World's Largest N-body Simulation "TianNu" Discovers the Differential Neutrino Condensation Effect


KIAA Postdoctoral Fellow Hao-Ran Yu (于浩然), together with his research team, has completed the World’s largest N-body simulation “TianNu” on the Chinese Tianhe-2 supercomputer. This 3-trillion-particle N-body simulation coevolve the cold dark matter and neutrino fluids throughout the cosmic evolution, and discovered the differential neutrino condensation effect. This research, with Hao-Ran Yu being the first author, is published in the June 5 issue of the journal Nature Astronomy.


Astrophysical techniques have pioneered the discovery of neutrino mass properties. Currently, the known neutrino effects on the large-scale structure of the Universe are all global, and neutrino masses are constrained by attempting to disentangle the small neutrino contribution from the sum of all matter using precise theoretical models. We investigate an alternative approach: to detect the difference between the neutrinos and that of dark matter and baryons. Here, by using one of the largest N-body simulations yet, we discover the differential neutrino condensation effect: in regions of the Universe with different neutrino relative abundance (the local ratio of neutrino to cold dark matter density), halo properties are different and neutrino mass can be inferred. In ‘neutrino-rich’ regions, more neutrinos can be captured by massive halos compared with ‘neutrino-poor’ regions. This effect differentially skews the halo mass function and opens the path to independent measurements of neutrino mass in current or future galaxy surveys.


Figure caption (above): Two-dimensional visualization of CDM and neutrino structures in TianNu. CDM is represented in blue-white and neutrinos in orange. The two subpanels focus on regions with similar CDM structure but different neutrino-to-CDM density ratios. The upper panel shows a neutrino-rich region whereas the lower panel shows a neutrino-poor region. The difference in neutrino condensation seen in these two panels leads to systematically different halo properties between the two regions.



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