I only recently heard about the death late last year of Dutch particle theorist Pierre van Baal. Pierre was my office mate when we were both postdocs at Stony Brook during the mid-eighties, and he was one of the people I most enjoyed talking with about physics during those years. He arrived at Stony Brook after completing a Ph.D. with Gerard ‘t Hooft, and later went on to CERN and ultimately a professorship in Leiden. I last saw him at a conference in Stony Brook in 2008 (described here) where he told me that he had suffered a serious stroke in 2005. Pierre was quite modest, and always a cheerful and optimistic presence in the room. In 2008 he was still very much himself, but more halting in his speech. From what I remember, he told me that he was resuming teaching, but was frustrated that he was no longer capable of engaging in research work.
The lecture notes of his class on quantum field theory are available (an online version here, a published version here). Like Pierre himself, they’re a model of clear and concise thinking and exposition. Last year a book with a selected collection of his papers was published, see here.
A major theme in Pierre’s work was the study of quantum gauge theory via semi-classical methods, for the case of a system in a “box”, i.e. finite extent in space and time dimensions. In the Euclidean picture, periodic boundary conditions in time correspond to doing computations at non-zero temperature, inversely proportional to the size of the time dimension. As a result, this work is quite relevant to the study of QCD at finite temperature, including the expected deconfining phase transition.
While Pierre was not really a lattice gauge theorist, his work was highly relevant to lattice gauge theory, where computer simulations inherently take place in a finite box, and understanding the effects of this on the physics is crucial. As a result, Pierre was well-known in the lattice gauge theory community. This week Columbia University is hosting Lattice 2014, the big yearly meeting for lattice gauge theorists (plenary talks are streamed on livestream.com). This morning I attended the talk by Michael Mueller-Preussker on Recent results on topology on the lattice, which was given in memory of Pierre. The slides have a lot more information about Pierre and his work, as well as surveying the latest on lattice results involving the topology of gauge fields.