I spent research time on the weekend and today working on a NASA TESS proposal, led by Tyler Pritchard (NYU) in which we deliver image differences (using the CPM) and light curves (with assistance from ZTF public data). It is a big project but the proposal has a four-page limit, so the writing isn't trivial!
This morning, Kate Storey-Fisher (NYU) and I met with Alex Barnett (Flatiron) to discuss estimators for the correlation function. Barnett has discovered that the cosmological literature on the correlation function makes essentially no reference to the mathematics literature on point processes, and the point-process literature makes no reference to the Landy–Szalay estimator or anything like it! So there is work to do.
But of great interest today, Barnett has discovered that the Landy–Szalay estimator (and even the more trivial estimators) that we use in cosmology is non-trivially biased! It does not estimate the mean of the correlation function in an annular separation bin! It estimates a different integral of the correlation function. This has potentially disastrous consequences for things we have done related to the baryon acoustic feature.
Hello David, sorry for commenting on an old blog post, I was just wondering if you were aware of any publication or write-up on this Landy-Szalay estimator bias. I took a quick look at Alex Barnett’s webpage but didn’t see anything.
ReplyDeleteThanks and best wishes,
Graeme Addison
Johns Hopkins University