Ratio of the linear (solid lines) and non-linear (dashed lines) power spectra of several 1b-DDM models to that of a pure ΛCDM model with the same cosmological parameters, parameterised by the fraction $f_{\mathrm{ddm}}^{\mathrm{ini}}$ and the decay rate Γ_ddm. We work in the basis $(f_{\mathrm{ddm}}^{\mathrm{ini}},{\mathrm{\Gamma }}_{\mathrm{ddm}}{f}_{\mathrm{ddm}}^{\mathrm{ini}})$ to show that only the product of the two DDM parameters affects the linear power spectrum. The other parameters (${\mathrm{\Omega }}_{\mathrm{dm}}^{\mathrm{ini}}$, Ω_b, h, A_s, n_s) are kept fixed, and the spectra are computed today (z = 0). The non-linear spectra are predicted by the emulator introduced in Sect. 3.2 and plotted up to the maximum wavenumber at which this emulator is trusted.