title: Quasi-Nambu-Goldstone modes in Bose-Einstein condensates.
abstract: We show that quasi-Nambu-Goldstone (NG) modes, which play prominent roles in high energy physics but have been elusive experimentally, can be realized with atomic Bose-Einstein condensates. The quasi-NG modes emerge when the symmetry of a ground state is larger than that of the Hamiltonian. When they appear, the conventional vacuum manifold should be enlarged. Consequently, topological defects that are stable within the conventional vacuum manifold become unstable and decay by emitting the quasi-NG modes. Contrary to conventional wisdom, however, we show that the topological defects are stabilized by quantum fluctuations that make the quasi-NG modes massive, thereby suppressing their emission.
authors.affiliation: Department of Physics, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan.
authors.forename: Shun
authors.initials: S
authors.lastname: Uchino
authors.forename: Michikazu
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Muneto
authors.initials: M
authors.lastname: Nitta
authors.forename: Masahito
authors.initials: M
authors.lastname: Ueda