The Mira-Titan Universe. II. Matter Power Spectrum Emulation

Abstract

We introduce a new cosmic emulator for the matter power spectrum covering eight cosmological parameters. Targeted at optical surveys, the emulator provides accurate predictions out to a wavenumber k ∼ 5Mpc −1 and redshift z ≤ 2. Besides covering the standard set of ΛCDM parameters, massive neutrinos and a dynamical dark energy of state are included. The emulator is built on a sample set of 36 cosmological models, carefully chosen to provide accurate predictions over the wide and large parameter space. For each model, we have performed a high-resolution simulation, augmented with sixteen medium-resolution simulations and TimeRG perturbation theory results to provide accurate coverage of a wide k-range; the dataset generated as part of this project is more than 1.2Pbyte. With the current set of simulated models, we achieve an accuracy of approximately 4%. Because the sampling approach used here has established convergence and error-control properties, follow-on results with more than a hundred cosmological models will soon achieve ∼ 1% accuracy. We compare our approach with other prediction schemes that are based on halo model ideas and remapping approaches. The new emulator code is publicly available. Subject headings: methods: statistical -cosmology: large-scale structure of the universe

Modelling baryonic feedback for survey cosmology

“…As we discuss in the next section, to find conclusive evidence in this regard would require a large suite of simulations spanning a wide range of sub-grid models and cosmologies. 6 http://astro.uchicago.edu/~gnedin/WL/ This would in turn allow for "emulation" of the matter power spectrum over a parameter space beyond that of existing darkmatter-only emulators [127].…”

Dark Energy Survey Year 1 results: Cosmological constraints from cosmic shear

“…The impact of neutrino mass on the matter power spectrum is implemented in HALOFIT from [113], which introduces some additional uncertainty of potentially up to 20% (e.g., [114][115][116]). This is not a significant concern for this analysis, however, given our scale cuts and the fact that cosmic shear alone is insensitive to the effects of neutrino mass (see Appendix C).…”

On the road to per cent accuracy – II. Calibration of the non-linear matter power spectrum for arbitrary cosmologies

“…Although our emulation strategy requires a few hundred training nodes to reach per cent accuracy, it is important to realise that it provides non-linear power spectrum predictions for a much broader class of cosmologies, including the ΛCDM model. Moreover, with the aid of pairing and fixing techniques (Angulo & Pontzen 2016;Euclid Collaboration et al 2018) the total number of training simulations required is analogous to that of other GP emulators (Lawrence et al 2010(Lawrence et al , 2017.…”

“…(v) Given the set of values of the base cosmological parameters and PCA weights for the queried model, the emulator predicts ln B(k, z). The advantage of our emulator scheme over existing approaches (Heitmann et al 2014;Lawrence et al 2017;Euclid Collaboration et al 2018;Winther et al 2019) is twofold: the modelindependent parameterisation enables predictions for beyond-oneparameter extensions to ΛCDM, effectively expanding the domain of applicability to a much broader class of cosmologically interesting models; and the simulations required for the training phase are all based on the standard ΛCDM cosmology, which makes them easier and faster to run.…”