1-form Symmetries of 4d N=2 Class S Theories

Understand

We determine the 1-form symmetry group for any 4d N = 2 class S theory constructed by compactifying a 6d N=(2,0) SCFT on a Riemann surface with arbitrary regular untwisted and twisted punctures.

• The 6d theory has a group of mutually non-local dimension-2 surface operators, modulo screening.
• Compactifying these surface operators leads to a group of mutually non-local line operators in 4d, modulo screening and flavor charges.
• Complete specification of a 4d theory arising from such a compactification requires a choice of a maximal subgroup of mutually local line operators, and the 1-form symmetry group of the chosen 4d theory is identified as the Pontryagin dual of this maximal subgroup.