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Neutrinos are one of the more elusive particles in the standard model of particle physics. While neutrinos are established to be massive and the squared mass differences have been measured, the absolute neutrino mass values remain unknown. Many neutrino properties including hierarchy and chirality, i.e. whether neutrinos are Majorana or Dirac particles, are also unclear. Cosmic neutrinos with finite mass slightly suppress the matter power spectrum below the neutrino free streaming scale and this effect can be used to constrain neutrino masses. However, the challenge is to disentangle the complex and poorly understood baryonic physics from the neutrino effects and the precision is limited by the uncertainties in the measurement of the optical depth to the primary CMB. In this talk, I will discuss the relative velocity between dark matter and neutrino fluids and how to obtain robust constraints on neutrino properties with this new effect. The new methods are not affected by most systematics and baryonic effects which are parity even and not limited by the optical depth to the CMB, rendering it a new promising probe of neutrino properties.
Hongming Zhu is currently a postdoctoral fellow at the Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto. He obtained his PhD from University of Chinese Academy of Sciences in 2017 and bachelor degree from Nanjing University in 2012. He has been a BCCP postdoctoral fellow at the Berkeley Center for Cosmological Physics, University of California, Berkeley from 2017 to 2020. His research interests include cosmology, large-scale structure, CMB lensing, cosmic neutrinos and pulsar scintillation.
Video record is available: https://vshare.sjtu.edu.cn/open/1df0b6d5f648ca090154203770d871c6