| Summary: | 2-group symmetries arise when 1-form symmetries and 0-form symmetries of a
theory mix with each other under group multiplication. We discover the
existence of 2-group symmetries in 5d N=1 abelian gauge theories arising on the
(non-extended) Coulomb branch of 5d superconformal field theories (SCFTs),
leading us to argue that the UV 5d SCFT itself admits a 2-group symmetry.
Furthermore, our analysis determines the global forms of the 0-form flavor
symmetry groups of 5d SCFTs, irrespective of whether or not the 5d SCFT admits
a 1-form symmetry. As a concrete application of our method, we analyze 2-group
symmetries of all 5d SCFTs, which reduce in the IR, after performing mass
deformations, to 5d N=1 non-abelian gauge theories with simple, simply
connected gauge groups. For rank-1 Seiberg theories, we check that our
predictions for the flavor symmetry groups match with the superconformal and
ray indices available in the literature. We also comment on the mixed 't Hooft
anomaly between 1-form and 0-form symmetries arising in 5d N=1 non-abelian
gauge theories and its relation to the 2-groups.
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