Equilateral bispectrum configuration
= Equilateral bispectrum configuration
{title2=$k_1=k_2=k_3$}
An equilateral <primordial bispectrum> configuration has equal external wavenumbers. For a <cubic time-derivative curvature bispectrum>, $S\propto k_1k_2k_3/(k_1+k_2+k_3)^3$ is maximized here at fixed perimeter by the <arithmetic-geometric mean inequality>.