As part of the program on Spacetime and Quantum Mechanics, the CMSA will be hosting a weekly seminar on Thursdays at 2:30pm in room G10.
Date  Speaker  Title/Abstract 

9/12/2019  Pasha Pylyavskyy (University of Minnesota)  Title: Vectorrelation configurations and plabic graphs 
19/18/2019
2:00pm G02 
Francis Brown (University of Oxford)  Title: Amplitudes, Polylogs and Moduli Spaces 
9/19/2019  Chuck Doran (University of Alberta)  Title: CalabiYau geometry of the Nloop sunset Feynman integrals
Abstract: I will present an overview of the algebraic and transcendental features of the computation of Nloop sunset Feynman integrals. Starting from the realization of arbitrary Feynman graph hypersurfaces as (generalized) determinantal varieties, we describe the CalabiYau subvarieties of permutohedral varieties that arise from the Nloop sunset Feynman graphs and some key features of their geometry and moduli. These include: (1) an iterated fibration structure which allows one to “bootstrap” both periods and PicardFuchs equations from lower N cases; (2) specialization to and interpretation of coincident mass loci (“jump loci”) in moduli; (3) a significant generalization of the GriffithsDwork algorithm via “creative telescoping”; and (4) the realization of CalabiYau pencils as LandauGinzburg models mirror to weak Fano varieties. Details of each of these will be discussed in later lectures this semester. This is joint work with Pierre Vanhove and Andrey Novoseltsev. 
9/26/2019  Tomasz Taylor (Northeastern)  Title: Celestial Amplitudes 
10/3/2019  Simon CaronHuot (McGill)  Title: Poincare Duals of Feynman Integrals 
10/10/2019
3:30pm 
Yutin Huang (National Taiwan University)  Title: Dualities of Planar Ising Networks and the Positive Orthogonal Grassmannian 
10/15/2019
Tuesday 3:30pm 
Sergey Fomin (Univ. of Michigan)

Title: “Morsifications and mutations” (joint work with P. Pylyavskyy, E. Shustin, and D. Thurston). 
10/18/2019
Friday G02 
Sebastian Franco (The City College of New York)  Title: Graded quivers, generalized dimer models, and topic geometry 
10/31/2019  Junjie Rao (Albert Einstein Institute)  Title: Allloop Mondrian Reduction of 4particle Amplituhedron at Positive Infinity 
11/1/2019
SC 232 1:30pm 
George Lusztig (MIT)  Title: Total positivity in Springer fibres 
11/12/2019
Tuesday G02 3:30pm 
Pierpaolo Mastrolia (University of Padova) 
Title: Feynman Integrals and Intersection Theory 
11/14/2019
G02 
Pierpaolo Mastrolia (University of Padova)  Title: Feynman Integrals and Intersection Theory Pt. II 
11/21/2019  Cristian Vergu (Niels Bohr Institute)  Title: The Octagonal Alphabet 
11/26/2019  Stephan Stieberger (IAS)  Title: Strings on the Celestial Sphere 
12/4/2019  Hadleigh Frost (Oxford)  Title: BCJ numerators, $\mathcal{M}_{0,n}$, and ABHY
Abstract: We relate the BCJ numerator Jacobi property to the classical fact that the top homology group of $\mathcal{M}_{0,n}$ is isomorphic to a component of the free Lie algebra. We describe ways to get BCJ numerators, and caution that the BCJ Jacobi property doesn’t imply the existence of what has been called a ‘kinematic algebra.’ 
12/5/2019  David Kosower (IAS)  Title: From scattering amplitudes to classical observables 
12/10/2019  Ramis Movassagh (MIT)  Title: Highly entangled quantum spin chains: Exactly solvable counterexamples to the area law
Abstract: In recent years, there has been a surge of activities in proposing “exactly solvable” quantum spin chains with surprising high amount of ground state entanglement–exponentially more than the critical systems that have $\log(n)$ von Neumann entropy. We discuss these models from first principles. For a spin chain of length $n$, we prove that the ground state entanglement entropy scales as $\sqrt(n)$ and in some cases even extensive (i.e., as $n$) despite the underlying Hamiltonian being: (1) Local (2) Having a unique ground state and (3) Translationally invariant in the bulk. These models have rich connections with combinatorics, random walks, Markov chains, and universality of Brownian excursions. Lastly, we develop techniques for proving the gap. As a consequence, the gap of Motzkin and Fredkin spin chains are proved to vanish as 1/n^c with c>2; this rules out the possibility of these models to be relativistic conformal field theories in the continuum limit. Time permitting we will discuss more recent developments in this direction and ‘generic’ aspects of local spin chains. 