Theory Group Seminars

Non-relativistic Nambu-Goldstone modes: the cases of vortices and solitons

by Muneto Nitta

248 (Building C, First Floor)


Building C, First Floor

In non-reliativistic systems such as condensed matter systems, two kinds of gapless Nambu-Goldstone (NG) modes can appear when a continuous symmetry is spontaneously broken; type-I NG modes with linear dispersion relation and type-II NG modes with quadratic dispersion relation. The counting rule has been recently derived for internal symmetry breaking by Watanabe and Murayama and Hidaka independently, but the general rule is not yet known for space-time symmetry breaking. Here, I discuss NG modes for space-time symmetry breaking in the presence of quantized vortices in superfluids, a domain wall in anisotropic ferromagnets, a skyrmion line in isotropic ferromagnets, and a domain wall in two-component Bose-Einstein condensates (BECs). They all have gapless modes associated with translational symmetry breaking in addition to gapless modes associated with internal symmetry and/or scale symmetry breaking. When zero modes are non-normalizable such as a vortex or domain wall in superfluids (or BECs), dispersion relations become non-integer. I also discuss quantum effects on NG modes, with an example of non-Abelian NG modes localized in a non-Abelian vortex core in multi-component BECs.