HMcode-2020: Improved modelling of non-linear cosmological power spectra with baryonic feedback

TL;DR

This paper introduces an improved halo model, HMcode-2020, for accurate non-linear matter power spectrum predictions across various cosmologies, including baryonic feedback effects, with high precision and broad applicability.

Contribution

The paper presents an updated HMcode with enhanced modeling of BAO damping, massive neutrinos, and baryonic feedback, achieving higher accuracy than previous models and fitting to hydrodynamical simulations.

Findings

Achieves 2.5% RMS error in power spectrum predictions across cosmologies

Models baryonic feedback effects with <1% accuracy for z<1

Provides publicly available code integrated into CAMB and soon in CLASS

Abstract

We present an updated version of the HMcode augmented halo model that can be used to make accurate predictions of the non-linear matter power spectrum over a wide range of cosmologies. Major improvements include modelling of BAO damping in the power spectrum and an updated treatment of massive neutrinos. We fit our model to simulated power spectra and show that we can match the results with an RMS error of 2.5 per cent across a range of cosmologies, scales $k < 10\,h\mathrm{Mpc}^{-1}$, and redshifts $z<2$. The error rarely exceeds 5 per cent and never exceeds 16 per cent. The worst-case errors occur at $z\simeq2$, or for cosmologies with unusual dark-energy equations of state. This represents a significant improvement over previous versions of HMcode, and over other popular fitting functions, particularly for massive-neutrino cosmologies with high neutrino mass. We also present a simple halo model that can be used to model the impact of baryonic feedback on the power spectrum. This six-parameter physical model includes gas expulsion by AGN feedback and encapsulates star formation. By comparing this model to data from hydrodynamical simulations we demonstrate that the power spectrum response to feedback is matched at the $<1$ per cent level for $z<1$ and $k<20\,h\mathrm{Mpc}^{-1}$. We also present a single-parameter variant of this model, parametrized in terms of feedback strength, which is only slightly less accurate. We make code available for our non-linear and baryon models at https://github.com/alexander-mead/HMcode and it is also available within CAMB and soon within CLASS.