Determining σ8 sensitivity to systematic bias in nEPT power spectra

An nth-order Eulerian perturbation theory (nEPT) can model the power spectrum of the dark matter density field accurately only beyond certain scales. We infer σ8, which is the amplitude of dark matter density fluctuations, from the power spectrum data in N-body simulations by forwarding the power spectrum with nEPT. We determine the critical scales below which the inferred σ8 becomes biased and conclude that σ8 is insensitive to the systematical error in nEPT power spectrum.