Modelling the matter bispectrum towards nonlinear scales - two and three loops in perturbation theories

Abstract

I compute the matter bispectrum of large-scale structure up to two loops in the Standard Perturbation Theory and up to three loops in the MPTbreeze renormalised perturbation theory, determining the contributing loop diagrams and evaluating them numerically. In the process I remove the leading divergences in the integrands, thus making them infrared-safe. By comparing the results to numerical simulations, I show that in the case of the Standard Perturbation Theory, the bispectrum at two loops is more accurate than at one loop, up to $k_{\textrm{max}} \sim 0.09 \, h/\textrm{Mpc}$ at $z=0$ and $k_{\textrm{max}} \sim 0.11 \, h/\textrm{Mpc}$ at $z=1$. The MPTbreeze can be employed to accurately model the matter bispectrum up to $k_{\textrm{max}} \sim 0.17 \, h/\textrm{Mpc}$ at $z=0$ and $k_{\textrm{max}} \sim 0.24 \, h/\textrm{Mpc}$ at $z=1$ using the results at three loops.