non-Gaussianity in the CMB

Kendrick Smith (Perimeter) gave the astrophysics seminar today. He talked about non-Gaussianity. Various impressive things in his talk. One was the fact that they can measure, at high signal-to-noise, even four-point functions in the Planck data, and confidently see expected deviations from the Gaussian. This may be the only data set in the physical sciences in which a four-point function can be measured at very high precision. Another impressive thing is that, in the context of various inflationary scenarios (in which small non-Gaussian effects arise), he can evaluate the probability of a non-Gaussian initial condition, and therefore use MCMC to generate a realization. He is thinking in terms of initializing n-body simulations, but this is also critical for CMB data analysis: It means, potentially, that he could do full, non-approximate inference of inflationary parameters given the CMB data. It was a great talk, filled with good ideas about using very good mathematical physics to tractably connect theory to observations.

At group meeting, Sanderson asked us about potential statistics we could be using to see the effect of dark-matter substructure on old accreted stellar debris in the Milky Way. She is thinking about hot, old structures, not cold, young streams. In the afternoon, Malz and I talked about redshift likelihoods and photometric redshifts and the overlaps between what we have been thinking about and HETDEX with the thought that he might be able to become a collaborator on that project, given his past work there.

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