Multi-interacting dark energy and its cosmological implications

In the effort to define the main features a successful solution to the Hubble tension should have, growing evidence has emerged pointing to the need for models able to modify the expansion (and possibly thermal) history of the universe both prior and after recombination, and that could thereby restore the overall concordance between early- and late-time observations without introducing nor worsening other cosmological tensions in the process. In precisely this spirit, here we consider a multi-interacting dark energy model with two complementary interaction channels: one with the dark matter and one with the photons. The former most significantly affects the matter dominated epoch as well as the very late universe, and has been shown to be able to significantly resolve the $S_8$ tension. The latter has been introduced in this work to allow for a larger and natural time dependence of the evolution of the universe since it mostly impacts the radiation dominated epoch as well as the temperature scaling of the photons, as extensively explained in the text. As a result, considering data from Planck+BAO+Pantheon+KV450+DES (which can be combined since the $S_8$ value is lowered even neglecting the weak lensing data) we find that the significance of the $H_0$ tension only reduces to about 3.5$\sigma$, while that of the $S_8$ tension falls below the 2$\sigma$ level. Also, the statistical analysis we perform strongly favors $\Lambda$CDM in all considered cases. Overall, we conclude that the specific multi-interacting dark energy model considered here, despite its broad generality and very rich cosmological phenomenology, cannot successfully restore the aforementioned overall concordance between early- and late-time observations.