Abstract
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 baryon-acoustic oscillation (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 root mean square (RMS) error of 2.5 per cent across a range of cosmologies, scales $k \lt 10\, h\, \mathrm{Mpc}^{-1}$, and redshifts z < 2. The error rarely exceeds 5 per cent and never exceeds 16 per cent. The worst-case errors occur at z ≃ 2, 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 active galactic nuclei (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 $k\lt 20\, h\, \mathrm{Mpc}^{-1}$. 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.
Highlights
The halo model (Seljak 2000; Peacock & Smith 2000; Ma & Fry 2000) is just such a semi-analytical model of clustering
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
We have presented HMCODE-2020, an updated and augmented halo model for the non-linear matter–matter power spectrum that has an RMS error compared to simulated data of less than 2.5 per cent across a wide range of cosmologies, scales and redshifts
Summary
The halo model (Seljak 2000; Peacock & Smith 2000; Ma & Fry 2000) is just such a semi-analytical model of clustering. In Mead et al (2015) the original HMCODE1 was presented, in which the standard halo-model calculation was augmented with fitted parameters so as to provide a better match to simulated matter power spectra data. More recently Heitmann et al (2016) and Lawrence et al (2017) have created a new emulator, MIRA TITAN, based on a new set of simulations and an improved emulation technique They added the parameters ων and wa to the FRANKEN EMU parameter space and quote an accuracy of 4 per cent for k < 7 hMpc−1, but plan to improve this in the future as more simulations are added to the hypercube. A confounding issue in the field of modelling the non-linear matter power spectrum is that of ‘baryonic feedback’ (e.g., Semboloni et al 2011; Chisari et al 2019): The models and emulators discussed previously were fitted or trained on data from ‘gravityonly’ simulations, in which the effect of gas physics is ignored. Appendix D shows comparisons between the non-linear power from HMCODE-2020 and that from some popular emulators
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