Unstable Nambu-Goldstone modes

Nambu-Goldstone (NG) modes for 0-form and higher-form symmetries can become unstable in the presence of background fields. Examples include instability a photon with time-dependent axion or chirality imbalance, known as chiral plasma instability, dynamical electric field. We show that all these phenomena be universally described by symmetry algebra symmetries. prove counting rule number NG terms correlation functions broken generators. Based on our unified description, we further give simple new example where one associated spontaneous breaking $U(1)\ifmmode\times\else\texttimes\fi{}U(1)\ensuremath{\rightarrow}{1}$ becomes unstable.