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Abstract
Accurate predictions for the nonlinear matter power spectrum are needed to confront theory with observations in current and near future weak lensing and galaxy clustering surveys. We propose a computationally cheap method to create an emulator for modified gravity models by utilizing existing emulators for ΛCDM. Using a suite of Nbody simulations we construct a fitting function for the enhancement of both the linear and nonlinear matter power spectrum in the commonly studied HuSawicki ƒ (R) gravity model valid for wavenumbers k ≲ 5 − 10 hMpc^{−1} and redshifts z ≲ 3. We show that the cosmology dependence of this enhancement is relatively weak so that our fit, using simulations coming from only one cosmology, can be used to get accurate predictions for other cosmological parameters. We also show that the cosmology dependence can, if needed, be included by using linear theory, approximate Nbody simulations (such as COLA) and semianalytical tools like the halo model. Our final fit can easily be combined with any emulator or semianalytical models for the nonlinear ΛCDM power spectrum to accurately, and quickly, produce a nonlinear power spectrum for this particular modified gravity model. The method we use can be applied to fairly cheaply construct an emulator for other modified gravity models. As an application of our fitting formula we use it to compute Fisherforecasts for how well galaxy clustering and weak lensing in a Euclidlike survey will be at constraining modifications of gravity.
Original language  English 

Article number  123540 
Number of pages  13 
Journal  Physical Review D  Particles, Fields, Gravitation and Cosmology 
Volume  100 
Issue number  12 
DOIs  
Publication status  Published  23 Dec 2019 
Keywords
 astroph.CO
 grqc
 RCUK
 STFC
 ST/N000668/1
 ST/P000541/1
 ST/L00075X/1
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Winther, H. (Creator), Casas, S. (Creator), Baldi, M. (Creator), Koyama, K. (Creator), Li, B. (Creator), Lombriser, L. (Creator) & Zhao, G. (Creator), American Physical Society, 5 Dec 2019
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