Perturbation Theory Remixed II: Improved Modeling of Nonlinear Bispectrum
Abstract
We present the application of the $n$th order Eulerian Perturbation Theory ($n$EPT) for modeling the matter bispectrum in real space as an advancement over the Standard Perturbation Theory (SPT). The $n$EPT method, detailed in Wang et al. (2023) \cite{Wang2023nEPT}, sums up the density perturbations up to the $n$th order before computing summary statistics such as bispectrum. Taking advantage of gridbased calculation of SPT (GridSPT), we make a realizationbased comparison of the analytical nonlinear bispectrum predictions from $n$EPT and SPT against a suite of $N$body simulations. Using a sphericalbispectrum visualization scheme, we show that $n$EPT bispectrum matches better than SPT bispectrum over a wide range of scales in general $w$CDM cosmologies. Like the power spectrum case, we find that $n$EPT bispectrum modeling accuracy is controlled by $\sigma_8(z) \equiv \sigma_8 D(z)$, where $D(z)$ is the linear growth factor at a redshift $z$. Notably, the 6EPT doubles the bispectrum model's validity range compared to the oneloop SPT for $\sigma_8(z) < 0.5$, corresponding to redshifts $z\ge1$ for the bestfitting Planck2018 cosmology. For $n\ge5$, however, $n$EPT bispectrum depends sensitively on the cutoff scale or the grid resolution. The percentlevel modeling accuracy achieved for the spherical bispectrum (where we average over all triangular configurations) becomes much degraded when fixing configurations. Thus, we show that the validity range of the fieldlevel cosmological inferences must be different from that derived from averaged summary statistics such as $n$point correlation functions.
 Publication:

arXiv eprints
 Pub Date:
 August 2024
 DOI:
 10.48550/arXiv.2408.06413
 arXiv:
 arXiv:2408.06413
 Bibcode:
 2024arXiv240806413W
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Submitted to Physics Review D. Comments are welcome