Differential neutrino condensation onto cosmic structure

Abstract

Astrophysical techniques have pioneered the discovery of neutrino mass properties. Current cosmological observations give an upper bound on neutrino masses by attempting to disentangle the small neutrino contribution from the sum of all matter using precise theoretical models. We discover the differential neutrino condensation effect in our TianNu N -body simulation. Neutrino masses can be inferred using this effect by comparing galaxy properties in regions of the universe with different neutrino relative abundance (i.e. the local neutrino to cold dark matter density ratio). In "neutrino-rich" regions, more neutrinos can be captured by massive halos compared to "neutrino-poor" regions. This effect differentially skews the halo mass function and opens up the path to independent neutrino mass measurements in current or future galaxy surveys.Neutrinos are elusive elementary particles whose fundamental properties are incredibly difficult to measure. 40 years after their first direct detection 1, 2 , flavour oscillation experiments [3][4][5] confirmed that at least two neutrino types are massive and placed a lower bound on the sum of their mass:. This discovery has a profound impact on our understanding of the early Universe, where neutrinos are produced in great numbers. First in a relativistic state, they contribute to the radiation energy density, thereby modulating the matter-to-radiation ratio in a way that depends on their mass. This leaves an imprint on the Cosmic Microwave Background 1 arXiv:1609.08968v1 [astro-ph.CO]

Large-scale dark matter simulations

“…The TianNu simulated the cosmic density field with 2:97 Â 10 12 particles in a 1:2h À1 Gpc box which included the effects of massive neutrinos. The base simulation contained 6912 3 CDM particles, and at z ¼ 5 a new set of 13824 3 particles representing M m ¼ 0:05eV neutrinos were added with which subtle differences between CDM and neutrinos were studied (Inman et al 2015;Yu et al 2017a).…”

CUBE -- Towards an Optimal Scaling of Cosmological N-body Simulations

“…Due to using fixed-point compression, CUBE has significantly smaller bpp than any other cosmological N -body simulation codes. For example, TianNu [2] simulates 2.97 trillion particles on Tianhe-2. Each Tianhe-2 node holds an average of 576 3 neutrino particles and 288 3 CDM particles, and uses 40GB memory.…”

“…Another example is the study of neutrino mass using cosmological effects. To model small but nonlinear cosmic neutrino background, we need a large N to suppress the Poisson noise (e.g., [2]). These problems need a dynamical range of 4 to 5 orders of magnitude, corresponding to, at least, 10 12 (trillion) particle N -body simulations.…”

“…However, achieving the largest N with the PM-based algorithms is typically bound by memory capacity, instead of computing capacity. For example, TianNu [2], one of the world's largest N -body simulations, used the P 3 M algorithm [3] to complete an N 3 × 10 12 cosmological N -body simulation on the Tianhe-2 supercomputer. The simulation used all the memory of Tianhe-2, but only 30% of its computing resource 1 .…”

Neutrino effects on the morphology of cosmic large-scale structure

“…Specifically, we adopt a pair of high-resolution N-body simulations (i.e., TianZero with Σm ν = 0 eV and TianNu with Σm ν = 0.05 eV [65]) realized using publicly-available code, CUBEP3M [66], for resolving the subtle neutrino effects between neutrinos and CDM, especially on non-linear scale [67,68]. CUBEP3M here is optimized using hybrid-…”