Improving initialization and evolution accuracy of cosmological neutrino simulations

Abstract

Neutrino mass constraints are a primary focus of current and future large-scale structure (LSS) surveys. Non-linear LSS models rely heavily on cosmological simulations — the impact of massive neutrinos should therefore be included in these simulations in a realistic, computationally tractable, and controlled manner. A recent proposal to reduce the related computational cost employs a symmetric neutrino momentum sampling strategy in the initial conditions. We implement a modified version of this strategy into the Hardware/Hybrid Accelerated Cosmology Code (HACC) and perform convergence tests on its internal parameters. We illustrate that this method can impart 𝒪(1%) numerical artifacts on the total matter field on small scales, similar to previous findings, and present a method to remove these artifacts using Fourier-space filtering of the neutrino density field. Moreover, we show that the converged neutrino power spectrum does not follow linear theory predictions on relatively large scales at early times at the 15% level, prompting a more careful study of systematics in particle-based neutrino simulations. We also present an improved method for backscaling linear transfer functions for initial conditions in massive neutrino cosmologies that is based on achieving the same relative neutrino growth as computed with Boltzmann solvers. Our self-consistent backscaling method yields sub-percent accuracy in the total matter growth function. Comparisons for the non-linear power spectrum with the Mira-Titan emulator at a neutrino mass of mν = 0.15 eV are in very good agreement with the expected level of errors in the emulator and in the direct N-body simulation.

Aemulus ν: precise predictions for matter and biased tracer power spectra in the presence of neutrinos

“…∼ 0.3 eV and below, treating the neutrino component linearly while solving for the full non-linear evolution of the CDM distribution is sufficient [18][19][20][21][22]. At larger masses, a non-linear treatment of the neutrino component is necessary to achieve sub-percent accuracy above k ∼ 1 hMpc −1 [22][23][24][25][26]. Including neutrinos as a separate particle species in N -body simulations has been shown to be an accurate route for such a treatment [27,28].…”

Galaxy Clustering in the Mira-Titan Universe. I. Emulators for the Redshift Space Galaxy Correlation Function and Galaxy–Galaxy Lensing

“…The accuracy of our neutrino implementation (neutrinos are not included as a separate species but instead are modeled in the evolution of the background cosmology) is discussed in Upadhye et al (2014). This approximation is accurate to 1% in the matter power spectrum when compared to simulations that treat neutrinos as separate particles for the range of light neutrino masses that are spanned by the emulator (Castorina et al 2015;Sullivan et al 2023).…”