Super-sample covariance in simulations

Li, Yin; Hu, Wayne; Takada, Masahiro

doi:10.1103/physrevd.89.083519

Cited by 223 publications

(423 citation statements)

References 39 publications

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“…This alternative physical picture allows for a direct and self-consistent simulation of this situation using standard cosmological N-body codes. Previously, this approach was worked out to the lowest order in δL0 (McDonald 2003;Sirko 2005;Li et al 2014) and used to compute the linear response function of the power spectrum (Li et al 2014). Here, we extended the separate universe approach to all orders in the overdensity δL0 and also pointed out the validity of the approach for certain DE models beyond ΛCDM.…”

Section: Discussionmentioning

confidence: 99%

“…In order to reduce the sample variance when comparing simulations with different overdensities δL0, it is desirable that the simulations start from the same realization of the initial density field. However, there are two options in doing this (Li et al 2014): Either the random fluctuations coincide on comoving scales at all times or the random fluctuations coincide on physical scales at only one specific time. In the former case one setsL/h = L/h, while in the latter one requires a(tout)L/h = a(tout)L/h, which implies that for each output time tout a different value forL is needed (when keeping L fixed) and hence a new simulation has to be performed.…”

Section: N-body Simulationsmentioning

confidence: 99%

“…The idea of the separate universe technique is to absorb the overdensity δρ into the background density of a modified cosmologyρ(t) as (Sirko 2005;Baldauf et al 2011;Sherwin & Zaldarriaga 2012;Li et al 2014)…”

Section: Separate Universementioning

confidence: 99%

“…However, the implementation of the separate universe picture in N-body simulations is relatively new and was only worked out to the lowest order in δρ (McDonald 2003;Sirko 2005). 1 Recently, this technique was used to measure the linear response of the non-linear power spectrum from simulations (Li et al 2014). Here, we will not assume that δρ is small.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Separate universe simulations

Wagner¹,

Chiang²,

Komatsu³

2014

Monthly Notices of the Royal Astronomical Society: Letters

123

164

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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.

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Section: Discussionmentioning

confidence: 99%

Section: N-body Simulationsmentioning

confidence: 99%

Section: Separate Universementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Separate universe simulations

Wagner¹,

Chiang²,

Komatsu³

2014

Monthly Notices of the Royal Astronomical Society: Letters

123

164

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“…We hypothesise that this arises due to the absence of modes larger than the unreplicated box size, which would otherwise couple with the small scale modes within the simulation and increase the small scale covariance. This coupling is referred to as the Super-Sample covariance by Takada & Hu (2013) and Li et al (2014), who also explore corrections for this effect that could be applied to replicated simulations.…”

Section: Effects Of Replication On the Covariancementioning

confidence: 99%

L-PICOLA: A parallel code for fast dark matter simulation

Howlett

Manera

Percival

2015

Astronomy and Computing

160

181

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Robust measurements based on current large-scale structure surveys require precise knowledge of statistical and systematic errors. This can be obtained from large numbers of realistic mock galaxy catalogues that mimic the observed distribution of galaxies within the survey volume. To this end we present a fast, distributed-memory, planar-parallel code, L-PICOLA, which can be used to generate and evolve a set of initial conditions into a dark matter field much faster than a full non-linear N-Body simulation. Additionally, L-PICOLA has the ability to include primordial non-Gaussianity in the simulation and simulate the past lightcone at run-time, with optional replication of the simulation volume. Through comparisons to fully non-linear N-Body simulations we find that our code can reproduce the z = 0 power spectrum and reduced bispectrum of dark matter to within 2% and 5% respectively on all scales of interest to measurements of Baryon Acoustic Oscillations and Redshift Space Distortions, but 3 orders of magnitude faster. The accuracy, speed and scalability of this code, alongside the additional features we have implemented, make it extremely useful for both current and next generation large-scale structure surveys. L-PICOLA is publicly available at https://cullanhowlett.github.io/l-picola.

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Large-scale dark matter simulations

Angulo

Hahn

2022

Living Rev Comput Astrophys

111

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We review the field of collisionless numerical simulations for the large-scale structure of the Universe. We start by providing the main set of equations solved by these simulations and their connection with General Relativity. We then recap the relevant numerical approaches: discretization of the phase-space distribution (focusing on N-body but including alternatives, e.g., Lagrangian submanifold and Schrödinger–Poisson) and the respective techniques for their time evolution and force calculation (direct summation, mesh techniques, and hierarchical tree methods). We pay attention to the creation of initial conditions and the connection with Lagrangian Perturbation Theory. We then discuss the possible alternatives in terms of the micro-physical properties of dark matter (e.g., neutralinos, warm dark matter, QCD axions, Bose–Einstein condensates, and primordial black holes), and extensions to account for multiple fluids (baryons and neutrinos), primordial non-Gaussianity and modified gravity. We continue by discussing challenges involved in achieving highly accurate predictions. A key aspect of cosmological simulations is the connection to cosmological observables, we discuss various techniques in this regard: structure finding, galaxy formation and baryonic modelling, the creation of emulators and light-cones, and the role of machine learning. We finalise with a recount of state-of-the-art large-scale simulations and conclude with an outlook for the next decade.

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Super-sample covariance in simulations

Cited by 223 publications

References 39 publications

Separate universe simulations

Separate universe simulations

L-PICOLA: A parallel code for fast dark matter simulation

Large-scale dark matter simulations

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