Infrared computations of defect Schur indices

We conjecture a formula for the Schur index of four-dimensional N=2$$ \mathcal{N}=2 $$ theories in the presence of boundary conditions and/or line defects, in terms of the low-energy effective Seiberg-Witten description of the system together with massive BPS excitations. We test our proposal in a variety of examples for SU(2) gauge theories, either conformal or asymptotically free. We use the conjecture to compute these defect-enriched Schur …