DESI results: Hint towards coupled dark matter and dark energy

TL;DR

The paper addresses DESI's hints of evolving dark energy and phantom-crossing by proposing an interacting dark sector model in which a quintessence field is Yukawa-coupled to dark matter. It demonstrates that the observable equation of state $w_{\rm eff}$ can cross the phantom barrier while the intrinsic field equation of state $w_{\phi}$ remains above $-1$, achieving compatibility with DESI (and Planck/Union3) within 2$\sigma$ for certain parameter choices. The authors solve the coupled Klein-Gordon and Friedmann equations for two self-interaction potentials, showing late-time crossing around $z\sim0.5-1$ under thawing dynamics, and highlight the need for forthcoming MCMC analyses and perturbation studies. This framework offers a viable path to interpret DESI data without phantom fields, motivating further cosmological and particle-physics investigations.

Abstract

We investigate a scenario where a dark energy quintessence field $φ$ with positive kinetic energy is coupled with dark matter. With two different self-interaction potentials for the field and a particular choice of the coupling function, we show explicitly how the observable effective equation of state parameter $w_{\rm eff}$ for the dark energy field crosses the phantom barrier ($w_{\rm eff} = -1$) while keeping the equation of state of the quintessence field $w_φ> -1$. With appropriate choices of parameters, $w_{\rm eff}$ crosses the phantom divide around redshift $z\sim 0.5$, transitioning from $w_{\rm eff} <-1$ in the past to $w_{\rm eff}>-1$ today. This explains DESI observations well. Our analysis reveals that the model remains consistent within the $2σ$ confidence intervals provided by DESI for several combinations of the scalar field parameters, highlighting its potential in explaining the dynamics of dark energy arising from a simple Yukawa-type long-range interaction in the dark sector. While the current findings offer a promising framework for interpreting DESI observations, future work, including a comprehensive Markov Chain Monte Carlo (MCMC) analysis, is necessary to constrain the parameter space further and strengthen the statistical significance of the results.

Figures (4)

• Figure 1: Schematic plot of $V_{\text{eff}}(\phi) = V(\phi) + \rho_{\rm DM}f(\phi)$.
• Figure 2: A typical dynamics of $\phi$ and $\phi^\prime=\frac{d\phi}{da}$ with the scale factor for the polynomial self-interaction potential is shown here with different initial positions of the field. The left (right) figure depicts the dynamics for a field that starts on the right (left) side of the effective minimum for $\alpha=0.14$ and $\beta=0.45$, with initial field value $\phi_{\rm initial}=0.15 M_{\rm pl} (0.05 M_{\rm pl})$ and final value $\phi_0=0.28 M_{\rm pl} (0.30 M_{\rm pl})$. Here $M_{\rm pl}$ is the reduced Planck mass.
• Figure 3: Fitting of $w(z)$ for polynomial self-interaction potential within the $2$-$\sigma$ contours of DESI (light purple) and DESI+Union3+Planck (light grey). The initial value of phi, $\phi_{\rm in}$ is considered as $0.15 M_{\rm pl}$(top-left), $0.15 M_{\rm pl}$ (top-right), $0.15 M_{\rm pl}$ (bottom-left) and $0.21 M_{\rm pl}$ (bottom-right).
• Figure 4: Fitting of $w(z)$ for exponential self-interaction potential within the $2$-$\sigma$ contours of DESI (light purple) and DESI+Union3+Planck (light gray). The initial value of phi, $\phi_{\rm in}$ is considered as $0.08 M_{\rm pl}$(top-left), $0.05 M_{\rm pl}$ (top-right), $0.05 M_{\rm pl}$ (bottom-left) and $0.025 M_{\rm pl}$ (bottom-right).