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r-th roots: better negative than positive

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Nitin Kumar Chidambaram
University of Edinburgh
Tue, 01/11/2022 - 14:00 - 15:00

Online talk
Connection link:
Contact: Gaetan Borot (


I will talk about the construction and properties of a cohomological field theory (without a flat unit) that parallels the famous Witten r-spin class. In particular, one can view it as the negative r analogue of the Witten r-spin class. For r=2, it was constructed by Norbury in 2017 and called the Theta class, and we generalize this construction to any r. By studying certain deformations of this class, we prove relations in the tautological ring, and in the special case of r=2 they reduce to relations involving only Kappa classes (which were recently conjectured by Norbury-Kazarian). In the second part of this talk, we will exploit the relation between cohomological field theories and the Eynard-Orantin topological recursion to prove W-algebra constraints satisfied by the descendant potential of the class. Furthermore, we conjecture that this descendant potential is the r-BGW tau function of the r-KdV hierarchy, and prove it for r=2 (thus proving a conjecture of Norbury) and r=3. This is based on joint work with Alessandro Giacchetto and Elba Garcia-Failde.

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