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 SH0ES. Our
analysis shows a mild preference for a higher nonzero dark sector coupling, compared to earlier works on similar models, for two particular combinations of datasets: (i) Planck + DESI DR2 BAO +.Pantheon+ and (ii) Planck + SDSS BAO + Pantheon+ + SH0ES. Notably, the inclusion of DESI DR2 and SH0ES data increases the
inferred interaction strength to β ∼ 0.3 (68% C.L.) and yields weak and positive evidence in favor of the model
over ΛCDM, with = –4.75, –6.41 min 2 and ΔAIC= –0.75, –2.41, respectively. This model remains consistent
with a phantom crossing at redshift z ∼ 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 weff → −1. leading to only weak evidence in favor of this model when analyzed using the DESI DR2 dataset.
