Cosmological density power spectrum

The density power spectrum records the squared Fourier-mode amplitude, up to the chosen statistical normalization. Scale dependence acquired from primordial amplitudes and subsequent growth determines its spectral shape.

If primordial horizon-crossing perturbations satisfy $V⟨|{\delta }_k{|}^2⟩=C/k^3$, remain frozen during radiation domination, and grow as $a$ during matter domination, then