Hint of dark matter-dark energy interaction in DESI DR2 and current cosmological dataset?

TL;DR

This work tests an interacting dark matter–dark energy scenario where a Chameleon scalar field tracks the minimum of an effective potential sourced by dark matter. The model is implemented by numerically solving the Klein-Gordon equation with a shooting algorithm inside a modified CLASS code, and parameter constraints are derived via MCMC using Planck, DESI DR2 BAO, Pantheon+, and SH0ES data. They find a mild preference for a nonzero dark-sector coupling when DESI DR2 BAO and SH0ES are included (β ≈ 0.26–0.34), with a phantom crossing around z ≈ 0.5, though the present effective equation of state remains close to −1 due to the field settling at the minimum. The results suggest potential hints of DM–DE interactions in late-time cosmology and motivate future non-linear-scale analyses (e.g., N-body simulations) to further test these models with upcoming surveys.

Abstract

We present new constraints on an interacting dark matter-dark energy scenario motivated by string compactification, where a scalar field adiabatically tracks the minimum of an effective potential sourced by dark matter density. In this study, we focus on the Chameleon dark energy model and numerically solve the Klein-Gordon equation using a shooting algorithm to determine precise initial conditions such that the field rests at effective potential minima today. We perform a comprehensive Markov Chain Monte Carlo (MCMC) analysis using a combination of datasets, including Planck, BAO (SDSS and DESI DR2), Pantheon+, and SH$_0$ES. Our analysis shows a mild preference for a higher non-zero dark sector coupling, compared to earlier works on similar models, for two particular combinations of datasets: (i) Planck + DESI DR2 BAO +.Pantheon+, (ii) Planck + SDSS BAO + Pantheon+ + SH$0$ES. Notably, the inclusion of DESI DR2 and SH$0$ES data increases the inferred interaction strength to $β\sim 0.3$ (68\% C.L.) and yields weak and positive evidence in favor of the model over $Λ$CDM, with $Δχ^2_{\rm min} = -4.75, -6.41$ and $Δ$AIC= $-0.75, -2.41$ respectively. This model remains consistent with a phantom crossing at redshift $z\sim 0.5$, in agreement with the trend indicated by DESI observations. However, due to the settlement of the scalar field at the minima of the effective potential at the present epoch, the effective dark energy equation of state asymptotically approaches $w_{\rm eff}\to -1$. leading to only weak evidence in favor of this model when analyzed using the DESI DR2 dataset.

Figures (3)

• Figure 1: Two-dimensional marginalized posterior distributions of the model parameters ($\omega_{\rm dm}$, $H_0$, $\alpha$, $\beta$, $\Omega_m$, and $S_8$) obtained from our MCMC analysis. The contours correspond to the 68% and 95% confidence regions. Different colors represent different dataset combinations: Planck-only, Planck+SDSS BAO, Planck+SDSS BAO+Pantheon+, Planck+DESI DR2 BAO+Pantheon+, and Planck+SDSS BAO+Pantheon+ + S$H_0$ES.
• Figure 2: The scalar field dynamics with redshift is plotted here for best-fit values obtained from MCMC analysis for different combinations of datasets. The left panel shows the field value normalized to its initial value at the initial redshift, and the corresponding initial value is provided in the legend box. The right panel shows the corresponding dynamics of field velocity for the same set of best-fit values. Here $\dot{\phi}$ means derivative with respect to conformal time.
• Figure 3: The effective dark energy equation of state for the chameleon model is plotted with redshift for best-fit values obtained from MCMC analysis for different combinations of datasets. It highlights a phantom crossing at low redshift.