Gapped Goldstones at the cut-off scale: a non-relativistic EFT
Abstract At finite density, the spontaneous breakdown of an internal non-Abelian symmetry dictates, along with gapless modes, modes whose gap is fixed by the algebra and proportional to the chemical potential: the gapped Goldstones.Generically the gap of these states is comparable to that of other non-universal excitations or to the energy scale wh