Dimensionless cosmological power spectrum
= Dimensionless cosmological power spectrum
{title2=$\Delta_X=k^3P_X/(2\pi^2)$}
= Dimensionless power spectrum
{synonym}
The dimensionless spectrum is the contribution to a statistically isotropic field variance per logarithmic <wavenumber> interval: $\langle X^2\rangle=\int d\log k\,\Delta_X(k)$, with any necessary smoothing or regulators. Some conventions denote this same quantity $\Delta_X^2$. The definition, not the superscript convention, fixes its meaning.