SZE-21 cm (in units of brightness temperature relative to the CMB) for a non-thermal plasma with s = 3.5 and p₁ = 0.1 (upper panel) and 10 (lower panel) and with τ = 1 × 10^-4 for a modified CMB spectrum with a fiducial model without DM (solid line), an extreme model without DM (dashed line), a fiducial model with DM with M_min = 10^-3M_⊙ (dot-dashed line), and a fiducial model with DM with M_min = 10^-6M_⊙ (three dots-dashed line).