 Constant primordial bispectrum

A constant primordial bispectrum means a constant bispectrum shape function, not a bispectrum independent of wavenumber. With $P(k)=2{\pi }^2{\Delta }_{\zeta }^2/k^3$ and scale-independent ${\Delta }_{\zeta }^2$, one normalization is $B=f_{\mathrm{NL}}[P(k_1)P(k_2)P(k_3){]}^{2/3}=4{\pi }^4{f}_{\mathrm{NL}}{\Delta }_{\zeta }^4/(k_1{k}_2{k}_3{)}^2$.