Hint of dark matter-dark energy interaction in the current cosmological data? (2403.14247v3)

Abstract: We present new constraints on an interacting dark matter\textendash 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, for the first time, numerically solve the Klein-Gordon equation using a shooting algorithm to determine precise initial conditions, improving upon earlier works that relied on approximations. We perform a comprehensive MCMC analysis using a combination of datasets including Planck, BAO (SDSS and DESI DR2), Pantheon+, and SH$0$ES. Our results show a clear preference for a non-zero dark sector coupling, overcoming previous upper-bound-only constraints due to improved numerical accuracy and data precision. This preference is primarily driven by the late-time ISW effect. Notably, the inclusion of DESI DR2 and SH$_0$ES data increases the inferred interaction strength to $\beta \sim 0.3$ (68\% C.L.) and yields strong statistical support over $\Lambda$CDM, with $\Delta\chi^2{\rm min} = -4.75, -6.41$ and $\Delta{\rm AIC} = -0.75, -2.41$ respectively. If future data further supports a fifth force in the dark sector, non-linear structure formation could offer additional observational tests of such long-range interactions. This work also remains consistent with recent DESI observations of evolving dark energy, with the effective dark energy equation of state crossing the phantom divide around redshift $z \sim 0.5$, a feature that emerges naturally in our framework due to the scalar field dynamics.