Decaying Dark Matter as a Possible Solution for Cosmological Tensions

Recent cosmological observations have revealed persistent tensions between early- and late-time measurements of cosmic structure, most notably the S₈ discrepancy between predictions from the Planck cosmic microwave background (CMB) and weak lensing surveys such as DES and DESI. While evolving dark energy models offer a partial resolution, they alone cannot account for all observed anomalies. In this work, we explore a decaying dark matter (DDM) scenario in which a fraction of the dark matter, χ, slowly decays into a lighter particle, φ, and a neutrino, ν. We investigate how this decay modifies the growth of cosmic structures and the matter power spectrum, particularly on large and intermediate scales, thereby alleviating the observed S₈ tension. Using measurements of the galaxy power spectrum, galaxy-galaxy lensing, and weak lensing shear correlations, we demonstrate that the DDM model reproduces the suppression of late-time clustering while preserving the large-scale power consistent with standard ΛCDM predictions. Our results indicate that decaying dark matter, coupled with baryonic physics, provides a viable framework to reconcile discrepancies between early- and late-time cosmological observations, offering new insights into the microphysics of the dark sector and its role in cosmic structure formation.