Dark sector to restore cosmological concordance

We develop a new phenomenological model that addresses current tensions between observations of the early and late Universe. Our scenario features: (i) decaying dark energy fluid (DDE), which undergoes transition at $z \sim 5,000$, to raise today's value Hubble parameter -- addressing $H_0$ tension, (ii) an ultra-light axion (ULA), starts oscillating $z\gtrsim 10^4$, suppress matter power spectrum $S_8$ tension. Markov Chain Monte Carlo analyses show such Dark Sector fits combination Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations, Large Scale Structure (LSS) data slightly better than $\Lambda$CDM model, while importantly reducing both with universe probes ($\lesssim 3\sigma$). Combined measurements from cosmic shear surveys, we find discrepancy on is reduced $1.4\sigma$ level, further raised. Adding local supernovae measurements, are $1.2\sigma$ level respectively, significant improvement $\Delta\chi^2\simeq -18$ compared model. With this complete dataset, DDE ULA detected $\simeq 4\sigma$ $\simeq2\sigma$, respectively. discuss possible particle physics realization confining gauge sector its associated axion, although embedding full details within microphysics remains urgent open question. will be decisively probed future CMB LSS surveys.