Algebraic Geometry Seminar: Birational Contractions of Mg,n and Their Dependence on the Characteristic, by Daebeom Choi
April 13, 2026
3:00 PM - 3:50 PM
Daebeom Choi (University of Pennsylvania): Birational Contractions of Mg,n and Their Dependence on the Characteristic
In this talk, we discuss the existence and nonexistence of certain birational contractions of \(\overline{\mathrm{M}}_{g,n}\). Somewhat surprisingly, this depends on the characteristic of the base field: many such contractions exist only in positive characteristic. We present a precise form of this phenomenon and discuss two examples that highlight the difference between characteristic zero and positive characteristic. The first is a simple and explicit contraction that exists only in positive characteristic, and the second is a modular interpretation of the morphisms associated with psi classes on \(\overline{\mathrm{M}}_{1,n}\). We also offer some speculation on why such characteristic-dependent phenomena arise.
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Date posted
Apr 14, 2026
Date updated
Apr 14, 2026
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