canonical scalar field, reconstructing the potential $V(phi)$ and the field trajectory, and finds a past phantom crossing for representative values. It then presents a concrete thawing model with an axion-like potential $V(phi)= abla^2 f^2[1+cos(phi/f)]$ that achieves DESI-like $w_0,w_a$, respects Swampland bounds $M_{ m Pl}|V'/V|>1$ and $M_{ m Pl}^2V''/V>1$, and yields a sub-Planckian decay constant, while predicting a tiny $g_{gamma\u00gamma}$ that could account for cosmic birefringence via $eta=g_{gamma\u00gamma}phi/2$. The work further explores the possible future fate of the Universe (acceleration or Big Crunch) depending on the long-term potential, and argues that deviations from the linear $w(a)$ form in the thawing regime are observationally testable with upcoming data.

Abstract

The recent result of Dark Energy Spectroscopic Instrument (DESI) in combination with other cosmological data shows evidence of the evolving dark energy parameterized by $w_0w_a$CDM model. We interpret this result in terms of a quintessential scalar field and demonstrate that it can explain the DESI result even though it becomes eventually phantom in the past. Relaxing the assumption on the functional form of the equation-of-state parameter $w=w(a)$, we also discuss a more realistic quintessential model. The implications of the DESI result for Swampland conjectures, cosmic birefringence, and the fate of the Universe are discussed as well.

Figures (6)

• Figure 1: The $1\sigma$ and $2\sigma$ contours of the allowed values of $V$ and $V'$ at the present time. The blue, green, and orange contours correspond to Pantheon$+$, DES, and Union, respectively, combined with CMB and DESI. We set $\Omega_{\text{m,}0} = 0.3$ for simplicity.
• Figure 2: The reconstructed scalar potential $V(\phi)$ at the benchmark point. The potential is negative for $\phi /M_\mathrm{Pl} > 1.44$.
• Figure 3: Dynamics of $a(t)$ (vermilion solid line) and $\phi(t)$ (sky-blue dashed line) at the benchmark point.
• Figure 4: The $1\sigma$ and $2\sigma$ contours of the allowed values of $\Delta \phi$ and $c_\text{max}$. The color coding is same as in Fig. \ref{["fig:contour_V-V'"]}.
• Figure 5: Time evolution of the EoS parameter in the axion-like thawing model \ref{['eq: cos']} with the parameters $(\Lambda^2/H_0^2,f/M_\mathrm{Pl},\phi_\mathrm{i}/f)=(8.7,0.41,0.55)$. The blue line is the numerical result of the background equations of motion, the orange dashed one corresponds to the analytic formula \ref{['eq: anal w']}, and the black dotted one is the linear fitting today \ref{['w(a)']} with $(w_0,w_a)=(-0.7,-1)$.