In the standard ΛCDM picture with nearly Gaussian, adiabatic initial fluctuations, different Fourier or multipole modes of the primordial curvature perturbation are statistically independent, so large- and small-scale modes should not be strongly coupled in the CMB beyond weak lensing and non-linear effects (Hu & White 1997; Dodelson 2003). Reports that very long-wavelength curvature perturbations or anisotropic backgrounds might modulate smaller-scale CMB power—producing scale-dependent anomalies, hemispherical asymmetry, or other signatures of mode coupling—challenge this assumption and often require non-standard inflation, non-Gaussian initial conditions, or exotic curvature dynamics to explain correlated behavior between modes that ΛCDM treats as effectively uncorrelated (Hanson & Lewis 2009; Planck Collaboration XVI 2016).