Effects of the neutrino mass on the linear total matter (solid) or cold-plus-baryonic matter (dashed) power spectrum, presented as ratios with respect to the ΛCDM spectrum with massless neutrinos for four different values of the summed neutrino mass. Top: Singling out the effect of neutrino free-streaming, we keep the parameters {Ω_m, 0h², Ω_b, 0h², Ω_Λ} fixed. Bottom: Quantities best constrained by CMB data, that is, {z_eq, Ω_b, 0h², θ_s}, are fixed to show what is left for Euclid to measure. The mass is always equally split between the three neutrino species.