Remarks on nonrelativistic Goldstone bosons

Abstract

We discuss excitations in nonrelativistic field theories with spontaneous breaking of a continuous global symmetry. It is known that in such systems there are two types of Goldstone bosons (Type A and Type B) whose dispersion law is generically linear or quadratic, respectively. We show that Type B Goldstone bosons may have gapped partners which we call almost-Goldstone bosons. With some nondegeneracy assumption about the low-energy effective action, the total number of Goldstone and almost-Goldstone bosons adds up to the number of broken symmetry generators. We propose that deviations of the dispersion law of Goldstone bosons from linearity at small momenta may serve as a signature of small breaking of time-reversal symmetry.

arXiv comment9 pages, latex

References in corpus (4)

• Unified Description of Nambu-Goldstone Bosons without Lorentz Invariance
• Nonrelativistic effective Lagrangians
• Kaon Condensation and Goldstone's Theorem
• On the number of Nambu-Goldstone bosons and its relation to charge densities

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