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February 2017

Uladzimir Shtukar, NC Central University, “Canonical bases, subalgebras, reductive pairs of Lie algebras, and possible applications”

February 6, 2017 | 3:00 pm - 4:00 pm EST

Subalgebras of Lie algebra of Lorentz group will be discussed as the basic examples at the beginning of the report. The corresponding analysis is performed by canonical bases for subspaces of a vector space. All canonical bases for 5-dimensional and…

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Jamie Pommersheim, Reed College, “Euler-Maclaurin summation formulas for polytopes”

February 20, 2017 | 3:00 pm - 4:00 pm EST

Discovered in the 1730s, the classical Euler-Maclaurin formula may be viewed as a formula for summing the values of a function over the lattice points in a one-dimensional polytope. Several years ago, Berline and Vergne generalized this formula to polytopes…

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March 2017

Rosa Orellana, Dartmouth College, “The partition algebra, symmetric functions and Kronecker coefficients”

March 20, 2017 | 3:00 pm - 4:00 pm EDT

The Schur-Weyl duality between the symmetric group and the general linear group allows us to connect the representation theory of these two groups. A consequence of this duality is the Frobenius formula which connects the irreducible characters of the general…

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April 2017

Max Glick, University of Connecticut, “The Berenstein-Kirillov group and cactus groups”

April 3, 2017 | 12:00 am EDT

Berenstein and Kirillov have studied the action of Bender-Knuth moves on semistandard tableaux. Losev has studied a cactus group action in Kazhdan-Lusztig theory; in type A this action can also be identified in the work of Henriques and Kamnitzer. We…

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Mark Shimozono, Virginia Tech, “Quiver Hall-Littlewood symmetric functions and Kostka-Shoji polynomials”

April 21, 2017 | 3:00 pm - 4:00 pm EDT

We associate to any quiver a family of symmetric functions, defined by creation operators which are generalizations of Jing's creation operators. For the cyclic quiver the coefficient polynomials were studied by Finkelberg and Ionov. Shoji has recently shown that the…

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May 2017

Ben Cox, College of Charleston, “On the universal central extension of certain Krichever-Novikov algebras”

May 15, 2017 | 2:00 pm - 3:00 pm EDT

We will describe results on the center of the universal central extension of certain Krichever-Novikov algebras. In particular we will describe how various families of classical and non-classical orthogonal polynomials appear. We will also provide certain new identities of elliptic…

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June 2017

Rekha Biswal, Université Laval, “Demazure flags, Chebyshev polynomials and mock theta functions”

June 5, 2017 | 2:00 pm - 3:00 pm EDT

The g-stable Demazure modules are a lot of interest because of their connections to representation theory of quantum affine algebras. These modules are indexed by a pair (ell, lambda) where ell is a positive integer and lambda is a dominant…

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September 2017

Richard Rimanyi, UNC Chapel Hill, Counting partitions and quantum dilogarithm identities

September 11, 2017 | 3:00 pm - 4:00 pm EDT

In the theory of Donaldson-Thomas invariants for quivers one finds identities for quantum dilogarithm series. The combinatorial interpretation of the simplest of these identities is equivalent to a clever way of counting partitions. The combinatorial interpretation of more involved dilogarithm…

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Leonardo Mihalcea, Chern-Schwartz-MacPherson classes for Schubert cells: geometry and representation theory

September 18, 2017 | 3:00 pm - 4:00 pm EDT

A compact manifold has a tangent bundle, and a natural question is to find a replacement for the Chern classes of the tangent bundle, in the case when the space is singular. The Chern-Schwartz-MacPherson (CSM) classes are homology classes which…

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Heekyoung Hahn, Duke University, Langlands’ beyond endoscopy proposal and related questions on algebraic groups and combinatorics

September 25, 2017 | 3:00 pm - 4:00 pm EDT

Langlands' beyond endoscopy proposal for establishing functoriality motivates the study of irreducible subgroups of $\mathrm{GL}_n$ that stabilize a line in a given representation of $\mathrm{GL}_n$. Such subgroups are said to be detected by the representation. In this talk we present…

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October 2017

Joshua Hallam, Wake Forest University, Whitney duals of graded partially ordered sets

October 2, 2017 | 3:00 pm - 4:00 pm EDT

To each graded poset one can associate two sequences of numbers; the Whitney numbers of the first kind and the Whitney numbers of the second kind. One sequence keeps track of the Möbius function at each rank level and other…

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Shira Viel, NC State,Folding and dominance: relationships among mutation fans for surfaces and orbifolds

October 23, 2017 | 3:00 pm - 4:00 pm EDT

The $n$-associahedron is a well-known $n$-dimensional polytope whose vertices are labeled by triangulations of an $(n+3)$-gon with edges given by diagonal flips. The $n$-cyclohedron is defined analogously using centrally-symmetric triangulations of a $(2n+2)$-gon, or, modding out by the symmetry, triangulations…

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January 2018

Tomoyuki Arakawa, RIMS and MIT, Vertex algebras and symplectic varieties

January 12, 2018 | 3:00 pm - 4:00 pm EST

In my talk I will discuss some remarkable correspondence between symplectic varieties and vertex algebras, which has been discovered by physicists in the study of the four-dimensional N = 2 superconformal field theories. In the special class of the four-dimensional N = 2 superconformal…

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Michael Singer, NC State, Walks, Difference Equations and Elliptic Curves

January 29, 2018 | 3:00 pm - 4:00 pm EST

Many questions in combinatorics, probability and thermodynamics can be reduced to counting lattice paths (walks) in regions of the plane. A standard approach to counting problems is to consider properties of the associated generating function.  These functions have long been well understood for walks…

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February 2018

Natasha Rojkovskaia, Kansas State University, Factorial Schur Q-functions

February 9, 2018 | 3:00 pm - 4:00 pm EST

Classical Schur Q-functions describe  characters of a queer Lie superalgebra, projective representations of a symmetric  group and provide solutions of a BKP hierarchy. This talk is devoted to properties of a generalization of  Schur  Q-functions -  factorial  Q-functions, including a particular important case of shifted…

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Harm Derksen, University of Michigan, Matrix Invariants and Complexity

February 19, 2018 | 3:00 pm - 4:00 pm EST

We consider the action of the group SL_n x SL_n on the space of m-tuples of n x n matrices by simultaneous left-right multiplication. Visu Makam and the speaker recently proved that invariants of degree at most mn^4 generate the invariant ring. This…

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Nathan Reading, NC State, To scatter or to cluster?

February 26, 2018 | 3:00 pm - 4:00 pm EST

Scattering diagrams arose in the algebraic-geometric theory of mirror symmetry. Recently, Gross, Hacking, Keel, and Kontsevich applied scattering diagrams to prove many longstanding conjectures about cluster algebras. Scattering diagrams are certain collections of codimension-1 cones, each weighted with a formal power series. In this…

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March 2018

Karola Mészáros, Cornell University, Product formulas for volumes of flow polytopes

March 26, 2018 | 3:00 pm - 4:00 pm EDT

The flow polytope associated to an acyclic graph is the set of all nonnegative flows on the edges of the graph with a fixed netflow at each vertex. We will examine flow polytopes arising from permutation matrices, alternating sign matrices…

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April 2018

Sergi Elizalde, Dartmouth College, Cyclic descents of standard Young tableaux

April 16, 2018 | 3:00 pm - 4:00 pm EDT

Cyclic descents of a permutation were defined by Cellini, by allowing the permutation to wrap around as if the last entry was followed by the first. A natural question is whether a similar, well-behaved notion of cyclic descents exists for…

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Ying Zhou, Brandeis University, Tame Hereditary Algebras have finitely many m-Maximal Green Sequences

April 23, 2018 | 3:00 pm - 4:00 pm EDT

Keller introduced the concept of maximal green sequences. Brustle-Dupont-Perotin proved that tame quivers have finitely many maximal green sequences. We have generalized the result to m-maximal green sequences. This talk will include a gentle introduction to tame path algebras, their indecomposable modules, silting objects…

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