Tightening the reins on nonminimal dark sector physics: Interacting dark energy with dynamical and nondynamical equation of state

We present a comprehensive reassessment of the state of interacting dark energy (DE) cosmology, namely models featuring a nongravitational interaction between dark matter and DE. To achieve high generality, we extend the dark sector physics by considering two different scenarios: a nondynamical DE equation of state $w_0\ne -1$, and a dynamical $w\left(a\right)=w_0+w_a(1-a)$. In both cases, we distinguish two different physical regimes resulting from a phantom or quintessence equation of state. To circumvent early time superhorizon instabilities, the energy-momentum transfer should occur in opposing directions within the two regimes, resulting in distinct phenomenological outcomes. We study quintessence and phantom nondynamical and dynamical models in light of two independent cosmic microwave background (CMB) experiments—the Planck satellite and the Atacama Cosmology Telescope. We analyze CMB data both independently and in combination with supernovae distance moduli measurements from the Pantheon-Plus catalog and baryon acoustic oscillations from the SDSS-IV eBOSS survey. Our results update and extend the state-of-the-art analyses, significantly narrowing the parameter space allowed for these models and limiting their overall ability to reconcile cosmological tensions. Although considering different combinations of data leaves some freedom to increase $H_0$ towards the value measured by the SH0ES collaboration, our most constraining dataset ($\mathrm{CMB}+\mathrm{baryon}$ acoustic $\mathrm{oscillations}+\mathrm{supernovae}$) indicates that fully reconciling the tension solely within the framework of interacting DE remains challenging.