Dark Matter-Dark Energy Coupling: A New Paradigm in Cosmology

Abstract

The search for interactions between dark matter and dark energy represents a frontier in modern cosmology as it challenges the standard ΛCDM paradigm where these components evolve independently. This review synthesizes theoretical and observational advances in understanding such couplings, which offer compelling solutions to longstanding cosmological problems. Theoretically, interacting models naturally address the cosmic coincidence problem through dynamical attractor solutions, while phenomenologically they provide mechanisms to alleviate tensions in Hubble constant and structure growth measurements. This paper demonstrates how different coupling scenarios such as scalar field interactions, modified gravity theories, and phenomenological models distinctly modify both cosmic expansion history and structure formation. Current constraints from cosmological probes, including CMB, large-scale structure, and supernovae data, severely restrict but do not eliminate viable parameter space for interactions. The coupling strength is constrained to ξ ≲ 0.01 which leaves room for detectable signals in next-generation surveys. Future observations from CMB-S4, Euclid, and LSST will provide critical tests through multi-messenger approaches combining expansion history and growth of structure measurements.