4.45 Pflops astrophysical N-body simulation on K computer -- The gravitational trillion-body problem

Ishiyama, Tomoaki; Nitadori, Keigo; Makino, Junichiro

doi:10.1109/sc.2012.3

Cited by 62 publications

(71 citation statements)

References 36 publications

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“…To follow the gravitational evolution of the dark matter particles, we employ publicly available tree-PM codes, Gadget2 (Springel et al 2001;Springel 2005) for the large-box simulation (L100) and GreeM (Ishiyama et al 2009(Ishiyama et al , 2012 for the small-box simulation (L10). GreeM is tuned to accelerate the tree gravitational calculation, and it is faster than Gadget2 especially in the strongly non-linear regime.…”

Section: N -Body Simulationmentioning

confidence: 99%

Constraints on warm dark matter from weak lensing in anomalous quadruple lenses

Inoue

Takahashi

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We investigate the weak lensing effect by line-of-sight structures with a surface mass density of 10 8 M ⊙ /arcsec 2 in QSO-galaxy quadruple lens systems. Using highresolution N -body simulations in warm dark matter (WDM) models and observed four quadruple lenses that show anomalies in the flux ratios, we obtain constraints on the mass of thermal WDM, m WDM 1.3 keV(95%CL) assuming that the density of the primary lens is described by a singular isothermal ellipsoid (SIE). The obtained constraint is consistent with those from Lyman-α forests and the number counts of high-redshift galaxies at z > 4. Our results show that WDM with a free-streaming comoving wavenumber k fs 27 h/Mpc is disfavoured as the major component of cosmological density at redshifts 0.5 z 4 provided that the SIE models describe the gravitational potentials of the primary lenses correctly.

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Section: N -Body Simulationmentioning

confidence: 99%

Constraints on warm dark matter from weak lensing in anomalous quadruple lenses

Inoue

Takahashi

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…Since the numerical difficulty grows at least proportional to the number of particles, simulations can only handle particle ensembles up to a certain size which is typically many orders of magnitude smaller than the physical ensemble. The presently largest N -body simulations [39,40] comprise about 10 12 particles. If we would want these to represent elementary particles we could only describe a volume of about ∼ (100 km)…”

Section: Numerical Recipesmentioning

confidence: 99%

N -body methods for relativistic cosmology

Adamek

Durrer

Kunz

2014

Class. Quantum Grav.

104

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Abstract. We present a framework for general relativistic N -body simulations in the regime of weak gravitational fields. In this approach, Einstein's equations are expanded in terms of metric perturbations about a Friedmann-Lemaître background, which are assumed to remain small. The metric perturbations themselves are only kept to linear order, but we keep their first spatial derivatives to second order and treat their second spatial derivatives as well as sources of stress-energy fully nonperturbatively. The evolution of matter is modelled by an N -body ensemble which can consist of free-streaming nonrelativistic (e.g. cold dark matter) or relativistic particle species (e.g. cosmic neutrinos), but the framework is fully general and also allows for other sources of stress-energy, in particular additional relativistic sources like modifiedgravity models or topological defects. We compare our method with the traditional Newtonian approach and argue that relativistic methods are conceptually more robust and flexible, at the cost of a moderate increase of numerical difficulty. However, for a ΛCDM cosmology, where nonrelativistic matter is the only source of perturbations, the relativistic corrections are expected to be small. We quantify this statement by extracting post-Newtonian estimates from Newtonian N -body simulations.PACS numbers: 98.80. Jk, 04.25.Nx

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“…To follow the gravitational evolution of the dark matter particles, we employ a publicly available tree-PM code GreeM (Ishiyama et al 2009(Ishiyama et al , 2012. GreeM is tuned to accelerate the tree gravitational calculation, and it is fast especially in the strongly non-linear regime.…”

Section: Cosmological N-body Simulationsmentioning

confidence: 99%

Constraints on small-scale cosmological fluctuations from SNe lensing dispersion

Ben-Dayan

Takahashi

2015

Mon. Not. R. Astron. Soc.

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We provide predictions on small-scale cosmological density power spectrum from supernova lensing dispersion. Parameterizing the primordial power spectrum with running α and running of running β of the spectral index, we exclude large positive α and β parameters which induce too large lensing dispersions over current observational upper bound. We ran cosmological Nbody simulations of collisionless dark matter particles to investigate non-linear evolution of the primordial power spectrum with positive running parameters. The initial small-scale enhancement of the power spectrum is largely erased when entering into the non-linear regime. For example, even if the linear power spectrum at k > 10hMpc −1 is enhanced by 1 − 2 orders of magnitude, the enhancement much decreases to a factor of 2 − 3 at late time (z 1.5). Therefore, the lensing dispersion induced by the dark matter fluctuations weakly constrains the running parameters. When including baryon-cooling effects (which strongly enhance the small-scale clustering), the constraint is comparable or tighter than the PLANCK constraint, depending on the UV cut-off. Further investigations of the non-linear matter spectrum with baryonic processes is needed to reach a firm constraint.

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4.45 Pflops astrophysical N-body simulation on K computer -- The gravitational trillion-body problem

Cited by 62 publications

References 36 publications

Constraints on warm dark matter from weak lensing in anomalous quadruple lenses

Constraints on warm dark matter from weak lensing in anomalous quadruple lenses

N -body methods for relativistic cosmology

Constraints on small-scale cosmological fluctuations from SNe lensing dispersion

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