Hao-Ran Yu

Precision reconstruction of the cold dark matter-neutrino relative velocity from

Discovering the mass of neutrinos is a principle goal in high energy physics and cosmology. In addition to cosmological measurements based on two-point statistics, the neutrino mass can also be estimated by observations of neutrino wakes resulting from the relative motion between dark matter and neutrinos. Such a detection relies on an accurate reconstruction of the dark matter-neutrino relative velocity which is affected by non-linear structure growth and galaxy bias. We investigate our ability to reconstruct this relative velocity using large N-body simulations where we evolve neutrinos as distinct particles alongside the dark matter. We find that the dark matter velocity power spectrum is overpredicted by linear theory whereas the neutrino velocity power spectrum is underpredicted. The magnitude of the relative velocity observed in the simulations is found to be lower than what is predicted in linear theory. Since neither the dark matter nor the neutrino velocity fields are directly observable from galaxy or 21 cm surveys, we test the accuracy of a reconstruction algorithm based on halo density fields and linear theory. Assuming prior knowledge of the halo bias, we find that the reconstructed relative velocities are highly correlated with the simulated ones with correlation coefficients of 0.94, 0.93, 0.91 and 0.88 for neutrinos of mass 0.05, 0.1, 0.2 and 0.4 eV. We confirm that the relative velocity field reconstructed from large scale structure observations such as galaxy or 21 cm surveys can be accurate in direction and, with appropriate scaling, magnitude.

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So far there is only indirect evidence that the Universe is undergoing an accelerated expansion. The evidence for cosmic acceleration is based on the observation of different objects at different distances and requires invoking the Copernican cosmological principle and Einsteins equations of motion. We examine the direct observability using recession velocity drifts (Sandage-Loeb effect) of 21-cm hydrogen absorption systems in upcoming radio surveys. This measures the change in velocity of the same objects separated by a time interval and is a model-independent measure of acceleration. We forecast that for a CHIME-like survey with a decade time span, we can detect the acceleration of a ΛCDM universe with 5σ confidence. This acceleration test requires modest data analysis and storage changes from the normal processing and cannot be recovered retroactively.

-body simulations

Constraining neutrino mass remains an elusive challenge in modern physics. Precision measurements are expected from several upcoming cosmological probes of large-scale structure. Achieving this goal relies on an equal level of precision from theoretical predictions of neutrino clustering. Numerical simulations of the non-linear evolution of cold dark matter and neutrinos play a pivotal role in this process. We incorporate neutrinos into the cosmological N-body code CUBEP 3 M and discuss the challenges associated with pushing to the extreme scales demanded by the neutrino problem. We highlight code optimizations made to exploit modern high performance computing architectures and present a novel method of data compression that reduces the phase-space particle footprint from 24 bytes in single precision to roughly 9 bytes. We scale the neutrino problem to the Tianhe-2 supercomputer and provide details of our production run, named TianNu, which uses 86% of the machine (13 824 compute nodes). With a total of 2.97 trillion particles, TianNu is currently the world’s largest cosmological N-body simulation and improves upon previous neutrino simulations by two orders of magnitude in scale. We finish with a discussion of the unanticipated computational challenges that were encountered during the TianNu runtime.

Method for Direct Measurement of Cosmic Acceleration by 21-cm Absorption Systems

Many researchers have performed cosmological-model-independent tests for the distance-duality (DD) relation. Theoretical work has been conducted based on the results of these tests. However, we find that almost all of these tests were perhaps not cosmological-model-independent after all, because the distance moduli taken from a given type Ia supernovae (SNe Ia) compilation are dependent on a given cosmological model and Hubble constant. In this Letter, we overcome these defects and by creating a new cosmological-model-independent test for the DD relation. We use the original data from the Union2 SNe Ia compilation and the angular diameter distances from two galaxy cluster samples compiled by De Filippis et al. and Bonamente et al. to test the DD relation. Our results suggest that the DD relation is compatible with observations, and the spherical model is slightly better than the elliptical model at describing the intrinsic shape of galaxy clusters if the DD relation is valid. However, these results are different from those of previous work.

Cosmological neutrino simulations at extreme scale

Our real universe is locally inhomogeneous. Dyer and Roeder introduced the smoothness parameter α to describe the influence of local inhomogeneity on angular diameter distance, and they obtained the angular diameter distance-redshift approximate relation (Dyer-Roeder equation) for locally inhomogeneous universe. Furthermore, the Distance-Duality (DD) relation, DL(z)(1+z)−2/DA(z) = 1, should be valid for all cosmological models that are described by Riemannian geometry, where DL and DA are, respectively, the luminosity and angular distance distances. Therefore, it is necessary to test whether if the Dyer-Roeder approximate equation can satisfy the Distance-Duality relation. In this paper, we use Union2.1 SNe Ia data to constrain the smoothness parameter α and test whether the Dyer-Roeder equation meet the DD relation. By using χ2 minimization, we get α = 0.92−0.32+0.08 at 1σ and 0.92−0.65+0.08 at 2σ, and our results show that the Dyer-Roeder equation is in good consistency with the DD relation at 1σ.

AN IMPROVED METHOD TO TEST THE DISTANCE-DUALITY RELATION

Derek Inman, 2, ∗ Hao-Ran Yu, 3, 4 Hong-Ming Zhu, J.D. Emberson, Ue-Li Pen, 7, 8, 9, † Tong-Jie Zhang, 10, 11, ‡ Shuo Yuan, Xuelei Chen, and Zhi-Zhong Xing 14 Canadian Institute for Theoretical Astrophysics, University of Toronto, M5S 3H8, Ontario, Canada Department of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada Kavli Institute for Astronomy & Astrophysics, Peking University, Beijing 100871, China Department of Astronomy, Beijing Normal University, Beijing 100875, China Key Laboratory for Computational Astrophysics, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China ALCF Division, Argonne National Laboratory, Lemont, IL 60439, USA Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada Canadian Institute for Advanced Research, Program in Cosmology and Gravitation Perimeter Institute for Theoretical Physics, Waterloo, ON, N2L 2Y5, Canada Shandong Provincial Key Laboratory of Biophysics, School of Physics and Electric Information, Dezhou University, Dezhou 253023, China National Supercomputer Center in Guangzhou, Sun Yat-Sen University, Guangzhou, 510275, China Department of Astronomy, Peking University, Beijing 100871, China School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China

Constraining smoothness parameter and the DD relation of Dyer-Roeder equation with supernovae

We study the power of current and future observational Hubble parameter data (OHD) on non-parametric estimations of the dark energy equation of state,

Simulating the cold dark matter-neutrino dipole with TianNu

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Nonparametric reconstruction of dynamical dark energy via observational Hubble parameter data

. We propose a new method by conjunction of principal component analysis (PCA) and the criterion of goodness of fit (GoF) criterion to reconstruct

Constraints on smoothness parameter and dark energy using observational H(z) data

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