TT spectrum plotted for the ΛCDM best-fit values and for values of c²_s and ﹩{c}_{\mathrm{vis}}^{2}﹩ that are close to our ﹩99.7 \% ﹩ CL. The residuals of the c²_s, ﹩{c}_{\mathrm{vis}}^{2}\ne 0﹩ curves with respect to the best-fit C_ls have been multiplied by a factor of 50 to make them more visible as in Figure 2. The key difference between the GDM and ΛCDM curves is the reduced smoothing of the peaks in the GDM model, caused by the reduced lensing potential.