Sign switching in dark sector coupling interactions as a candidate for resolving cosmological tensions

The ΛCDM model has successfully explained a wide range of cosmological observations, but is increasingly challenged by the emergence of cosmological tensions, particularly the Hubble tension H0 and the S8 tension. The Hubble tension, with a significance above 5σ, and the S8 tension, showing a discrepancy of approximately 2-4σ, highlight inconsistencies between measurements of the local and early Universe. The ΛCDM model has been highly successful in explaining cosmological observations but is increasingly challenged by the H0 tension (>5σ) and the S8 tension (2-4σ). These tensions expose significant inconsistencies between measurements of the local Universe and those of the early Universe. This paper expands a well-established interacting dark energy (IDE) phenomenological scenario, where dark matter (DM) can transfer energy to dark energy (DE) or vice versa, depending on the sign of the coupling parameter ζ. The novel feature consists in a transition mechanism which reverses the direction of the energy-momentum transfer after the redshift where the densities of the dark species are the same. We evaluate this model using a comprehensive set of recent observational data, including baryon acoustic oscillations (BAO) from the DESI survey, type Ia supernovae from the PantheonPlus, DESY5, and Union3 samples, and cosmic microwave background (CMB) data from Planck. Our analysis shows that this scenario relaxes the H0 and S8 tensions, particularly when Cepheid distance calibration in the SH0ES samples or DESI data are included. Our analysis shows that this scenario can potentially relax both the H0 and S8 tensions simultaneously. We find the new model to be weakly preferred over ΛCDM by BAO-DESI data. However, we show that the IDE model features positive Bayesian evidence compared to ΛCDM only when Cepheid distance calibration in the SH0ES sample is used to calibrate SNIa data from PantheonPlus.