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## G. Arunkumar

 Description: Speaker: G. Arunkumar Date & Time : Monday Feb 26, at 11:30am Venue: Ramanujan Hall Title: Chromatic polynomials and Lie algebras Abstract: In this talk, I will prove a connection between root multiplicities for Borcherds-Kac-Moody algebras and graph coloring. I will show that the generalized chromatic polynomial of the graph associated to a given Borcherds algebra can be used to give a closed formula for certain root multiplicities. As an application, using the combinatorics of Lyndon words, we construct a basis for the root spaces corresponding to these roots and determine the Hilbert series in the case when all simple roots are imaginary. In last ten minutes, We will talk about chromatic discriminant of a graph: The absolute value of the coefficient of q in the chromatic polynomial of a graph G is known as the chromatic discriminant of G and is denoted $\alpha(G)$. We start with a brief survey on many interesting algebraic and combinatorial interpretations of $\alpha(G)$. We use two of these interpretations (in terms of acyclic orientations and spanning trees) to give two bijective proofs for a recurrence formula of $\alpha(G)$ which comes from the Peterson recurrence formula for root multiplicities of Kac-Moody algebras. Location: Ramanujan Hall, Department of Mathematics Date: Monday, February 26, 2018 Time: 11:30am IST Access: Public