Line defect Schur indices, Verlinde algebras and U(1) r fixed points

Abstract Given an N=2 $$ \mathcal{N}=2 $$ superconformal field theory, we reconsider the Schur index ℐ L (q) in the presence of a half line defect L. Recently Cordova-Gaiotto-Shao found that ℐ L (q) admits an expansion in terms of characters of the chiral algebra A $$ \mathcal{A} $$ introduced by Beem et al., with simple coefficients υ L,β (q). We report a puzzling new feature of this expansion: the q → 1 limit of the coefficients υ L,β (q) is linearly related to the vacuum expectation values 〈L〉 in U(1) r -invariant vacua of the theory compactified on S 1. This relation can be expressed algebraically as a commutative diagram involving three algebras: the algebra generated by line defects, the algebra of functions on U(1) r -invariant vacua, and a Verlindelike algebra associated to A $$ \mathcal{A} $$. Our evidence is experimental, by direct computation in the Argyres-Douglas theories of type (A 1, A 2), (A 1, A 4), (A 1, A 6), (A 1, D 3) and (A 1, D 5). In the latter two theories, which have flavor symmetries, the Verlinde-like algebra which appears is a new deformation of algebras previously considered.

Abstract licence: CC BY

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