Enabling matter power spectrum emulation in beyond-$\Lambda$CDM cosmologies with COLA

Abstract

We compare and validate COLA (COmoving Lagrangian Acceleration) simulations against existing emulators in the literature, namely Bacco and Euclid Emulator 2. Our analysis focuses on the non-linear response function, i.e., the ratio between the non-linear dark matter power spectrum in a given cosmology with respect to a pre-defined reference cosmology, which is chosen to be the Euclid Emulator 2 reference cosmology in this paper. We vary three cosmological parameters, the total matter density, the amplitude of the primordial scalar perturbations and the spectral index. By comparing the COLA non-linear response function with those computed from each emulator in the redshift range $0\le z\le 3$, we find that the COLA method is in excellent agreement with the two emulators for scales up to $k\sim 1h$/Mpc as long as the deviations of the matter power spectrum from the reference cosmology are not too large. We validate the implementation of massive neutrinos in our COLA simulations by varying the sum of neutrino masses to three different values, $0.0$ eV, $0.058$ eV and $0.15$ eV. We show that all three non-linear prescriptions used in this work agree at the $1\%$ level at $k\le 1h$/Mpc. We then introduce the Effective Field Theory of Dark Energy in our COLA simulations using the $N$-body gauge method. We consider two different modified gravity models in which the growth of structure is enhanced or suppressed at small scales, and show that the response function with respect to the change of modified gravity parameters depends weakly on cosmological parameters in these models.

29 pages, 15 figures, Comments are welcome. Version accepted by JCAP

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• Studying large-scale structure probes of modified gravity with COLA
• Sesame: A power spectrum emulator pipeline for beyond-$\Lambda$CDM models
• Revisiting Vainshtein Screening for fast N-body simulations
• A field-level emulator for modified gravity
• Euclid preparation. Simulations and nonlinearities beyond $\Lambda$CDM. 1. Numerical methods and validation
• Dynamics of pairwise motions in the fully non-linear regime in LCDM and Modified Gravity cosmologies
• Non-Linearity-Free prediction of the growth-rate $f{\sigma }_8$ using Convolutional Neural Networks
• Fast simulation mapping: from standard to modified gravity cosmologies using the bias assignment method
• Cosmological perturbation theory for large scale structure in phase space
• Fast Generation of Weak Lensing Maps in Modified Gravity with COLA
• Dark energy constraints in light of theoretical priors
• A simple prediction of the nonlinear matter power spectrum in Brans-Dicke gravity from linear theory