Speaker
Description
The nature of dark energy and dark matter remains one of the central open problems in modern cosmology. In this context, the Effective Field Theory (EFT) of dark energy provides a general and systematic framework to investigate departures from the standard cosmological model and to describe possible interactions in the dark sector. In this work, we study interacting dark energy scenarios induced by conformal and disformal couplings between dark matter and the scalar field, with particular emphasis on degeneracies that arise between the corresponding EFT functions. Our main goal is to identify cases in which the interaction can be hidden at the background level, reproducing a ΛCDM-like expansion history, while still generating observable signatures at the level of linear perturbations. We analyze the modified background and perturbation equations, impose theoretical viability and stability requirements, including no-ghost and no-gradient conditions, and consider compatibility with gravitational-wave constraints by adopting luminal tensor propagation. A central part of the project is the construction of coupling configurations in which the background interaction term vanishes through a specific relation between the conformal and disformal parameters, leaving the perturbative sector as the main probe of the interaction.