Same as Fig. 9, but for the 1b-DDM model, parameterised by the DDM fraction $f_{\mathrm{ddm}}^{\mathrm{ini}}$ and decay rate Γ_ddm. The forecast assumes flat priors on ($f_{\mathrm{ddm}}^{\mathrm{ini}}$, ${\mathrm{\Gamma }}_{\mathrm{ddm}}{f}_{\mathrm{ddm}}^{\mathrm{ini}}$) because the effect of 1b-DDM on the linear matter power spectrum scales with the product ${\mathrm{\Gamma }}_{\mathrm{ddm}}{f}_{\mathrm{ddm}}^{\mathrm{ini}}$ (see Sect. 2.2). The model is equivalent to pure ΛCDM in the small ${\mathrm{\Gamma }}_{\mathrm{ddm}}{f}_{\mathrm{ddm}}^{\mathrm{ini}}$ limit. The shaded grey area restricts the parameter space to the region where τ_ddm = 1/Γ_ddm ≥ 31.6 Gyr in which the emulator was trained.