Tianlai Collaboration Meeting

Tuesday Aug 4, 2026, 8:00 AM → 8:50 AM America/Chicago

Zoom

Minutes

Peter and Albert reviewed a recent preprint by Gil Holder et al.  https://arxiv.org/abs/2605.22934  on a new idea for measuring  x_HI/Ts, the ratio of the neutral fraction of hydrogen to the hydrogen spin temperature as a function of redshift.  It exploits the fact that we have high precision maps made at cm and mm wavelengths of the CMB temperature anisotropies over the full sky.  These can be used as templates for what CMB maps at meter wavelengths should look like, before the CMB radiation interacts with neutral hydrogen along the line of sight.   Specifically, the CMB signal should be attenuated when it passes through epochs when Ts is < Tcmb, which is expected to happen during the cosmic dark ages and cosmic dawn/EoR.  Hence, the proposal is an alternate means to measure the sky-averaged (global) 21 cm spectrum.    As always, Galactic foregrounds make this a difficult project.   However, the key advantage comes from the fact that the relevant signal comes from a cross-correlation of well-known CMB temperature anisotropy maps.  

8:00 AM → 8:02 AM Notes from last telecon (July 7) are available

8:10 AM → 8:30 AM Discussion of "The Tau of Neutral Hydrogen: Increased CMB Optical Depth at Long Wavelengths"

Peter and Albert will review this recent paper by Holder et al: https://arxiv.org/abs/2605.22934

Speakers: Albert Stebbins (Fermilab), Peter Timbie (UW - Madison Department of Physics)