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Deciphering CMB measurements with volunteer computing and Bayesian thinking

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If you have a question about this talk, please contact Tobias Baldauf.

The Planck satellite has provided exquisite measurements of cosmic microwave background (CMB) temperature and polarization, measuring scales in the CMB which had never before been probed. While finding overall good agreement with predictions from the standard LCDM model of cosmology, Planck also found some tantalizing hints of beyond LCDM physics in the form of shifts in the constraints on some parameters as compared to previous measurements. For example, the inferred Hubble constant shifted to ∼67 km/s/Mpc, lower than before and in larger tension with non-CMB measurements of this value. I will describe our efforts to quantify and understand these shifts within the Planck data, and how we used the massive computing resources provided by the volunteer computing cluster that I run, Cosmology@Home, to do so. Some of these shifts are related to an apparent enhancement in the amount of gravitational lensing in the Planck maps, and this effect stands to be further elucidated by high-fidelity measurements of the lensing potential by future CMB probes such as CMB -S4. The analysis of such data, however, poses a challenge as our current lensing estimators will be statistically sub-optimal at future noise-levels. I will describe our recent work building new optimal Bayesian tools for CMB lensing analysis, including a new reformulation of weak gravitational lensing called LenseFlow which may have useful applications beyond the CMB , e.g. to galaxy, Lyman-alpha, or 21cm lensing.

This talk is part of the Cosmology Lunch series.

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