Speaker
Description
Large-scale structure is a powerful probe of dark matter beyond the standard cold paradigm, since even a subdominant warm component can leave observable signatures through its free-streaming effects. In mixed dark matter cosmologies, where cold and warm components evolve jointly, these effects generate not only total density fluctuations but also relative density and velocity perturbations that can leave distinct imprints on galaxy clustering. I present a perturbative framework to describe these signatures using a two-fluid treatment of cold and warm dark matter. In recent work (arXiv:2508.21481), we derived the linear solutions for the coupled system and showed that the relative modes induce new contributions to the galaxy bias expansion. Including these effects, I computed the linear galaxy power spectrum in both real and redshift space and performed Fisher forecasts for DESI and PFS, showing that neglecting relative perturbations can significantly bias constraints on the warm dark matter fraction, particularly for light warm relics. I will then present ongoing work, now nearing completion, that extends this framework beyond linear order by incorporating the nonlinear evolution of mixed dark matter perturbations together with the associated relative-mode bias contributions. This yields a more accurate and systematically improvable description of galaxy clustering across a wider range of scales and strengthens the interpretation of upcoming survey data in searches for non-standard dark matter.