Interacting Dark Energy and Its Implications for Unified Dark Sector

Alternative dark energy models were proposed to address the limitation of the standard concordance model. Though different phenomenological considerations of such models are widely studied, scenarios where they interact with each other remain unexplored. In this context, we study interacting dark energy scenarios (IDEs), incorporating alternative dark energy models. The three models that are considered in this study are time-varying \(\varvec{\Lambda }\), Generalized Chaplygin Gas (GCG), and K-essence. Each model includes an interaction rate \(\varvec{\Gamma }\) to quantify energy density transfer between dark energy and matter. Among them, GCG coupled with an interaction term shows promising agreement with the observed TT power spectrum, particularly for \(\varvec{\ell <70}\), when \(\varvec{\Gamma }\) falls within a specific range. The K-essence model (\(\varvec{\Gamma \le 0.1}\)) is more sensitive to \(\varvec{\Gamma }\) due to its non-canonical kinetic term, while GCG (\(\varvec{\Gamma \ge 1.02}\)) and the time-varying \(\varvec{\Lambda }\) (\(\varvec{\Gamma \le 0.01}\)) models are less sensitive, as they involve different parameterizations. We then derive a general condition when the non-canonical scalar field \(\varvec{\phi }\) (with a kinetic term \(\varvec{X}^{\varvec{n}}\)) interacts with GCG. This has not been investigated in general form before. We find that current observational constraints on IDEs suggest a unified scalar field with a balanced regime, where it mimics quintessence behavior at \(\varvec{n<1}\) and phantom behavior at \(\varvec{n>1}\). We outline a strong need to consider alternative explanations and fewer parameter dependencies while addressing potential interactions in the dark sector.