On a smoothness characterization for good moduli spaces, joint with Dan Edidin and Matt Satriano, published in Advances in Mathematics in April 2024.
A preprint is available for free on the arXiv. I was responsible for writing the second section of this paper (pp. 5 - 20 in the preprint).
In mathematics, we are often interested in the spaces that result when taking a large space and 'identifying' some points (making a new, smaller space by declaring some points to be indistinguishable from each other). A typical example would be folding a piece of paper in half: so the top left corner is identified with the bottom left corner, and so on. Identifications that arise from a procedure like folding a sheet of paper leave a crease in the paper, points that are not identified to any other point. Mathematicians call such points singular (meaning 'exceptional/rare'), as the crease line is a one-dimensional object, while the paper itself is two-dimensional. The opposite of singular is smooth.
We considered the general problem of identifying which paper-folding rules were singular, and which were smooth (in mathematical jargon: which complex representations of a group have smooth GIT quotients?) The answer for a list of finitely many rules has been known since the 1950s, due to Shephard and Todd—the space is smooth only when the rules are generated by those rotating one dimension and leaving fixed a hyperplane. In our work, we allow for infinitely many rules, and recovered in some cases a natural generalization of the theorem of Shephard and Todd: we prove roughly that smoothness follows when the rules are generated by a rotation in one dimension leaving fixed a hypersurface.