Surface operators in = 2 4d gauge theories

Abstract$$ \mathcal{N} $$ = 2 four dimensional gauge theories admit interesting half BPS surface operators preserving a (2, 2) two dimensional SUSY algebra. Typical examples are (2, 2) 2d sigma models with a flavor symmetry which is coupled to the 4d gauge fields. Interesting features of such 2d sigma models, such as (twisted) chiral rings, and the tt* geometry, can be carried over to the surface operators, and are affected in surprising ways …