2-group global symmetries, hydrodynamics and holography

2-group global symmetries are a particular example of how higher-form and conven-tional global symmetries can fuse together into a larger structure. We construct a the-ory of hydrodynamics describing the finite-temperature realization of a 2-group global symmetry composed out of U(1) zero-form and U(1) one-form symmetries. We study aspects of the thermodynamics from a Euclidean partition function and derive consti-tutive relations for ideal hydrodynamics from various points of view. Novel features of the resulting theory include an analogue of the chiral magnetic effect and a chiral sound mode propagating along magnetic field lines. We also discuss a minimalist holographic description of a theory dual to 2-group global symmetry and verify predictions from hy-drodynamic descriptions. Along the way we clarify some aspects of symmetry breaking in higher-form theories at finite temperature.