Combinatorics, Physics and Probability Seminar

During the 2021-22 academic year, the CMSA will be hosting a seminar on Combinatorics, Physics and Probability, organized by Matteo Parisi and Michael Simkin. This seminar will take place on Tuesdays at 9:30am – 10:30am (Boston time). The meetings will take place virtually on Zoom. To learn how to attend, please fill out this form, or contact the organizers Matteo ( and Michael (

The schedule below will be updated as talks are confirmed.

9/21/2021Nima Arkani-Hamed
IAS (Institute for Advanced Study), School of Natural Sciences
Title: Surfacehedra and the Binary Positive Geometry of Particle and “String” Amplitudes
9/28/2021Melissa Sherman-Bennett
University of Michigan, Department of Mathematics
Title: The hypersimplex and the m=2 amplituhedron

Abstract: I’ll discuss a curious correspondence between the m=2 amplituhedron, a 2k-dimensional subset of Gr(k, k+2), and the hypersimplex, an (n-1)-dimensional polytope in R^n. The amplituhedron and hypersimplex are both images of the totally nonnegative Grassmannian under some map (the amplituhedron map and the moment map, respectively), but are different dimensions and live in very different ambient spaces. I’ll talk about joint work with Matteo Parisi and Lauren Williams in which we give a bijection between decompositions of the amplituhedron and decompositions of the hypersimplex (originally conjectured by Lukowski–Parisi–Williams). Along the way, we prove the sign-flip description of the m=2 amplituhedron conjectured by Arkani-Hamed–Thomas–Trnka and give a new decomposition of the m=2 amplituhedron into Eulerian-number-many chambers (inspired by an analogous hypersimplex decomposition).
10/5/2021Daniel Cizma, Hebrew University
10/12/2021Lisa Sauermann, MIT
10/19/2021Pavel Galashin
UCLA, Department of Mathematics
10/26/2021Candy Bowtell
Oxford, Mathematical Institute
11/2/2021Jacob Bourjaily
Penn State University, Department of Physics
11/9/2021Steven Karp
Universite du Quebec a Montreal, LaCIM (Laboratoire de combinatoire et d’informatique mathématique)
11/23/2021Lutz Warnke
Georgia Tech

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