Tilts from 2-Groups

2-group global symmetries intertwine 0-form and 1-form symmetries in an interesting way. We analyze universal constraints on lines which are charged under the 1-form subgroup of a 2-group, and show that they generically break the 0-form symmetry explicitly. This gives rise to a family of line defects parameterized by the broken symmetry generators, whose existence is invariant under the renormalization group flow of the bulk-defect system. The symmetry breaking is enforced by a `family anomaly,' which is a topological obstruction to a symmetric defect. Our main tools are the Wess-Zumino consistency condition and a generalized anomaly inflow formalism for defects and boundaries. For nonabelian continuous 2-groups the family anomaly stems from a higher Berry connection on the moduli space of defects, and constrains response functions that probe the local action of the broken symmetry. In the continuous abelian case we apply differential cohomology to the 2-group background fields to uncover a subtle generalization of the Wess-Zumino condition, while in the discrete case we recast it in terms of the associativity of symmetry defects. We give numerous illustrative examples, computing when possible explicit forms of the tilt operator (which probes the linear response of the defect to the broken symmetry) and its higher analogs, which are crucial for matching the family anomaly. We also discuss universal features such as how symmetry violation by charged line defects is related to symmetry breaking hierarchies in the bulk, and highlight a number of subtle points including the distinction between simple and non-simple lines, and Postnikov class resolution.