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Events happening on February 11, 2021

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Feb. 11, 2021 9:10am (Zoom 9…	Ulam Libor Barto (Charles University) X The Promise Constraint Satisfaction Problem (PCSP) is a generalization of the Constraint Satisfaction Problem (CSP) that includes approximation variants of satisfiability and graph coloring problems. In a [LICS '19] paper it was shown that a specific PCSP, the problem to find a valid Not-All-Equal solution to a 1-in-3-SAT instance, is not finitely tractable in that it can be solved by a trivial reduction to a tractable CSP, but such a CSP is necessarily over an infinite domain (unless P=NP). We further explore this phenomenon: we give a general necessary condition for finite tractability and characterize finite tractability within a class of templates - the "basic" tractable cases in the dichotomy theorem for symmetric Boolean PCSPs allowing negations by Brakensiek and Guruswami [SODA'18]. This is a joint work with Kristina Asimi. Finitely tractable PCSPs
Feb. 11, 2021 11am (Zoom)	Noncomm Geometry Manuel Rivera (Purdue University) X I will describe the sense in which the coalgebraic structure of the singular chains on a connected space determines its fundamental group in complete generality. An extension of Adams’ classical cobar theorem, from simply connected spaces to spaces with arbitrary fundamental group, lies at the bottom of this new observation. The key idea is to consider the singular chains as an E-infinity coalgebra under a notion of weak equivalence drawn from the Koszul duality theory of co/associative structures. This leads to an extension of rational homotopy theory of nilpotent spaces to spaces with arbitrary fundamental group, where the notion of weak equivalence between spaces is defined to be a continuous map inducing an isomorphism on fundamental groups and an isomorphism on higher rationalized homotopy groups. I will also describe how these constructions may be used to obtain a Hochschild type model for the free loop space of a non-simply connected space that is potentially useful for studying string topology. Algebraic models for non-simply connected spaces and their loop spaces
Feb. 11, 2021 4pm (Zoom (vir…	Rep Theory Tomoyuki Arakawa (Kyoto University) X The 4D/2D duality discovered by Beem et at in physics gives a remarkable connection between 4D N=2 SCFTs and VOAs. It gives not only many new interesting examples of VOAs but also new perspectives to known VOAs, such as Frenkel-Styrkas’s modified regular representation of the Virasoro algebra and Adamovic’s realization of N=4 small superconformal algebra. In this talk I will discuss the 4D/2D duality from the VOA perspective, starting from these examples. 4D/2D duality and VOA theory

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