The speaker and his research team examine the cosmology of warm dark matter (WDM), both stable and decaying, from the point of view of structure formation. They scrutinize the effects associated to the warm nature of dark matter, as well as the fact that it decays. The majoron arises as a Nambu-Goldstone boson, and picks up a small mass from gravitational effects, which necessarily decays to neutrinos. Using N-body simulations, the speaker and his research team show that their Dense Wavelength Division Multiplexing (DWDM) picture leads to a viable alternative to the Lambda Cold Dark Matter (ΛCDM) scenario, with predictions that can differ substantially on small scales.