title: Nonrelativistic Nambu-Goldstone modes associated with spontaneously broken space-time and internal symmetries.
abstract: We show that a momentum operator of a translational symmetry may not commute with an internal symmetry operator in the presence of a topological soliton in nonrelativistic theories. As a striking consequence, there appears a coupled Nambu-Goldstone mode with a quadratic dispersion consisting of translational and internal zero modes in the vicinity of a domain wall in an O(3) σ model, a magnetic domain wall in ferromagnets with an easy axis.
authors.affiliation: Department of Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Michikazu
authors.initials: M
authors.lastname: Kobayashi
authors.affiliation: Department of Physics and Research and Education Center for Natural Sciences, Keio University, Hiyoshi 4-1-1, Yokohama, Kanagawa 223-8521, Japan.
authors.forename: Muneto
authors.initials: M
authors.lastname: Nitta