Separate Universe Simulations

Abstract

The large-scale statistics of observables such as the galaxy density are chiefly determined by their dependence on the local coarse-grained matter density. This dependence can be measured directly and efficiently in N-body simulations by using the fact that a uniform density perturbation with respect to some fiducial background cosmology is equivalent to modifying the background and including curvature, i.e., by simulating a "separate universe". We derive this mapping to fully non-linear order, and provide a step-by-step description of how to perform and analyse the separate universe simulations. This technique can be applied to a wide range of observables. As an example, we calculate the response of the non-linear matter power spectrum to long-wavelength density perturbations, which corresponds to the angle-averaged squeezed limit of the matter bispectrum and higher $n$-point functions. Using only a modest simulation volume, we obtain results with percent-level precision over a wide range of scales.

5 pages, 2 figures, submitted to MNRAS. References added, typos corrected. Added a paragraph on DE perturbations

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Cited by in corpus (92)

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• Complete super-sample lensing covariance in the response approach
• Testing one-loop galaxy bias: joint analysis of power spectrum and bispectrum
• Hydrodynamic Response of the Intergalactic Medium to Reionization
• Large-scale assembly bias of dark matter halos
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• Galaxy bias and primordial non-Gaussianity: insights from galaxy formation simulations with IllustrisTNG
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• Conformal Fermi Coordinates
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• Large-scale tidal effect on redshift-space power spectrum in a finite-volume survey
• Galaxy power-spectrum responses and redshift-space super-sample effect
• Separate Universe Simulations with IllustrisTNG: baryonic effects on power spectrum responses and higher-order statistics
• Imprints of Oscillatory Bispectra on Galaxy Clustering
• Bispectrum Supersample Covariance
• Position-dependent correlation function from the SDSS-III Baryon Oscillation Spectroscopic Survey Data Release 10 CMASS Sample
• Response Approach to the Matter Power Spectrum Covariance
• The impact of large-scale tides on cosmological distortions via redshift-space power spectrum
• Cosmological N-Body Simulations with a Large-Scale Tidal Field
• Measuring the Tidal Response of Structure Formation: Anisotropic Separate Universe Simulations using TreePM
• Learning to Concentrate: Multi-tracer Forecasts on Local Primordial Non-Gaussianity with Machine-Learned Bias
• A robust measurement of the first higher-derivative bias of dark matter halos
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• Fast and easy super-sample covariance of large scale structure observables
• Principal Shapes and Squeezed Limits in the Effective Field Theory of Large Scale Structure
• Separating the Universe into the Real and Fake
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• Correcting correlation functions for redshift-dependent interloper contamination
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• Local Primordial Non-Gaussianities and Super-Sample Variance
• Lagrangian approach to super-sample effects on biased tracers at field level: galaxy density fields and intrinsic alignments
• The position-dependent matter density probability distribution function
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• Large-Scale Tides in General Relativity
• On Soft Limits of Large-Scale Structure Correlation Functions
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• The halo squeezed-limit bispectrum with primordial non-Gaussianity: a power spectrum response approach
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• fNL - gNL mixing in the matter density field at higher orders
• Quintessential Isocurvature in Separate Universe Simulations
• Euclid preparation. LII. Forecast impact of super-sample covariance on 3x2pt analysis with Euclid
• Cosmology in the non-linear regime : the small scale miracle
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• Probabilistic Estimators of Lagrangian Shape Biases: Universal Relations and Physical Insights
• A spherical hydrodynamical model of cosmic voids in ΛCDM and beyond
• Reconstructing the Long-wavelength Matter Density Fluctuation Modes from the Scalar-Type Clustering Fossils
• Cosmological boost factor for dark matter annihilation at redshifts of $z=10$-$100$ using the power spectrum approach
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• Modelling the environmental dependence of the growth rate
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• Gaussian Lagrangian Galaxy Bias
• Iterative mean-field approach to the spherical collapse of dark matter halos
• A semi-analytic estimate for the effective sound speed counterterm in the EFTofLSS
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