Speaker
Yoshimasa Hidaka
(RIKEN)
Description
The theory of spontaneous symmetry breaking and Nambu-Goldstone modes (bosons) was developed in 1960’s. When a global symmetry is spontaneously broken, there appears a gapless excitation mode, the Nambu-Goldstone (NG) mode. The theorem is based on Lorentz invariance of the grand state, and it implies that the number of NG modes coincides with the number of broken generators, and they have the linear dispersion relation. In QCD, the pions are nothing but the NG modes associated with spontaneous breaking of chiral symmetry.
In contrast, in non-Lorentz invariant systems, it is known that NG modes possessing quadratic dispersion relation may appear. The number of NG modes does not coincides with the number of broken generators. An example in QCD matter is the NG mode in the Kaon condensed color locked phase.
The relation between broken generators and NG modes were not completely understood until recently. I review recent developments in the theory of spontaneous symmetry breaking in non-Lorentz invariant systems. I also discuss the spontaneous breaking of space-time symmetries and NG modes.
Primary author
Yoshimasa Hidaka
(RIKEN)
