1σ-detection limits for μ, μ₁, μ₂ and μ₃ caused by dissipation of small-scale acoustic modes for PIXIE-like settings. We used the standard parametrization for the power spectrum with amplitude, A_ζ, spectral index, n_S, and running n_run around pivot scale k₀ = 45 Mpc⁻¹. The heavy lines are for n_run = 0, while all other lines are for n_run = {−0.1, 0.1} in each group. For reference, we marked the case n_run = 0.1.